EGU General Assembly 2024  

Detection, attribution and projection of glacier and ice-sheet change characterize much of our community’s work, motivated in part by the associated impacts ranging from local hazards to regional water supply to global sea-level rise. Toward improved attribution of glacier change on local to regional scales, I profile work aimed at discerning the internal versus external drivers of glacier behaviour through process-oriented studies. Using examples from northern Canada, combining observational and numerical approaches improves our understanding of fundamental processes that define the boundary conditions at the ice interface with bedrock, water and atmosphere. These studies have allowed us to revisit questions related to glacier surging, hydrology and ice-dammed lakes and the co-evolution of glacier geometry and thermal structure, with occasionally surprising and counter-intuitive results.

While the internal dynamics of glacier systems have the potential to confound the climate signal on societally relevant timescales, the direct effects of climate via surface mass balance remain as important as ever. Improved observational platforms, advances in modelling and the growing abundance and availability of remotely sensed data have amplified our capacity to study these systems, and more generously than ever reveal information archived by glacier processes. Using these tools, we are now beginning to disentangle the contributions of the geologic substrate, environmental setting, internal ice dynamics and climate forcing to observed glacier change in globally significant ice-rich parts of the world.

How to cite: Flowers, G.: Understanding glacier processes to decode the drivers of glacier change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6597, https://doi.org/10.5194/egusphere-egu24-6597, 2024.

Supraglacial lake drainages are isolated events that deliver the largest observable fluxes of surface melt to the ice-sheet bed. This talk will present advances in the study of these lake drainages, through which we piece together an empirical understanding of glacier hydrology. We examine the ways in which lakes both respond to, and determine, the hydrologic and glaciologic conditions under which they exist. We begin with the process puzzle of what mechanisms drive the opening of fractures within the compressive regions where lakes form, allowing hydro-fracture-driven drainages to occur. Next, we follow drained lake water in time and space, using the natural experiments provided by the drainages to infer subglacial-drainage-system transmissivity and structure beneath kilometer-thick ice flowing at rates of tens to thousands of meters per year in Greenland. In widening our view to previous subglacial-flood events observed at other ice-sheet locations—as well as at alpine, valley, and tidewater glaciers—we observe surprising similarities across a wide range of ice thicknesses, flow speeds, and types of flood events. The similarities we observe are encouraging because they suggest that information on drainage-system structure and evolution gleaned from these episodic events can be used to understand the wider picture. Finally, we examine current challenges: how do we move from the observed mechanisms of individual lake drainages to an integrated understanding of the importance of hundreds of drainages for long-term ice-sheet response and ice-shelf collapse? Progress will require the combination of geodetic observations, hydrologic simulations, and geophysical models to deconvolve the differing mechanisms that result in clusters of drainages in the multiple settings in which lakes form.

How to cite: Stevens, L. A., Banwell, A. F., Behn, M. D., Chase, D. L., Das, S. B., Dell, R. L., Falconer, E., Joughin, I. R., Lai, C.-Y., Larochelle, S., Lu, G. J., McGuire, J. J., Nettles, M., Okal, M., Rines, J., and Willis, I. C.: Supraglacial Lake Drainage: from process puzzle to subglacial diagnostic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11275, https://doi.org/10.5194/egusphere-egu24-11275, 2024.

Given its profound implications for future water security, the response of High Mountain Asia (HMA) glaciers to climate change remains a topic of critical concern. While recent studies have primarily focused on small glaciers (with glacierised areas of less than 1 to ~20 km²) to understand the impact of climate change on HMA water resources, these studies assume that smaller glaciers are regionally representative. However, it has been shown that smaller glaciers respond differently due to their smaller accumulation area particularly during warm years and lesser hydrological contribution. On the other hand, large glaciers in a catchment often serve as major contributors to runoff, thus influencing long-term water availability. Hence, larger glaciers may offer a more representative understanding of regional changes and are essential for future water security.

In this study, we calculate the geodetic mass balance of four very large glaciers —Fedchenko (with a total area of 664 km²), Baltoro (809 km²), Bara Shigri (112 km²), and Gangotri (122 km²)— covering the period from 2009 to 2022. The analysis is conducted over two different time intervals, utilizing digital elevation models generated from ASTER stereo imagery. We examined distinct glacier surfaces — debris-covered, clean-ice, and accumulation areas — to discern mass loss patterns with elevations. Bias-corrected in-situ meteorological data along with surface ice velocity data (from ITS_LIVE and Sentinel-1) were used to elucidate recent mass balance patterns.

Results reveal an amplified mass loss rate during the recent period of ~2015-2022 compared to the preceding period of ~2009-2015. Bara Shigri is an exception, experiencing a slight reduction in mass loss during ~2015-2022. The increased mass loss is driven by rising local summer temperatures and declining winter precipitation. Thinning was prominent at higher elevations (> 5000 m a.s.l.) across all four glaciers, with its intensity increasing over time. This indicates warming in the accumulation areas of these glaciers. Furthermore, upper glacier areas near the equilibrium line altitude exhibited stable ice velocities in certain glaciers, and the lower ablation zones experienced gradual slowdown, likely due to persistent mass loss.

These findings highlight the propagation of up-glacier thinning in large HMA glaciers, indicating mass loss across higher elevations and underscoring the vulnerability of local river systems and water resources.

How to cite: Mandal, A., Bhardwaj, A., Azam, M. F., Vishwakarma, B. D., and Angchuk, T.: Increased up-glacier thinning in four major glaciers of High Mountain Asia revealed by geodetic mass balance estimates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-920, https://doi.org/10.5194/egusphere-egu24-920, 2024.

Mt Elbrus being the highest peak in Europe (5642 m a.s.l.) is an inactive volcano currently covered by nearly thirty glaciers. Glaciated area is 112.20 ± 0.58 km³ and 5.03 ± 0.85 km³ in volume as revealed by Kutuzov et al., (2019) for the year of 2017. Current and future deglaciation of the Caucasus in general and of the Elbrus glacial massif in particular can be the reason for various negative consequences for the local economy and environment. Therefore, relevant prognostic studies are of great value both for the academicians and for the policymakers.

In this research, we consider probable scenarios of Elbrus glacier change in the 21st century. We mostly focus at the phenomena accompanying degradation of glaciation, such as the formation of glacial lakes and areas of “dead” ice buried under the moraine, which is relevant for predicting Glacial Lake Outburst Floods (GLOFs). Future climate projections, based on SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5 scenarios, were employed. Surface mass balance is calculated using temperature-index method (Huss and Hock, 2015). Glacier dynamics is emulated in 1-D global glacier model GloGEMflow (Zekollari et al., 2019) updated by incorporation of the module responsible for the description of debris cover evolution (Postnikova et al., 2023). Model adaptation for Elbrus involves the model transition from colluvial (e.g. slope erosion) to exarational (e.g. emergence of subglacial sediments) debris-cover sources, which aligns with the region's geological setting. These two modes of modelling the debris cover transformation in time are compared. While model validation reveals a slight underestimation of mass loss in the early 21st century, it accurately reproduces general mass loss patterns.

Under the warmest climate change scenarios, almost all of the remaining ice mass in the Central Caucasus will be concentrated on Elbrus. At the same time, Elbrus glaciers are anticipated to retreat above the 4000 m elevation by 2100. In case of moderate warming the position of glacier fronts may stabilize at an altitude of 3600-3700 m. According to our estimates, glacier retreat may lead to the formation of up to 17 new proglacial lakes. Under a moderate warming scenario (SSP1-2.6), up to 8 proglacial lakes may appear. The largest of them is expected to form at the terminus of the Djikaughenkioz ice plateau dammed by debris-covered dead ice in the 2030s-2040s assuming no sufficiently effective runoff channels are established.

This study was funded by the RSF grant number 23-27-00050.

How to cite: Postnikova, T., Rybak, O., Gubanov, A., Zekollari, H., and Huss, M.: Projections of Elbrus glaciers, proglacial lakes and dead ice areas., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-930, https://doi.org/10.5194/egusphere-egu24-930, 2024.

Glaciers of Baffin Island and nearby islands of Arctic Canada have experienced rapid mass losses over recent decades. However, projections of loss rates into the 21^st century have so far been limited by the availability of model calibration and validation data. In this study we model the surface mass balance of the largest ice cap on Baffin Island, Penny Ice Cap, since 1959, using an enhanced temperature index model calibrated with in situ data from 2006–2014. Subsequently, we project changes to 2099 based on the RCP4.5 climate scenario. Since the mid-1990s, the surface mass balance over Penny Ice Cap has become increasingly negative, particularly after 2005. Using volume–area scaling to account for glacier retreat, peak net mass loss is projected to occur between ~2040–2080, and the ice cap is expected to lose 22% (377.4 Gt or 60 m w.e. a^–1) of its 2014 ice mass by 2099, contributing 1.0 mm to sea level rise. Our 2015–2099 projections are approximately nine times more sensitive to changes in temperature than precipitation, with an absolute cumulative difference of 566 Gt a^–1 (90 m w.e.) between +2°C and –2°C scenarios, and 63 Gt a^–1 (10 m w.e.) between +20% and –20% precipitation scenarios.

How to cite: Schaffer, N.: Modeling the surface mass balance of Penny Ice Cap, Baffin Island, 1959–2099, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1173, https://doi.org/10.5194/egusphere-egu24-1173, 2024.

Approximately 21% of Svalbard’s glaciers are classified as surge-type and undergo cyclical changes in ice velocity between quiescent (slow) and active (fast) phases. Whilst it is generally understood that processes at the glacier bed drive surge initiation, the physical mechanisms translating basal sliding to ice flow variability and cyclicity remain open questions. Recent mapping of glacier velocities across Svalbard has identified an acceleration in ice flow at the Borebreen tidewater glacier which terminates on the northwestern side of Isfjorden. Before 2018, average summer velocities at Borebreen were ~0.6 m/d but more than doubled to 2.4 m/d by 2023. Borebreen last surged ~100 years ago, hence the acceleration in ice velocity suggests it is the result of the glacier transitioning to an active surge. In this contribution, we will discuss results from a summer field campaign to Borebreen in August 2023. Using a multi-sensor network of seismic arrays, Terrestrial Laser Scanners (TLS), and drones, we characterise present day surge dynamics and use the data to understand the drivers. In addition, optical imagery from the PlanetScope constellation and Synthetic Aperture Radar (SAR) data from Sentinel-1 are used to determine surface conditions (e.g. surface melt patterns, crevasses, proglacial turbid plumes) and quantify ice velocities. Here, we will report on the following: 1) basal processes (e.g. stick-slip events, icequakes) under Borebreen; 2) calving processes at the over-steepened ice cliff of the surge front; 3) ice velocity extracted from drone photogrammetry, Planetscope imagery and Sentinel-1 SAR scenes; and 4) surface conditions (e.g. crevassing, surface melt) over the course of the ablation season and its relationship with ice dynamics. We find that the surge initiated at the glacier terminus and has been propagating upglacier. The glacier speed doubles each spring in response to elevated air temperatures which leads to surface melting and the delivery of meltwater to the glacier bed. Furthermore, we identify clusters of seismicity at the glacier bed, far from the terminus, which appear to indicate sliding. Our results push forward our understanding of the processes that initiate and sustain glacier surges and glacier instabilities in general.

How to cite: Harcourt, W. D., Gajek, W., Pearce, D., Hann, R., Luckman, A., Rea, B. R., Benn, D. I., James, M. R., Spagnolo, M., and Nanni, U.: Surge initiation at the terminus of Borebreen (Svalbard): Drivers and impact on calving, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1505, https://doi.org/10.5194/egusphere-egu24-1505, 2024.

Recent studies of Himalayan glacier recession indicate that there is wide variability in terminus retreat rate and mass balance in the different sectors of the mountain range, primarily linked to the topography and climate of the region. Variable retreat rates of glacier termini and inadequate supporting field data (e.g. mass balance, ice thickness, velocity, etc.) in the Himalayan glaciers make it difficult to develop a coherent picture of climate change impacts. The mass balance measurements of the Pensilungpa Glacier were conducted from 2016-2017 to 2021-2022 and the study was carried out by using the glaciological method, including fixed date measurement of net accumulation. The glaciological method includes measurements at stakes and in snow pits, which are interpolated to glacier-wide balance estimates. This six-year mass balance study shows a negative trend with an average rate of specific balance is -0.46 m water equivalent (w.e.) and annual mean mass balance was -4.1 x10⁶ m³ w.e. The Glacier lost ~45 ±18 m lengths with an average rate of 6.4 ±3 ma^-1, and 24.97 x10⁶ m³ w.e. cumulative volume loss. Also, results show that Pensilungpa Glacier declined the ELAs 20 m from the year 2016.

How to cite: Kunmar, P., Mehta, M., Kumar, V., Rana, A., and Nainwal, H.: 6 Years in-situ mass balance study of Pensilungpa Glacier from 2016 to 2022 in Suru River Valley, Ladakh Himalaya, India. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1728, https://doi.org/10.5194/egusphere-egu24-1728, 2024.

Glaciers in the Himalaya are often covered by debris, which affects melt rates and causes high spatial heterogeneity in surface elevation changes. In the past decade years, unmanned aerial system (UAS) data have been shown to be indispensable in mapping and monitoring this type of glacier and catalysed new research focusing on process understanding of ablation processes at unprecedented detail. In this study, we present the results of a five-year biannual UAS monitoring campaign in the Langtang Catchment in the Nepalese Himalaya in which we surveyed Lirung Glacier (9 surveys, 2013–2018) and Langtang Glacier (7 surveys, 2014–2018). Optical UAS imagery was processed into high-resolution image mosaics and elevation data, accurately positioned using ground control data and co-registered using tie points. Derived glacier surface velocities and modelled bed topography were used to perform fully distributed corrections for ice flow and emergence velocity. The resulting flow-corrected surface changes of the glacier were analysed and used to evaluate supraglacial ice cliff evolution, glacier retreat, and melt. Results show that on average the surveyed areas of Lirung Glacier and Langtang Glacier had comparable surface velocities ranging from about 1.0 to 3.5 m a^-1 and a melt of −1.40 ± 0.05 m a^-1 and -1.22 ± 0.08 m a^-1, respectively, with both glaciers having strong spatial heterogeneity and temporal variability. Supraglacial ice cliffs on both glaciers exhibit variable (rates of) change in morphology, largely irrespective of aspect. The terminus of Lirung Glacier, which is characterized by a debris-free ice cliff, experienced very fast retreat of 41 m a^-1. The five-year time series of UAS data presented in this study has provided unique insights in surface changes of debris-covered glaciers. UAS surveys are and continue to remain highly valuable tool to study such glaciers, with potential still to be unlocked.

How to cite: Kraaijenbrink, P. and Immerzeel, W.: Five years of change of two debris-covered glaciers monitored by unmanned aerial system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1758, https://doi.org/10.5194/egusphere-egu24-1758, 2024.

The Northern Patagonian Ice Field (NPI), Chile, is the second-largest ice body in the Southern Hemisphere outside Antarctica, and one of the two remnant parts of the Patagonian ice sheet that existed during the last glacial period. It is located in the Southern Andes, a region that was identified to have one of the most negative specific mass balances of the world’s glacierized regions. The NPI is a highly dynamic ice body, characterized by large accumulation/ablation rates and contains the equator nearest tidewater  calving glacier, Glaciar San Rafael. We used the ice-sheet model SICOPOLIS to reproduce the current state of NPI and realize projections under different climate change scenarios. Calving is treated by implementing an additional specific mass loss for grid cells which are in contact with the ocean (San Rafael Lagoon). Forcing the model with a constant present-day surface mass balance a steady state is achieved which shows much similarity with the current state of the NPI. When forcing the model with different climate change scenarios, a mostly constant mass loss during the 21st century and a stabilization of the NPI during the 22st century is observed. The representation of Glaciar San Rafaels' front position improves clearly when implementing a simple (constant) calving law, however, the effect on the projected overall ice volume is low. Our simulation suggest that even if climate stabilized during 21st century, glacier changes on NPI would continue during the 22nd century.

How to cite: Schaefer, M., Tabone, I., Greve, R., Fürst, J., and Braun, M.: Projecting the evolution of the Northern Patagonian Ice Field until the year 2200, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2575, https://doi.org/10.5194/egusphere-egu24-2575, 2024.

Greenland's snow and ice melting trends have increased since the conclusion of the Little Ice Age (LIA), leading to the emergence of new ice-free zones. Given its significant impacts on ecosystems and climate, a comprehensive understanding of the spatiotemporal patterns of Greenland meltwater, snow and ice cover is crucial. This study conducts a comparative analysis of recent snow and ice dynamics (1985-2022) within the Central-Western Greenland Ice-Sheet (GrIS) and Nuussuaq Peninsula Greenland peripheral glaciers (GICs). Specifically, we examine the extension of snow and ice cover, changes in mass balance, and the climatic evolution in these geographical areas. The regions of GICs and GrIS demonstrate a statistically significant (p-value <= 0.05) positive temperature trend, particularly during the accumulation season at GIC (R2 = 0.19) and GrIS (R2 = 0.13). However, precipitation trends reveal minimal and statistically non-significant changes. Despite their geographical proximity, the terminus positions of land-terminating glaciers in GrIS and GICs exhibit different spatial patterns and trend rates. Over the last two decades, Nuussuaq Peninsula GICs display an average negative mass loss of -0.3 GT/year, with the minimum mass loss recorded in 2007 (-0.2 GT/year), constituting an anomaly of -25% compared to the average mass loss for the temporal period analyzed. In contrast, peak mass loss values are observed in 2009, reaching anomalies of -0.4 GT/year. Further, the snow and ice cover area of GICs indicates a reduction of approximately 20% from the previous delineations of the LIA, with the most significant decreases observed in the southern-exposed Nuusuaq Peninsula GICs. Conversely, small differences in GrIS land-terminating terminus positions are detected from 1985 to 2022, despite substantial meltwater anomalies since the 1990s. These results highlight the different sensitivity of terminus positions between GICs and GrIS despite their proximity. Our findings contribute to a better understanding of the recent spatiotemporal evolution of glaciers in Western Greenland.

How to cite: Bonsoms, J., Oliva, M., and López-Moreno, J. I.: Contrasting glacier terminus position trend rates between Central-Western Greenland peripheral glaciers and ice sheet:  spatiotemporal patterns and trends (1985 to 2022), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3207, https://doi.org/10.5194/egusphere-egu24-3207, 2024.

High-resolution climate data is crucial for accurate glacier modeling in topographically complex regions. This study investigates the necessity of such data for accurate simulations of glacier and freshwater dynamics for the Flade Isblink Ice Cap (FIIC), Northeast (NE) Greenland. It also explores the potential of achieving comparable results using coarse-resolution global datasets with region-specific scaling.

The study employed an advanced subdivision of FIIC, consisting of 299 glaciers, including six active marine-terminating ones. Four climate datasets (ERA5, CRU, W5E5, and ERA-Interim dynamically downscaled using polar WRF for NE Greenland) with 5-50 km spatial resolutions were used to force the Open Global Glacier Model (OGGM) from 2014 to 2018. OGGM was calibrated glacier-by-glacier against high-resolution geodetic-altimetric mass balance, frontal ablation, and volume data. Sensitivity analyses were conducted with and without regional scaling for all selected climate datasets and calibration parameters.

The high-resolution WRF dataset provided an accurate initial regional volume estimate (with a minimal deviation of -0.6 % from the reference) without any local corrections, while other datasets underestimated volume, increasing with decreasing resolution from 8 % to 15 %. However, applying regional temperature bias and precipitation factor significantly improved the accuracy of these estimates, reducing the underestimation from just 2.1 % to 2.4 %. Sensitivity analysis revealed that the precipitation factor has a moderate influence, while temperature bias has a higher influence on the modeled volume. Without scaling, coarse datasets underestimated annual freshwater runoff by 25 % to 34 %, but with regional scaling, this discrepancy was markedly reduced to a near alignment with the WRF dataset at 0.5 % to 1.6 %, corresponding to 9.8 Gt/yr. Across datasets, summer months (June, July, August) runoff estimates showed no significant differences (p>0.05) after regional scaling.

The study concludes that high-resolution climate data enhances the accuracy of initial volume estimates, thereby increasing confidence in simulated results. However, appropriate local adjustments to coarser datasets can yield comparable glacier and freshwater runoff simulations. Initial volume estimates are crucial for future projections. Future modeling efforts will explore the sensitivities of regional scaling and parametrization on improving projections of freshwater contributions into the ocean and their feedback on glacier-ocean interactions.

How to cite: Shafeeque, M., Vlug, A., and Marzeion, B.: Assessing the Influence of Climate Forcing Data Resolution on Simulations of Glacier and Freshwater Dynamics for the Flade Isblink Ice Cap, Northeast Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5140, https://doi.org/10.5194/egusphere-egu24-5140, 2024.

The development of a katabatic boundary layer can decouple near surface air temperature changes over glaciers from their surrounding environment during the ablation season, impacting the response of glaciers to ongoing climate change. Current glacier modelling efforts mostly neglect such processes and assume that glacier mass balance will evolve linearly with large-scale (ambient) air temperature changes into the future. Recent work has established that glacier evolution with climate will likely be non-linear, including in its sensitivity to ambient temperature. While past studies have explored this near-surface decoupling at a number of individual sites, the derived patterns have not been generalisable. We compile an extensive new inventory of on-glacier weather station data to explore this phenomena, with over 175 glacier-year sets, including more than 350 individual AWS locations and > 1.3 million hourly air temperature observations. Combining in situ on-glacier and near-glacier meteorological data with reanalysis and surface topography information we are able to explore how the climatic setting and local processes (e.g. wind interactions and local topography) may shape a glacier’s ability to become more or less coupled to the ambient climatic warming. Across all sites studied we find a mean (std.) cold bias of on-glacier vs. ambient temperatures of 1.22±1.35°C and a ratio of above-ice temperature changes compared to ambient, non-glacier conditions of 0.75±0.17 (i.e. a 1°C increase off-glacier equals ~0.75°C change on-glacier). We highlight the relevance of this to glacier modelling applications at select glacier sites and demonstrate hotspots around the world where above-glacier temperature changes during the recent decades are likely to have become decoupled from background warming. Preliminary results show how larger glaciers in maritime climates and those with minimal debris cover are most likely to decouple from ambient warming. However, as glaciers shrink and debris cover expands, the influence of the climatic setting in controlling this decoupling is diminished.

How to cite: Shaw, T., Miles, E., Buri, P., McCarthy, M., Guyennon, N., Carturan, L., Salerno, F., and Pellicciotti, F.: Temperature Decoupling on the World’s Mountain Glaciers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5815, https://doi.org/10.5194/egusphere-egu24-5815, 2024.

Mountain glaciers significantly impact sea level rise and water availability during droughts. Models project continued glacier mass loss in the 21^st century due to past and future rising temperatures. Our study delves into the repercussions of overshooting the 1.5°C Paris Agreement target and returning to it afterwards. For the first time, we explore the effects of these peak-and-decline overshoot scenarios on glacier volume and runoff using the Open Global Glacier Model (OGGM) framework. We apply novel climate simulations from 2000 to 2500  conducted with a  comprehensive  Earth System Model. These simulations either stabilise at global warming levels of 1.2°C (current warming), 1.5°C and 3°C, or temporally overshoot 1.5°C peaking at 3°C before declining and stabilising at 1.5°C after 2300. Although some glacier regions regrow within a century after the overshoot, the slow global glacier response results in irreversible ice loss over centuries. In 2500, overshooting the 1.5°C scenario temporarily by a peak at 3°C results in 10% more global glacier loss than directly stabilising at 1.5°C. While glacier runoff may temporarily increase in some basins in the coming decades, all basins will see a reduced contribution of glacier runoff to streamflow by the end of the 22^nd century under global stabilisation scenarios at 2°C or higher. In regions where glaciers regrow within the simulation period to reach a new equilibrium after a temporal temperature overshoot, glacier runoff contribution reduces temporally further than if temperature stabilises ("trough water"). The consequences of this newly documented "trough water" will depend on local conditions such as the local temperature overshoot magnitude, volume response time, future precipitation shifts, and melt versus precipitation seasonality. This study lays the first conceptual groundwork for overshoot scenarios on glaciers and introduces the potential of trough water risks. Additional Earth System Model realisations are needed for a detailed regional analysis and adaptation planning.

How to cite: Schuster, L., Maussion, F., Schmitt, P., Rounce, D. R., Ultee, L., Lacroix, F., and Frölicher, T.: Irreversible glacier change and trough water for centuries after overshooting the Paris Agreement temperature goal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5843, https://doi.org/10.5194/egusphere-egu24-5843, 2024.

Understanding the response of Himalayan glaciers to global warming is vital because of their role as a water source for the Asian subcontinent. However, great uncertainties still exist on the climate drivers of past and present glacier changes across scales. Here, we analyse continuous hourly climate station data from a glacierized elevation (Pyramid station, Mount Everest) since 1994 together with other ground observations and climate reanalysis. We show that a decrease in maximum air temperature and precipitation occurred during the last three decades at Pyramid in response to global warming. Reanalysis data suggest a broader occurrence of this effect in the glacierized areas of the Himalaya. We hypothesize that the counterintuitive cooling is caused by enhanced sensible heat exchange and the associated increase in glacier katabatic wind, which draws cool air downward from higher elevations. The stronger katabatic winds have also lowered the elevation of local wind convergence, thereby diminishing precipitation in glacial areas and negatively affecting glacier mass balance. This local cooling may have partially preserved glaciers from melting and could help protect the periglacial environment (Salerno, Guyennon, et al., 2023).

Salerno, F., Guyennon, N., et al. Local cooling and drying induced by Himalayan glaciers under global warming. Nat. Geosci. 16, 1120–1127 (2023). https://doi.org/10.1038/s41561-023-01331-y

How to cite: Salerno, F., Guyennon, N., Yang, K., E. Shaw, T., Lin, C., Colombo, N., Romano, E., Gruber, S., Bolch, T., Alessandri, A., Cristofanelli, P., Putero, D., Diolaiuti, G., Tartari, G., Thakuri, S., Miles, E. S., Bonomelli, S., and Pellicciotti, F.: Local cooling and drying induced by Himalayan glaciers under global warming, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6253, https://doi.org/10.5194/egusphere-egu24-6253, 2024.

Glaciers adapt to changing climatic conditions by losing or gaining mass, translating into a geometry change. Due to ice-dynamical processes within glaciers that gravitationally transport mass from high to low elevation, the adaptation of the glacier geometry to changing climatic conditions is not immediate but requires timescales ranging from decades up to millennia. As a consequence, today glaciers are in imbalance with current climatic conditions and will respond on timescales that extend beyond the 21^st century time horizon that is typically considered in today’s glacier evolution studies.

As part of the Glacier Model Intercomparison Project – Phase 3 (GlacierMIP3), a global glacier modelling community effort, we quantify how glaciers will stabilize under a wide range of climatic conditions. Using 8 large-scale glacier models, we estimate the committed loss of all glaciers on Earth outside the ice sheets under current climate conditions (corresponding to +1.2°C above pre-industrial levels) and their long-term stabilization under various policy-relevant global warming scenarios, such as +1.5°C and +2°C (Paris agreement), and the projected warming following current policies (+2.7°C). The forcing is derived from historical and future simulations (3 SSP emission scenarios) from 5 GCMs, from which climatic conditions for given time periods are continuously repeated over millennial time scales, leading to an eventual glacier stabilization.

We find that the committed glacier loss is substantial, with about one third of global glacier volume to be lost under current climatic conditions. The final (steady state) global glacier volume strongly depends on future temperatures, with an increase in the order of 2-3% of global glacier loss per 0.1°C warming. We also evaluate regional differences and quantify the time scales involved in glacier stabilization. Here we find that the topographical features such as the elevation range and the surface slope of glaciers play an important role.

How to cite: Zekollari, H., Schuster, L., Hock, R., Marzeion, B., Maussion, F., and GlacierMIP3 participants, T.: Effect of climate policies on the long-term equilibration of glaciers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6780, https://doi.org/10.5194/egusphere-egu24-6780, 2024.

Recent research indicates a substantial reduction in glacier mass within the Himalayas, primarily attributed to rising temperatures, leading to heightened uncertainties regarding downstream water availability. This study specifically investigates the impact of variations in thickness within the Gangotri glaciers, focusing on the Raktavaran and Chaturangi regions, during the period from 2011 to 2020. Employing a two-model coupling approach, the study integrates Glacier Bed Topology (GlabTop2) and Spatial Process in Hydrology (SPHY). Calibration is meticulously carried out through a two-step process, incorporating observed discharge data and Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover information. The achieved R2 values for SPHY-modeled runoff (Q) and observed Q at Bhojwasa exhibit a commendable level of comparability, standing at approximately 0.73 on a daily scale. The analysis highlights that glacier-derived Q contributes to 22.11% of the total Q, with snow-derived Q accounting for 66.91%, underscoring their distinct roles in the hydrological system. A comparative assessment between Chaturangi and Raktavaran with the Gangotri glaciers reveals that the latter experienced a more substantial rate of thickness change, resulting in an estimated reduction of about 9.40% in mean glacier thickness over the period from 2011 to 2020. In consideration of these findings, the study emphasizes the urgent necessity for a comprehensive understanding of the intricate interplay between glacier dynamics and hydrological processes within the context of changing climatic conditions. This research contributes valuable insights that can serve to inform adaptive strategies and resource management practices aimed at addressing the evolving challenges posed by glacier melt and its downstream implications.

How to cite: Singh, J., Singh, V., and Ojha, C. S. P.: Quantifying runoff variability and Glacier thickness variations from 2011 to 2020 in Gangotri glaciated region, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7118, https://doi.org/10.5194/egusphere-egu24-7118, 2024.

Glaciers are archives of past climatic conditions, reflected in the yearly amount of ice accumulation or depletion. Ice coring allows access to the information stored in glacial layers. However, discontinuities in an ice core create problems in reliably dating the core layers and questions regarding the origin of the discontinuity.

The analysis of an ice core from 2017 on Weißseespitze, a cold-based ice cap located at 3498 m a.s.l. in Tyrol (Austria), could be explained by the presence of a discontinuity around 400 CE. Since the glacier is nowadays experiencing potentially similar mass loss conditions, this study analyses present day surface energy balance to identify the potential climatic drivers behind the supposed discontinuity.

Energy balance at the core site is modelled with the COupled Snowpack and Ice surface energy and mass balance model in Python (COSIPY), forced with data collected between 2017 and 2022 by an automatic weather station on the glacier. COSIPY initialisation was optimised by comparing modelled and observed snowheight, the observed albedo was introduced as an input variable and the precipitation input was modified to better suit high altitude locations.

Comparison of the modelled and observed snowheight shows minor mismatches, connected in part to the absence of a wind erosion parameterization in the model and in part to the overestimation of surface temperature from the energy balance optimization algorithm. Nevertheless, COSIPY ice melt gradient agrees very well with observations and the simulation of the ablation season is not deeply affected by such problems.

Weißseespitze lost on average about 3 m of ice at the summit since 2018. The summer characterised by maximum ice melt in the observational period was 2022, where ablation stakes recorded on average 1.5 m of ice loss. On the contrary, summer 2020 was the only summer where most of the summit registered no ice loss. Comparison of energy balance components between the summer 2022 and 2020 showed that 2022 was characterised by positive and more intense sensible (9.8 W m^-2 vs 5.8 W m^-2) and latent (1.0 W m^-2 vs -1.0 W m^-2) heat fluxes and a lower outgoing shortwave energy flux (118.8 W m^-2 vs 166.1 W m^-2). The latter is caused by an abrupt albedo lowering at the beginning of July, which aligns with a period of uninterrupted positive air temperature of almost two weeks removing the snow from the previous winter. Therefore, air temperature and its impact on the glacier surface seems to be the main driver of ablation in 2022, which had about 20 positive temperature days more than 2020, resulting in an average air temperature 1.2 °C warmer.

These preliminary results will be shortly complemented by research in local archives of paleotemperature to verify whether the time of the hypothesised discontinuity was characterised by similar conditions.

How to cite: Baldo, A., Nicholson, L., Hartl, L., and Stocker-Waldhuber, M.: Ablation drivers over a cold-based ice cap in the Eastern Alps: a surface energy balance analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7454, https://doi.org/10.5194/egusphere-egu24-7454, 2024.

Most glaciers and ice caps (GIPs) are out of balance with the current climate, exhibiting continuous retreat and thinning. These changes impact regional runoff and contribute to sea level rise, causing glacier-related hazards. In this study, we estimate the area and volume losses for current GIPs to reach equilibrium through modelling the steady state accumulation area ratios (AAR₀) and time-averaged AAR of each GIP. The modelled global average AAR₀ is 0.541 ± 0.082, which is lower than most previous studies due to the inclusion of numerous unobserved GIPs. Ice caps exhibit a higher AAR₀ (0.612 ± 0.11) compared to glaciers (0.538 ± 0.08). For regional distribution, the largest AAR₀ appears in northern Arctic Canada (0.608 ± 0.114) and low latitude areas (0.570 ± 0.067), while the smallest AAR₀ occurs in Central Europe (0.519 ± 0.066) and north Asia (0.522 ± 0.071). Accounting for debris-cover reveals a decrease in AAR₀ due to reduced sub-debris melting, while considering the frontal ablation of marine-terminating glaciers leads to an increase in AAR₀. Assessing the imbalance between global GIPs and the current (2000-2019) climate, we project an additional loss of 23 ± 6% in area and 29 ± 8% in volume. This corresponds to a sea level rise equivalent of 128 ± 34 mm. The Antarctic and subantarctic are the primary contributor to global mean sea level rise, accounting for 60 ± 20 mm. The GIPs in central and eastern Himalaya, as well as the Mt. Hengduan exhibit significant instability, characterized by an average imbalance ratio (AAR/AAR₀) of 0.72 ± 0.25.

How to cite: Yang, W., Chu, W., Li, Y., and Mackintosh, A.: Global glacier climate disequilibrium from modelling steady state AAR, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8079, https://doi.org/10.5194/egusphere-egu24-8079, 2024.

How to cite: Schuler, T. V., Nanni, U., Bouchayer, C., Åkesson, H., Lefeuvre, P.-M., Mannerfelt, E., Köhler, A., Schmidt, L. S., Hulth, J., and Renard, F.: Observed weakening of glacier ice-bed interface caused by climatic and hydro-mechanical feedbacks: towards glacier-wide acceleration?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8481, https://doi.org/10.5194/egusphere-egu24-8481, 2024.

Mountain glaciers form a critical component of the cryosphere and are sensitive to climate change. Snow
line altitude (SLA) at the end of the ablation season is an indicator of climate change and a proxy for
equilibrium line altitude (ELA). Here, we compute SLA by incorporating satellite imagery of 38 years
(1984-2022) through mapping snow and ice over the elevation. A digital elevation model is being utilized to
derive SLA over a period of time. This proxy database is quite useful in various glacier dynamics estimated
through numerical modelling such as mass balance reconstruction, thickness gradient, or glacier length
estimation. The study explores various techniques to estimate the snow and glacier cover area (Otsu, k-
means) apart from manual thresholding. Furthermore, the study also includes glacier surface shape changes
to reduce the occurrence of misclassification. We further evaluate the performance of these techniques,
however, each one has its own redundancies. In the case of Otsu image segmentation, the errors are quite eminent
as the technique does not take into account the variation in glacier dimensions. The results are better in
terms of classification in the case of manual thresholding but the whole process is quite cumbersome. In
the case of K-means, the clustering algorithm takes into account the glacier dynamics which improves the
classification but the technique does not work well in the case of large datasets. Furthermore, for validation,
Careser glacier is being considered as it has the longest monitored observational dataset in the Italian Alps.
The results are mostly in alignment with the observed dataset, particularly for years where the Sentinel
dataset is available. The SLA seems to depict a descending trend in the case of Careser in recent years.
However, this recent behavior further needs to be evaluated. The algorithm is then further applied to the
glaciers of Aosta Valley.

How to cite: Ayub, S., Camporeale, C., Ridolfi, L., Coppola, E., and Godio, A.:  Estimation of Snow Line Altitude Utilising Satellite Imagery of Alpine Glaciers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8865, https://doi.org/10.5194/egusphere-egu24-8865, 2024.

Mountain glaciers are a major source of sea-level rise and also represent an important freshwater resource in many mountainous regions. Thus, accurate estimations of their thickness and, therefore, the total ice volume are important both in predicting and mitigating the global and local effects of climate change. However, to date, only 2% of the world’s glaciers outside the ice sheets have any thickness observations, due to the logistical difficulties of obtaining such measurements, creating a large and policy-relevant scientific gap.

The recent development of a global-scale ice-velocity dataset, however, provides an ideal opportunity to fill this gap and determine ice thickness across the 98% of glaciers for which no thickness data is available. This can be done by inverting an ice-dynamics model to solve for ice thickness. For accurate thickness results, this needs to be a higher-order model, but such a model is far too computationally cumbersome to apply on a global scale, and simpler, quicker methods usually based on the shallow ice approximation (SIA) are unsuitable, particularly where sliding dominates glacier motion. The only attempt that has been made to leverage the global velocity dataset to retrieve ice thickness has, though, used the SIA, simply because higher-order approaches are not computationally realistic at this scale. Consequently, most of the widely-used global glacier models have made no systematic attempt to invert global ice thickness, owing to these limitations. Allied to this is that, once an inversion is done, subsequent forward modelling is rarely physically consistent with the physics used in the inversion, leading to model inconsistencies that affect the accuracy of simulations.

As a solution to these problems, we extend our recent work on the European Alps using a deep-learning-driven inversion model, the Instructed Glacier Model (IGM), that emulates the performance of state-of-the-art higher-order models at a thousandth of the computational cost. This model, by solving a multi-variable optimisation problem, can fully use and assimilate all available input datasets (surface velocity and topography, ice thickness, etc.) as components of its cost function to invert ice thickness. This approach also gives us the possibility of using consistent ice-flow physics for inversion and forward modelling, reducing the magnitude of the shock inherent in traditional modelling approaches. We present here the first results of glacier-ice-thickness inference at a global scale obtained by the inversion of a higher-order three-dimensional ice-flow model.

How to cite: Cook, S., Jouvet, G., Millan, R., Rabatel, A., Maussion, F., Zekollari, H., and Dussaillant, I.: Global ice-thickness inversion using a deep-learning-aided 3D ice-flow model with data assimilation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8944, https://doi.org/10.5194/egusphere-egu24-8944, 2024.

Most glaciers around the world are slowing down, but some marine-terminating outlet glaciers occur and trigger seasonal or shorter-term accelerations (up to 100% greater than the annual mean), and the speedup events of glaciers cause accelerated glacier loss. Although some speedup events have been observed in the Greenland and Antarctica, limited observed in the Tibetan Plateau and the trigger mechanism is also poorly understood. In this study, we used the high-frequency Global Navigation Satellite System (GNSS) observations collected on the Parlung No.4 Glacier in southeastern Tibetan Plateau in 2022 to characterize the seasonal dynamics of glacier velocity and analyze its mechanism. The results show that the velocity has a distinct seasonal variation, with highly fast in summer (1.42 times as fast as winter flow). A total of 9 speedup events were observed in spring and summer, with 3 GNSS stations simultaneously generating 5 acceleration events; the glacier accelerated frequently from 25 June to 3 July, with a total of 3 speedup events; with the maximum intensity occurred at the end of July, which was about 10 times as fast as others. In addition, we find that the speedup of the glacier is mainly consistent with precipitation and the glacial runoff, and we suggest that the speedup of the glacier is mainly due to enhanced meltwater leading to glacier basal motion.

How to cite: zhang, T., Yang, W., and Ren, S.: Seasonal speedup of glacier in the southeastern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9185, https://doi.org/10.5194/egusphere-egu24-9185, 2024.

Glaciers are retreating globally and are projected to continue to lose mass in the coming decades, directly affecting downstream ecosystems through changes in glacier runoff. Estimating the future evolution of glacier runoff involves several sources of uncertainty in the modelling chain, which have not been comprehensively assessed on a regional scale. In this study, we used the Open Global Glacier Model (OGGM) to estimate the evolution of each glacier (area > 1 km²) in the Patagonian Andes (40–56° S), which together represent 82% of the glacier area of the Andes. We used different glacier inventories (n = 2), ice thickness datasets (n = 2), historical climate datasets (n = 4), general circulation models (GCMs; n = 10), emission scenarios (SSPs; n = 4), and bias correction methods (BCMs; n = 3) to generate 1,920 possible scenarios over the period 1980–2099. For each scenario and catchment, glacier runoff and melt time series were characterised by ten glacio-hydrological metrics. We used the permutation feature importance of random forest regression models to assess the relative importance of each source on the metrics of each catchment. Considering all scenarios, 30% ± 13% of the glacier area has already peaked in terms of glacier melt (year 2020), and 18% ± 7% of the glacier area will lose more than 80% of its volume this century. In terms of glacier melt metrics, future sources of uncertainty (GCMs, SSPs and BCMs) were the main source for only 18% ± 21% of the total glacier area. In contrast, the reference climate was the main source in 78% ± 21% of the glacier area, highlighting the importance of the choices we made in the calibration procedure. The results provide a basis for prioritising future efforts to reduce glacio-hydrological modelling gaps in poorly instrumented regions, such as the Patagonian Andes.

How to cite: Aguayo, R., Maussion, F., Schuster, L., Schaefer, M., Caro, A., Schmitt, P., Mackay, J., Ultee, L., Leon-Muñoz, J., and Aguayo, M.: Unravelling the sources of uncertainty in glacier runoff in the Patagonian Andes (40–56° S) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9831, https://doi.org/10.5194/egusphere-egu24-9831, 2024.

The Patagonian ice fields have been rapidly losing mass in the last decades, but little is known about the driving processes. Here we use state-of-the-art regional climate models to reconstruct the contemporary climate and glacier surface mass balance (SMB), i.e., the difference between snowfall accumulation and meltwater runoff, in the Southern Andes at 5 km spatial resolution for the period 1940-2022. Model outputs are further statistically downscaled to a 500 m grid that resolves SMB processes in high spatial detail. Our high-resolution SMB products show good agreement with both in-situ observations and GRACE/GRACE-FO satellite mass change measurements, when combined to solid ice discharge. We link recent glacier mass loss to an ongoing poleward shift of the subtropical highs that warms the ocean and atmosphere nearby Patagonian ice fields, in turn enhancing meltwater runoff.

How to cite: Noël, B., van den Broeke, M., Lhermitte, S., Wouters, B., and Fettweis, X.: Poleward shift of the subtropical highs drives Patagonian ice fields mass loss, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10112, https://doi.org/10.5194/egusphere-egu24-10112, 2024.

The Cordillera Darwin Icefield (CDI) in Tierra del Fuego is the third-largest temperate icefield in the southern hemisphere, covering an area of 2606 km² and storing at least twice the ice volume of the European Alps. More than half of the CDI glaciers are in direct contact with proglacial lakes or fjords, making them susceptible to both climatic surface mass change and ice-dynamic adjustments. Remote sensing studies have observed important mass losses in the region over the last decades. Despite the overall glacier retreat, individual glaciers show contrasting behavior, with some maintaining stable conditions or even thickening and advances, particularly in the central and southern part of the CDI. Associating the recent developments with atmospheric changes is challenging as in-situ observations of climatic conditions and glacier mass balance are scarce due to the harsh weather conditions and the difficult accessibility of the area.

We aim for generating a first, high-resolution simulation of surface mass balance for the entire CDI over the last two decades (2000-2022). Comprising all mass gain and loss terms at the surface, the surface mass balance is ultimately tied to robust high-resolution information on the atmospheric conditions. We will employ state-of-the-art statistical downscaling of atmospheric variables, paying special attention to downscaling of precipitation and the orographic effects over the high relief terrain. Moreover, climate conditions in Southern Patagonia are characterized by strong, year-round westerly winds, leading to efficient snow drift and increased spatially heterogeneity of snow deposition.

The results of our study will enable us to analyze variations in surface mass balance across space and time in the CDI. The key objective is to reliably disentangle the climatic imprint on glacier mass loss in the Cordillera Darwin for the last two decades. This climatic attribution is unprecedented and a unique opportunity to study the effects of climate variability and change in the higher mid latitudes of the southern hemisphere. Mass budgeting with remotely sensed mass balance observations will finally allow to derive a first estimate of frontal ablation and thus ice-dynamic controls on glacier changes in the CDI.

How to cite: Temme, F., Sommer, C., and Fürst, J. J.: Surface Mass Balance of the Cordillera Darwin Icefield, Tierra del Fuego, Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11243, https://doi.org/10.5194/egusphere-egu24-11243, 2024.

As the decline of alpine glaciers continues and accelerates, many glaciers are losing their firn area. Former accumulation zones are increasingly seeing melt conditions and mass loss. The loss of brighter snow and firn surfaces lowers albedo locally and at the glacier scale, impacting surface energy balance and leading to an albedo-mass balance feedback effect.

We assess the recent progression of firn loss into the (former) accumulation zone of Gepatschferner, Austria, focusing particularly on ice surfaces that have newly become exposed. Broadband albedo in the visible and near-infrared generally shows an altitudinal gradient in early summer from the darker, bare-ice glacier tongue to the snow covered region at higher elevations. As the melt season progresses and ablation of multi-year firn at higher elevations begins, albedo decreases substantially in areas that lose their firn cover. We find that these areas can become darker than ice in the ablation zone where no firn was present in previous years. In the extreme summer of 2022, the glacier surface of Gepatschferner was darkest in parts of the former accumulation zone where the firn-line shifted upwards. Newly exposed ice surfaces formed a “dark zone” between the remaining firn and previously exposed bare-ice areas. This zone of minimal albedo at relatively high elevations of the glacier persisted until the first snow falls in autumn and reemerged during the 2023 ablation season. 

Time series of satellite imagery show melt patterns as well as trends and variability of homogenized broadband albedo in the study region. In addition to remote-sensing based observations, multiple in-situ datasets are available for the summit region of Gepatschferner (i.e. on-ice weather station, ablation stakes, automatic camera, ice thickness measurements). Combining these datasets provides a unique opportunity to explore the impact of firn loss and albedo decrease on energy and mass balance, generate calibration and validation data for point scale and distributed modeling, and generally improve understanding of processes related to firn loss at different spatial and temporal scales. However, each observational dataset comes with uncertainties related to the scale and method of observation and the parameter being observed. Leveraging the potential of the rich available data basis requires careful consideration of the characteristics of the different data types and, when combined with energy and mass balance modeling approaches, the forcing requirements of the model. We present preliminary results from a project addressing the above for Gepatschferner and hope to connect with the community regarding the observation, modeling, and impacts of darkening mountain glaciers.

How to cite: Hartl, L., Stocker-Waldhuber, M., Covi, F., Baldo, A., and Naegeli, K.: The dark zone of an alpine glacier - considering albedo impacts of firn loss, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12014, https://doi.org/10.5194/egusphere-egu24-12014, 2024.

The contribution of Arctic glaciers and ice caps (GICs) to sea level rise in the last decades was similar to that of the Greenland Ice Sheet, however, their mass loss per unit area was larger. Between 2006 and 2015, mass changes were largest for GICs in Greenland when compared to other regions in the Arctic. Mittivakkat Gletsjer (Southeast Greenland) has the longest surface mass balance (SMB) record from field-based observations (since 1995/1996) for peripheral Greenland and is significantly out of balance with the current climate. Synthesizing ablation stake records (glaciological SMB), 1 km-downscaled RACMO 2.3p2 SMB output (modelled SMB) and volume changes from photogrammetrically-derived digital elevation models (geodetic MB) indicate a change from an almost balanced state for 1959-1995 to a negative mass balance regime for 1996-2022. RACMO is a regional atmospheric climate model forced by meteorological (reanalysis) data and estimates SMB from multi-layer snow cover simulations and albedo scheme. The model output shows SMB to be between 0.10 ± 0.14 m w.e. yr^-1 and -0.56 ± 0.14 m w.e. yr^-1 for the periods 1959-1995 and 1996-2022, respectively. The modelled SMB for the latter period is contrasted by the glaciological SMB of -1.06 ± 0.16 m w.e. yr^-1 for 1996-2022. The model output allows for assessing monthly and elevation-dependent changes in SMB between 1959-1995 and 1996-2022. Most months experienced a reduction in specific SMB with highest decreases in Jul (-0.19 m w.e.), Jun (-0.15 m w.e.) and Aug (-0.14 m w.e.), but Apr and Dec experienced no change (0.00 m w.e.) or an increase (0.10 m w.e.), respectively. The equilibrium line altitude increased from 600-650 to 800-850 m a.s.l., while there was a SMB decrease at each of the 11 altitude sections between 300-950 m a.s.l ranging from -0.59 to -0.70 m w.e yr^-1. The modeled SMB correlates well with the glaciological SMB (R² = 0.74; p < 0.01) but underestimates the glacier-wide mass loss by 47 % in the overlapping period.   The geodetic MB yields estimates of -0.73 ± 0.20 m w.e. yr^-1 for 1981-2013 (modelled SMB: -0.33 ± 0.14 m w.e. yr^-1) and -1.41 ± 0.76 m w.e. yr^-1 for 2014-2021 (modelled SMB: -0.59 ± 0.14 m w.e. yr^-1; glaciological SMB:  -1.15 ± 0.17 m w.e. yr^-1).  These differences highlight the challenges of synthesizing results of different mass balance methods such as spatial coverage, density assumptions, data quality, scaling and spatial extrapolation. We ran different configurations for the geodetic and modelled SMB outputs with varying agreement. The change to a more negative regime in the mid-1990s is discussed in the context of climate indices and are in line with modelled and ablation stake SMBs being negative in 24 out of 27 years between 1996 and 2022. The three years with a slightly positive balance can be associated with unusually high winter precipitation.

How to cite: Posch, C., de Villiers, S., Knudsen, N. T., Yde, J. C., Bjørk, A. A., Schöner, W., Abermann, J., and Sjursen, K. H.: Reanalysis of the surface mass balance of Mittivakkat Gletsjer (Southeast Greenland): Synthesizing data sources, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12396, https://doi.org/10.5194/egusphere-egu24-12396, 2024.

Avalanches are important contributors to the mass balance of glaciers located in mountain ranges with steep topographies. They result in localized mass inputs that are particularly difficult to quantify, due to the difficulty to access these avalanche cones in the field, and the need to account for ice dynamics when analyzing the elevation change signals from digital elevation models. Here, we aim to quantify the avalanche contribution to Argentière Glacier (Mont Blanc massif, French Alps) by inverting its distributed surface mass balance from remote sensing products and modeled ice thicknesses. Ultimately, we run the full-Stokes model Elmer-Ice with and without the additional contribution from avalanches to evaluate the importance of accounting for this process for future simulations of glacier evolution.

We used Pléiades satellite stereo acquisitions, captured at a high temporal resolution (more than 2 acquisitions per year), to generate detailed maps of elevation change and velocity spanning the years 2012 to 2021. We derived the distributed ice thickness of the glacier using three models of varying complexity, constrained by a dense array of ground penetrating radar measurements. To account for the uncertainty in ice thicknesses, we perturbed the modelled thicknesses using sequential gaussian simulations. We then combined ice thickness and velocity to derive the distributed flux divergence and surface mass balance at 20 m resolution across the whole glacier, carefully accounting for the uncertainties following a Monte Carlo approach. We evaluated our results against long-term mass balance measurements from stakes conducted as part of the French glacier monitoring service GLACIOCLIM, and in situ measurements of submergence on one of the main avalanche deposits.

There is a good agreement between our surface mass balance estimates and the stake observations (RMSE < 1.5 m.w.eq) for all ice thickness scenarios, even though ice thickness represents the most important source of uncertainty. Thus, the comparison of our distributed surface mass balance estimate with the mass balance gradient derived from the stake measurements allows us to 1) highlight the ability and potential of such an approach to provide robust estimates of distributed surface mass balance and 2) estimate the contribution of avalanches for Argentière Glacier with a relatively high accuracy. Notably, preliminary results show that the mass balance in avalanche-fed areas of the accumulation zone is approximately 2-10 times larger than in other areas at the same elevation.

How to cite: Kneib, M., Dehecq, A., Gilbert, A., Basset, A., Miles, E. S., Ducasse, E., Béraud, L., Mouginot, J., Mouginot, J., Jouvet, G., Laarman, O., Jourdain, B., Brun, F., and Six, D.: Distributed surface mass balance of the avalanche-fed Argentière glacier, French Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12488, https://doi.org/10.5194/egusphere-egu24-12488, 2024.

We present surface velocity maps of Grenzgletscher (Swiss Alps) obtained by terrestrial radar interferometry and compare them to velocity maps derived in earlier field campaigns to examine changes over time. To obtain recent velocity maps, we installed a Gamma Portable Radar Interferometer (GPRI) near Rotenboden Station facing the Grenzgletscher and collected data for five days in October 2023 with a three-minute sampling interval. From the resulting interferograms, the line-of-sight velocities can be calculated for various time intervals after averaging, which corrects for atmospheric noise. We find high line-of-sight velocities in the area of a steep ice fall, which suggests that the glacier is sliding in this area. We validate with concurrent GPS measurements and compare our velocity maps with those obtained in previous field campaigns, including a similar GPRI survey in 2008 and a survey utilizing unmanned aerial vehicles in 2017. This comparative analysis aims to identify temporal dynamic changes in areas where the various surveys overlap, ranging from sub-daily, to seasonal and yearly time intervals. This work will provide important observational boundary conditions to better understand mechanisms for the onset of basal sliding beneath glaciers in alpine and polar environments.

How to cite: Muhle, L. S., Wild, C. T., Drews, R., and Mantelli, E.: Do Grenzgletscher's Dynamics Shift? Insights from Terrestrial Radar Interferometry and Comparative Analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12617, https://doi.org/10.5194/egusphere-egu24-12617, 2024.

Glaciers in western North America (WNA) and Switzerland represent important sources of freshwater, especially during times of drought. We employ extensive airborne laser altimetry campaigns in WNA coupled with in-situ surface mass balance measurements for both regions to quantify recent mass change. Over the last three years glaciers within these regions respectively lost mass at rates of -22.8±7.4 and -1.7±0.3 Gt yr^-1 which, for both regions, represents an approximate twofold increase in mass loss compared to the period 2010-2020. Based on the estimated glacier volume in the year 2020, total volume change in these regions was depleted by 9% (WNA) and 10% (Switzerland) over the last three years. The year 2023 represents the year of greatest common mass loss for both regions where glaciers in both WNA and Switzerland respectively lost -37.1±10.4 and -1.8±0.3 Gt yr^-1. Meteorological conditions that favored high rates of mass loss included low winter snow accumulation, early-season heat waves, and prolonged warm, dry conditions. Loss of firn, high transient snow lines, and potential impurity loading due to wildfires (WNA) or Saharan dust (Switzerland) darkened glaciers and thereby accelerated melt via an increase in absorbed shortwave radiation available for melt. This ice-albedo feedback will lead to continued accelerated loss unless recently exposed dark firn and ice at high elevation can be buried by subsequent snowfall. Rates of mass loss for the years 2021-2023 exceed even those projected for unabated global emissions though the twenty-first century, signaling the need to rapidly mitigate greenhouse gas emissions if glaciers in both regions are to survive.   

How to cite: Menounos, B., Huss, M., Marshall, S., Ednie, M., and Florentine, C.: Western North American and Switzerland glaciers experience unprecedented mass loss over the last three years, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12833, https://doi.org/10.5194/egusphere-egu24-12833, 2024.

Tapado Glacier (30.15°S, 69.93°W) is a 1.6 km² ice mass located at high-altitude in Chile’s Desert Andes. This region reaches up to 6000 m a.s.l. and is characterised by high solar radiation and scarce and episodic precipitation. Despite its relatively small size, the glacier extends from 4500 to 5500 m a.s.l and contains several types of surfaces and features, such as a debris-covered section populated by ice cliffs and supraglacial ponds, a field of large snow and ice penitentes, a steep section with crevasses and seracs, and wind-exposed upper areas with minimal snow accumulation. As the ablation and evolution of these elements depend on several physical processes occurring at different rates, monitoring and modelling changes on Tapado Glacier is challenging. Our study describes and quantifies the main glacier changes over the last five years amidst rising summer temperatures and below-average precipitation from a process perspective. Monitoring techniques include direct mass balance and surface geometry measurements, flights of uncrewed aerial vehicles (UAVs), geophysical methods, satellite products, terrestrial LiDAR and automatic cameras.

Enhanced melt at ice cliffs and supraglacial ponds primarily drives ablation in the debris-covered section. Ice cliffs and ponds have persisted on the glacier surface since at least 1955. Satellite products and photogrammetrically derived Digital Elevation Models (DEMs) from UAV flights in the period 2020-2023 show that the ablation over a selected cliff and pond was about 10 times higher than over the rest of the debris-covered section. Analysis of historical satellite imagery tracks the evolution of the selected cliff from its formation between 1978 and 2000 to its recent disappearance in 2023, which was corroborated by an automatic camera. Geophysical measurements suggest the presence of ancient supraglacial lakes within the debris cover. The debris-free section shows consistent patterns of thinning and increasing surface roughness. Terrestrial LiDAR indicates an annual surface lowering of about −0.4 m, while UAV flights and direct observations show that the end-of-summer height of penitentes has increased from 1-2 m to more than 2 m, reaching up to almost 6 m in spots. In the upper parts of the glacier, we have observed increasing instability from a serac that produces frequent ice and rock falls into the penitentes-covered area. Summer ablation at the top of the glacier, mainly by sublimation, varied from 0.15 to 1.15 m during 2021-2023. Using recent data from ablation stakes and UAVs, we estimate a summer glacier mass balance of about −0.8 m w.e., which is equivalent to 1.3 million m³ of water.

Tapado Glacier exemplifies how different physical processes can drive glacier mass loss and runoff contribution. Recent changes in the glacier have made the field monitoring difficult and pose interesting challenges for glacier modelling.

How to cite: Ayala, Á., Robson, B., MacDonell, S., Navarro, G., Schaffer, N., Segovia, A., Petlicki, M., Kinnard, C., Schauwecker, S., Casassa, G., Vivero, S., and Lima, A.: Monitoring the physical processes driving the mass loss of Tapado Glacier, Desert Andes of Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13473, https://doi.org/10.5194/egusphere-egu24-13473, 2024.

Glaciers on Baffin Island present a mixture of abundant small to a few very large ice caps (Barnes, Penny) as well as thousands of valley glaciers, cirques and ice patches. Their large overall area (about 40,000 km²) combined with strong surface melting is responsible for their large contribution to sea-level rise over the past decades. However, area changes over the same time period are largely unknown, as a reliable glacier inventory for the year 2000 has only become available very recently. The previous version suffered from missing glaciers and missing debris cover on glaciers or outlines were outdated and had too large extents.

Here we present the results of a new glacier inventory for the entire region as obtained from Sentinel-2 and Landsat 8/9 satellite images acquired within a few days of August 2019. Although glacier mapping conditions were excellent in regard to seasonal snow, glacier boundaries were often polluted by dark material that was excluded from the applied automated mapping with a band ratio. Hence, all glacier boundaries were checked and manually adjusted when required. To obtain glacier specific area change rates, we used the same revised drainage divides as for the recent year 2000 inventory in RGI 7.0.

Overall, glacier area decreased by 10% from 2000 to 2019 i.e. at a rate of 0.54% per year. Thereby, glaciers <1 km² contribute 3% to the total area but 13% to the loss, whereas glaciers >10 km² contribute 70% to the total area and 40% to the loss. The area of Barnes Ice Cap decreased by 1.15%. As in other regions with glaciers, the shrinkage rate and scatter of values increases towards smaller glaciers and several glaciers melted away completely. Also some larger ice caps at low elevations suffered from substantial shrinkage and disintegration by down-wasting. The increasing extent of rock outcrops in the accumulation area of larger glaciers confirm the observed surface lowering over this period.

How to cite: Paul, F. and Rastner, P.: Glacier area changes on Baffin Island from 2000 to 2019 derived from Landsat and Sentinel-2 satellite images, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13526, https://doi.org/10.5194/egusphere-egu24-13526, 2024.

Glaciers retreating due to climate change have significant impacts both locally and globally. An essential part of understanding their evolution are mass balance measurements. Although the surface mass balance of glaciers is well known, non-surface components, more specifically basal and internal melt, are not well understood as they are inherently difficult to observe. Local maxima in basal melt on alpine glaciers are believed to result in the formation of large subglacial cavities, potentially leading to so called “collapse features”. The ice loss caused by these collapse features is likely to impact the retreat dynamics of glaciers.

Using a parameterized model based on a complete consideration of factors of sub- and englacial energy exchange, basal melt for all 1400 Swiss glaciers was estimated. The model operates with data sets on surface mass balance and glacier geometry, as well as with simplified considerations of the relevant processes. Our model considers energy advection through ice-marginal streams and subglacial air flow, potential energy release from melt water, friction-induced heat release, geothermal heat flux and dissipation of heat uptake by surface melt water. Field observations were used to constrain some of the parameters. Additionally, high-resolution aerial imagery and digital elevation models (DEMs) were used to perform a geostatistical analysis to better understand glacio-hydrological relationships and processes. Besides modelling glacier-wide basal melt, we analyzed the spatial and temporal dynamics of individual collapse features on a selected group of glaciers in the Swiss Alps, using high resolution DEMs.

The model results indicate that the advection of energy through ice-marginal streams and potential-energy release from melt water are the primary contributors to basal melt for Swiss glaciers. The relevance of the modelled components importantly varies between glaciers and depends on glacier size and topography among other factors. At the Swiss-wide scale, total basal melt is modelled to be in the range of a few millimeters to several tens of centimeters water equivalent per year (total mass balance of Swiss glaciers is on average -1 meter water equivalent per year). These results suggest that for some glaciers, basal melt is both a relevant fraction of total mass balance, as well as large enough to be measured using high-resolution in situ GNSS observations.

The analysis of glacier collapse features yielded an average life span of 3.5 years and volumes of non-surface ice loss ranging from a few thousand to more than 175’000 m³. These findings, along with the model results, emphasize the substantial role of basal melt in both local retreat dynamics and total glacier-wide mass balance.

How to cite: Hösli, L., Huss, M., Werder, M., and Farinotti, D.: Quantifying Basal Melt of Swiss Glaciers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14899, https://doi.org/10.5194/egusphere-egu24-14899, 2024.

The first-ever field measurements conducted at the outlet glaciers Gualas and Reichert at the Northern Patagonian Ice Sheet, Chile, provide the basis for this work. Both glaciers currently terminate in large (2 km resp. 9 km length) proglacial lakes. The glaciers have retreated rapidly over the past four decades, whereby Reichert glacier retreated by over 100 m per year. Our bathymetry measurements of these lakes make it possible to estimate the mass loss and make assumptions about floatation of these glaciers during retreat. The lakes have depths of up to 250 resp. 350 m and therefore the volume previously occupied by the glaciers is significant.
Recent UAV surveys of the final 3 km of the tongue of both glaciers and satellite data provide high-resolution elevation models and are employed to estimate mass loss since the 2000s. With this preliminary study we aim to investigate whether mass loss of these glaciers has been underestimated due to neglected subaqueous ice mass loss. Knowledge from this study will contribute to improving past, present and future mass change estimates of similar glaciers, with relevance for, e.g., sea level rise contribution from ice sheets and their outlet glaciers.

How to cite: Egli, P. E., Dussaillant, I., Irarrazaval, I., Somos-Valenzuela, M., Sotomayor González, B., Lizama, E., Morales, B., and Fernandez, J.: The rapid retreat of two lake-terminating outlet glaciers of the Northern Patagonian Ice Sheet and underestimation of mass loss due to subaqueous ice volume, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15836, https://doi.org/10.5194/egusphere-egu24-15836, 2024.

The Shishper Glacier in Pakistan has caused multiple incidents of glacier lake outburst flooding (GLOF), including recent events that occurred in consecutive years. The presence of an ice-dammed lake created by the Shishper Glacier poses significant risks to communities, infrastructure, and people's livelihoods downstream. To decrease the likelihood of GLOFs associated with the Shishper Glacier, it is important to implement an early warning system and effectively manage the water release from the glacial lake. This study used satellite imageries from Landsat and Sentinel 2, and ALOS 30 m DEM, to analyze the areal and volumetric expansion of glacial lake, formed by the blockade of Mochuwar Glacier by terminus of Shishper Glacier at the point of confluence. This terminus extends further downstream and has been the cause of several GLOF events in past. The Shishper Glacier has recently had many surges, the most recent of which occurred in 2022, 2020, 2019 and 2018. In this study, HEC-RAS 2D model was used to reproduce the Shishper glacier lake outburst flooding (GLOF2022) and assess its impacts on the areas located downstream. The findings of the study will contribute to proactive measures that can prevent future disasters and ensure the safety of the vulnerable population and critical infrastructure. 

How to cite: Urban, A., Naz, F., Azadi, H., Naeem, B., and Zaidi, A.: Enhancing Flood Preparedness: Modeling the Shishper glacier's Glacial Lake Outburst Flooding in Pakistan using Satellite Data and 2D Hydraulic Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16009, https://doi.org/10.5194/egusphere-egu24-16009, 2024.

High Mountain Asia (HMA) is a hotspot for research on global glacier change and its environmental impacts. Over the past few decades, HMA glaciers have undergone relatively slow but accelerating mass loss. However, our current understanding of the inter- and intra- annual variations in these glaciers remains insufficient. In this study, we derived glacier mass changes in HMA at different spatiotemporal scales through the integration of three altimetry products (i.e., ICESat, CryoSat-2, and ICESat-2). We constructed seasonal time series of glacier mass balance in HMA and its subregions and produced multiple elevation change maps for these glaciers over different periods. Our results showed that HMA glaciers experienced heterogeneous glacier ablation with a mean mass loss rate of 26.72 ± 3.30 Gt/yr during 2003 ‒ 2022. Among various subregions, the glaciers in Hengduan Shan experienced the most severe depletion and the most substantial mass loss (3.81 ± 0.47 Gt/yr). The glaciers in Western Himalaya and Eastern Himalaya suffered significant mass loss as well. The melting rate of HMA glaciers over the second decade has significantly accelerated compared to the preceding decade. Furthermore, in 2022, HMA glaciers experienced pronounced mass loss attributed to abnormally high temperatures, with the glacier ablation in the Qilian Mountains being the most severe on record. Our spatially explicit and high-temporal-resolution (monthly to seasonal) features of glaciers would improve understanding of HMA glacier changes and serve as a reference for future research in this field.

How to cite: Zhao, F., Long, D., Han, P., Wang, Y., Cui, Y., and Duan, X.: Satellite altimetry derived glacier mass changes over High Mountain Asia during 2003‒2022, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16092, https://doi.org/10.5194/egusphere-egu24-16092, 2024.

The Adamello Glacier, a rare example of a summit glacier in the Italian Alps, is undergoing profound transformations since the beginning of the century, with a substantial reduction in its surface area. Between 1995 and 2009, the net surface mass balance displayed an average decrease of -1439 mm w.e. per year. We analyze the retreat of the Adamello Glacier through diverse prospectives, discussing trends and variability in in-situ observations and remotely sensed images, and modelling its mass balance in the current and future climate. Firstly, we show the areal retreat of the glacierized area studied by means of satellite images (Landsat), obtaining an areal retreat of 11% every decade since 2007. Secondly, we present the timeseries of temperature and precipitation measured at nearby high elevation meteorological stations. Significant increasing trends are found in temperature, especially in the summer period (+0.8°C every decade since 1996). Accumulation variability and trends are also discussed, drawing insights from snow water equivalent measurements systematically collected since 1967, revealing concerning spring trends with a 5-6% decrease in water equivalent every decade on April 1, and no significant trends in winter. Thirdly, by means of the Physical based Distributed Snow Land and Ice Model (PDSLIM), validated by ablation measurements collected in August 2023, we compute the distributed surface mass balance of the Adamello glacier for the period 2010-2023, obtaining an average net mass balance of -2170 mm w.e., significantly larger than in the period 1995-2009. Finally, in order to assess the future evolution of the glacier, we make use of regional climate models (RCMs) simulations of the future climate conditions developed in the framework of the CORDEX experiment for different emission scenarios. Our results highlight the critical conditions the Adamello Glacier is experiencing nowadays, quantifying the surface mass balance in the current climate, and estimate its expected behavior by the end of the century considering different emission scenarios.

How to cite: Colosio, P., Liaqat, M. U., Grossi, G., and Ranzi, R.: The retreat of the Adamello Glacier (Italy) in a changing climate from snow and meteorological measurements, remote sensing observations and surface mass balance modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16523, https://doi.org/10.5194/egusphere-egu24-16523, 2024.

The evolution of hanging glaciers in a context of changing climate has significant implications because their stability is particularly sensitive to changes in their basal thermal regimes. Projections indicate that by the end of this century, all glaciers below 4000 m altitude in the European Alps will likely transition from a cold-based to a temperate-based state due to climate forcing. Unstable hanging glaciers already threaten villages, transport routes and ski infrastructure in the Alps. Given the high density of settlements, infrastructure and access for recreation, the evolution of hanging glaciers must be well understood. However, modelling the thermal regimes of hanging glaciers is often difficult because of their complex geometries, and the difficulties associated with data acquisition. Our study utilised ground-based ground-penetrating radar (GPR) techniques in a novel application to investigate the bedrock geometries of four hanging glaciers at two sites at the Pointes du Mourti (3563 m a.s.l.), Pennine Alps, Switzerland, and the Aiguille du Midi (3842 m a.s.l.), Mont-Blanc Massif, France.

By combining a GPR survey with two years of thermal data recorded in two boreholes, and two annually spaced UAV photogrammetric surveys, we investigated the geometry and the current evolution of the Pointes du Mourti hanging glacier. We were able to extract subglacial bedrock geometry and ice depths covering an area of 9791 m², representing 16.2% of the glacier area in 2022. We demonstrated that this hanging glacier, with a mean inclination angle of 43°, resides in a concave feature on the mountain slope with a rugged subglacial surface. Basal temperatures in the upper part of the hanging glacier are below -2.5 °C, indicating cold-based conditions, whereas the central part may be in a more temperate-based condition. Furthermore, the surface topography of all the investigated glaciers underwent substantial changes during the unusually hot summer of 2022, which followed the very dry winter of 2021/2022, exceeding historical norms. The Pointes du Mourti hanging glacier lost 0.86 m of thickness on average and more than 7% of its surface area between October 2021 and September 2022. Similarly, the Jumeau Ouest hanging glacier, at the Aiguille du Midi, lost 0.92 m between June and September 2022.

Our study shows that ground-based GPR can be successfully employed in challenging topographical environments to determine sub-glacial geometries of hanging glaciers. This method can be a valuable tool in a multi-faceted approach to hanging glacier investigations, effectively providing necessary ice depths and bedrock configurations. This research contributes valuable insights for both scientific and administrative communities invested in comprehending the consequences associated with the evolution of hanging glaciers.

How to cite: Robson, B., Lambiel, C., Ravanel, L., Irving, J., Baron, L., and Gentizon, J.: Combining ground-penetrating RaDAR, unmanned aerial vehicle photogrammetry and borehole thermal data to investigate the evolution of hanging glaciers in the western European Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16774, https://doi.org/10.5194/egusphere-egu24-16774, 2024.

The extreme melt during the years 2022 and 2023 resulted not only in up to 3 m w.e. ice loss, but also to rapid shrinkage of glacier area. As a result of thinning in all altitudes, an increase in pace of area loss can be expected for the next years. The area loss for long term mass balance glaciers reached up to 10% in 2023 for Jamtalferner. This similar to the area loss of the last decade and rises the question, how significant the tracking of the area loss influences the accuracy of in situ mass balance, as we traditionally calculate mass balance based on the area of the previous year.

Another open question regarding mass balance methods are effects of the repositioning of stakes into flat areas with low debris cover which is forced by increasing rock fall activities. There also is evidence of wide spread melt at the base of the glacier which is so far unquantified.

With rapidly shrinking areas, specific mass balance curves and total balance show larger differences, i.e. although specific mass balance increases, the areas shrink so rapidly that the total melt water runoff decreases. Equilibrium line is above summits for most of the mass balance glaciers in western Austria in most years of the last decade.

So far, the Austrian glacier inventories did not split up glaciers in smaller entities, to allow to tackle the evolution of formerly larger glaciers without accounting for parent and child IDs. Now, for some glaciers the ice remnants are clearly not fulfilling the criteria for a glacier, as they consist only of a small part of the former glacier tongue, where the ice has been thicker and survived the former ablation area. Tackling glacier loss in a consistent way turns out to be tricky, as remote sensing data often does not allow to distinguish debris covered glaciers from cold rocky landforms as frozen base moraines. Aerial photography or LiDAR elevation models would be needed in shorter repeat periods as the decadal intervals used so far. During summer 2023, some smaller glaciers disappeared within weeks, and it is also the pace of this loss which is quite informative and relevant for local hydrology and hazard situation.

How to cite: Fischer, A., Stocker-Waldhuber, M., Hartl, L., Seiser, B., Helfricht, K., Gschwentner, A., and Bertolotti, G.: How to balance the voids? Tackling rapid ice loss in western Austria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16984, https://doi.org/10.5194/egusphere-egu24-16984, 2024.

Research suggests that at least 40 % of mass loss from the Greenland ice sheet is related to calving at marine terminating glaciers and that the rate of calving is linked to glacier meltwater plume processes. Understanding plume extent and temporal and spatial variability is, therefore, important for estimating potential SLR.

This work presents satellite data observations of plume extents from multispectral sensors as well as the novel use of satellite synthetic aperture radar (SAR) sensors for this application. Ocean fronts, large-scale upwelling and estuarine plumes have been isolated in the past using SAR data but application of SAR to smaller-scale glacial meltwater plume extent has not so far been presented. With the advent of higher resolution SAR imagery in recent years there is an opportunity to apply the technique to study these glacial meltwater plumes as their presence modifies the wind, wave and current interactions on a water surface and so influence the backscatter signal presented in the SAR intensity image.

Plume observations from multispectral and SAR data are presented for the glacier-marine lagoon complex of Breiðamerkurjökull glacier and Jökulsárlón proglacial lake, Iceland. This system is a good analogue for a Greenlandic fjord-ocean systems and is where we will also conduct future fieldwork on the 3D structure of meltwater plumes.

How to cite: Edwards, L.: Glacial meltwater plume extent from multispectral and SAR satellite data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19184, https://doi.org/10.5194/egusphere-egu24-19184, 2024.

The subglacial hydrological system is a key component in understanding the response of glaciers to climate change. However, due to its inaccessibility, the subglacial system is logistically difficult to investigate. Here we use an Uncrewed Aerial Vehicle (UAV) to monitor variations in the lake area of Fjallsárlón, a large proglacial lake in SE Iceland, at high spatial and temporal resolutions to better understand the hydrology of the adjacent soft-bedded outlet glacier Fjallsjökull. Surveys were undertaken over 10 days in July and 7 days in September 2023, with the acquired imagery used to generate high-resolution orthomosaics and DEMs (0.01 m and 0.03 m, respectively). We then developed and applied a novel method to the resultant 3D models to measure variations in proglacial lake area on a diurnal scale, bridging the gap between ground and satellite-based observations. We were able to measure a minimum diurnal variation of ~9,800 m² and a maximum diurnal variation of ~56,000 m² in lake area during the study period. As such, our results indicate the potential of UAVs to monitor changes in proglacial lake area at high resolutions. We suggest that the novel method applied here can successfully be used to measure variations in the lake area of Fjallsárlón, which can be used alone or alongside satellite records of lake area change. From these data, insights into the outputs of the hydrological system can be obtained, which can be used alongside meteorological data to better understand the subglacial system of Fjallsjökull.

How to cite: Andrews, A., Baurley, N., Dash, J., and Hart, J.: Monitoring high resolution variations in proglacial lake area using an Uncrewed Aerial Vehicle (UAV) at Fjallsjökull, Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19339, https://doi.org/10.5194/egusphere-egu24-19339, 2024.

We have derived the glacier-specific Østrem curve to quantify the influence of a supraglacial debris cover on the mass and surface energy balance of the Djankuat Glacier, a northwest-facing and partly debris-covered temperate valley glacier in the Caucasus region (Russian Federation), which has been selected as a ‘reference glacier’ by the WGMS. A 2D energy balance model, in combination with meteorological data from automatic weather stations and ERA5-Land reanalysis data, is used to assess the melt-altering effect of supraglacial debris on the overall glacier runoff during 1 complete balance year. The main results show that both the surface energy balance and mass balance fluxes are modified significantly due to the presence of debris on the glacier surface, as the surface characteristics (albedo, emissivity, and roughness) and near-surface temperature, moisture and wind regimes are greatly altered when compare to bare ice surfaces.  As such, for very thin debris (< 3 cm), a slight relative melt-enhancement occurs due to a decreased surface albedo and/or the patchiness of the debris. If debris, however, further thickens (> 9 cm), the insulating effect becomes dominant and reduces the melt of the underlying ice significantly. Sensitivity experiments show that especially within-debris properties, such as the thermal conductivity and the vertical porosity gradient within the debris pack, highly impact the magnitude of the sub-debris melt rates. Moreover, the relative melt suppression of the debris cover is modelled to increase in a warming climate, regardless of debris thickness changes. The above-mentioned effects are found to be increasingly pronounced with an increasing thickness of the superimposed supraglacial debris cover and can be of great importance with respect to future glacio-hydrologic regimes and glacio-geomorphological processes. Quantifying such melt-modification effects is therefore also important to more accurately understand and assess the behavior of (partly) debris-covered glaciers under a future warming climate.

How to cite: Verhaegen, Y., Huybrechts, P., Rybak, O., and Popovnin, V.: Deriving the Østrem curve to quantify supraglacial debris-related melt-altering effects on the Djankuat Glacier, Caucasus, Russian Federation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20265, https://doi.org/10.5194/egusphere-egu24-20265, 2024.

Recent advancements in the numerical modelling of glaciers has enabled projections of glacier mass change at regional and global scales. However, this progress has been facilitated by the use of simple mass balance models that rely heavily on parameterisations, often with poorly constrained parameters. These models are typically calibrated by varying parameters in order to minimise the difference between modelled and observed mass balance. Though intuitive, this procedure risks an over-tuning of model parameters, ultimately resulting in an underestimation of uncertainty in projections of glacier change. In this study, we present a novel application of the calibration technique known as ‘history matching’. Rather than tuning parameters to obtain a single ‘best’ solution, this method is used to obtain an ensemble of plausible parameter sets; ultimately enabling an assessment of parameter uncertainty in projections. Here, we apply this approach to quantify parameter uncertainty in the GO model contribution to GlacierMIP3. We run the model for each experiment in GlacierMIP3 using a 250-member perturbed-parameter ensemble, generated using a Latin hypercube design. We then constrain this ensemble through history matching by filtering ensemble members that are inconsistent with geodetic mass balance observations outside defined limits of plausibility. The ensemble is used to assess the sensitivity of projections to total parameter uncertainty as well as individual model parameters. We find a high degree of equifinality in the ensemble, in which ensemble members that performed equally well in calibration produce contrasting responses to the same climate forcing. 

How to cite: James, M.: Quantifying parameter uncertainty in projections of glacier mass change in Iceland under GlacierMIP3 experiments , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20299, https://doi.org/10.5194/egusphere-egu24-20299, 2024.

In the Antarctic field seasons 2022/23 and 2023/24 the GHOST team (Geophysical Habitat of Subglacial Thwaites: https://thwaitesglacier.org/projects/ghost) as part of the International Thwaites Glacier Collaboration (ITGC), collected several hundred kilometers of multi-fold seismic reflection profile of Thwaites Glacier. The data cover the center flow line (first season) and across flow profiles (second season), starting 60 km upstream from the grounding line. The seismic profiling set-up consisted of a seismic vibrator source and 60 geophones on a 1.5 km long cable, all towed by a tracked vehicle. The combination of surface seismic source and towed geophone array allows for rapid and high quality data acquisition. The seismic signal penetrates approximately 200 meters into the bed with deeper structures imaged in places. The along-flow profile revealed a repeating of bedforms alternating between relatively flat and smooth regions a few km long, and regions of more pronounced topography of 10s to 100s of meter high bumps. In addition we imaged what we interpret as sediment filled basins.  Comparison with high-resolution ground-based swath radar allows the identification of geomorphological bedforms, such as megascale glacial lineations, sediment-filled basins and troughs, which can then be directly identified in the seismograms. We present a first preliminary evaluation of the subglacial characteristics and discuss the potential relevance of the subglacial boundary condition for ice flow dynamics.

How to cite: Eisen, O., Zeising, O., Hofstede, C., Laubach, H., Koch, F., Anandakrishnan, S., and Brisbourne, A. and the GHOST team: Properties of the bed of Thwaites Glacier, West Antarctica, estimated from vibroseismic surveys (2022-23 and 2023-24), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-267, https://doi.org/10.5194/egusphere-egu24-267, 2024.

Jutulstraumen, a major outlet glacier in East Antarctica, drains into the Fimbulisen (∼39,400 km²). Here, we produce the first long term (~ 60 years) record of its behaviour using optical satellite imagery to map changes in its frontal position between 1963 and 2022, together with more recent datasets of ice velocity, surface elevation changes and grounding line position. Our analysis reveals that the ice front has been steadily advancing since its last major calving event in 1967, with a consistent ice flow velocity of ~ 720 ± 20 m yr^-1(2000-2022). This has been accompanied by spatially variable ice surface thickening at an average rate of +0.15 ± 0.02 m yr^-1 (2003-2020) between 20 km and 120 km inland of the grounding line. We also find evidence to suggest a minor grounding line advance of ~ 200 m (~ 6 m yr^{- 1}) between 1990 and 2022, albeit with large uncertainties. Mapping of the major rifts on Jutulstraumen’s ice tongue from 2003 to 2022 (MODIS) reveals an overall increase in their lengths on both sides of the floating ice tongue, accompanied by some minor calving events. Given present-day ice front advance rates (~ 755 m yr^-1), it would take around 31 years for the ice tongue to reach its most recent maximum extent in the mid 1960s, but extrapolation of rift lengthening suggests the next major calving event could take place sooner, possibly as early as the 2040s. Overall, however, there is no evidence of any dynamic imbalance, with ice-tongue advance, inland thickening and grounding line advance mirroring other major glaciers in Dronning Maud Land.

How to cite: Sharma, A., Stokes, C. R., and Jamieson, S. S. R.: Ice dynamics and structural evolution of Jutulstraumen, Queen Maud Land, East Antarctica (1963 – 2022), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1033, https://doi.org/10.5194/egusphere-egu24-1033, 2024.

Fuelled by anthropogenic warming, the duration of sea ice and ocean circulation near the East Antarctic continent at present-day, is changing and contributing to further ice sheet melt. Studying the functioning of these parameters, atmosphere, ocean, and sea ice, during past climate transitions (such as warming stages, i.e., deglaciations, and cooling stages, i.e., glaciations) may give us more understanding to the stability of the East Antarctic ice sheet in the future. Fossil diatom records found in deep ocean sediment cores can provide indications of past sea ice and surface temperature variability and can therefore deepen our understanding of future outcomes of present-day anthropogenic warming, including ocean circulation changes. However, very few sea ice and sea surface temperature reconstructions exist from past warming stages (deglacials) near the Antarctic continent. This is partly due to the fact fossil records are lacking from sediment archives retrieved from the Antarctic continental margin, possibly as a result of extended ice sheets and prolonged periods or permanent sea ice cover. In this study we analysed diatom assemblages (based on relative abundances of identified species and statistical analysis), the Eucampia index, Thalassiothrix antarctica, ice rafted debris (IRD), and the geochemical productivity indicators (biogenic silica and XRF derived Si/Al and Ba/Ti) in core TAN1302-44, collected from the slope offshore Adélie Land. The results show a pattern of glacial (cool periods) to interglacial (warm periods) sedimentary facies changes and include last two deglacials and the last glaciation stage. Two diatom assemblages coincide well with changes in glacial (low IRD, low productivity) to interglacial (high IRD, high productivity) facies. The persisting presence of Thalassiosira lentiginosa, representative of Assemblage 1, suggests the last glacial (MIS 4-2) is characterised by an open ocean environment with respect to sea ice. However, due to the increasing presence of Fragilariopsis obliquecostata, representing Assemblage 2, we conclude the last glacial also comprised a gradual build-up of sea ice, reaching a maximum duration at the end of MIS 2, before rapidly vanishing. Following the decrease in sea ice, based on the increased of Thalassiothrix antarctica within the deglaciation facies, we conclude Circumpolar Deep Water (CDW) influx increased over the slope. This observation occurs in both deglacials, one leading to MIS 5e, and other to Holocene interglacial. Finally, based on IRD rich interglacial facies, we conclude the CDW increase occurred prior to regional ice sheet retreat, leading into the Holocene. Together, these datasets suggest major sea ice, and oceanographic changes occurred prior to the last major ice sheet retreat, suggesting a progression of events may influence the demise of the East Antarctic ice sheet in the future.

How to cite: Pesjak, L., McMinn, A., Chase, Z., and Bostock, H.: Sea ice and ocean circulation changes during the last 140 kyr, offshore Adélie Land, East Antarctic continental margin, with special emphasis on last two deglaciations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1039, https://doi.org/10.5194/egusphere-egu24-1039, 2024.

Antarctica is the most prolific place on Earth to find meteorites, which provide unique insights in the formation and evolution of our Solar System. Over 60% of all meteorite finds on Earth stem from so-called blue ice areas in the interior of the (East) Antarctic ice sheet. In these blue ice areas, a redirected ice flow and meteorological processes lead to the removal of surface layers. Meteorites once embedded in these layers of ice that are removed become exposed at the surface in high concentrations and are easy to spot in the field thanks to their contrasting dark color on blue ice. However, no meteorites have been found in areas where temperatures are relatively high. The absence of meteorites in these areas is explained by the fact that meteorites warm up under solar radiation, and as such these stones can melt the underlying ice, even when surface temperatures are well below zero. This very local melt causes the meteorite to move vertically downward into in the ice sheet, disappearing from the surface and hence impossible to see by eye and collect. Hence, in a warmer climate, meteorites are more prone to become unrecoverable.

Using a data-driven approach, we estimated that with the currently increasing surface temperatures, meteorite loss rates exceed recovery rates multiple times. To estimate this loss rate, we first performed regional climate model simulations, for a low and a high emission scenario, in which blue ice areas are prescribed. Next, we fed this data to a machine learning algorithm that identifies meteorite-rich sites using over 12,000 known meteorite finding locations and their corresponding properties such as ice flow velocity and surface temperature. Until mid-century, projected losses are identical for the emission scenarios, after which losses are reduced for the low emission scenario and nearly constant for the high emission scenario.

These meteorite losses demonstrate a (previously unnoticed) climate sensitivity of the interior of the Antarctic ice sheet. With temperatures remaining well below zero, even with several degrees of warming, meteorites are affected even by very minor (decimal) increases of surface temperatures during exceptionally warm events, which are expected to occur more frequently.

How to cite: Tollenaar, V., Zekollari, H., Kittel, C., Farinotti, D., Lhermitte, S., Debaille, V., Goderis, S., Claeys, P., Joy, K. H., and Pattyn, F.: The impact of climate change on meteorite finds in East Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1488, https://doi.org/10.5194/egusphere-egu24-1488, 2024.

Paleoceanographic records spanning the Oligocene (33.9–23.03 Ma) provide insights into Antarctic ice-sheet (AIS) dynamics in a world warmer-than-today, allowing to improve future projections linked to current global warming. While the long-term evolution of Oligocene glaciations is relatively well-known, current knowledge about the short-term (i.e., orbital to suborbital scale) AIS dynamics is still limited. Here, we investigate short-term dynamics of the AIS during the late Oligocene (spanning ~26–25 Ma), using a high-resolution multi-proxy record from Ocean Drilling Program Site 689 (Maud Rise, Southern Ocean). Variations in ice volume were quantified using the stable oxygen isotope composition of seawater (δ¹⁸O_SW) inferred from benthic foraminiferal δ¹⁸O and Mg/Ca-based bottom-water temperatures. Changes in sediment provenance and weathering inputs were characterised using detrital neodymium isotopic compositions (εNd) of the sediments. The δ¹⁸O_SW record reflects a highly dynamic AIS during the late Oligocene, with glacial conditions characterised by an AIS volume larger than the modern one (up to +14%) and interglacial conditions characterised by a much smaller AIS volume (up to -29%) than today. Detrital εNd varies from -12 to -9, with less radiogenic εNd signatures generally matching higher δ¹⁸O_SW values (i.e., glacials) and vice-versa. This co-variation between an ice-volume proxy and a tracer of sediment provenance characterises crustal sequences exposure to weathering as the ice-sheet retreated. The detrital εNd record thus supports recent interpretations of a highly dynamic AIS during the late Oligocene, which is mirrored by large changes in the provenance of weathering products induced by the waning and waxing of the AIS.

How to cite: Creac'h, L., Brzelinski, S., Friedrich, O., Frank, M., Gutjahr, M., and Lippold, J.: Short-term Antarctic ice-sheet dynamics during the late Oligocene: Multi-proxy records from ODP Site 689, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2465, https://doi.org/10.5194/egusphere-egu24-2465, 2024.

Recent advances in the Elmer/Ice modelling suite have allowed 3D simulation of unrestricted calving geometries at tidewater glaciers such as Jakobshavn Isbrae. We present the first use of this model in an Antarctic setting. The more stochastic nature of calving at Antarctic ice sheets when compared to a Greenlandic setting has discouraged the development of calving laws and models. For shorter term calving simulations, it is sufficient to determine the local attractor or pinning point where the terminus stabilises following a transient period of retreat or advance. Importantly, this can only be achieved through a position-based law, as a positional attractor is independent of velocity.

Using a deterministic position-based crevasse depth calving law it is possible to simulate the observed calving behaviour at the western ice front of Thwaites Glacier. The calving law identifies the attractor point beyond which ice will calve following a variable but short delay. The geometric attractor is defined by local topography along with grounding zone dynamics. Beyond this point there are a lack of lateral or basal pinning points, so any downstream ice is effectively lost from the system. More generally, across the floating extensions of Thwaites Glacier, the model reliably predicts regions of crevasse formation. Accurately simulating crevasse formation on ice shelves along with determining the attractor within the glacier retreat and advance cycle is the first step towards a reliable Antarctic calving law. 

How to cite: Wheel, I., Benn, D., and Crawford, A.: Simulating 3D calving dynamics at Thwaites Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3600, https://doi.org/10.5194/egusphere-egu24-3600, 2024.

The glaciers terminating in the Cook Ice Shelf and the Ninnis Glacier drain most of the Antarctic marine ice sheet covering the Wilkes Subglacial Basin (WSB), whose ice volume is equivalent to 3-4 m of global sea level rise. Long-term climate projections and multiproxies studies of ice records suggest that ice sheet retreat in this area, thought to be colder and more stable, may be triggered by warm ocean water intrusion.
During the 2022 campaign of the Italian Programma Nazionale delle Ricerche in Antartide (PNRA) with the icebreaker L. Bassi, the project COLLAPSE (Cook glacier-Ocean system, sea LeveL and Antarctic Past Stability) mapped two systems of canyons and hills located at the mouth of suspected glacial valleys off Cook and Ninnis glaciers. The combination of geomorphological, seismic, oceanographic, and sedimentary data (see abstract from Torricella et al.) allowed identification of a variety of processes active on the seafloor today and in the late Quaternary. The geophysical data show evidence of slope instability offshore of the presumed major glacial troughs. Sediment drifts controlled by bottom currents grow on channel-levees and slope terraces. This information will help, albeit indirectly, to reconstruct the dynamics of different glaciers in relation to paleoclimatic changes and ocean circulation, and to estimate their respective contributions to global sea-level rise.
In addition to the co-authors listed in this summary who are involved in the analysis of the geophysical and oceanographic data, the project PNRA COLLAPSE includes a large group of scientists for the analysis of the sediment cores, from the Universities of Trieste, Siena and Milan-Bicocca, CNR-ISP e ISMAR, INGV (I), Univ. Bordeaux, Grenoble and LOCEAN, Paris (F), CSIC (E), Colgate Univ. (USA), Australian National University and Univ. of Tasmania (AUS), Russian FSBI VNIIOkeangeologia, (RU), Alfred Wegener Institute (D), GNS (NZ).

How to cite: De Santis, L., Accaino, F., Accettella, D., Bensi, M., Colleoni, F., Cova, A., Donda, F., Facchin, L., Kovacevic, V., Martellucci, R., Mauri, E., Ursella, L., and Zgur, F.: Cook glacier-Ocean Antarctic Past Stability (COLLAPSE) project preliminary results from geophysical and oceanographic data analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3663, https://doi.org/10.5194/egusphere-egu24-3663, 2024.

While most of West Antarctic ice shelves are thinning due to ongoing oceanic warming, East Antarctic ice shelves, except a few ones, are apparently more stable. One sector in particular, the Wilkes Subglacial Basin, is not showing any or very little sign of weakness to ongoing climate change. This sector of Antarctica is drained by the Cook ice shelf, the Ninnis ice shelf and the Mertz ice tongue. Those ice shelves have experienced some observed calving events in the past decades, but actual ice flow does not indicate that this sector is retreating and contributing to global mean sea level rise. But can we really measure the sensitivity of a sector only accounting for two decades of observations? Geological archives and morphological evidence of the George V Land continental margin in front of those glaciers suggest, on the contrary, that the ice sheet over the WSB has been one of the most active of East Antarctic sectors through its glaciological history. A multi-year sea ice cover, reducing only under exceptional atmospheric conditions, does not allow the systematic exploration of the area.  Rare geophysical, glaciological, oceanographical, geological and geographical hampers a proper assessment of the instability potential of this area. International cooperation not only is needed to reach and operate in such difficult sector of Antarctica, both at land and on sea, but is also needed to perform multi-disciplinary measurements.

How to cite: Colleoni, F., De Santis, L., Barruol, G., and Dutrieux, P.: The critical importance of Wilkes Land Subglacial Basin stability (East Antarctica), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4151, https://doi.org/10.5194/egusphere-egu24-4151, 2024.

Recent studies have indicated that the migration of grounding line is extremely sensitive to basal melt in the grounding zone. Different representations of melting at the grounding line introduce significant uncertainties in predictions of ice mass loss and global sea level rise. However, there remains an absence of targeted, systematic studies grounded in real-domain, and robustly representing melt in partially floating cells of ice sheet models remains a pressing technical challenge. This study delves into four distinct melt schemes at the grounding line within the Wilkes Subglacial Basin (WSB) model, focusing on their impact on ice loss predictions. Specifically, we analyse the No Melt Parameterization (NMP), Full Melt Parameterization (FMP), and two variants of the Sub-Element Melt parameterization (SEM1, SEM3) as applied to partially floating elements at the grounding line. We found that both the SEM and NMP schemes outperform FMP in terms of convergence with finer mesh resolution, with each exhibiting varying advantages over the other.  Notably, the discrepancies in results attributed to various melt schemes are significantly amplified when high melt rates are applied near the grounding line. Our results consistently suggest that the FMP should be avoided under all circumstances due to its poor convergence and substantial overestimation of ice mass loss. We recommend that future ice sheet models carefully evaluate the choice between NMP and SEM in their specific model contexts.

How to cite: Wang, Y., Zhao, C., Gladstone, R., Zwinger, T., Galton-Fenzi, B., and Christoffersen, P.: Parameterization Solutions for Basal Melting at the Grounding Line in Ice Flow Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4251, https://doi.org/10.5194/egusphere-egu24-4251, 2024.

Large-scale climate modes have recently been shown to dominate the non-linear variability of Antarctic mass over the last 20 years. We explore these results in further detail in the context of East Antarctica and expand on this work to report on new analyses of Antarctic elevation change from satellite altimetry. Altimetric measurements provide insights into spatial variation of these signals at two orders of magnitude higher spatial resolution than mass-change measurements from GRACE, allowing for resolution of variability at sub-glacier scale. Exploring the same period as the GRACE data (2002-2021) we show that about 75% of the variance of the Totten Glacier elevation can be explained by a combination of Southern Annular Mode (SAM) and ENSO. Denman Glacier shows almost no non-linear variance over 2002-2021 but about 30% of the present signal is explainable by SAM with no evident ENSO response. Despite this, much of the signal is not focused on the outlet glaciers but diffusely spread across the interior, consistent with surface mass balance. We show that much of this signal can be explained by models of firn densification, although different models have different levels of agreement with the data at relevant decadal periods. We will show detailed results for Wilkes Subglacial Basin and Dronning Maud Land.

How to cite: King, M., Ayabilah, J. B., Christoffersen, P., Vance, T., and Udy, D.: Large-scale climate modes dominate recent ice mass and elevation variations in much of East Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4785, https://doi.org/10.5194/egusphere-egu24-4785, 2024.

East Antarctic Ice Sheet (EAIS) has an overall balanced or slightly positive mass balance. However, Wilkes Land and Totten Glacier (TG) in EAIS have been losing ice mass significantly since 1989. There is a lack of knowledge of long-term mass balance in the region which hinders the estimation of its contribution to global sea level rise. We reconstruct ice flow velocity fields of 1963–1989 in TG from the first-generation satellite images of ARGON and Landsat-1&4, and build a five decade-long record of ice dynamics. Based on these velocity maps, we show that this acceleration trend in TG has occurred since the 1960s. Combined with recently published velocity maps, we find a persistent long-term ice discharge rate of 68 ± 1 Gt/y and an acceleration of 0.17 ± 0.02 Gt/y2 from 1963 to 2018, making TG the greatest contributor to global sea level rise in EA. We attribute the long-term acceleration near grounding line from 1963 to 2018 to basal melting likely induced by warm modified Circumpolar Deep Water. The speed up in shelf front during 1973–1989 was caused by a large calving front retreat. As the current trend continues, intensified monitoring in the TG region is recommended in the next decades.

How to cite: Li, R., Cheng, Y., Chang, T., Gwyther, D. E., Forbes, M., An, L., Xia, M., Yuan, X., Qiao, G., Tong, X., and Ye, W.: 60 Years of satellite record reveals high level velocity and mass discharge in Totten Glacier, East Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4890, https://doi.org/10.5194/egusphere-egu24-4890, 2024.

The sub-ice topography of East Antarctica provides a crucial record of the long-term geological, geomorphological, and glaciological evolution of the continent. In particular, the morphology of the East Antarctic Ice Sheet (EAIS) bed is a valuable and hitherto underexploited archive of past ice-sheet behaviour. Analysis of the subglacial landscape can therefore help improve our understanding of the response of the ice sheet to episodes of warming in the geological past that serve as analogues for current and projected future climate change.

Here, we conduct a systematic search of the extensive repositories of airborne ice-penetrating radar data acquired in the past two decades to map the distribution of low-relief subglacial bed surfaces close to the East Antarctic ice margin between Princess Elizabeth Land and George V Land (70°E to 160°E). Individual surfaces are characterised by consistent elevations over distances of 10s to 100s of kilometres and relatively low-amplitude, high-frequency roughness (i.e., valleys and inselbergs). We map 31 separate low-relief bed surfaces, which range from 500 to 50,000 km² in area and comprise ~40% of the perimeter of this sector of the East Antarctic margin. The surfaces are typically overlain by cold-based, slow-moving ice and bounded by deep subglacial troughs that host fast-flowing ice streams and outlet glaciers.

Underneath the modern-day EAIS, these low-relief bed surfaces are situated at a broad range of elevations. However, when the elevations are isostatically adjusted for the removal of the EAIS, the distribution narrows substantially and, alongside cluster analysis of the morphology of the surfaces, indicates that they constitute a single, statistically consistent population around the entirety of this sector of the EAIS margin. Under ice-free conditions, the coastal surfaces would be situated above sea level and gently dipping in a seaward direction, and we suggest that they are remnants of a widespread fluvial planation surface formed following Gondwana break-up and preserved with only minor geomorphological modification since EAIS inception. The presence of these ancient surfaces has important implications for the past, present, and future behaviour of this sector of the EAIS.

How to cite: Paxman, G., Jamieson, S., Ross, N., Carter, C., Bentley, M., Jordan, T., Cui, X., Lang, S., and Siegert, M.: Widespread near-coastal bedrock erosion surfaces in East Antarctica and their implications for long-term ice-sheet behaviour, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5419, https://doi.org/10.5194/egusphere-egu24-5419, 2024.

The Aurora Subglacial Basin contains 7 m of global sea level equivalent (SLE). The Totten Glacier is currently the dominant outlet glacier of the Aurora Subglacial Basin; however, neighbouring the Totten Glacier, the smaller Vanderford Glacier drains a region containing 0.67 m of SLE. Vanderford Glacier is the fastest retreating glacier in East Antarctica, with over 18 km of grounding line retreat in the last two decades. The warmest modified circumpolar deep water in East Antarctica has been observed offshore the Vanderford Glacier, highlighting the potential vulnerability of this region to a warming climate. Here, we run transient simulations of the Ice-sheet and Sea-level System Model to examine the sensitivity of the Vanderford Glacier to key drivers of mass loss, namely sub-ice shelf basal melt and ice-front retreat. Simulations show that grounding line retreat is more sensitive to changes in basal melt than ice-front retreat, except for scenarios of extreme ice-front retreat. We show that the rate and extent of grounding line retreat comparable with observations only occurs under high magnitude basal melt conditions, while a similar extent of grounding line retreat occurs under the extreme ice-front retreat scenarios, but the temporal response of the grounding line is lagged. Given that grounding line retreat similar to observations is only achieved with basal melt magnitudes far exceeding those indicated by satellite remote sensing, our results highlight the need for methods to better estimate basal melt in this vulnerable region.

How to cite: Bird, L., McCormack, F., Beckmann, J., Mackintosh, A., and Jones, R.: What's driving change at the Vanderford Glacier, East Antarctica?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6760, https://doi.org/10.5194/egusphere-egu24-6760, 2024.

A giant submarine landslide in front of the Wilkes subglacial basin along the Cook continental margin—one of the least explored areas on Earth—has been documented for the first time. This area is critical to understanding the stability of one among the most vulnerable sectors of the Antarctic Ice sheet to climate and ocean warming. It is named as Cook mega-slide complex (CMSC), which occurred in the early Pliocene according to the seismic interpretation correlated to the IODP Exp 318 sites. The giant submarine landslide is well imaged on the seismic profiles and exhibits various kinematic indicators with the basal glide planes and original headwall scarps. It affected the area of c. 22, 686.5 km², approximately 3399 km³ of sediments evacuated from the continental margin. With a scale similar to Storegga Slide on the Norway margin, the size of the CMSC is mostly likely the largest submarine landslide ever discovered around the Antarctic margin. We propose that glacial isostatic adjustment and glacial outburst floods caused by the East Antarctic Ice Sheet (EAIS) retreat lead to the formation of the large slides and create the condition for slope instability and erosion. The development and collapse of peripheral bulge has been firstly observed from Antarctic margin, associated with the glaciation and subsequent deglaciation of the EAIS, led to a distinct spatial variation in sea level changes and further affected the deposition on the slope. Our results yield intriguing insights into the relationship of stratigraphic evolution, submarine landslides, and past EAIS instabilities throughout the warm periods of the late Miocene-Pliocene, and thereby provide important constraints for ice sheet modeling and sea level prediction.

How to cite: Huang, X., De Santis, L., Leitchenkov, G., and Escutia, C.: Submarine landslides unravel the dynamics of the past East Antarctic Ice Sheet , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7756, https://doi.org/10.5194/egusphere-egu24-7756, 2024.

We provide a summary of new insights into the contemporary dynamics of Thwaites and Pine Island Glacier, West Antarctica, obtained through series of recent modelling studies.  By conducting ice-flow modelling studies with three independent models (ISSM, StreamIce, Úa), all initialized to current day conditions, we show that all models provide very similar future estimates of future mass loss for a given forcing scenario. Importantly, while description of basal processes does impact our results to some degree, we nevertheless find that estimates of mass loss over time scale of 50 to 100 years, are insensitive to the choice of basal sliding law. This can be understood to be related to the compensating impact of the initialisation process that in each case produces correct initial state for the ice sheet (i.e. surface velocities and current rates of mass loss) irrespectively of the sliding law used. Furthermore, we find that inversion produces (e.g. estimates of basal slipperiness and englacial ice rate factors) can be exchanged between models, showing that these products are to large degree model independent. A common feature found in all our ice-flow studies, and coupled ice+ocean studies, is the existence of multiple tipping points within the Thwaites and Pine Island system. In all our ice-flow simulations, the grounding line of Thwaites always becomes unstable once it has retreated by about 75km upstream from its current position. We also conclude that the grounding line of Pine Island Glacier has recently undergone a phase of irreversible retreat, and that the glacier has at least 3 further tipping points that can be crossed in the near future (centennial time scale). Additionally, the western ice shelf of Thwaites has been dramatically weakening over the past decade and we used our three independent models to assess the effect of a potential complete collapse of Thwaites’ floating extension. First, we find that this ice shelf provides limited buttressing, and disintegrations of the ice shelf, in its current configuration, will not significantly impact upstream grounded. Second, it has been suggested that Thwaites would be subject to the Marine Ice Cliff Instability (MICI) if its ice shelf collapses, as it would expose a tall ice cliff. Using recently proposed cliff-height dependent calving laws, we find no indication that such calving laws give rise to an irreversible or unstable calving-front retreat.  Thus, those calving laws do not lead to a marine ice cliff instability despite prescribing calving rates as strongly increasing functions of cliff height.

How to cite: Gudmundsson, G. H., Morlighem, M., Goldberg, D., Barnes, J., De Rydt, J., and Rosier, S.: New insights into the current dynamics of Thwaites and Pine Island Glaciers, West Antarctica., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8454, https://doi.org/10.5194/egusphere-egu24-8454, 2024.

Thwaites and Pine Island glaciers serve as main outlets for ice draining the West Antarctic Ice Sheet into the Amundsen Sea Embayment (ASE). Observational records show that these ice streams exhibit continuous and substantial thinning and grounding-line retreat since the 1940s, particularly accelerating from the 1990s onwards . Furthermore, modeling studies suggest that ASE glaciers are susceptible to runaway retreat. Thus, the rate and magnitude of potential mass loss from these ice streams presents a major source of uncertainty for future sea level rise predictions.

Ocean-driven melting of the underside of ASE glacier ice-shelves, caused by the upwelling of warm Circumpolar Deep Water (CDW) at the shelf break and its advection across the continental shelf, is thought to be the main driver of mass loss. CDW upwelling onto the ASE shelf has varied due to natural decadal variability, longer centennial variability as well recent changes in anthropogenic forcing (Holland et al., 2022). However, regional observational records are limited to the last few decades, and the onset and evolution of the oceanic forcing, prior to the instrumental period, remains uncertain. Here, we present high-resolution foraminiferal geochemical data from marine sediment cores recovered from the ASE shelf, including material collected during the Thwaites Glacier Offshore Research (THOR) expeditions in 2019, 2020 and 2021. Preliminary Mg/Ca records of benthic foraminifera shells, a proxy for bottom-water temperature, accompanied by benthic foraminiferal δ¹³C records, used as a water mass tracer, reveal that CDW incursions onto the ASE shelf contributed to glacier retreat on centennial to millennial timescales. Future work will aim to further constrain changes in CDW advection to the inner ASE shelf, particularly in western Pine Island Bay and at the Dotson Ice Shelf front, for the 20^th century and beyond.

How to cite: Smith, J. A., Radionovskaya, S., Mawbey, E. M., Hillenbrand, C.-D., Wellner, J. S., and Klages, J. and the THOR team: The history of deep-water upwelling and heat delivery to the Amundsen Sea Embayment, West Antarctica: a palaeoceanographic perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8638, https://doi.org/10.5194/egusphere-egu24-8638, 2024.

As part of the PNRA_BOOST project (Bridging Onshore-Offshore STructures at the Pacific Coast of North Victoria Land, Antarctica: an integrated approach), new offshore geophysical data (multichannel high-resolution seismic lines, bathymetric and magnetic data) were acquired on board of OGS R/V Laura Bassi (Feb 2023, XXXVIII Italian Antarctic Expedition), along the Pacific side of North Victoria Land, an underexplored key area at the boundary between East and West Antarctica. A preliminary analysis of the seismic and bathymetric data allows the identification and interpretation of morphological and tectonic features representing key hints for the study of the influence of lithosphere dynamics on ice-sheet evolution.

In the study area, the northern sector of the shelf has an outer concave shape of its break and slope and is incised by several gullies; on the contrary the southern sector shows a stepped geometry with a WNW-ESE straight linear trend abruptly turning to a NW-SE trend. The continental shelf consists of a thin, horizontally layered succession lying on a crystalline basement dissected by two U-shaped glacial troughs several kilometers wide. The slope consists of seaward-prograding sedimentary strata that are truncated on the shelf by a regional unconformity (RSU 1). In the upper part of the slope of the NW sector, three distinct seaward prograding wedges were recognized, whereas they were not identified in the southern sector.

NW-trending basement highs, bounded by faults, are visible both on the shelf and on the continental rise (towards the abyssal plain). Growth strata associated with these faults allow a tentative dating of activation to Oligocene times. The unconformity at the top of the growth strata may be related to the U3 surface (36 Ma) of Sauermilch et al. (2019). In addition, a ca. 20 km-long ridge of basement, covered by drift deposits, revealed at a depth of about 2500 m, is bounded by faults with indications of recent tectonic activity. The observed faults could have reactivated inherited zones of weakness that bound rift blocks formed during the breakup between Australia and Antarctica. In particular, the U3 surface is associated with the beginning of the phase of fast seafloor-spreading between Australia and Antarctica.

In the SW part of the study area, two broad “linear” volcanic zones occur along a roughly NNW-SSE direction; i.e. the orientation of the main tectonic lineaments inland. These zones consist of individual volcanic edifices and small volcanic ridges composed of coalescing bodies. Several volcanoes are clearly active and fluid-related features are visible cutting through the surrounding sedimentary successions. This volcanism correlates well with airborne magnetic observations and may represent the NNW continuation of the Mid-Miocene to Quaternary Hallett Volcanic Province forming the Adare Peninsula, or may be related to the post-spreading Pliocene-Recent volcanism of the Adare Basin.

Sauermilch et al., 2019. JGR: Solid Earth, 124, 7699–7724 (doi.org/10.1029/2018JB016683).

How to cite: Crispini, L., Civile, D., Ferrante, G. M., Locatelli, M., Morelli, D., Volpi, V., Accettella, D., Accaino, F., Busetti, M., Läufer, A., Armadillo, E., Colizza, E., Salvini, F., and Ruppel, A.: Lithosphere-cryosphere interactions at the Pacific coast of North Victoria Land: new evidence of past to recent geodynamic processes from offshore geophysical data (PNRA_BOOST Project), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10149, https://doi.org/10.5194/egusphere-egu24-10149, 2024.

The West Antarctic Ice Sheet (WAIS) is considered one of the tipping points of the Earth System. Its retreat due to climate change progressively results in sea level rise, affecting large numbers of the world's population. We aim to understand the potential consequences of a future WAIS collapse by implementing a mid-Pliocene Warm Period (MP) Antarctic Ice Sheet configuration, based on reconstructions, where the WAIS is severely reduced.

We perform simulations with the EC-EARTH3.3 model at low resolution spanning 1400 years under 280, 400, and 560 ppmv of CO₂ and derive the mean state of the last 200 years of simulation and the variability of climate patterns for the entire runtime.

With the near removal of the WAIS, we find a non-linear response in Antarctic Bottom Water (AABW) formation to increasing CO₂ levels. The AABW formation is highly sensitive to increased stratification, which results from sea surface temperature increase driven by current climate change. With the presence of a modern WAIS, Antarctic surface air temperature and Southern Ocean sea surface temperature are positively correlated to atmospheric CO₂, and we see a strengthening of the positive phase of the Southern Annular Mode (SAM). This affects mid-latitude westerlies and reinforces the negative feedback between surface warming and AABW formation.

However, with the near removal of WAIS, we observe a dampening in the otherwise doubling of atmospheric warming observed with increasing CO₂ and the same pattern occurs for the SAM. This results in a non-linear behaviour of AABW formation, where the AABW is suppressed up to 4 Sv during a longer period compared to the control experiments (modern WAIS), followed by a recovery to pre-industrial strength levels that is not sustained under 560 ppmv. This response also induces a further weakening of the Atlantic Meridional Overturning Circulation (AMOC) and a reduced reach of the AABW transport into the Atlantic and Pacific Oceans, with potential cascading effects on the global climate.

Our longer simulations reveal that the AABW formation thresholds are highly dependent on atmospheric CO₂concentrations and the freshwater input into the surrounding basins of the Antarctic region. These results suggest that WAIS retreat already deeply impacts societal development, but a collapse would induce a new climate regime that needs further investigation to allow for climate adaptation.

How to cite: Power, K., Matos, F., and Zhang, Q.: The non-linear response of the AABW to the removal of the West Antarctic Ice Sheet and implications to future climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10259, https://doi.org/10.5194/egusphere-egu24-10259, 2024.

The retreat of the Antarctic Ice Sheet is conventionally attributed to ocean melting of fringing ice shelves, potentially enhanced by internal instability due to the proximity of its grounding lines to retrograde bed slopes. Ocean melting is enhanced by increased intrusion of modified Circumpolar Deep Water (mCDW) within ice shelf cavities. Several processes can enhance the ability of mCDW to melt ice shelves. Upwelling from the release of subglacial melt water at the grounding line is arguably one of the least well constrained and understood and is currently not accounted for in projections of ice sheet loss.

The Thwaites glacier in the Amundsen Sea sector of the west Antarctic ice sheet has been the focus of recent investigations given its current rapid retreat, potential instability, and its impact on rates of future sea level change. In 2013, a network of subglacial lakes under the Thwaites glacier drained, the combined outflow reached a peak discharge in excess of 500 m³ s^-1 and likely reached the grounding line. During this period, several other processes took place at the grounding line and under the fringing floating ice. This event offers a natural experiment to examine the impact of subglacial outflow on ocean melting of ice shelves.

In this presentation we revisit the various events affecting the Thwaites system during this period and generate several new observations of lake discharge, rates of ice shelf basal melting, and grounding line thinning and retreat. We focus the discussion on the potential feedback between lake discharge, variation in ocean melting, and grounding line retreat, and on the contribution of subglacial discharge to the recent retreat of the Thwaites glacier.

How to cite: Gourmelen, N., Jakob, L., Holland, P., Goldberg, D., and Dutrieux, P.: Ice-ocean-subglacial hydrology interactions, and recent evolution of the Thwaites glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10321, https://doi.org/10.5194/egusphere-egu24-10321, 2024.

Following rapid ice thinning in the mid-Holocene, Pope Glacier (adjacent to Thwaites Glacier in the Amundsen Sea sector) was at least 30-35 m thinner than present for at least 3 kyr in the mid- to Late Holocene. The timing of the end of this ice lowstand and subsequent rethickening of ice to near its present configuration is poorly constrained. We present five paired ¹⁰Be and ²⁶Al cosmogenic nuclide exposure ages that provide constraints on the timing of this ice sheet readvance. The ages are sourced from samples collected from a moraine <1 km from the grounding line of Pope Glacier on a nunatak between Thwaites and Pope glaciers. To help interpret the new exposure ages, we measure the morphology of the moraine and assess modern ice flow directions to provide an insight into the processes that formed it. We conclude that the moraine is a type of medial moraine and hypothesise that it was formed by englacial thrusting during the advance of a small glacier on the flanks of Mount Murphy approximately 1.4 ± 0.5 ka. We infer that the timing of this glacier advance coincides with the Late Holocene thickening of the adjacent Pope Glacier and speculate that it also coincides with thickening of ice in the wider Amundsen Sea sector. We also note that it coincides with glacier readvances on the Antarctic Peninsula. Our results indicate an ice thickness change from 35 m beneath to 50 m above present levels occurred ~1.4 ka, a scale of ice thickness change that has implications for the interpretation of GPS measurements of ongoing surface uplift used to model the solid Earth’s response to surface mass loading and, in turn, on our ability to understand both past and future ice sheet dynamics.

How to cite: Nichols, K., Adams, J., Brown, K., McKenzie, M., Venturelli, R., Goehring, B., Johnson, J., Rood, D., Wilcken, K., Woodward, J., and Roberts, S.: Does this moraine constrain a Late Holocene readvance in the Amundsen Sea sector of the West Antarctic Ice Sheet?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10527, https://doi.org/10.5194/egusphere-egu24-10527, 2024.

At present, considerable uncertainty surrounds the details of how Earth’s ice sheets interact with the surrounding ocean. This inhibits the reliability of future sea level rise projections from ice sheet models and highlights a need to better constrain ice-ocean interactions with in situ observations. Here, we present detailed ice and ocean data from beneath Thwaites Eastern Ice Shelf, Antarctica, collected with the underwater vehicle Icefin as part of the ITGC MELT project. The observations are a subset of the full data set that focus on the ice-ocean interactions within one 4-m-tall and 200-m-wide terrace formation in the ice base. We present ocean conditions in the terrace from 18 hydrographic profiles that reached within 1 cm of the ice along the feature’s flat roof and 13 cm from its steep sidewall. The ocean observations depict highly stable near-ice ocean stratification within 1 m of the terrace roof that break down near its sidewall, allowing warmer and more saline water to contact the ice there. The ocean observations are combined with ice base elevations and scaled morphological melt patterns in the ice to understand the dominant mechanisms driving ice-ocean interactions within this feature. We then input these data into the three-equation melt parameterization to estimate spatial variability in melt rates within these topographic features. We test various parameterizations for ocean heat flux into the flat and sloped ice surfaces, and compare the results to melt rates sampled along a nearby terrace sidewall and roof with a phase sensitive radar. This work in progress aims to better understand how ocean conditions interact with ice slope on small scales to drive variable melting in warm, highly stratified environments, with hopes of refining existing parameterizations of this process. We expect regions beneath much of the ice shelves occupying West Antarctica to interact similarly with the underlying ocean to what we observe beneath Thwaites. Hence, our observations hold relevance for how ice sheet models parameterize ocean-driven melting in this type of melt-driven regime.

How to cite: Washam, P., Schmidt, B., Nicholls, K., Davis, P., Eayrs, C., Hegelein, V., Lawrence, J., Meister, M., Quartini, E., Holland, D., and Bryson, F.: Direct observations of coupled ice-ocean interactions within a basal terrace beneath Thwaites Eastern Ice Shelf, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10545, https://doi.org/10.5194/egusphere-egu24-10545, 2024.

Predicting future change to the Antarctic Ice Sheets requires high quality data to constrain numerical ice sheet models. A major uncertainty stems from a lack of knowledge regarding the late Holocene trajectory of the West Antarctic Ice Sheet (WAIS). There are two hypotheses regarding the late Holocene behaviour of the WAIS. A) Steady retreat throughout the Holocene with stabilisation at or near the present-day position (ice relaxation hypothesis) or, B) retreat to a smaller-than-present configuration with subsequent readvance to the present-day position (the retreat-readvance hypothesis). The two hypotheses represent profoundly different ice sheet trajectories. These hypotheses have been discussed with particular reference to the Amundsen, Ross and Weddell Sea sectors of the WAIS.

Initial studies proposing the retreat-readvance model suggested that GIA related uplift caused re-grounding of ice rises in the Weddell Sea, increasing ice shelf buttressing and leading to grounding line re-advance. In the southern Weddell Sea major ice streams are currently at threshold positions on reverse bed slopes where they are vulnerable to Marine Ice Sheet/Cliff Instabilities. As this region drains ~22% of Antarctica the lack of geological constraint on the current ice sheet trajectory contributes significant uncertainty to future predictions. Any groundling line retreat beyond present day limits would be accompanied by up-stream ice sheet thinning thus retreat to a smaller-than-present configuration would be accompanied by thinning of the ice sheet surface below the present-day level. Consequently, determining whether sub-glacial rock samples from the Weddell Sea sector have been exposed in the recent past can robustly test for a smaller-than-present ice sheet configuration.

We present an update on two field seasons where, using a modified Winkie Drill, we recovered sub-glacial rock samples from the Ellsworth Mountains and Pensacola Mountains. These mountain ranges bracket the proposed zone of retreat and can thus provide limiting data points on the extent and duration of any retreat. The subglacial cores are to be analysed using in situ ¹⁴C and luminescence to test for any past exposure to cosmic rays and sunlight respectively. We will present a summary of the field season outcomes and preliminary analytical data along with initial interpretations.

How to cite: Small, D., Smedley, R., Dunai, T., Lees, T., Trabucatti, S., and Boeckmann, G.: New geological constraints on Holocene retreat-readvance of the West Antarctic Ice Sheet in the Weddell Sea Embayment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12136, https://doi.org/10.5194/egusphere-egu24-12136, 2024.

The Wilkes Subglacial Basin (WSB) continues to attract significant international attention as a potential area of substantial East Antarctic Ice Sheet (EAIS) retreat. Determining whether this sector of East Antarctica was indeed a major contributor to past global sea level rise and whether it will be again in the future beyond 2100, remains a key priority for new interdisciplinary research.

Aerogeophysical exploration has unveiled that the bedrock dips inland and is grounded up to 2.1 km below sea level (bsl) within its remarkably deep sub-basins and remains at a depth <500 m bsl along the length of this huge and geologically enigmatic basin. Its northern sector is particularly critical, as it hosts the catchments of the Cook and Ninnis glaciers that are fast flowing, dynamic and potentially unstable systems that penetrate >500 km inland of the present-day grounding zone.

Despite a growing body of knowledge, geological, geomorphological, and oceanographic evidence for the location, amount and rate of EAIS ice sheet retreat within the WSB remains incomplete and in parts controversial, and numerical model predictions for retreat during past warmer periods (e.g. the mid-Pliocene, mid-Miocene and even more recent Quaternary times) also differ significantly.

Here we review some of the results from different existing aerogeophysical campaigns and data compilations in the WSB to discuss the importance of also considering the heterogeneity in basal boundary conditions affecting and modulating EAIS behaviour, such as bed topography, geology, subglacial hydrology and geothermal heat flux, and also present several interpretations for past changes, including their associated uncertainties, unresolved issues and outstanding questions.

We conclude by presenting our case for major new international aerogephysical exploration efforts such as in our newly proposed ICEOLIA ERC initiative to:

1) provide key missing bathymetric and geological data coverage over the much less well surveyed continental shelf and ice shelf cavities, which is critical to study ice sheet-ocean interactions and to link marine geological/geophysical and drilling observations with the dynamics of the EAIS;

2) glean an improved understanding of past processes and tipping points and finally

3) help investigate 4D (i.e. both space and time dependent) Solid Earth influences on past, present and future ice sheet behaviour in this key sector of East Antarctica.

How to cite: Ferraccioli, F., Eagles, G., Greenbaum, J., Armadillo, E., Young, D., Blankenship, D., Paxman, G., and Seigert, M.: Aerogeophysical views of a major vulnerable marine-based sector of the East Antarctic Ice Sheet: the Wilkes Subglacial Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13054, https://doi.org/10.5194/egusphere-egu24-13054, 2024.

With ongoing climate change, research into the biological changes occurring in particularly vulnerable ecosystems, such as Antarctica, is critical. The Totten Glacier region, Sabrina Coast, is currently experiencing some of the highest rates of thinning across all East Antarctica. An assessment of the microscopic organisms supporting the ecosystem of the marginal sea-ice zone over the continental rise is important, yet there is a lack of knowledge about the diversity and distribution of these organisms throughout the water column, and their occurrence and/or preservation in the underlying sediments. Here, we provide a taxonomic overview of the modern and ancient marine bacterial and eukaryotic communities of the Totten Glacier region, using a combination of 16S and 18S rRNA gene amplicon sequencing (modern DNA) and shotgun metagenomics (sedimentary ancient DNA, sedaDNA). Our data show considerable differences between eukaryote and bacterial signals in the water column versus the sediments. Proteobacteria and diatoms dominate the bacterial and eukaryote composition in the upper water column, while diatoms, dinoflagellates, and haptophytes notably decrease in relative abundance with increasing water depth. Little diatom sedaDNA was recovered from the sediments. Instead, sedaDNA was dominated by Proteobacteria and Retaria. We compare the diatom microfossil and sedaDNA record and link the weak preservation of diatom sedaDNA to DNA degradation while sinking through the water column to the seafloor. This study provides the first assessment of DNA transfer from ocean waters to sediments and an overview of the microscopic communities occurring in the climatically important Totten Glacier region. Such knowledge is important when reconstructing past ecosystems using the emerging sedaDNA approach as a new paleo-proxy, and the interpretation of biological changes in response to Antarctic ice sheet advances and retreats.

How to cite: Armbrecht, L., Focardi, A., Lawler, K.-A., O’Brien, P., Leventer, A., Noble, T., Opdyke, B., Duffy, M., Evangelinos, D., George, S. C., Lieser, J., López-Quirós, A., Post, A., Ostrowski, M., Paulsen, I., and Armand, L.: From the Surface Ocean to the Seafloor: Linking Modern and Paleo-Genetics at the Sabrina Coast, East Antarctica (IN2017_V01), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13090, https://doi.org/10.5194/egusphere-egu24-13090, 2024.

It is now well accepted that ice shelves and grounding zones experience changes in elevation synchronous with ocean tides, atmospheric loading and other processes. Recent studies have demonstrated that tidal pumping at the grounding zone can cause a transient migration of the grounding line hundreds of meters upstream relative to the grounded zone at low tide. As the grounded edge shifts inland, ocean intrusion leads to enhanced basal melting and grounding zone retreat, as demonstrated by previous InSAR-based studies on Thwaites Glacier in the Amundsen Sea Embayment. In this work, we use ICESat 2 elevation profile data spanning the Thwaites Glacier grounding zone and demonstrate the uplift of grounding zone topography in high tides with ocean intrusion ranging from ~1–9 km inland. The uplift of surface topography in high tides and our inferred ocean intrusion underneath the ice is heterogenous both in the along-track direction and along the width of the grounding zone. This work using ICESat 2 provides evidence in support of similar InSAR-based observations of the dynamic grounding zone and permits an independent assessment of the scale and volume of ocean water intrusion underneath Thwaites Glacier.

How to cite: Das, I., Goldberg, D., and Scambos, T.: Grounding Zone Processes at Thwaites Glacier from ICESat-2 Data and Ice-Ocean Modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13155, https://doi.org/10.5194/egusphere-egu24-13155, 2024.

A pair of automated multi-sensor stations with satellite data downlinking were installed near the center of the Thwaites Eastern Ice Shelf (TEIS) in January, 2020 and continued operating (at least partially) until November, 2022. The stations, situated 4 km apart (initially near 75.05°S, 105.5°W) recorded and transmitted weather and snow accumulation data, position, images, firn and ice temperature, and ocean conditions through a suite of instruments managed with software and uplinked commands to conserve power and/or maximize observations of events. The stations, called Automated Meteorology-Ice-Geophysics Observing Systems, mark III (AMIGOS-III) are installed on a tower and adjacent ice borehole to measure air, ice, and ocean parameters. Weather and accumulation data from the stations spanning 22 months show a mean annual air temperature for TEIS of -14.6°C, with observed extremes of +1.7°C (08 Feb 2020) to -51.0°C (17 Aug 2021). Mean air pressure was 973.7 mbar (at ~25 m elevation). Winds are highly directional and dominated by dry katabatic flow from the southeast (from 115° to 130°); however, higher snowfall is correlated with winds from more easterly and northeasterly directions. Average annual snowfall in the observation period was 0.72 to 0.90 m water equivalent. Ice flow speed was observed to accelerate throughout the observation period, ranging from ~1.7 m/d in January 2020 to more than 2.2 m/d in late 2021. The rate of acceleration increased markedly after July 2020, coinciding with satellite observations of a more disrupted northern and western shear margin for TEIS. Maximum tidal amplitude is ~1.6 meters. Comparison with the CATS2008 tide model, after correction for IBE, showed a mean difference of ±17 cm. Ocean data was acquired from the two sub-shelf cavity moorings, each of which included paired SeaBird microCAT and Nortek Aquadopp sensors at mid-cavity depths (~520 m and ~317 m) and near-seabed depths (~746 m and ~785 m), in the modified Circumpolar Deep Water (mCDW) layer. These were augmented by a fiber optic thermal profiler system that measured both ice and ocean temperatures for 19 months. The fiber optic thermal data show a minimum temperature of -19.0°C in the interior, and lower temperature gradient suggesting truncation of the ice shelf base due to basal melting. Time-series of the profile data show very little basal melting of the ice at the two sites, but a thickening of the mCDW layer over the observation period. Overall, the AMIGOS-III data have supported six published studies to date, on ice shelf dynamics, ocean flow and layer properties, basal conditions, atmospheric river events, and weather. The units demonstrate the benefit of long-duration multi-sensor observing platforms in ice shelf or ice tongue areas.

How to cite: Scambos, T., Truffer, M., Collao-Barrios, G., Dotto, T., Kratt, C., Tyler, S., and Pettit, E.: Climate, Ice, and Ocean Characteristics of the Thwaites Eastern Ice Shelf from two In-Situ Multi-Sensor Automated Stations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13668, https://doi.org/10.5194/egusphere-egu24-13668, 2024.

Increasing Antarctic snow accumulation can mitigate sea level rise, but considerable uncertainty surrounds both past snowfall trends and future sea level projections. Here, we present a reconstruction of 19th and 20th century Antarctic accumulation, and the 20th century cumulative impact on global mean sea level. Using the Last Millenium Reanalysis framework to integrate ice core accumulation and water isotope records with a multi-model ensemble of CMIP5 climate simulations, we produce annually resolved reconstructions from 1801-2000 CE. Reconstructions demonstrate significant skill through strong satellite-era correlation with instrumental reanalysis; we find a positive Antarctic accumulation trend over the 20th century, translating to a modest amount (~1 mm) of sea level mitigation. Mitigation is primarily driven by an accelerating trend since around 1970. These findings contrast with previous 20th century mitigation estimates of ~10-12 mm; we determine that this discrepancy is due to unconstrained baseline estimates of 19th century accumulation in East Antarctica. Our results suggest that uncertainties in East Antarctic accumulation history preclude a confident estimate of Antarctic sea level mitigation, thus highlighting the need for new, high-quality accumulation records from East Antarctica.

How to cite: Eswaran, A., Truax, O., and Fudge, T.: Antarctic 20th-Century Sea Level Mitigation Dominated By Uncertainty in 19th-Century East Antarctic Snow Accumulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14163, https://doi.org/10.5194/egusphere-egu24-14163, 2024.

Detecting and understanding potential changes in annual mean temperature and accumulation rate at the East Antarctic Plateau is crucial to assess the sensitivity and future response of the Antarctic ice sheet to global warming. Due the very low accumulation rate and its spatial variability the interpretation of climate proxies from shallow firn cores with centennial to decadal time resolution is challenging. A major limitation is the available time resolution obtained by available dating approaches and a reliable assessment of its uncertainty.
In this study a 204 m long firn core, B56, drilled in 2016 on the East Antarctic Plateau, is analysed. The major goal of this study is dating of the firn core by combining different dating methods on the basis of available density data, dielectric properties, and ion chromatography (non-sea-salt sulphate) data. In order to utilize density, the Herron-Langway Model is used for determining the depth-age relation. In this model temperature and snow accumulation are assumed to be constant and the relationship between the snow density and the depth below the snow surface does not change over time. Depending on the used accumulation rate, the resulting age at 200 m depth varies between 6200 to 7200 years. Secondly, the dielectric profile and non-sea-salt sulphate's (nssSO4-2) concentration data are used for constructing another depth-age model, thereby matching prominent data peaks to known volcanic eruptions that have been recorded in the past. Here, the resulting age at 200 m depth is determined to about 4400 years, which compares well to published age models of firn cores from the East Antarctic Plateau. In comparison we find all age models to be consistent within the upper 40 of meters (approximately 1000years), but the Herron-Langway model to overestimate the age at greater depths. We propose that our findings indicate changes in accumulatıon rate in the past leading to the offset in the Herron-Langway model (using a constant accumulation rate).
However, by combining the dating methods we are able to not only provide a reasonable dating over the full firn core, but also to improve the time resolution of the derived age model. This will improve the interpretation of the climate proxies of this firn core and serve as a role model for other shallow firn cores from the East Antarctic Plateau.

How to cite: Sagol, F. K., Schwamborn, G., Freitag, J., Kipfstuhl, S., Wilhelms, F., and Hörhold, M.: Dating and interpreting a firn core from the East Antarctic Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15484, https://doi.org/10.5194/egusphere-egu24-15484, 2024.

Totten Glacier is the largest contributor to the global sea level rise from the East Antarctic Ice Sheet and has been losing mass since the earliest satellite observations in the 1970s. However, unlike other outlet glaciers that are losing mass in Antarctica (e.g. Pine Island and Thwaites), there has been no obvious long-term speed-up and subsequent increase in ice discharge over the satellite observational record, despite large interannual variability in ice flow. This indicates that the imbalance at Totten Glacier must have initiated prior to our earliest satellite observations.

Utilizing the complete record of satellite imagery, we track the pattern of surface undulations that form near the Totten grounding line and are preserved for decades as they are subsequently transported downstream. In our earliest satellite image from 1973, we observe surface undulations estimated to have formed near the grounding line in the 1920s. We suggest that changes in the size and formation of these surface undulations are caused by changes in the melt rate and ice thickness near the grounding line that alters the degree of contact between the ice shelf and a nearby pinning point. By monitoring the size of these surface undulations, we provide a qualitative record of ice thickness change near the grounding line from the 1920s to the present day. We reveal a clear shift in pattern in the mid-20th century, where, despite pronounced and consistent surface undulation formation between the 1920s and 1950s, no detectable surface undulations were formed between the late 1950s and 1980s.

Elsewhere on the glacier, we demonstrate the long-term opening of a previously identified channel connecting the eastern ice shelf to the open ocean and observe grounding line changes since the 1970s.

How to cite: Miles, B. and Bingham, R.: Change in melt pattern at Totten Ice Shelf in the 1950s, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16595, https://doi.org/10.5194/egusphere-egu24-16595, 2024.

The Thwaites Eastern Ice Shelf stands as the last remaining floating extent of the consequential Thwaites Glacier in West Antarctica. In the past, it has provided buttressing of the grounded glacier ice, but in the last decade the ice shelf has undergone significant weakening that has reduced its ability to buttress the glacier. Important signs of weakening include: 1) the ice flow measured by ground-based GPS shows continuous acceleration, nearly doubling in speed from 1.65 m/d in 2019 to 2.85 m/d by early 2023; 2) a recent breakout of sea ice has accelerated retreat at the western calving front of the Eastern Ice Shelf; 3) increased damage in a confined shear zone along the north-western pinning point has effectively separated the ice shelf from this pinning point.; 4) five rifts formed since 2016 and have propagated episodically into the center of the most coherent section of the shelf; and 5) several full thickness “gashes” have opened and continue to open parallel to and just downstream of the grounding zone to accommodate the recent ice-shelf speed up through localized strain. Due to these full-depth rifts, the ice shelf has nearly entirely detached from the upstream grounded ice, and is now functioning as a relatively thin, floating ice plate that provides minimal support to the grounded sections of Thwaites Glacier. This accumulation of damage in the ice shelf is happening during a period in which we observe  suppressed basal melt rates and little measurable thinning, suggesting that melt is not the primary driver of ongoing changes. Here, we present the most up-to-date synthesis assessment of the structural integrity of this ice shelf, as well as its relation to ocean conditions underneath and the pinning point, and consider the stability of the ice shelf within the context of ice flow off the continent and projections for sea-level rise.

How to cite: Wild, C., Pettit, E., Alley, K., Truffer, M., Scambos, T., Heywood, K., Muto, A., Hall, R., Sharp, M., Smith, H., Carroll, G., Wanzer, L., Trunz, C., Wahlin, A., Collao-Barrios, G., Maclennan, M., Ochwat, N., Dotto, T., Luckman, A., and Kachuck, S. and the TARSAN team: Assessing the Structural Stability of Thwaites Eastern Ice Shelf and Its Influence on the Future Evolution of Thwaites Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16837, https://doi.org/10.5194/egusphere-egu24-16837, 2024.

Thwaites Glacier (TG) is a wide, fast moving ice stream that, along with Pine Island Glacier, drains much of the West Antarctic Ice Sheet (WAIS). This work presents preliminary results of ice fabric, bed topography, and englacial layering from a 200-km-long Autonomous phase-sensitive Radio Echo Sounder (ApRES) survey along the trunk of TG as part of the International Thwaites Glacier Consortium’s GHOST project in 2022-2023. From 235 point measurements and 47 polarimetric measurements, we find a variable, complex ice fabric that changes in strength and orientation along the transect and with depth. Fabric strength, measured as horizontal anisotropy, is on average stronger downstream than upstream, and the fast axis (also known as the symmetry axis) is more aligned along flow than across, as expected in an ice stream. Ice fabric is useful to both meaure and model because it both serves as a record of past stress and deformation, and affects viscosity, directionally softening the ice and impacting the glacier’s response to future stresses.

How to cite: Case, E. and Kingslake, J.: Ice Fabric on Thwaites Glacier from ApRES Polarimetric Measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16990, https://doi.org/10.5194/egusphere-egu24-16990, 2024.

Understanding ocean-ice sheet interactions in the geological past is critical for evaluating the ice sheet sensitivity to ocean forcing in future climate warming. Geological evidence suggests major oceanographic changes across the Southern Ocean during the Middle Miocene Climate Transition (MMCT) (~15-12 Million years ago (Ma)). However, the response of the East Antarctic Ice Sheet to these changes remains poorly constrained. Here we explore ocean-ice interactions during the MMCT by presenting data from two marine sedimentary cores along a latitudinal transect offshore Prydz Bay (East Antarctica). Ocean Drilling Program (ODP) Site 1165 is located on the continental rise off Prydz Bay (64◦27.27^o S, 67◦13.08^o E, 3537.5 water depth) and ODP Site 744 is located on the Southern Kerguelen Plateau (61^o 34.66´S, 80^o 35.43´E, 2307 m water depth). Neodymium and strontium isotopic compositions of fine-grained (< 63μm) detrital sediments from ODP Site 1165 were generated to constrain potential changes in sediment provenance, revealing potential changes in ice sheet dynamics (expansion/retreat). Neodymium isotope ratios (ε_Nd) from fossil fish teeth from ODP Site 744 were used to trace regional water masses and Southern Ocean circulation changes for the same period. Additionally, marine productivity records generated from both ODP sites were used to track changes on the position of the Southern Ocean frontal system. We report an equatorward migration of the Southern Ocean frontal system around 13 Ma, associated with global climate cooling, sea ice expansion and CO₂ decline during the MMCT. Despite this major ocean-climate reorganization, our data suggest the presence of a rather stable and large ice sheet in the Prydz Bay throughout the MMCT, implying that the ice sheet was less sensitive to ocean forcing during the MMCT.

How to cite: Evangelinos, D., van de Flierdt, T., Paredes, E., D. Pena, L., and Cacho, I.: East Antarctic Ice Sheet response to ocean forcing during the Middle Miocene Climate Transition: Insights from Prydz Bay, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18013, https://doi.org/10.5194/egusphere-egu24-18013, 2024.

Knowledge of the past dynamics of the Antarctic ice sheets is essential for better understanding their present and future stability and, importantly, the resulting effects on global mean sea level rise in a warming world. The petrology and geochemistry of iceberg-rafted debris (IRD; >150 μm) produced by these ice sheets can provide vital information about past ice sheet extent, but the characteristics of geological sources are poorly constrained in ice-covered Antarctica. Lead isotope ratios (controlled by protolith age) in West Antarctic basement and derived sedimentary rocks (mostly <500 Ma) have previously been assumed to be largely homogenous, and therefore useful only for distinguishing West Antarctic IRD from older (0.5-3 Ga) East Antarctic IRD in Southern Ocean sediments. Laser ablation analysis of individual mineral grains, however, avoids the averaging effects of bulk mineral separate, sediment, or rock analyses and reveals the full variation of isotopic signatures in a sample of detrital grains. Here, we present a survey of lead isotope ratios determined in ~600 iceberg-rafted feldspar grains from 26 seafloor surface sediment samples from the West Antarctic continental shelf. Machine-learning clustering of the lead-isotope data reveals at least two major populations, including a previously unknown population of grains which are less radiogenic than the main cluster. These less radiogenic grains are only found in two areas: near the ice-shelf front of Thwaites Glacier and near the eastern edge of the Ross Ice Shelf. The Thwaites signal is not present at sites on the middle and outer continental shelf, suggesting an offshore dilution effect. Supervised clustering of the main group reveals additional subdivisions in Pb-isotope space that are geographically restricted to: (i) the wider Amundsen Sea, (ii) the Bellingshausen Sea, and (iii) Sulzberger Bay at the boundary between the Amundsen and Ross seas. These subdivisions will be further investigated using ⁸⁷Rb-⁸⁷Sr dating of a subset of the feldspar grains used for Pb-isotope analysis. Together, these new data provide a novel IRD provenance tool, allowing tracing of offshore IRD back to either Thwaites Glacier or the eastern Ross Ice Shelf source areas. Given the observed offshore dilution effect, detection of this signal in sediment cores from the outer shelf or deep-sea would indicate a significantly increased supply of detritus sourced from Thwaites Glacier or the Ross Ice Shelf, both important iceberg outlets of the West Antarctic Ice Sheet.

How to cite: Arney, T., Hillenbrand, C.-D., Milton, J. A., Siddoway, C., Foster, G., Wilson, P., Wellner, J. S., and Bohaty, S. M.: Ice-rafted feldspar grains in recent shelf sediments of West Antarctica: provenance pathways via lead isotope compositions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18206, https://doi.org/10.5194/egusphere-egu24-18206, 2024.

A number of studies have defined a boundary in the Amundsen Sea embayment between an inner continental shelf, which contains areas where crystalline bedrock is at or near the seabed, and the shelf further offshore, which is underlain by sedimentary strata that increase in overall thickness oceanward. Other studies have shown that much of the inner shelf in Pine Island Bay is covered by a drape of sandy mud averaging about 1 m in thickness, interpreted as having been deposited from meltwater plumes during the mid-late Holocene. Much thicker sediments have been shown to be present in isolated deep basins based on acoustic sub-bottom profiles and sparse seismic reflection profiles, including an estimated maximum thickness of >400 m in one basin close to the front of Pine Island Glacier.  Thus, the widespread impression exists that, apart from the thin Holocene drape, sedimentary cover in Pine Island Bay is restricted to isolated basins.

Here we examine the distribution and thickness of sediments in Pine Island Bay using a network of high-resolution seismic reflection profiles collected in 2020 on RV Nathaniel B Palmer cruise NBP20-02. We show that more extensive thick sediments are present near the front of Pine Island Glacier than have been reported previously. In some places sediment units exhibit characteristics that suggest their deposition was influenced by bottom currents. We also show that sedimentary deposits are present over the tops and on the flanks of some bathymetric highs that must have been former ice shelf pinning points. Finally, we consider what the extent, thickness and character of the sedimentary units identified tell us about glacial/glacimarine processes and ice sheet history in the area, and what could be learned by further study and sampling.

How to cite: Larter, R., Hogan, K., Graham, A., Nitsche, F., Wellner, J., Hillenbrand, C.-D., Totten, R., Smith, J., Miller, L., Anderson, J., Mawbey, E., Clark, R., Hopkins, R., Lehrmann, A., Lepp, A., Marschalek, J., Munevar Garcia, S., and Taylor, L.: How much, how deposited, how old – what can we learn from sediments in Pine Island Bay?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19707, https://doi.org/10.5194/egusphere-egu24-19707, 2024.

Existing marine sedimentological constraints on the timing of deglaciation in the Weddell Sector are sparse, owing to the combination of inaccessibility due to thick sea ice, and chronological difficulties typical of Antarctic shelf sediments. Here, we present new results from near the calving line in the Hughes Trough, located in the central-southern Weddell Sea. Ramped pyrolysis 14C dating was used to determine a robust chronology from the 5.0 m long sediment core, PS111_53. The core preserves a full glaciomarine sequence from subglacial, sub-ice shelf, and open marine / polynya environments. The sedimentological transition interpreted to be formed at the grounding zone during ice shelf retreat was dated to 18.2 – 19.0 ka, indicating that grounded ice retreat was underway by this time. Further, the sedimentation rate was drastically reduced at ~6 ka, indicating that the oceanographic and glaciological regimes of the continental shelf may have changed at this time.

The proposed timing of glacial mass loss is well placed in the context of recent studies from the continental ice sheet and off-shelf marine sediments, which have suggested that a significant ice mass loss event from the Weddell Sector of the Antarctic Ice Sheet (AIS) may have occurred early in the deglaciation. A synchronous timing of deglaciation between the Weddell Sector of the AIS and Laurentide Ice Sheets during MWP-1A0 points towards bi-polar tele-connections.

How to cite: Bollen, M., Müller, J., Gutjahr, M., and Jaccard, S.: Sedimentological evidence for an early deglaciation in the Weddell Sector at ~19 ka, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19800, https://doi.org/10.5194/egusphere-egu24-19800, 2024.

The recent Ice sheet Mass Balance Inter-comparison Exercise (IMBIE) suggests that between 2012 and 2017 the East Antarctic Ice Sheet was approximately in balance, experiencing a rate of mass change of 23 ± 38 Gt yr^-1.  While this study provided an important statistical reconciliation of various studies across several techniques, the root cause of the differences amongst the estimates remains unresolved.  Satellite gravimetry provides a direct measurement of mass change; however, it is sensitive to all mass changes, and the necessary corrections for solid earth changes are substantial and poorly constrained.  Satellite altimetry provides measurements of volume change, which includes changes in ice mass and non-ice mass.  The latter is largely driven by changes in the density of the snow and firn requiring poorly constrained models for conversion to mass.  Here, rather than deriving ice-sheet mass balance using a single technique, we use both satellite gravimetry and altimetry to better: (1) reconcile mass balance estimates between the two techniques, (2) improve constraint on firn dynamics, and (3) attempt to partition the driver of change.  Because these two measurements are sensitive to different processes, using them in conjunction provides additional constraint of the most unknown processes.

Our new technique solves for the change in total firn air content through time for the entire Antarctic Ice Sheet that provides a best-fit mass solution between altimetry and gravimetry.  In such a way, we produce ice-sheet mass change at the fine-scale resolution of ice elevation measurements (10 km) that best matches the coarsely resolved (>100km) mass change from gravimetry.  Our results indicate that during the ICESat-2 era (April 2019 through June 2023), the East Antarctic Ice Sheet gained mass at a rate of 160 Gt yr^-1, three times the average mass gain over the two decades prior (52 Gt yr^-1).  The sector that spans 60E to 130E received the largest anomalous gains in mass (precipitation).  These gains, in conjunction with minor gains from the Antarctic Peninsula (23 Gt yr^-1), fully balance the continued mass losses from West Antarctica (-139 Gt yr^-1).  Large precipitation events over both East Antarctica and the Antarctic Peninsula are driving the mass gains; however, more time is needed to determine whether these changes are long-term or only short-lived given the ICESat-2 time series is just over 4 years in length.  These results suggest that atmospheric dynamics play a key role in driving the mass balance of the East Antarctic Ice Sheet and have potential to rapidly change the overall mass balance of the ice sheet.

How to cite: Medley, B. and Sutterley, T.: Modern-day mass gains over East Antarctica exceed the two decades prior, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20880, https://doi.org/10.5194/egusphere-egu24-20880, 2024.

Our understanding of Antarctic Ice Sheet evolution has largely relied on geological evidence from a combination of onshore and offshore archives. In particular, terrestrial cosmogenic nuclides (e.g., ¹⁰Be, ²⁶Al, ³⁶Cl, ¹⁴C) have now been extensively employed to assess the timing and drivers of past ice sheet change. Yet, such chronologies are incomplete, can be compromised by complex burial-exposure histories, and are not ideally suited to reconstructing the long-term (hundreds of thousands to millions of years) evolution of the ice sheet.

To address this gap in understanding long-term Antarctic Ice Sheet evolution, we investigate the application of a cross-disciplinary approach that incorporates a combination of geological and biological evidence. Recent work has implied that certain biota, such as Antarctic springtails (Arthropoda: Collembola), survived consecutive glacial periods in ice-free refugia by shifting up and down nunataks or on moraines above the ice (see: Stevens and Mackintosh, 2023; https://doi.org/10.1098/rsbl.2022.0590). Due to these prolonged periods of isolation, springtails have now developed high levels of species endemism across Antarctica. These species are often short-range endemics, and now combined with extensive molecular data are the only terrestrial invertebrate group with unequivocal Antarctic provenance across successive glacial maxima on the continent. As a result, incorporating these growing records of Antarctic springtail distribution into chronological studies may yield a more complete understanding of ice sheet evolution through time. Here, we demonstrate the use of this combined approach across the whole of Dronning Maud Land, East Antarctica. 

How to cite: Cooper, E.-L., Stevens, M. I., and Mackintosh, A. N.: A cross-disciplinary approach to understanding Antarctic Ice Sheet histories: combining cosmogenic nuclides with records of Antarctic springtails in Dronning Maud Land, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21830, https://doi.org/10.5194/egusphere-egu24-21830, 2024.

The Cook Ice Shelf and Ninnis Glacier drain a large part of the Wilkes Land Basin, which contains the equivalent of about 4 metres of sea level. The glaciers in this region are thought to have retreated during the warm climatic phases of the Pleistocene, but the extent of the retreat and the identification of the driving forces are still controversial. The aim of this study is to contribute to the understanding of regional depositional processes and environmental conditions that shed light on the dynamics of the ice sheet and the factors that determine its stability and instability (ocean and atmospheric temperature and precipitation), and ultimately to refine the projected evolution of these glaciers. We here present the preliminary results of a multidisciplinary study (textural analyses, geochemical, chemical and petrographic analyses, paleomagnetic and micropaleontological determinations) carried out on six sediment cores collected on the continental slope off the Cook Ice Shelf and Ninnis Glacier in the framework of the Programma Nazionale di Ricerca in Antartide - PNRA project COLLAPSE ("Cook glacier-Ocean system, sea LeveL and Antarctic Past Stability'). We are currently documenting sedimentological processes and oceanographic conditions in this region during the Late Pleistocene. We identified three main units: the first unit consists of laminated silt with low microfossil content and is interpreted as influenced by bottom current; the second unit is a massive silt with ice debris, and very low microfossil content and is interpreted as indicating a period with intense ice calving with iceberg production; the third unit is a bioturbated mud with high microfossil content.   The microfossil content, especially the diatoms, suggest that this unit is deposited during a period of open water.

How to cite: Torricella, F., Andò, S., Battaglia, F., Caburlotto, A., Colizza, E., Crosta, X., De Santis, L., Etorneau, J., Gallerani, A., Gentz, T., Leventer, A., Macrì, P., Melis, R., Perotti, M., Salvi, G., Tesi, T., and Zurli, L.: Pleistocene evolution of Ninnis and Cook glaciers (East Antarctica) from a micropaleontological and sedimentological study: Preliminary result, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22344, https://doi.org/10.5194/egusphere-egu24-22344, 2024.

Quantifying the mechanical properties of snow is crucial for various applications, including the assessment of slope stability, vehicle mobility on snow-covered terrain, and the understanding of snowpack evolution. To build our understanding of snowpack evolution, we utilize a novel non-contacting laser ultrasound system (LUS). This system collects ultrasonic wavefield data from tens to hundreds of kilohertz in a controlled cold lab environment, allowing us to interpret acoustic measurements and measure mechanical properties on a microscale and upscale this to the field scale.

 We investigated the relationship between P-wave velocity changes and snow properties such as density, snow crystal type, and metamorphism through sintering. We controlled the density of the snow samples by adjusting the volume while maintaining the same mass. We controlled the microstructure by manipulating the supersaturation and temperature (controlling air and water temperatures within an artificial snow maker) within a cold lab to make artificial snow of a specific crystal type (i.e., Dendritic, plate, column, and needle snow crystals). Homogeneous snow samples, each composed of their own single crystal type, were created and compacted to a density of 250 kilograms per cubic meter.

Over a period of 72 hours, we measured acoustic wave propagation through  these artificial snow samples to periodically observe changes in waves peed during metamorphism. This allowed us to monitor changes in mechanical properties as sintering occurred, for different snow crystal types. We also measured snow microstructure and micromechanical properties with destructive techniques, using the SnowMicroPen and MicroCT. Finally, we examined the relationship between velocity changes and snow crystal types, specifically in terms of sintering time. Our findings suggest that the crystal type, as influenced by time under isothermal temperature conditions, affects the observed bulk mechanical properties and their rate of change.  Observations of ultrasonic wavefields show that snow strengthened by a factor of 1 to 2 within 72 hours, depending on the snow crystal type. 

How to cite: McCaslin, J., Mikesell, T., Marshall, H.-P., and Courville, Z.: Characterization of snow mechanical properties using laser ultrasound: Role of snow crystal type, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-728, https://doi.org/10.5194/egusphere-egu24-728, 2024.

In the Central Andes of Argentina, glaciers are crucial components of the mountain hydrological system, as they can provide up to 60% of river flow in the driest season. This region concentrates 82% of the debris-covered glaciers in the country. Most of them are small valley glaciers (< 2 km²). Nevertheless, a few large debris-covered valley glaciers (>10 km²) concentrated the most significant ice volume. Despite their abundance and regional importance, the processes underlying mass exchange and response to climate change in debris-covered glaciers have been little studied.

We process over 60,000 images from Landsat and Sentinel satellites through Google Earth Engine to study changes in the extent of the debris-covered area and Debris Emergence Elevation (DEE) for 128 valley glaciers of the Central Andes of Argentina (42.6% of the debris-covered glacier area). Using an automated classification algorithm, we identified the different surface facies (snow, ice, debris, and water) at each glacier between 1985 and 2022. We validated our classification against the National Glacier Inventory of Argentina, obtaining coincidence in the classifications in more than 94% of the cases.

Assuming there were no changes in glacier extent, we found a 27 ± 15% increase in debris cover along the studied glaciers. Between 1985 and 2009, the debris-covered area had a significant interannual variation, and from 2009 to 2022, there was a substantial increase in the debris-covered area. Indeed, almost 68% of the increase in debris-covered areas occurred in the last decade. During the last four decades, DEE showed a mean increase of 127 ± 109 meters for simple basin valley glaciers. These changes follow a similar pattern but with greater interannual variability than changes in debris-covered area.

The increase of debris-covered area and DEE in the last decade coincides with an extensive drought period and an increase in the glacier mass loss in the Central Andes. Nevertheless, the automated classification algorithm cannot differentiate between debris-covered ice and internal outcrops. Thus, the increase in the debris-covered area includes the expansion of internal rock outcrop due to a loss of ice mass. Furthermore, we hypothesized that hypsometry and glacier morphology control the extent and elevation debris can reach. We found that low-slope glaciers are the ones that increase their debris cover the most. Meanwhile, glaciers with a very steep accumulation area or a strong slope change around the Equilibrium Line Altitude do not significantly change the debris-covered area. Also, due to the expansion of internal rock, the calculation of DEE at large compound or complex-basin glaciers shows more significant dispersion than at simple-basin glaciers. Improving the classification algorithm and assessing the influence of glacier morphology in the changes in debris-covered areas are crucial to better constrain the change in debris-covered glaciers.

How to cite: Ghilardi Truffa, J. C. and Ruiz, L.: Debris-covered area increased in the Central Andes of Argentina glaciers over the past four decades, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1171, https://doi.org/10.5194/egusphere-egu24-1171, 2024.

No current remote sensing technique can accurately measure snow water equivalent (SWE) from space for mountain hydrologic applications. Optical sensors are robust for measuring the fractional snow-covered area (fSCA) at various spatial and temporal resolutions. Yet, these optical methods are limited by cloud cover and do not provide information on SWE. Synthetic aperture radar (SAR) can penetrate clouds, has a fine spatial resolution, and various algorithms allow us to quantify both SWE magnitude and changes. However, SAR cannot discriminate between snow-free and snow-covered areas when the snow is dry. To address this SWE monitoring challenge, we evaluate a multisensor approach that leverages the strengths of both optical and radar sensors. Our study aims to better understand the variability between common snow cover data products and how that uncertainty propagates into InSAR-based SWE retrieval techniques. We analyzed four UAVSAR InSAR pairs from one flight line over the Sierra Nevada, CA, during the SnowEx 2020 campaign and compared six satellite-based snow cover products. First, we computed InSAR-based SWE change estimates using in situ snowpack data. We then compared the summed SWE change values with a moving window analysis to quantify product variability. Lastly, we tested the volumetric SWE results for statistical differences. Results show that moderate-resolution (375–500 m) NDSI-based products provide broadly similar volumetric SWE change results to those using more complex spectral unmixing and machine learning retrieval methods. This suggests that the readily available moderate-resolution snow cover products from MODIS are adequate for an optical-radar SWE monitoring approach. Future work should focus on understanding how sub-canopy snow in forested regions affects snow cover product accuracy and variability. Furthermore, near-real-time, high-resolution cloud- and gap-filled optically-derived snow cover data will be important for supporting water resources decision-making.

How to cite: Tarricone, J., Palomaki, R., Rittger, K., Marshall, H.-P., Nolin, A., and Vuyovich, C.: Comparing multisensor optical-radar approaches for snow water equivalent retrievals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4137, https://doi.org/10.5194/egusphere-egu24-4137, 2024.

Monitoring the amount of snow, its spatiotemporal distribution as well as the onset and amount of snow-melt induced runoff generation are key challenges in alpine hydrology. Cryo-hydro-gravimetry is a non-invasive method of observing temporal gravity variations after the reduction of all other geophysical signals as the integral of all cryospheric and hydrological mass variations including snow accumulation and ablation. It has an accuracy of up to 9 decimals on a wide spectrum from high temporal resolution of up to 1 min to several years within footprints up to approx. 50 km². At the Zugspitze Geodynamic Observatory Germany (ZUGOG) with its worldwide unique installation of a superconducting gravimeter at a high-alpine summit (2.962 m a.s.l.), this method is applied for the first time on top of a well-instrumented, snow-dominated catchment. We use this instrumental setup in synthesis with in situ measured data, detailed physically-based snowpack modelling with Alpine3D as well as satellite-based snow depth maps derived by stereo photogrammetry. We will give an introduction into the novel sensor setup and will show first results, including the sensitivity of the integrative gravimetric signal regarding the spatially distributed snowpack and the cryo-hydro-gravimetric signal changes since 2019. The amount of the simulated snow water equivalent within the footprint of the gravimeter correlates well with the gravimetric signal (Pearson correlation coefficient r = 0.98). Based on the applied snowpack modelling approach including the snow depth maps for precipitation scaling, topography information as well as Newton’s Law of Gravitation, the gravimetric signal contribution and footprint can be described spatiotemporally over winter periods.

How to cite: Koch, F., Gascoin, S., Achmüller, K., Schattan, P., Wetzel, K.-F., Rehm, T., Schulz, K., and Voigt, C.: Tracking high-alpine snow mass evolution using signals of a superconducting gravimeter combined with snowpack modelling and stereo satellite imagery, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5825, https://doi.org/10.5194/egusphere-egu24-5825, 2024.

Snow is a crucial factor determining plant species distributions in alpine and arctic environments. Therefore, metrics like the duration of snow cover are important predictors to model plant distributions. Many studies employed snow cover metrics derived from optical satellite image time series. Such satellite-derived observations are easily accessible and highly consistent, making them a viable choice for current and past conditions. However, an inherent limitation is their applicability for future projections of snow cover, which is only possible by establishing statistical relationships to ancillary data sets. Snow cover simulated by a physically-based snow model could circumvent these constraints, but it was rarely employed for predicting alpine plant species distributions. Increasing availability of input data, computational power and data sets for validation nowadays allow for modeling at reasonably high resolutions.

To this end, we report first results of several modeling experiments, to quantify the differences of using snow cover metrics derived from webcam time series and modeled snow data for a study site of approximately 5 km² in the Stubaier Alps (Tyrol, Austria). Melt-out date is one of most commonly used snow metrics in species distribution models. Hence, we derive the melt-out dates from two seasons (2022 and 2023) of webcam-based and modeled snow cover. Subsequently, we modeled the distribution of 79 plant species with the melt-out dates as predictors along with several proxies for topographic heterogeneity at spatial resolutions of 1 m and 20 m in order to account for the small-scale variability of snow cover in alpine landscapes. The study demonstrates how the usage of modeled and observed snow data affects modeling of high-alpine vegetation distribution. These insights are important for appropriately designing species distribution modeling studies based on modeled rather than observed snow data.

Acknowledgements: This work has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 883669).

How to cite: Kollert, A., Chytrý, K., Mayr, A., Hülber, K., and Rutzinger, M.: Investigating the usage of physically modeled snow cover vs. webcam-based snow cover for driving plant species distribution models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6297, https://doi.org/10.5194/egusphere-egu24-6297, 2024.

Estimates of glacier accumulation are a vital part of determining annual glacier mass balance. Here, the annual accumulation of the Khumbu Glacier, Nepal, is estimated using data from a dense network of high-altitude weather stations in the Khumbu Valley, extending to the summit of Mount Everest. Observations of precipitation phase are used to refine methods of phase modelling using logistic regression in conjunction with weather station and precipitation gauge data. Seasonal temperature lapse rates and spatio-temporal patterns of precipitation are inferred from weather station data, and observed precipitation is adjusted for snow undercatch based on modelled precipitation phase and wind speed. These methods are then combined and distributed over the glacier surface to produce an overall estimate of seasonal and annual accumulation rates of the Khumbu Glacier. 

How to cite: Graves, B.: Estimating the annual accumulation of the Khumbu Glacier, Nepal, using weather station data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6336, https://doi.org/10.5194/egusphere-egu24-6336, 2024.

How to cite: Farías-Barahona, D., Schaefer, M., Braun, M., Peña, V., and Hernández, J. and the Team QFuego-Patagonia: QFuego-Patagonia: a comprehensive glacier-related dataset for Patagonia and Tierra del Fuego, South America, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6979, https://doi.org/10.5194/egusphere-egu24-6979, 2024.

The existing snow depth products have mainly focused on influence of varying snow characteristics and forests, while neglecting the complicated mountainous terrain. Therefore, examining the influence of mountainous terrain on microwave radiation transmission of snowpack is beneficial for improvement of snow depth retrieval algorithms in mountainous areas. In this study, we established microwave emission transfer model of snowpack in Mountainous areas within the framework of MEMLS, thereafter, called MEMLS-T. MEMLS-T considers the influence of complicated terrain on the microwave radiation transmission of snowpack from three perspectives: 1) the varied hill slopes alter the local incidence angle; 2) the diverse hill slopes and aspects induce the polarization rotation; 3) The reduced sky visibility in mountainous regions results in an escalation of downward background radiation reaching the snow surface, as a consequence of the illumination from neighboring slopes. We simulate brightness temperatures at varying sky visibilities, slopes and aspects using MEMLS-T, and find that, in compared with flat terrain, brightness temperature gradient decreases in mountainous area, and the extent of reduction depends on complexity (Figure 1). The brightness temperatures are simulated based on various spatial resolutions of DEM and integrated into a grid of 6.25km×6.25km. The results reveal that coarser DEM results in greater sky visibility (Figure 2) and higher brightness temperature (Figure 3). Therefore, a fine DEM is necessary to simulate the brightness temperatures in mountainous areas. Additionally, the observation footprints vary with satellites and frequencies, resulting in discrepancies in snow depth retrieval and temporal consistency.

figure 1Brightness temperature difference between K and Ka bands varies with aspect, slope and sky radiation

figure 2 Comparison of sky visibility obtained from DEMs with different resolutions.

Figure 3 Comparison of brightness temperature simulated from DEMs with different resolutions

How to cite: Che, T. and Dai, L.: Terrain effects on microwave emission transmission of snowpack and snow depth retrieval, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7043, https://doi.org/10.5194/egusphere-egu24-7043, 2024.

Climate change significantly affects snow, emphasizing the urgency to comprehend the temporal and spatial variations in snowfall trends. Analysing historical snowfall data across large areas is often impeded by the lack of continuous long-term time series. This study investigates snowfall trends (HN) by examining observed time series from 46 Alpine sites at various elevations spanning the period 1920-2020. In addition to HN, the analysis focuses on key parameters such as precipitation (P), mean temperature (TMEAN), and large-scale synoptic descriptors — the North Atlantic Oscillation (NAO), Arctic Oscillation (AO), and Atlantic Multidecadal Oscillation (AMO) indices — to discern patterns and variations in HN over the years.

The study reveals that over the past century, below 2000 m a.s.l., there has been a decline in HN across the Alps, particularly in southern and low-elevation sites, despite a slight increase in winter precipitation. The South-West and South-East regions experienced average losses of 4.9% and 3.8% per decade, respectively, while the Northern region showed a smaller relative loss of -2.3% per decade. The negative HN trends are primarily attributed to a TMEAN increase of 0.15 °C per decade. The majority of the HN decrease occurred between 1980 and 2020, as a result of a more pronounced increase in TMEAN. This is reinforced by changes in the running correlation between HN and TMEAN, NAO, AO over time; before 1980, there was no correlation, while in later years, the correlation increased. This suggests that in recent times, the right combination of temperature, precipitation, and atmospheric patterns has become crucial for snowfall. On the other hand, no correlation was found with the AMO index.

How to cite: Bozzoli, M., Crespi, A., Matiu, M., Majone, B., Giovannini, L., Zardi, D., Brugnara, Y., Bozzo, A., Cat Berro, D., Mercalli, L., and Bertoldi, G.: Centennial observed snowfall trends and variability in the European Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7703, https://doi.org/10.5194/egusphere-egu24-7703, 2024.

Plant phenology is highly sensitive to climate change, and the Arctic region is experiencing rapid changes in vegetation and snowpack. However, the specific climatic drivers of these changes are poorly understood. This study aimed to investigate the effects of snowpack phenology and environmental variables on the onset of vegetation phenology in the Alaskan Arctic. The results showed that Snow cover end date (SCED) had a stronger correlation with the Start of the growing season (SOS) compared to other factors, with consistent spatial and temporal patterns. Forested vegetation exhibited strong positive feedback between SCED and SOS, while grassland, shrub, and tundra communities showed insignificant positive feedback. Temperature and Fractional photosynthetically active radiation (FPAR) also significantly affected SOS. Snow density and snow depth played a larger role in SOS variation during the short pre-season period. These findings highlight the need for further investigation into the role of snowpack in specific vegetation types, particularly after observing widespread greening. Future studies should consider factors such as changes in snowmelt timing and photoperiod and traditional climatic factors like temperature and precipitation.

How to cite: Mu, Y. and che, T.: Unraveling the Influence of Snow Phenology on Vegetation across Alaskan Plant Communities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9574, https://doi.org/10.5194/egusphere-egu24-9574, 2024.

The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor onboard Joint Polar Satellite System (JPSS) satellites will replace the Moderate-Resolution Imaging Spectroradiometer (MODIS) to prolong data recording in the future. 
Therefore, it is a fundamental task to analyze the consistency and assess the accuracy of the snow cover products retrieved from the two sensors. 
In this study, snow cover products from MODIS/Terra, MODIS/Aqua, VIIRS/SNPP and VIIRS/JPSS-1, were evaluated in terms of Normalized Difference Snow Index (NDSI) consistency and accuracy assessment using higher resolution images of Landsat and Sentinel-2 snow cover products. Paired comparisons were performed among the four products in five major snow distribution regions over the world: Northeast China (NE), Northwest China (NW), the Qinghai–Tibet Plateau (QT), Northern America (NA), and European Union (EU). The two categories of snow products are utilized: The L3 Daily Tiled products, referenced by their Earth Science Data Type (ESDT) names of VJ110A1, VNP10A1, MOD10A1, MYD10A1, and L3 Daily Cloud-Gap-Filled (CGF) products, VJ110A1F, VNP10A1F, MOD10A1F, MYD10A1F. The important conclusions demonstrated as follows.
(1) During the snow season, the four types of 10A1 snow products demonstrated good consistency, with higher R values and smaller BIAS under clear sky. VIIRS exhibited a higher snow cover percentage than MODIS. By combining the four 10A1snow products, it is effective and feasible to produce cloud-free snow products.
(2) The consistency of the four 10A1F snow products was lower than that of the 10A1 products under clear skies. SNPP showed good consistency with JPSS-1, and the same to TERRA with AQUA.
(3) In the 10A1F products based on the previous day's clear-sky cloud-filling algorithm, VJ1 and VNP products exhibited larger fluctuations compared to MOD and MYD products. Among the 10A1F products, the smaller fluctuations and higher snow cover percentage of MODIS, along with a cloud persistence duration higher than VIIRS, led to an overestimation in MODIS's 10A1F snow products.
(4) The snow-cloud confusion is existing both in products with the same sensor and with different sensors for the 10A1products, and the latter is much larger than the former, the percentage of which is approximately 10% in the five regions.
(5) High-resolution snow product validation indicates that VIIRS has higher accuracy in both snow products than MODIS. 
(6) The newest JPSS-1 snow cover products display good agreement with that of SNPP. The pixels with the flag of ‘no decision’ in VNP10A1, MOD10A1, MYD10A1 are labelled as land, waterbody, and mostly clouds in VJ110A1 product, respectively.               
Above all, in spite of existing sensor differences affecting consistency of snow cover products, the paired comparisons indicated that under clear skies, the four snow products exhibit good consistency, with higher consistency observed in snow products from the same sensor. The evaluations by higher resolution snow products assured the high accuracy. It is effective and feasible to produce cloud-free snow products considering the overestimation of 10A1F products.

How to cite: Liu, A. W. and Che, T.: Consistency and Accuracy Assessment of Snow Cover Products from Terra, Aqua, SNPP and JPSS-1 Satellites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9925, https://doi.org/10.5194/egusphere-egu24-9925, 2024.

Surface snow cover is an important and highly interactive component of global and regional climate systems and has already clearly responded to past warming trends in many regions of the world. Moreover, it is a key ingredient for tourism industry, water supply, irrigation, and hydro-power generation in many mountainous and high-latitude regions. Accurate information about the past, present and future evolution of snow cover is therefore of high importance.

In this context, we here present and evaluate a newly developed gridded SWE climatology for Switzerland, available at daily resolution since 1961 and at a 1 km grid spacing. The climatology is based on a variant of the snow cover model of the Operational Snow Hydrological Service (OSHD) of Switzerland, driven by gridded atmospheric input and bias-adjusted towards in-situ snow depth measurements. In accordance with previous works, the analysis shows that the Swiss snow cover has changed strongly over the last decades. The comparison of two climatological long-term periods, 1962-1990 and 1991-2020, in terms of mean September-May SWE and the number of snow days (SWE > 10 mm) within the snow season, reveals a decrease in both indicators over the majority of the country. Low elevations < 1000 m show relative decreases larger than 50% of the mean SWE and larger than 30% regarding the mean number of snow days (about -22 days). The largest absolute difference of mean SWE is found at medium elevations between 1500 and 2000 m with a decrease of about 45 mm (about -26%).

The validation of the new snow climatology indicates a high general agreement with in-situ observations and independent remote sensing products. Larger uncertainties and limitations are found at the highest elevations (> 3000 m). They originate from different sources, such as temporal inconsistencies in the gridded input data of the underlying OSHD snow model or the lack of stations at high elevations that are needed for the bias adjustment of the model. Nevertheless, the new snow climatology is able to provide adequate information on past snow cover for Switzerland as a whole and will, among others, serve as a reference for the development of future snow cover scenarios.

How to cite: Kotlarski, S., Danioth, S., Gubler, S., Muelchi, R., Michel, A., Jonas, T., Steger, C. R., and Marty, C.: Swiss snow cover in a changing climate: Evaluation of a long-term, high-resolution SWE climatology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11117, https://doi.org/10.5194/egusphere-egu24-11117, 2024.

Satellite datasets are especially useful to monitor the cryosphere in vast and remote environments, such as the Arctic, where seasonal snowpack controls permafrost distribution, surface runoff, plant growth and animal survival rate. The recent availability of free, high-precision and high-resolution elevation datasets show promises to map snow depth on a large scale, a key bulk variable of the snowpack. Here, we mapped the snow depth distribution across Iceland (65°N) using elevation data from ICESat-2, a photon-counting laser altimetry satellite, and the ArcticDEM, a large set of digital elevation models from satellite stereoimages. The snow depth was retrieved through comparison of acquisitions with snow-on conditions (ICESat-2, ArcticDEM) and snow-free (summer ArcticDEM). Despite the heterogeneous spatial coverage of the two datasets, negative impacts of clouds, polar night and a shallow snowpack often close to the limit of detection, we successfully retrieved snow depth from 2018 to 2023, at monthly resolution. By leveraging large publicly available datasets, this approach is promising to further monitor the snowpack in other regions of the Arctic.

How to cite: Deschamps-Berger, C., Belart, J., Gunnarsson, A., Revuelto, J., Aðalgeirsdóttir, G., and Lopez-Moreno, J. I.: Mapping snow depth in the Arctic with public satellite elevation datasets, a case study in Iceland with ICESat-2 and the ArcticDEM, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11228, https://doi.org/10.5194/egusphere-egu24-11228, 2024.

Snow in mountainous areas changes fast in space and time, resulting in strong spatial and temporal heterogeneity, which highly impacts the radiation balance and hydrological cycle. However, gaps still exist between observations and modeling due to serval issues. One issue is the absence of wind drifting and blowing snow (WDBS) processes in most mesoscale atmospheric models. A newly developed WDBS-coupled atmospheric model, CRYOWRF, was used to evaluate the snow distribution in the Tarim area and Namco area, to assess the impact of WDBS and its sublimation on the snow distribution. Field observations were also carried out to validate the modeling, which showed good agreement.  A highly temporal heterogeneity pattern is shown in High Mountain Asia due to the strong blowing snow sublimation. Our works prove that CRYOWRF has a good performance in High Mountain Asia.

How to cite: Li, G., Yu, H., and Huang, N.: Snow Distribution  Evaluation in High Mountain Asia: Observations and Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11303, https://doi.org/10.5194/egusphere-egu24-11303, 2024.

There are two main limitations to understanding large-scale impacts of environmental change on snow resources, 1) observational snow data at the point scale is highly limited, and 2) extrapolation using models can be challenging due to data availability and performance. This study seeks to address these limitations using widely available climate network data combined with a temperature-index snow model to derive large-scale estimates of mean snow water equivalent conditions across the Northern Hemisphere. Temperature-index modelling is a common approach for simulating snow accumulation and melt in hydrological models. Many studies use this method because of its simplicity, efficiency, and generally good performance if properly calibrated. The approach relies on three assumptions and parameters, namely the snowfall and snowmelt temperature thresholds and the degree-day factor. At scales beyond single gauged catchments, the estimation of these parameters was difficult to date due to a lack of observations on snowmelt. Using the new Northern Hemisphere snow water equivalent dataset (NH-SWE) and co-located climate network observations of temperature and precipitation, this work provides the first large-scale evaluation of temperature-index melt model assumptions and parameters across a diverse range of snow climates. Our study reveals the 0°C as snowfall air temperature threshold captures most snowfall events, especially in cold climates, but risks missing 13% of snowfall events, especially in climates hovering at near-freezing temperatures. Similarly, a snowmelt air temperature threshold of 0°C performs well for most daily snowmelt observations but may incorrectly identify the onset of the melt season too early. Estimated degree-day factors converge towards 3-5 mm/°C/day for deeper snowpack climates (> 300 mm), but their estimation may be more challenging for colder climates with shallower snowpacks (< 300 mm), conditions where the degree-day factors have much higher interannual variability. For estimating mean values of seasonal snow onset and snowmelt season onset and mean snow accumulation at a given location, the temperature-index melt model performs consistently well on average despite its simplicity, but challenges may arise due to warm biases in temperature records or solid precipitation undercatch, mainly over higher elevation areas. This study provides valuable insights into temperature-index melt modelling for large-scale applications, and the results should help refine modelling approaches to enhance our understanding of snowpack responses to global warming.

How to cite: Fontrodona-Bach, A., Larsen, J., Schaefli, B., and Woods, R.: Can we estimate snow accumulation and melt across climates using simple temperature-index modelling?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11617, https://doi.org/10.5194/egusphere-egu24-11617, 2024.

In semiarid Andean regions, rock glaciers are more prevalent than debris-free glaciers and their relatively extensive areal coverage suggest the existence of significant frozen water reserves. Although there are some doubts whether permafrost landforms constitute a readily available water resource due to the effective thermal insulation provided by the active layer, there is some suggestion that permafrost can act as a primary factor controlling water flow and delivery to the catchment. The hydrogeomorphological connections and water system processes linking different hydrological units impacts the fate of the generated water, making it paramount to understand how water is transmitted from the headwater hydrological system to the wider catchment to better predict future impact of climate change in this important environment. However, unravelling their role is reasonably complicated since in semiarid regions glacial complexes (i.e. combination of glaciers and rock glaciers) are common and contain not only complicated structures but also complex hydrological connections.

In this study, the scientific understanding of the hydrological role of ice-debris glacial landforms is analysed to better understand how the transfer of water by glacier complexes relates to their internal structure. The research analyses the lower section of the Tapado glacier complex, in the Chilean semiarid Andes (30°S), which comprised the lower section of the debris-covered Tapado Glacier, that is in morphologic continuity to a rock glacier and a moraine at lower elevations. Geophysical measurements and elevation changes using uncrewed aerial vehicles (UAVs) were employed to inspect the internal structure of the selected ice-debris units in order to evaluate how it controls hydrological routing and storage, and in the delivery of cryospheric waters to the wider catchment.

Overall, internal structural arrangement and composition affect water routing and storage on the explored ice-debris landforms. Impermeable zones, characterised by massive glacial ice, ground ice or interstitial ice, not only represent a water storage capacity but are also a barrier to water flow. Therefore, at their interface with air-filled debris they also play a role in downstream water transmission, since sectors such as the debris layer (debris-covered glacier), active layer (rock glacier), intra-permafrost sectors (rock glacier), and main interstitial ice-free body of the moraine play important roles in the downglacier flow transfer. In addition, the potential subpermafrost hydrological connection between the rock glacier and the moraine area was recognised to occur as baseflow. Importantly, a potentially relevant hydrological role of the rock glacier is described based on its observed heterogenous internal structure associated with enhanced vertical infiltration compared to the debris-covered glacier. Lastly, in general, the moraine acts as a transmissive medium between generated glacial and snow meltwater and the proglacial area and river, buffering incoming flows due to the existence of interstitial ice within moraine structure, which also potentially enables deep groundwater circulation.

How to cite: Navarro, G., MacDonell, S., Valois, R., de Pasquale, G., and Robson, B.: Impact of Internal Structure on Water Routing in a Semiarid Andean Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12946, https://doi.org/10.5194/egusphere-egu24-12946, 2024.

In the dry Chilean North, the impact of the mountain snowpack on freshwater availability in the adjacent lowlands areas is crucial. The correlation between the snow water equivalent record and regionally averaged river discharges suggests that ~85% of the streamflow variance could be explained by the snowpack record alone. As seasonal snow cover depends on few winter events, there is a large year-to-year variability in the snow water equivalent (SWE). Typically, there are some dry years with very low annual precipitation which are compensated by wet years. However, since around 2010, the almost continuous extraordinarily dry conditions (so-called Central Chile “mega drought”) and increased water consumption in the region have led to significant stress on the water system. Hence, for an efficient water allocation and water management, it is crucial to know the actual SWE stored in the mountain snowpack. Until now, decisions have been based on scarce point measurements of the SWE or snow area estimates from MODIS. A drawback of these estimates is the large uncertainty that hampers efficient water allocation with important implications for water security of different sectors such as hydropower, agriculture and domestic use. 

To address this problem, we have developed a new operational SWE Estimation Tool for water resources decision making in the Coquimbo region (SWEET-Coquimbo), able to estimate current SWE in near real-time with a latency of ~10 days. SWE is estimated using a data assimilation framework that combines bias-corrected meteorological forcing ensembles from reanalysis data (ERA5, 5-day latency), hydrological modeling (Snowmodel) and satellite observations (Landsat) of the snow-covered area. SWEET-Coquimbo is placed in an open-access web platform, visualizing the current state of the SWE of five main catchments. The data can be downloaded and used for research and diagnostic purposes. 

The newly generated data show SWE for the period 2000-2023. We can now better understand the response of the regional snow cover to the Central Chile megadrought on snow cover and general trends in SWE over the last two decades. SWEET-Coquimbo has allowed, for the first time, a catchment-based estimation of the water available from the snowpack, which can now be used to improve seasonal runoff forecasts. Furthermore, our method has a great potential to be validated and applied to other mountainous regions with sparse in-situ data, as it does not rely directly on in-situ data.

How to cite: Schauwecker, S., Ayala, Á., Cortés, G., Yáñez, E., MacDonell, S., Goubanova, K., and Orrego, C.: SWEET (Snow Water Equivalent Estimation Tool): A new tool to generate updated SWE estimates for poorly monitored regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13564, https://doi.org/10.5194/egusphere-egu24-13564, 2024.

Winter snow accumulation is important for summer water supply in Central Asia, and contributes more than 50 % to the annual runoff. The region’s water availability is highly dominated by snow reserves in the mountain, which will be affected by climate change. Volumetric snow data play a vital role for hydrologic forecast in mountainous river basins, where snow is considered as a dominating hydrological component. This study quantifies decadal snow depth changes in the Western Tian-Shan in the Chirchik River Basin in Uzbekistan. The snow depth measurements from Uzhydromet have been used in this research. The historical changes in snow depth has been statistically analyzed for the 1963-2020 hydrological years. Correspondingly, the impact of climatic factors (temperature and precipitation) on snow dynamics were assessed as well. The results of hydrometeorological parameters such as snow depth, air temperature at 2 meters and precipitation were plotted as the trend line on monthly, seasonal, and annual scales. To verify statistical significance of the trend dynamics, the slope method and the Mann-Kendall trend test were applied. Our results show that snow cover (duration) days were significantly decreased by 4 days per decade or 21 days for 57 years from 1963 to 2020. Particularly, the initial occurrence of a permanent snow onset day was significantly delayed by 3 days per decade or 16 days for 57 years. Likewise, annual peak snow depth day was significantly shifted earlier by 4 days per decade or 20 days for 57 years. Interestingly, the maximum snow depth did not change statistically significant, but we observe a decline of 3.33 cm per decade or 19 cm for 57 years. Overall, we conclude that the duration of snow cover (snow reserve) has significantly decreased in the Chirchik basin due to climate warming in the last 57 years.     

How to cite: Mamaraimov, A., Gafurov, A., Güntner, A., and Bookhagen, B.: Decadal changes of the snow in the western Tian- shan derived from in-situ snow depth measurements , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16383, https://doi.org/10.5194/egusphere-egu24-16383, 2024.

The current and future evolution of snow cover in the Vosges massif (N-E of France) was simulated at a resolution of 4 km with the regional climate model MAR (version 3.14) forced by the ERA5 reanalysis. Thanks to the adjustment of only few parameters, MAR (initially developed for the polar regions) was optimized and validated with respect to daily observations of temperature, precipitation and height of the snowpack. Over the 62 winters (DJF) 1960-2021, MAR suggests a statistically significant decrease of about a factor of two in the average snow depth due to the significant increase in temperatures (~+2°C/62 years). Although precipitation has slightly increased (+10-20%/62 years) due to a non-significant strengthening of the westerly circulation, it falls more and more in the form of rain, especially below 1000 m. Above 1000 m, it does not snow less than before but there is more melting reducing the snowpack between two snow events. By extrapolating current trends, an anomaly of +2.5°C (resp. +3.8°C) compared to the winters of 1960-90 would be sufficient to no longer have snowpack on average below 750m (resp. 1000m). This trend is fully confirmed by MAR forced by 5 global models (EC-EARTH3, IPSL-CM6A-LR, MIROC6, MPI-ESM1-HR, NorESM2) from the CMIP6 database using both SSP245 and SSP585 scenarios over 1980-2100. In 2050, the average winter snow cover at 1000m will be reduced by half and will become almost non-existent in 2100 following SSP585. While with SSP245, MAR suggests skiing conditions still possible until 2100 above 1000m.

How to cite: Fettweis, X., Ambroise, B., David, P.-M., Ghilain, N., and Paul, P.: Present and future evolution of the winter snow cover in the French Vosges massif with the help of the regional climate MAR model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17058, https://doi.org/10.5194/egusphere-egu24-17058, 2024.

It is well understood that snow is a complex, porous material, whose microstructural changes directly affect its physical properties. Therefore, – to gauge the snow's role within the climate system – it is of interest to accurately measure and characterize the spatio-temporal variability of snow surfaces and snowpacks.

On a local scale, for example inside a snowpit during a field campaign, snow measurements are often taken in a manual, point-like fashion resulting in single, one-dimensional profiles with a sampling resolution of a few centimeters. At this resolution thin layers are difficult to observe and spatial inhomogeneities of the snowpack are missed. State-of-the-art X-ray microtomography (μ‑CT) scans of snow provide excellent spatial resolution,¹ however, the added experimental constraints prevent sampling extended spatio-temporal domains.

To address some of these limitations, we propose to use near-infrared (NIR) photography² with 940 nm illumination to determine the snow's specific surface area (SSA) and density. Our device – called SnowImager – achieves millimeter resolution and covers a spatial extent of a few square meters, such as the surface area of a snowpit wall. While the SSA is determined directly from the measured NIR image using the well-established asymptotic radiation transfer theory,^3–6 the density dependence is introduced by physically truncating the illuminating and back-scattered light. It results non-trivially from the lateral component of the sub-surface scattering process and enables us to recover density profiles that compare well to reference data from density cutter and μ‑CT measurements. As a demonstration, we present the spatial variability of an Antarctic snowpack at an unprecedented level of detail, revealing an extremely high spatial variability of the snow microstructure.

Using near-infrared photography enables accurate and fast determination of snow material properties, whenever millimeter spatial resolution and a spatial extent of several square meters are required. It is thus ideally suited to simultaneously capture thin layers within the snowpack and spatial inhomogeneities over a centimeter to meter scale, which is relevant as ground truth measurement for climate research, remote sensing and avalanche forecasting among others.

1. Kerbrat, M. et al., Atmos. Chem. Phys. 8, 1261–1275 (2008).

2. Matzl, M. & Schneebeli, M., J. Glaciol. 52, 558–564 (2006).

3. Bohren, C. F. & Barkstrom, B. R., J. Geophys. Res. 79, 4527–4535 (1974).

4. Warren, S. G., Rev. Geophys. 20, 67–89 (1982).

5. Kokhanovsky, A. A. & Zege, E. P., Appl. Opt. 43, 1589–1602 (2004).

6. Libois, Q. et al., The Cryosphere 7, 1803–1818 (2013).

How to cite: Mewes, L., Walter, B., Buchli, J., Büchel, V., Suter, M., Schneebeli, M., and Löwe, H.: Determining snow material properties from near-infrared photography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17505, https://doi.org/10.5194/egusphere-egu24-17505, 2024.

Seasonal alpine snow is subject to fluctuating meteorological conditions with diurnal temperature cycles around the freezing point and a mix of snow and rain. Throughout the season, fresh snow accumulations repeatedly contribute to the snowpack whereas older layers beneath contain snow at various stages of the metamorphosis often including melting and refreezing periods. The increasing complexity of the snowpack throughout the snow season affects the interaction of radar signals with the snowpack and underlying ground.

Numerous radar/SAR missions, operating at different frequencies, aim to retrieve snow parameters such as snow mass, snow water equivalent, and snow cover extent. These include missions like CRISTAL, TSMM, ROSE-L, and NISAR, each utilizing specific frequency bands to study the temporal variations in snow properties. Understanding the vertical structure of seasonal snow and its interaction with radar signals at various microwave frequencies from L- to Ka-band is therefore essential.

In our study, we investigated tower-mounted rail-based tomographic SAR measurements obtained within the ESA SnowLab project in Davos Laret, Switzerland. The SAR tomography technique provides non-destructive measurements of the vertical structure of the snowpack by means of vertical profiles of radar backscatter, co-polar phase differences, and interferometric phase differences. The measurements were taken with the ESA SnowScat and the ESA Wide-Band Scatterometer, covering a wide range of frequency bands. Additional data on snow characteristics and meteorology complemented the radar measurements. We present time series of SAR tomographic profiles over entire snow seasons at different frequency bands (1-6 GHz, 12-18 GHz, and 28-40 GHz) with reference snow characterizations obtained from snow pits and SnowMicroPen measurements. Detailed analyses include depth-resolved co-polar phase differences, anisotropy, and differential interferometric phase, revealing insights into changes in snow properties over time.

The high-resolution SAR tomographic profiles offer valuable information on microwave interactions with seasonal alpine snow. Analysis of vertical radar backscatter profiles indicates relative changes in location and intensity within the snowpack, correlating with factors like melting and refreezing cycles, snow accumulation, and liquid water content.

We find that distinctive features of seasonal snow, such as melt-freeze crusts, varying penetration depths, and anisotropy can be tracked over time using a SAR tomography approach. To exploit this information for snow mass and structure retrieval, further research tailored to specific spaceborne SAR mission objectives is required. The ESA SnowLab time series of SAR tomographic profiles is a rich dataset covering a broad spectrum of frequencies and providing an opportunity to advance the understanding of scattering mechanisms in alpine snow for various spaceborne SAR missions. The comprehensive coverage includes frequency bands relevant to existing and future mission concepts.

How to cite: Frey, O., Wiesmann, A., Werner, C., Caduff, R., Löwe, H., and Jaggi, M.: High-resolution snow parameter/structure retrieval from tower-based radar time series of seasonal snow obtained with the ESA SnowScat and the ESA Wideband Scatterometer in SAR tomographic profiling mode, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17561, https://doi.org/10.5194/egusphere-egu24-17561, 2024.

Mountain precipitation is a key feature of the hydrological cycle since it feeds snowpack, glaciers, river runoff and supports ecosystems and human life both locally and downstream. However, available precipitation datasets are affected by large uncertainties in mountain regions, especially during the cold season when most of the precipitation falls as snow: on one hand, commonly used precipitation gauges can have systematic losses up to 80-100% in case of snow precipitation, mainly owing to wind undercatch; on the other hand, reanalysis datasets generally provide much larger precipitation amounts when compared to observations and observation-based datasets. So, an accurate quantification of the snowfall component is crucially needed to reduce the uncertainty on mountain total precipitation in the cold season.    

In this work we present an extensive analysis of snowfall precipitation over the Greater Alpine Region (GAR) considering snowfall data from different data sources, including long-term in-situ observations, reanalysis and gridded datasets. We analyze: i) the most comprehensive observational dataset of monthly fresh snow depth (commonly employed as a measure of snowfall precipitation), consisting of more than 2000 in-situ station time series, covering 6 alpine countries (Switzerland, Austria, Germany, Slovenia, Italy and France); ii) the snowfall dataset provided by the ECMWF ERA5 global reanalysis at 0.25° spatial resolution, and iii) the HISTALP gridded snowfall dataset at 0.08° spatial resolution, which is based on temperature and precipitation observations. We compare the three datasets over the last decades to investigate i) climatological features of seasonal and monthly snowfall over the GAR; ii) snowfall variability and trends in relation to elevation; iii) snowfall trends in relation to temperature and total precipitation, based on the best available observational datasets; iv) uncertainties in the snowfall climatology and trends, by comparing the different data sources. This study provides a first comprehensive evaluation of the quality of ERA5 and HISTALP snowfall datasets against ground observations. Moreover, by quantifying the snowfall component, it contributes to better characterize mountain precipitation in the cold season.  

How to cite: Terzago, S., Gatti, L. M., Arnone, E., and Matiu, M. C.: Snowfall variability, trends and their altitudinal dependence in the European Alps from ERA5, HISTALP and in-situ observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17624, https://doi.org/10.5194/egusphere-egu24-17624, 2024.

The seasonal snow cover is of great interest in Austria due to its immense importance for numerous economic, ecological and social sectors. Meteorological conditions, expressed as the snowline altitude determine whether rain or snow falls on the ground. If the intensity of precipitation is sufficiently high and there is little atmospheric mixing, the melting of solid precipitation in valley areas can lead to a cooling of the atmosphere and to a further drop in the snowline altitude – the snowline depletion effect.  In the course of a changing climate, an increase in snowline altitude is predicted. However, these predictions do not consider the described effect of snowline depletion. From the theory, the increase of the snowline has nonlinear consequences for the frequency and intensity of the subsequent depletion effect. In this study, we investigate this effect for Austria during past precipitation events on the basis of station observations and gridded now-casting products, develop and test a simplified parametrization, and subsequently show its potential future evolution based on simulations.

How to cite: Günther, D., Koch, R., and Olefs, M.: Exploring potential nonlinear developments of snowline depletion in a changing climate in Austria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17847, https://doi.org/10.5194/egusphere-egu24-17847, 2024.

Snow information from mountain regions worldwide is of high relevance but its spatial and temporal distribution inhomogeneous. The currently running IACS Joint Body on the Status of Mountain Snow Cover, a joint initiative of IACS together with MRI and WMO GCW aims at improving the snow information, data availability and the access to the data for mountain regions worldwide. As part of the initiative, an inventory was initiated which should provide a first and overall picture on the spatial and temporal availability of snow information in the various mountain regions of the world. As there is no strict delineation of mountain from non-mountain regions, it has been up to the contributing experts to decide on what is part/not part of a mountain region. For larger mountain regions with rather different snow climates, the spatial resolution of the inventory was split into several parts. The inventory was launched in May 2023 and was implemented as on online tool.

The paper presents initial analyses of the inventory, looking at the spatial and temporal patterns of snow information at a global scale. The picture derived from the feedback of the inventory shows fairly clear global differences, with regions where individual researchers (e.g. Central Asia) are driving access to snow information, while other regions have well established access routines/portals provided by the institutions operating the snow networks (e.g. the US). A preliminary analysis based on metadata from the inventory, a digital elevation model and the GMBA mountain delineation identifies the distribution of in-situ station and their snow information worldwide and how this varies by region and elevation. Information on already estimated spatial and temporal trends of key snow cover variables from mountain regions, such as for snow depth HS and depth of snowfall HN (from unpublished and published papers), are compiled together, although the different trend periods do not make comparison easy. Overall, a rather inhomogeneous picture emerges with regions such as the Alps or the Scandinavian mountains on the one hand, in which the snow information is spatially and temporally dense (with many published studies), and on the other hand regions (such as Greenland or Patagonia) in which the snow information from observations is extremely sparse.

How to cite: Schöner, W., Matiu, M., and Wydra, C.: First results of an inventory of mountain snow information at global scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18184, https://doi.org/10.5194/egusphere-egu24-18184, 2024.

The Peruvian Andes contains the largest mass of glaciers in the tropics and these glaciers have shown considerable decay over the past 4 decades and into the present day. The historic and future runoff is tied to the cryospheric changes in the region and this could have important consequences for water resources, given the importance of snow and ice melt for dry season runoff. To disentangle the role of the cryosphere in the water cycle in the tropical Andes we run the fully distributed, hourly glacier-hydrological model TOPKAPI-ETH, both in the past (from 1987) and into the future over the upper Rio Santa catchment in the Cordillera Blanca. Meteorological forcing is provided by bias-corrected WRF simulations, which are also used for statistical downscaling of CMIP5 model projections to provide the future climatology. Calibration of model parameters is conducted using a step-wise approach using a wealth of ground-based data and model outputs are evaluated against gauged runoff data and remote sensing estimates of snow cover, glacier cover and glacier mass balance. 

We find that under present conditions (2008-2018) snowmelt is an important contributor to runoff, comprising 16% to 47% of inputs (the range in weekly average as a proportion of all snow melt (on and off-glacier), ice melt and rain contributions) into the catchment with its proportional contribution largest at the beginning of the dry season (early June). Off-glacier snowmelt is important in the wet season, but snow is confined to on-glacier areas by the mid-dry season. Snow cover <5000 m is ephemeral, lasting hours to days, with correspondingly thin average snow depths and rapid fluctuations in the wet season snowline. Meanwhile, ice melt is an important contributor to runoff in the dry season (up to 54% of the inputs in early August) in all glacierised catchments, even those with a small glacier cover, but the wet season contribution is small. We also explore the long term evolution of glaciers and snow cover in the catchment and its implications for catchment runoff. Through the long term modelling we investigate the timing of peak water in the catchment and the key drivers of runoff change in the past. Our future projections will allow us to examine the impact of future climate changes on the glaciers and snow dynamics. A key vulnerability is the impact of temperature increases on the ephemeral snowpack and the consequences for glacier mass balance. We will also investigate the potential implications for catchment runoff and dry season water availability.

How to cite: Fyffe, C., Potter, E., Miles, E., Shaw, T., McCarthy, M., Orr, A., Loarte, E., Medina, K., Fatichi, S., and Pellicciotti, F.: On the importance of the cryosphere in a tropical Andean basin: the past, present and future of the glaciers and runoff in the Rio Santa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18472, https://doi.org/10.5194/egusphere-egu24-18472, 2024.

Snow is an important hydrological component in Central Asia. The snowmelt contributes to about 50 % of total water formation in the region, depending on geographic conditions. Many hydro-meteorological phenomena such as floods or drought conditions can be triggered by snowmelt amounts in Central Asia. The amount of snow accumulation in the mountains of Tian-Shan and Pamir also defines the availability of water for summer months to be used for agricultural production or re-filling of reservoirs for energy production in the winter period. Thus, it is of high importance to better understand the seasonal variation of snow and if the over the global average climate warming in the region is affecting the processes related to snow accumulation and melt.

In this study, we analyze 22 years of daily Moderate Resolution Imaging Radiometer (MODIS) snow cover data that was processed using the MODSNOW-Tool, including cloud elimination. Additionally, observed snow depth data from meteorological stations were used to estimate trends related to snow cover change. We used several parameters such as snow cover duration, snow depth, snow cover extent, and snowline elevation to analyze changes.  We conducted this analysis in 18 river basins across the Central Asian domain with each river basin having different geographic conditions and the results show varying tendencies. In many river basins, a clear decrease of snow cover was found to be significant, whereas in some river basins also increase in the snow cover extent in particular months could be identified. We attributed the changes related to snow cover to available historical temperature and precipitation records from meteorological stations to better understand the driving forces. The results of this study indicate seasonal snow cover variations but also potential water shortages in particular months as well as water abundance in months where water demand is not high in Central Asia.

How to cite: Gafurov, A., Mamaraimov, A., Friedrich, B., and Gafurov, A.: Seasonal snow cover variations in Central Asia based on remote sensing data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19588, https://doi.org/10.5194/egusphere-egu24-19588, 2024.

Synthetic aperture radar will be at the forefront of future advancements in global

remote sensing of snow depth and snow water equivalent. Recently, snow depth

retrievals using an empirical volume scattering approach with C-band Sentinel-1 (S1)

data have been demonstrated over the European Alps and Northern Hemisphere, with

the most accurate results obtained in regions with dry, deep (>1.5 m) snowpacks and

little vegetation influence. However, these S1-based snow depth retrievals have

previously been compared only to point-based measurements or modeled snow depth

products. In this study we develop an open-source version of the S1 snow depth

retrieval technique and compare the results to spatially-distributed lidar snow depth

measurements. The highly accurate and fine resolution lidar datasets were collected

during the NASA Snow SnowEx 2020 and 2021 field campaigns at six study sites

across the western United States. These regions represent different snow environments

and characteristics than the datasets used for comparison in previous investigations.

We compare the S1 and lidar snow depths at a range of spatial resolutions and interpret

the results within the context of snowpack, vegetation, and terrain characteristics. At 90

m resolution, comparisons between lidar and S1 snow depth retrievals show low to

moderate correlations (R = 0.38) and high RMSE (0.98 m) averaged across the study

sites, with improved performance at 500 m resolution (R = 0.59, RMSE = 0.69 m). The

distribution of S1 and lidar snow depths are more similar in regions of deeper snow,

lower forest coverage, higher incidence angles, dry snow, and at coarser spatial

resolutions. Our results highlight limitations of the current S1 snow depth algorithm and

present opportunities to improve the technique for future snow depth retrievals across

varied snow environments.

How to cite: Hoppinen, Z., Palomaki, R., Tarricone, J., Brencher, G., Dunmire, D., Gagliano, E., Marziliano, A., Adebisi, N., Bonnell, R., and Marshall, H.-P.: Evaluating Sentinel-1 volume scattering based snow depth retrievals over NASA SnowEx sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21766, https://doi.org/10.5194/egusphere-egu24-21766, 2024.

With the dawn of future L-Band satellite interferometric missions (e.g., NISAR - NASA/ISRO SAR and ESA ROSE-L) upon us, there are unique opportunities to explore the use of radar methods and techniques across a variety of applications. Moreover, through the advancement of radar remote sensing hardare and software, additional opportunities exist to specifically target and explore the development of snow estimation, snowmelt impact, and resulting soil moisture detection applications. With the development of mobile interferometric synthetic aperture (InSAR) hardware and software solutions, we present findings from field campaigns using a multi-polarization L-band (1.6 GHz) InSAR system (Gamma Remote Sensing) deployed from mobile vehicle (car), unmanned aerial vehicle (UAV), and helicopter-based platforms. These platforms allow us to control the temporal repeat of InSAR acquisitions assessing the role of changing environmental conditions on InSAR coherence, bracketing synoptic weather events to identify change in the radar signal, as well as simulating the temporal repeat of future satellite missions to estimate what may be done with these data when available. Results from time-series of InSAR acquisitions exploring snow water equivalent estimation, soil moisture, and airborne deployments (e.g., helicopter and UAV) show sensitivity to L-Band coherence and phase for application development. Future work will also be discussed exploring interferometric tomography and bistatic radar applications.

How to cite: Deeb, E., Meehan, T., Hoppinen, Z., Werner, C., Frey, O., Forster, R., and LeWinter, A.: Use of mobile L-Band interferometric synthetic aperture radar observations to inform snow property estimation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22452, https://doi.org/10.5194/egusphere-egu24-22452, 2024.

While airborne Light Detection and Ranging (LiDAR) surveys are routinely used to measure snow volume in many types of mountain watersheds, those that are heavily forested and lie within maritime environments have been largely ignored to date. Here, we summarise our findings from a four-year study (2020-2023) of eight watersheds within the coastal rainforests of southwest British Columbia, which collectively represent an area of >330 km². Aerial LiDAR surveys were conducted 3 to 5 times per year between March and June in order to measure snow depth across each watershed. Spatiotemporally-distributed snow density was estimated using a random forest model incorporating weather station data, LiDAR-derived metrics and in-situ snow density observations. At peak snow volume, we find typical mean catchment-wide snow water equivalent values of ~600-1200 mm, verified by a widespread field campaign consisting of > 25,000 in-situ measurements of snow depth and density. We show that, typically, ~60-90 % of the snow water volume is stored at mid-elevations of between 800 and 1500 m, where air temperatures are close to melting point and forest cover is prevalent, leaving the snowpack vulnerable to early seasonal melt onset and impacts due to forest management. We find that while peak measured snow volume typically represents ~20-40 % of surface runoff, providing an important buffer towards droughts within the region, snowmelt volumes can be insufficient to safeguard downstream water supply during extreme seasonal drought events. Overall, the results of this work provide valuable insights into the vulnerability of the snowpack in coastal maritime regions and the potential knock-on effects of a changing snowpack on regional water security.

How to cite: Bisset, R., Floyd, B., Menounos, B., Bishop, A., Marchenko, S., Marshall, P., and Geospatial, H.: Quantifying snow water storage from aerial LiDAR surveys in eight Pacific coastal watersheds, British Columbia, Canada, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22543, https://doi.org/10.5194/egusphere-egu24-22543, 2024.

Natural gas hydrates represent a significant and widely distributed potential energy source globally. Furthermore, hydrates are also considered a possible carbon capture and storage method in the permafrost and deep ocean sea areas. Hydrate morphology is critical in determining the sediments' flow properties and production/storage efficiency. However, the dynamic morphology remains unclear, especially in the microscale. This study was performed by MH21-S and funded by the Ministry of Economy, Trade and Industry, and we used our self-invented micromodels (micron level) for hydrate formation in an air bath of 1 °C for several months. Meanwhile, the state-of-the-art high-resolution microscope was used to detect the dynamic morphology of hydrate formation and dissociation. The result showed that the hydrate growth mechanism could be divided into four stages due to different driving forces: hydrate fingering formation, Ostwald ripening phenomenon, hydrate contraction, and heterogeneous hydrate dissociation processes. In the first stage, the hydrate fingering formation process consistently occurs from the inlet to the outlet area, and the fingering process stops after several days. In the second stage, the Ostwald ripening phenomenon was detected in the microscale for the first time. Smaller hydrate particles first dissolved and then redeposited onto larger hydrate particles, which is a spontaneous process. In the third stage, the surface area of hydrates tends to reduce to reach a more stable phase, resulting in the hydrate contraction. Finally, manual temperature increases induce heterogeneous hydrate dissociation. Our study aims to enhance the understanding of hydrate behaviors in sediments over an extended period.

How to cite: Xu, Z. and Konno, Y.: Dynamic morphology of clathrate hydrates in porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9891, https://doi.org/10.5194/egusphere-egu24-9891, 2024.

Over the last decade, our research team at Ohio State University has analyzed geophysical well logs in over 1000 petroleum industry wells for natural gas hydrate. This is the largest well log assessment for gas hydrate and includes a number of basins: the northern Gulf of Mexico, offshore Western Australia, the Norwegian Sea, the Barents Sea and the UK Atlantic Margin.

We find evidence for gas hydrate in nearly half of industry wells, indicating that hydrate is widespread in sediments on Earth’s continental margins. Hydrate typically occurs in discrete, cm to m-scale intervals with depth and is at relatively low concentration (~35% saturation or less in a hydrate bearing layer). In addition, we observe that most of these hydrate bearing layers are not near the base of hydrate stability.  

At most locations in our assessment, hydrate is not susceptible to current anthropogenic warming. However, our assessment lacks information about a crucial location on continental margins because this interval is not typical measured by industry well logs: the updip edge of hydrate stability. The updip edge of hydrate stability (~300-500 m water depth) is a critical, largely uncharacterized zone where ocean warming can affect hydrate stability. Scientific ocean drilling is required to characterize the global gas hydrate occurrence and modern seafloor carbon flux along this sensitive boundary.

How to cite: Cook, A., Naim, F., Majumdar, U., Portnov, A., Jones, B., and Heber, R.: Widespread gas hydrate on Earth’s continental margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10226, https://doi.org/10.5194/egusphere-egu24-10226, 2024.

On many marine continental slopes, gas hydrate has been observed filling fractures in marine muds.  Fracture filling hydrate likely forms because the pore size of clays is small, and therefore, hydrate can only form in secondary porosity; some scientists have suggested the process of hydrate formation causes these fractures to form. On borehole image logs, these fractures were found to have high angles and form in 3D planes. While the plane is filled with hydrate, the overall bulk concentration of hydrate can be quite low. In X-ray computed tomography (XCT) images, similar high angle planar fractures have been found that cut through whole round core. Typically, these fractures appear to have diffuse, wispy edges in comparison to other fractures that form due to core expansion or core collection. 

We have found new, smaller 3D planer fractures that are likely the initial stages of hydrate fracture formation. These hydrate-filled fractures range in lengths from around 10 – 400 mm with widths ranging from 0.5 - 15 mm. The fractures tend to be well oriented, having a high dip angles (>40°) and going through the whole core on a plane. The wispy, diffused edges suggest sediment displacement due to the hydrate formation process and are distinctly different than other fractures seen in the XCT data. The fractures must be unconnected to any other break in the sediment, existing solely as a fracture with a high dip angle, with diffused edges.

In New Zealand, IODP Site 1517, we found that these specific fractures appear near the sulfate-methane transition zone (SMTZ). We hypothesize that if more sediment cores and XCT data were collected through and close to the SMTZ, more similar small fractures would be imaged, potentially indicating nascent gas hydrate formation.

How to cite: Martin, S., Brunet, M., and Cook, A.: Small fractures in marine muds indicating nascent hydrate formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12146, https://doi.org/10.5194/egusphere-egu24-12146, 2024.

Natural gas hydrates form at elevated pressure and low temperatures in the presence of sufficient quantities of gas and water and have therefore been discovered on all continental margins and in permafrost regions. In the marine hydrate-bearing sediments, gas hydrates, depending on their content, can transform a loose sediment into a consolidated rock with a strongly increased strength. In permafrost regions the hydrate stability zone can extent deep into the ice-bearing permafrost and, therefore, both, ice and hydrate can consolidate the sediment. However, the strength of methane hydrate is much higher than that of ice, which behaves much more ductile. Consequently, the resulting strength of a sediment, containing both components, strongly depends on the ice to hydrate ratio. Conversely, the decomposition of natural gas hydrates in marine or permafrost sediments leads to a reduction in the mechanical strength of the host sediment. In addition, the release of gas can create overpressure in the pore spaces, reducing the effective stress and leading to instabilities in the sediment structure.

Since both continental margins and permafrost regions are used by humans for various activities that largely depend on the mechanical stability of the sediments, knowledge of the main factors and processes that determine the stability of weakly consolidated sediments is crucial. Both the thawing of ice and the decomposition of gas hydrates in permafrost soils lead to a change in the geo-mechanical properties of the host sediment. The residual and peak shear strengths of ice- and hydrate-bearing sediments were investigated using a ring shear cell developed at the GFZ. Based on literature data and our results, we discuss the dependence of the geo-mechanical properties of sediments on ice and hydrate saturation and the possible consequences if their proportion diminishes.

How to cite: Spangenberg, E., Cook, A., Schicks, J., and Heinig, F.: A diminishing stabilizer? Studies on the influence of ice and gas hydrates on the geo-mechanical properties of sediments., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12671, https://doi.org/10.5194/egusphere-egu24-12671, 2024.

Natural gas hydrates are known to exist in vast quantities beneath the permafrost and deep-sea sediment layers worldwide, transcending national borders, making them a promising future energy resource. While test productions have been conducted by a few countries such as Japan, China, and the United States, a commercially viable production method has yet to be established. The technologies developed so far have limitations, as laboratory-scale experiments and computational models often fail to accurately predict production behavior in actual field conditions. To achieve reliable predictions of production patterns, it is crucial to understand the changes in phase distribution within hydrate-bearing sediment layers and the corresponding multiphase fluid behavior. This study utilizes low-field Nuclear Magnetic Resonance (NMR) to quantitatively analyze phase distribution, saturation, and pore occupancy changes within rock samples during hydrate formation and dissociation processes. Particularly, experiments on hydrate formation and dissociation, along with NMR signal analysis, were conducted under conditions where water is abundant to investigate the role and influence of excessive water. In cases of high initial water saturation (presence of movable water), it was observed that the phase saturation distribution during hydrate formation becomes heterogeneous due to water migration in an unexpected manner. During the depressurization-driven dissociation process, a quantifiable increase in water saturation due to dissociated water was observed, revealing the occurrence of hydrate reformation even during the dissociation process. This research provides a methodology and analytical data to understand phenomena that are challenging to predict during hydrate formation and dissociation processes.

How to cite: Ahn, T., Lee, J., and Park, C.: Quantitative Analysis of phase saturation distribution during hydrate formation and dissociation under high water saturation condition using low-field NMR, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14348, https://doi.org/10.5194/egusphere-egu24-14348, 2024.

During the last 1 Ma in the Canadian Arctic, permafrost and permafrost-associated gas hydrates formed extensively due to mean annual subaerial temperatures of approximately -20°C. Following the last glaciation, a marine transgression occurred and former terrestrially exposed shelves became inundated, resulting in present submarine bottom water temperatures around -1°C. Relict submarine permafrost and gas hydrates in the Canadian Beaufort Sea are still responding to this thermal change resulting in their ongoing degradation. Thawing of permafrost and destabilisation of permafrost-associated gas hydrates can release previously trapped greenhouse gases and can lead to even further gas hydrate dissociation with important implications for the global climate. However, both the extent of the submarine permafrost and the permafrost-associated gas hydrates are still not well known. In this study, we use marine multichannel seismic data to model the base of permafrost from the depth of the base of the gas hydrate stability zone. From this depth, we estimate the theoretical gas hydrate dissociation temperature, which allows us to model the depth of the thermal base of permafrost (0°C isotherm). The base of permafrost we modelled correlates with the lower boundary of a diffuse zone of high diffractivity in seismic data suggesting the presence of ice-bearing permafrost. These results combined show that the base of permafrost still extends close to the shelf edge indicating less permafrost retreat than previously suggested. Our study provides a different approach to accessing the current depth and extent of submarine permafrost on the outermost Canadian Beaufort Shelf.

How to cite: Grob, H., Riedel, M., Krastel, S., Preine, J., Duchesne, M. J., Jin, Y. K., and Hong, J. K.: Modelling the base of submarine permafrost in the Canadian Beaufort Sea from seismic data and the depth of the gas hydrate stability zone , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15668, https://doi.org/10.5194/egusphere-egu24-15668, 2024.

Molecular and stable isotopic compositions of light (C₁–C₃) hydrocarbons in sediments provide information on their formation pathways and postgenetic alterations. In 2018, gas hydrate-bearing sediment cores and borehole logging data were collected with R/V SONNE (cruise SO266) and the seafloor drill rig MARUM-MeBo200 at two sites off SW Taiwan (Bohrmann et al., 2023). The two sites are located on the passive continental margin and on the tectonically active convergent margin in the northern part of the South China Sea (SCS). Geophysical surveys have demonstrated the presence of hydrates at both sites as well as the base of the hydrate stability zone at ∼400 and 450 meters below seafloor (mbsf), respectively (Berndt et al., 2019; Bohrmann et al., 2023). At the passive margin, holes were drilled to a depth of ∼126 mbsf at the southern summit of Formosa Ridge (SSFR, ∼1,140 m water depth). A depth of ~144 mbsf was reached at Four-Way Closure Ridge (FWCR, ~1,320 water depth) on the active margin. Macroscopically, no hydrates were detected in recovered cores from either site, but hydrate-related proxies unequivocally demonstrated the in-situ presence of hydrates. For example, signals in sediment electrical resistivity detected during well logging correlated with anomalies in sediment temperature and pore water chloride concentrations detected in cores. Whereas two hydrate-bearing intervals were identified on SSFR (∼13–39 mbsf, ∼98–120 mbsf), a single interval was found on FWCR (∼65–120 mbsf).
Considerable variations in relative hydrocarbon concentrations expressed as C₁/(C₂–C₃) values were observed in gas accumulated in voids in the cores from each site. C₁/(C₂–C₃) values <10.000 in the hydrate-bearing sections, which contrast with values ranging between 10.000 and 25.000 in sections lacking hydrates, indicate that ethane (C₂) and to a lesser extent propane (C₃) are enriched during hydrate precipitation. Molecular fractionation is also observed for CO₂, which is strongly depleted in the hydrate-bearing sections. The δ¹³C- (–79 to –69‰) and δ²H- (–197 to –187‰) values of methane (C₁) indicate that microbial carbonate reduction is the major source of light hydrocarbons (Milkov & Etiope, 2018) at both sites. Based on pore water sulfate and methane concentrations, the zone of the microbially-mediated sulfate-dependent anaerobic oxidation of methane was identified at a depth of ~10–12 mbsf at both sites. Preferential consumption of C₁ in this zone is indicated by low C₁/(C₂–C₃) values. The process also resulted in depletions of C₁ in ¹³C and ¹H (δ¹³C-C₁ as low as -100‰, δ²H-C₁ as high as -179‰ at 18 mbsf at FWCR) as reported from other regions (e.g., Nankai Trough off Japan; Riedinger et al., 2015).
Our results show that physical fractionation and bio(chemical) transformation of individual light hydrocarbons can significantly change the molecular and isotopic composition of upward migrating gases. Therefore, the composition of shallow gas does not necessarily reflect that of the gas in the deeper subsurface, for example as bound in capacious hydrate reservoirs. The cores from the SCS are excellent for studying how hydrate occurrences and microbial transformation lead to alteration of gas composition.

How to cite: Pape, T., Tu, T.-H., Lin, S., Berndt, C., Wallmann, K., Tseng, Y., Freudenthal, T., and Bohrmann, G.: Gas hydrate precipitation and microbial transformation affect the composition of gases migrating through sediments drilled off SW Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16042, https://doi.org/10.5194/egusphere-egu24-16042, 2024.

This work outlines the theretical and field activities conducted under the Bulgarian Science Fund Project GEOHydrate: Geothermal evolution of marine gas hydrate deposits - Danube paleodelta, Black Sea. The purpose of this research is to enhance our understanding and perspectives of the study the connection between marine gas hydrate deposits formation and the measured in situ heat flow in seafloor sediments.

The aim of the GEOHydrate project is to prove the hypothesis about the existence on the seafloor of measurable temperature and heat flow (T&HF) anomalies above gas hydrates deposits (GHDs) and the possibility to restore the 4D-process of GHDs growth from these anomalies.

GEOHydrate data include 2D and 3D seismic and CSEM; in situ heat flow; hydro- and geo-physicochemical measurements; scientific drilling and logging. They are results from the projects BLASON, ASSEMBLAGE, GHASS and specially developed tools and methods for GHDs research from the German projects SUGAR I-III. The applied methods include seismic data interpretation; basin analysis; forward and inverse geothermal problems. The new heat flow approach continues to develop in the EU project DOORS with new cruise data and interpretation. Expected practical results are contribution to direct methods for GHDs search, resource estimation with a high signal-to-noise ratio, and a reduction in the future production costs from proper planning and reducing the number of production wells.

Results contribute to mitigating the effects of 3 modern global threats - climate change, clean air, and the cost of energy. European GHDs production is the most prospect and important for Bulgaria and Romania.

Acknowledgments: This work was supported by:

• Bulgarian Science Fund project KP-06-OPR04/7 GEOHydrate “Geothermal evolution of marine gas hydrate deposits - Danube paleodelta, Black Sea” (2018-2023);
• European Union project 101000518 DOORS: Developing Optimal and Open Research Support for the Black Sea (2021-2025).

How to cite: Vasilev, A., Pehlivanova, R., and Genov, I.: Danube Fan gas hydrates: GEOHydrate project results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16228, https://doi.org/10.5194/egusphere-egu24-16228, 2024.

Ocean warming threatens methane hydrate stability in continental margins, potentially leading to methane release into marine sediments, the water column, and ultimately the atmosphere. Over the decadal to millennial timescales during which hydrate-sourced methane release is anticipated, microbially mediated anaerobic oxidation of methane (AOM) in marine sediments may mitigate benthic methane efflux. While traditionally considered a highly efficient biofilter, recent studies reveal significant variability in the AOM sink efficiency. For instance, in cold seep settings, efficiency ranges from 80% to 20% with slow to high fluid flow, respectively, and this decreases to around 10% in pristine seepage environments. This variability is directly related to the balance between multiphase methane transport and the growth dynamics of microbial communities.

In this study, we use a novel 1D multiphase reaction-transport model to investigate the transient evolution of the AOM sink efficiency and its impact on seafloor methane emissions in response to a centennial-scale methane release caused by climate-driven hydrate destabilization. We examine the combined influence of gaseous methane transport, including induced tensile fracturing by pore fluid overpressure, and methanotrophic biomass dynamics on weakening the efficiency of the AOM sink. Preliminary findings suggest that the AOM sink is notably limited to mitigating benthic methane emissions in gassy sediments. Additionally, the slow growth rate of methane-oxidizing microorganisms may lead to significant temporal windows for methane to escape into the ocean. This integrated analysis provides insights into the intricate dynamics governing the efficiency of the benthic AOM sink subjected to hydrate-sourced methane. It contributes to a more comprehensive assessment of potential methane emissions in continental margins in the context of global warming.

How to cite: De La Fuente Ruiz, M., Arndt, S., Marín-Moreno, H., Minshull, T. A., and Vaunat, J.: Exploring the efficiency of anaerobic oxidation of methane as a sink to hydrate-sourced methane, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16392, https://doi.org/10.5194/egusphere-egu24-16392, 2024.

Given the scale and urgency of the climate crisis, the exploration of innovative approaches for greenhouse-gas CO₂ capture and sequestration is imperative. This hinges on capturing of CO₂ emissions from sources, and storing it into other long-lived, stable carbon “pools” or “sinks”, such as in the form of gas hydrates. Being crystalline solids, gas hydrates have the ability to store gas effectively therein –with gas molecules “imprisoned” in cavities within an otherwise ice-like lattice. To address the limitations of hydrate-based methods for carbon capture, such as stability, scalability, and environmental impacts, gas-nanobubble technology may be integrated into hydrate formation to enhance the efficiency and viability of gas-hydrate formation. Nanobubbles (NBs) have been confirmed to accelerate gas-hydrate crystallisation through the so-called memory effect. However, the mechanism of interactions between NBs and hydrate crystals has not been fully addressed. It is also vital to investigate the optimal conditions for hydrate formation in the presence of NBs for higher stability and scalability.

In this study, a novel method, combining NBs and gas hydrates to enhance the capturing of CO₂, is reported. It aims to demonstrate the effects of NBs on hydrate-formation kinetics, and reveals the mechanism of their interactions during the hydrate-crystallisation process by an integration of laboratory experiments and molecular dynamics simulations. NBs were generated by external electric fields with CO₂ gas in deionized water. By controlling the processing time and applied voltage, different size and concentration of NBs were expected. DLS measurements were applied to characterise the generated NBs. The kinetic properties of CO₂ hydrate formed by NBs solution were analysed experimentally. Numerical dynamics simulations were also applied to simulate the hydrate-formation process in the presence of CO₂ NBs with different concentrations. These modelling efforts help in predicting the behavior of the system under different conditions. The simulation results revealed that throughout the growth process, the size and shape of NBs changed, progressively reducing in size. It appears that the hydrate clusters absorbed gas molecules from the surrounding gas clusters, leading to the disappearance of the NB in some systems. These bubble remains in the vicinity of the hydrate interface and supplies CO₂ for the hydrate growth. When these bubbles reached a critical size where stability was compromised, they collapsed, resulting in a localized increase in CO2 concentration in the aqueous phase, further promoting hydrate growth. The interaction between water and CO₂ molecules increased as the hydrate surface absorbed the gas molecules from the solution and consumed them to form new hydrate cavities. Therefore, CO₂ molecules have less preference to interact with each other and thus the gas clusters were shrinking during the simulation.

The outcome of this study deepens the understanding of nanobubble dynamics and addresses the critical role of nanobubbles in CO₂ hydrate-crystallization processes - directly contributing to the mitigation of climate-change impacts. 

How to cite: English, N., Naeiji, P., and Pan, M.: Mitigating climate change: investigating the synergistic effects of nanobubbles and gas hydrates for enhanced carbon capture, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16492, https://doi.org/10.5194/egusphere-egu24-16492, 2024.

Natural gas hydrates are crystalline compounds that are formed from hydrogen-bonded water molecules and gas molecules. They mainly contain climate-active CH₄, but also other light hydrocarbons, CO₂ or H₂S They exhibit a high sensitivity to variations in temperature and pressure, mainly driven by environmental changes. The oceanic or atmospheric warming resulting from climate change may trigger the decompositions of hydrates, potentially releasing significant amounts of CH₄. To assess the potential risks associated with CH₄ release from destabilized hydrate deposits, a precise understanding of the dissociation behaviour of gas hydrates becomes crucial.

In this study, a systematic investigation on the dissociation process of sI CH₄ hydrates, sII CH₄+C₃H₈ hydrates, and sII multi-component CH₄+C₂H₆+C₃H₈+CO₂ mixed hydrates was reported. We employed a combination of experimental and molecular dynamics (MD) simulations to provide a more nuanced understanding of the hydrate dissociation behaviours, which primarily shed light on the molecular aspects. The dissociation was induced through thermal stimulation to mimic climate warming. Both in situ and ex situ Raman spectroscopic measurements were performed continuously to characterize the hydrate phase. Throughout the dissociation process, hydrate composition, surface morphology, and the large-to-small cavity ratios were determined.  MD simulations were carried out under similar conditions, providing advanced insights and perspectives that couldn't be readily extracted from experimental observations alone.

Both experimental and simulation outcomes indicate that intrinsic kinetics likely govern the early stage of hydrate dissociation. A significant development in the dissociation process is the hindrance caused by the formation of a quasi-liquid or amorphous phase at the surface of the hydrate particles after the breakup of the outer layer of hydrate cavities. The unstable (partial) hydrate cavities that form within this quasi-liquid phase are oversaturated with gas molecules. Consequently, gas hydrates undergo a cycle of decomposition-reformation-continuing decomposition until the crystal eventually disappears. With decomposition dominating the process, both experimental and numerical simulation results demonstrate that the breakup of large cavities (5¹²6²) is faster than that of small ones (5¹²) in sI hydrates. Conversely, a faster breakdown of small 5¹² cavities in sII hydrates is observed. Additionally, during the dissociation process of sII CH₄-C₃H₈ hydrate, the cavities occupied by CH₄ preferentially collapse compared to those filled with C₃H₈. Similarly, over the dissociation of multi-component hydrate, cavities filled with CH₄ exhibit a preferential collapse compared to those filled with C₃H₈, C₂H₆, and CO₂.  These findings show the complexity and differences in the dissociation behavior of natural gas hydrates depending on their composition and structure and can therefore make an important contribution to an accurate assessment of CH4 release from destabilized hydrate deposits in response to climate change.

How to cite: Schicks, J., Naeiji, P., and Pan, M.: Systematic Investigation of Natural Gas Hydrate Dissociation Processes with Regard to Global Warming, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17331, https://doi.org/10.5194/egusphere-egu24-17331, 2024.

Methane hydrates are the most abundant clathrates found in the environment, predominantly in the permafrost and marine continental margins. As such, they consitute an energy resource, a concern for climate change, as well as a potentially significant source of carbon for microorganisms. However, relatively little is known about the way that these microorganisms interact, if at all, with methane hydrate deposits in their environment. Recently, a porin produced by a marine methylotroph (Methylophaga aminisulfidivorans) was found to promote hydrate formation in conditions mimicking that of the seafloor. A specific peptide sequence (TAFDGGS) was shown to be at least partially responsible for this behaviour. However, the exact physico-chemical mechanisms underlying such effects are still unclear.

Our research employed a dual methodology, integrating experimental procedures with molecular dynamics simulations to answer the question of how naturally occurring peptides can influence methane hydrate formation. Initially, laboratory experiments were conducted to observe the kinetics of methane hydrate formation in the presence of the selected natural peptide (TAFDGGS) and the traditional hydrate promoter: sodium dodecyl sulfate (SDS). Methane hydrate formation from deionized water served as a reference. Parameters such as rate of formation, induction time and total gas consumption were meticulously recorded and analysed. In parallel, molecular dynamics simulations of the hydrate formation process with and without the peptide were carried out. The careful analysis of the interactions between water, methane and the peptide provided molecular-level insights on how peptides can influence the nucleation and growth of methane hydrate clusters. Our results indicate that the natural peptide exhibits a distinctive promoting effect on the formation kinetics of methane hydrates. However, the mechanistic hypothesis that the promotion effect is achieved by providing more nucleation sites was ruled out by comparison with the reference groups. Instead, the results suggest a more complex biocatalytic effect on hydrate kinetics.

These findings suggest a potential for peptides as eco-friendly alternatives to traditional chemical promoters in methane hydrate research and provide valuable insights into the design of more efficient and sustainable bio-based promoters. More fundamentally, this study lays a solid foundation for our understanding of the interactions between peptides and hydrates in nature and paves the way for further research on the role of proteins or microorganisms on hydrate deposits.

How to cite: Pan, M., Radola, B., Allen, C. C. R., and English, N. J.: The Pioneering Role of Natural-Occurring Peptides on Methane Hydrate Formation—Insights from Experiments and Numerical Simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18603, https://doi.org/10.5194/egusphere-egu24-18603, 2024.

Gas hydrate (GH) formation and dissociation in natural systems is a complex, multi-process phenomenon controlled by local pressure-temperature-salinity (p-T-s) conditions and availability of methane gas. Our recent findings based on detailed analyses of GH systems using high fidelity multi-physics numerical model suggest that the long-term stability of the natural gas hydrate systems is not straightforward. On time scales ranging from hundreds to hundred of thousands of years, natural gas hydrate systems are able to develop, so-called, periodic steady-states characterized by a cyclic growth and dissolution of gas hydrate layers as well as a free gas migration through the gas hydrate stability zone (GHSZ). In this presentation, we show how these new results directly affect the estimates of global GH inventories and how they can be used to investigate the development of multiple bottom simulating reflectors (BSRs), slope failures, pockmarks, and gas migration pathways observed in the geological records that may have occurred spontaneously due to the internal system dynamics (i.e. gas hydrate cyclicity).

On a global scale, we have quantified the potential effect of the periodic states expressed as a new uncertainty measure that sets the hard limits on the predictability of present-day gas hydrate inventories through steady-state analysis. On a regional scale, focused on high-latitude locations, we present a combination of system parameters leading to periodic states and provide uncertainty quantifications on the gas hydrate system stability and faith. In that context, we discuss the relation between the time-periods of the cyclic states and the external triggers affecting gas hydrate systems in the Arctic (e.g. anthropogenic warming, sea level changes, glacial- interglacial cycles, etc.).

Keywords: methane cycle, global carbon budget, natural gas hydrate systems, periodic steady-states

How to cite: Burwicz-Galerne, E. and Gupta, S.: The influence of gas hydrate cyclicity on global and regional gas hydrate inventories, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18754, https://doi.org/10.5194/egusphere-egu24-18754, 2024.

By using X-ray computeted tomography(XCT), low-field nuclear magnetic resonance(NMR), N₂ gas adsorption(N₂GA) method, the microscopic pore system of hydrate-bearing sediments in  KG Basin was comprehensively characterized. Results shown that the pore types are complex, with diverse pore geometry, poor connectivity, foraminiferal shells provide certain pores, 4-20μm micropores contribute the most to permeability. For the lacking of measuring closed pores by N₂GA leads to a significant difference in the total pore volume compared with NMR results.

Through monitoring the phase transition process in pores under temperature changes through NMR, the intensity value of the first peak signal of CPMG is collected, meanwhile the pure water signal is calibrated to calculate the unfrozen water content and pore size distribution. The results indicate that the water signal inside the macropores is constantly increasing, significantly weaker than in the micropores; the middle peak values corresponding to the mesopores are disorferly. Analysis shows that water migration occurs within the mesopores, the process of ice melting into water initial occurs in smaller pores.

How to cite: Guan, W.: Multi-scale characterization for pore systems of  hydrate-bearing reservoir, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20561, https://doi.org/10.5194/egusphere-egu24-20561, 2024.

Climate change is mainly monitored at the Earth's surface. However, it is well known that as part
of ongoing climate change, ocean circulation is also changing, and therefore the ocean floor is
also subject to temperature changes.
In this study, the depth of the global methane hydrate stability zone was assessed by analyzing its
changes over the period from 1993 to 2018 to investigate the effect of climate change on the
stability of methane hydrates.
Indeed, seafloor sediments are often permeated by a methane hydrate phase, the stability of
which depends on the pressure and temperature field, among other parameters, and any changes
in temperature conditions near the seafloor can bring the methane hydrate into unstable
conditions.
The data needed for the assessment of methane hydrate stability were obtained from The Global
Ocean Physics Reanalysis data set (GLORYS12V1), produced under the European Copernicus
Marine Environment Monitoring Service (CMEMS), and GEBCO- The General Bathymetric Chart
of the Oceans. The data were then processed with original data processing software developed in
Fortran and Python languages.
A quantitative estimate of the amount of methane released into ocean masses by the dissociation
of methane hydrate in shallow sediments over the period under consideration was also obtained.
The release of large amounts of methane could have an impact on submarine geological hazards,
such as submarine landslides, and the eventual reaching of the atmosphere by methane would
reinforce ongoing climate change.

How to cite: Riccucci, L., Camerlenghi, A., Salon, S., and Tinivella, U.: Temporal variability of the stability field of methane hydrates in the oceans, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21623, https://doi.org/10.5194/egusphere-egu24-21623, 2024.

Ice core archives allow us to retrieve the atmospheric CO₂ concentration of the past 800,000 years characterized by periodically lower and higher CO₂ levels corresponding to ice ages and interglacials, respectively. However, there is no broadly accepted consensus regarding the leading drivers of such variability. To a large extent, what prevents us from identifying the mechanisms that underlie changes in atmospheric CO₂ concentrations is our inability to split the overall atmospheric CO₂ budget into its sources and sinks terms, thereby assessing the fluxes of carbon among different reservoirs. Here, we use a reversible-jump Markov chain Monte Carlo (rj-McMC) algorithm to invert the atmospheric CO₂ concentration dataset provided by the EPICA ice core based on a general forward formulation of the geological carbon cycle. We can quantify the most likely temporal variability of atmospheric carbon fluxes in ppm/yr throughout the last 800,000 years. Results suggest that temperature changes have been driving the variations of atmospheric CO₂ until the Mid-Brunhes Event (MBE), when the onset of a progressive cyclic increase of  the atmospheric carbon fluxes marks a distinct behavioral change of the climate system. We ascribe such change to mechanisms internal to the Earth system, possibly related to the deglacial triggering of global volcanism and associated feedbacks on climate or a combination of geological, biological, and physical processes. Regardless, our unprecedented quantification of past atmospheric input and output CO₂ fluxes provide (1) new constraints for climate carbon cycle and paleoclimate models to assess dominant climate-driving mechanisms, and (2) the benchmark for climate models intercomparison projects and better assessing the anthropogenic perturbation to the geological carbon cycle an associated climatic effect.

How to cite: Castrogiovanni, L., Sternai, P., Pasquero, C., and Piana Agostinetti, N.: Input and output fluxes of surface CO2 over the Late Quaternary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1026, https://doi.org/10.5194/egusphere-egu24-1026, 2024.

One of the critical features of deglaciations is the sudden increase in atmospheric CO₂ levels. Regulating the Pleistocene atmospheric CO₂ variations requires the involvement of oceanic carbon storage changes. However, the mechanisms and pathways for air-sea carbon exchanges remain elusive, partly resulting from the insufficiency of marine carbonate system proxy data with a robust age control beyond Termination I.

The deglacial CO₂ rise toward Marine Isotope Stage (MIS) 9e (Termination IV) started from 197.1 ppm to 300.7 ppm^[1], representing the highest natural atmospheric CO₂ recorded in the Antarctic ice cores over the past 800 ka^[2]. Our high-resolution carbonate system records from the Iberian Margin with a robust age control suggest an expansion of southern-sourced Glacial Antarctic Bottom Water at the onset of the deglaciation, followed by a net release of CO₂ from the Atlantic sector of the Southern Ocean. However, our results indicate a different ocean circulation pattern during Termination III, when atmospheric CO₂ increases by 85 ppm^[2]. Unlike Termination III, the north-sourced water seems to take a large proportion of the deep Atlantic Ocean during this period.

References:

[1] Nehrbass-Ahles, C. et al. (2020), Science vol. 369 1000–1005.

[2] Bereiter, B. et al. (2015), Geophys. Res. Lett. 42, 542–549.

How to cite: Ji, X. and Yu, J.: The mechanism controlling air-sea CO2 exchange under different ocean circulation conditions, a case study from Iberian Margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1157, https://doi.org/10.5194/egusphere-egu24-1157, 2024.

Deglacial abrupt warming event is a ubiquitous feature of deglaciations during the Late Pleistocene. Nevertheless, during the last deglaciation an unusually early onset of abrupt Northern Hemisphere warming event, known as Bølling/Allerød (B/A) warming, complicates our understanding of their underlying dynamics, especially due to the large uncertainty in histories of ice sheet retreat and meltwater distributions. Here applying the latest reconstruction of ice sheet and meltwater flux, we conduct a set of transient climate experiments to investigate the triggering mechanism of the B/A warming. We find that the realistic spatial distribution of meltwater flux can stimulate the warming even under a persistent meltwater background. Our sensitivity experiments further show that its occurrence is associated with an orbitally induced climate self-oscillation under the very deglacial climate background related to atmospheric CO₂ level and ice sheet configurations. Furthermore, the continuous atmospheric CO₂ rising and ice sheet retreating appear to mute the oscillation by freshening the North Atlantic via modulating moisture transport by the Westerly. 

How to cite: Sun, Y., Zhang, X., Knorr, G., Werner, M., Tarasov, L., and Lohmann, G.: Bølling-Allerød warming as a part of orbitally induced climate oscillation , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3128, https://doi.org/10.5194/egusphere-egu24-3128, 2024.

Rising atmospheric CO₂ concentration is a major driver of climate change. One of the several processes proposed to explain the lower atmospheric CO₂ concentration during the last glacial period is an increase in aeolian iron flux into the Southern Ocean. As the Southern Ocean is a high-nutrient-low-chlorophyll region, increased iron deposition can impact Southern Ocean marine ecosystems,  increase export production, and reduce surface Dissolved Inorganic Carbon (DIC) concentration. Here, we investigate the responses of Southern Ocean marine ecosystems to changes in iron flux and their impact on ocean biogeochemistry and atmospheric CO₂ during the last glacial period. We use a recently developed complex ecosystem model that includes four different classes of phytoplankton functional types and fully incorporated iron, silica and calcium carbonate cycles. We show that the changes in atmospheric CO₂ are more sensitive to the solubility of iron in the ocean than the regional distribution of the iron fluxes. If surface water iron solubility is considered constant through time, we find a CO₂ drawdown of ∼4 to ∼8 ppm. However, there is evidence that iron solubility was higher during glacial times. A best estimate of solubility changing from 1 % during interglacials to 3 % to 5 % under glacial conditions yields a ∼9 to 11 ppm CO₂ decrease at 70 ka, while a plausible range of CO₂ drawdown between 4 to 16 ppm is obtained using the wider but possible range of 1 % to 10 %. We also show that the decrease in CO₂ as a function of Southern Ocean iron input follows an exponential decay relationship, which arises due to the saturation of the biological pump efficiency and levels out at ∼21 ppm in our simulations.

We also investigate the role of iron flux changes on the abrupt atmospheric CO₂ increase during Heinrich Stadials, which are associated with a near collapse of the Atlantic Meridional Overturning Circulation (AMOC), a sudden decrease in Greenland temperature and warming in the Southern Ocean. Previous modelling studies have investigated the role of the ocean circulation in driving changes in atmospheric CO₂ concentration during these abrupt events, while the role of reduced aeolian iron input during Heinrich stadials remained poorly constrained. We show that a weakened iron fertilisation during Heinrich Stadials can lead to ~6 ppm rise in CO₂ out of the total increase of 15 to 20ppm as observed. This is caused by a 5% reduction in nutrient utilisation in the Southern Ocean, leading to reduced export production and increased carbon outgassing from the Southern Ocean.

How to cite: Saini, H., Meissner, K., Menviel, L., and Kvale, K.: Impact of iron fertilisation on Southern Ocean ecosystems and global carbon cycle during the last glacial cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4269, https://doi.org/10.5194/egusphere-egu24-4269, 2024.

Despite intense efforts, current generation comprehensive Earth system models have, to our knowledge, not been able to simulate the full extent of the atmospheric pCO₂ drawdown (as recorded in ice cores) during the Last Glacial Maximum (LGM). Yet, the intermediate complexity model CLIMBER-2 has successfully been used to simulate not only the LGM drawdown but also the transient evolution of CO₂ concentrations during entire glacial–interglacial cycles. To better understand why this is the case, we compare the CLIMBER-2 results to pre-industrial and LGM simulations using two related models with increasing complexity, namely, the recently developed intermediate complexity model CLIMBER-X and the state-of-the-art comprehensive Earth system model MPI-ESM as used in the PalMod project, focusing on ocean carbon cycle changes.

How to cite: Heinemann, M., Brovkin, V., Willeit, M., Segschneider, J., and Schneider, B.: Simulating glacial-interglacial CO2 variations: What's right with CLIMBER?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4451, https://doi.org/10.5194/egusphere-egu24-4451, 2024.

The Southern Ocean is widely thought to have played a driving role in the atmospheric CO₂ fluctuations of the ice ages, ventilating carbon-rich deep waters to the atmosphere during interglacial periods and limiting this CO₂ leakage during glacial periods. A more efficient Southern Ocean biological pump during glacial periods is one of the leading hypotheses for how this “leak” might have been stemmed, but the exact dynamics responsible are still debated. Previous hypotheses have invoked reduced upwelling and/or enhanced stratification in reducing the carbon and nutrient supply to the glacial Southern Ocean surface, thus enhancing the net efficiency of its biological pump. Here we consider an alternative, complementary scenario in which the nutrient and carbon content of the upwelled water itself is reduced. Noting the striking similarity between proxy records from the North Pacific and Southern Ocean over the Last Glacial Cycle and given that carbon-rich waters upwelling in the Southern Ocean today are largely fed by the North Pacific, we propose that low-carbon/nutrient glacial Southern Ocean surface waters could have been sourced from a well-ventilated, low-carbon/nutrient glacial North Pacific. We then show in intermediate-complexity Earth system model simulations how a well-ventilated North Pacific can directly reduce the outgassing potential of waters upwelled in the Southern Ocean. While not precluding the possibility of changes to upwelling or mixing, our results demonstrate the ability of changes in the upwelled waters’ carbon content – outside of any changes to Southern Ocean physical dynamics (e.g., upwelling rate) – to change Southern Ocean carbon content and outgassing. This provides a novel mechanism linking Northern Hemisphere climate to Southern Ocean carbon cycling and may thus help explain the cyclic CO₂ variations of the ice ages.

How to cite: Shankle, M., MacGilchrist, G., Gray, W., de Lavergne, C., Menviel, L., Burke, A., and Rae, J.: Polar Twins: Glacial CO2 outgassing reduced in the Southern Ocean by upwelling of well-ventilated waters from the North Pacific , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4464, https://doi.org/10.5194/egusphere-egu24-4464, 2024.

Romé et al. (2022) present a new set of long-run Last Glacial Maximum experiments with millennial-scale climate oscillations between cold and warm modes. These oscillations are triggered by different snapshots of ice-sheet meltwater derived from the early stages of the last deglaciation. The overall characteristics of the oscillating events share similarities with δ¹⁸O records of the last glacial period. We test the robustness of these oscillations under different climate conditions, i.e., changes in atmospheric carbon dioxide concentration and orbital configuration. These experiments were run with intentions to better understand the range of conditions the oscillations can be sustained within the model and provide additional insight into the triggering mechanisms that control abrupt climate changes. The results of our sensitivity analysis show that small changes in carbon dioxide concentrations can impact the periodicity and existence of oscillations. A decrease in carbon dioxide concentration decreases periodicity, and an increase in carbon dioxide concentration increases periodicity, leading to an end of the oscillations. Our results also show that for changes in orbital configuration, an increase in Northern Hemisphere summer insolation decreases periodicity and potentially also amplitude. The results show that small changes in climate conditions can impact the shape and existence of oscillations and how this could relate to the changing periodicity and amplitude of observed Dansgaard-Oeschger events as well as transitions from glacial to interglacial states.

How to cite: Snoll, B., Ivanovic, R., Gregoire, L., Rome, Y., and Sherriff-Tadano, S.: Sensitivity of millennial-scale climate oscillations to boundary conditions in HadCM3 glacial simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5280, https://doi.org/10.5194/egusphere-egu24-5280, 2024.

Pleistocene temperatures correlate well with glacial-interglacial changes in global ice volume. While a discharge of ice-rafter debris (IRD) into the ocean directly reflects the rates of growth and decay (deglaciations) of glacial ice sheet margins at sea level, it is also the result of a rapidly changing global environment which affected both the meridional overturning in the ocean and the patterns in ocean-atmosphere circulation on a regional scale.  Circum-arctic land regions and adjacent ocean basins hold clues of varying ice sheet sizes through time. Understanding these records correctly is therefore an important asset to better appreciate Quaternary climate change also within a much broader global context. Marine sediment core data from the Nordic Seas show a stepwise trend of decreasing fluxes of IRD during major glaciations of the last 500 ka, i.e., marine isotope stages (MIS) 12, 6, and 2. Strongest IRD deposition occurred in MIS 12 (Elsterian), while it was lower in MIS 6 (Saalian) and 2 (Weichselian). These marine results of iceberg discharge rates from the western European margins, in particular, point to significant temporal changes in the ice-sheet coverage over northern Eurasia. Indeed, field data provide evidence for several major pre-Weichselian glaciations. Although their maximum limits were likely asynchronous in certain places, it seems evident that these ice sheets not only pre-date the Saalian time, they also extended much farther south (and east) than at any time later. The stepwise decreases in Eurasian ice-sheet extents during glacial maxima terminated in quite contrasting deglaciations and subsequent interglacial developments. It appears evident that such a systematic change in ice-sheet sizes were the result of specific ocean heat circulation, which influenced the pathways of atmospheric moisture transfer across northern Eurasia.

How to cite: Bauch, H.: Impact of waxing and waning of Northern Ice sheets on Pleistocene climate , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5426, https://doi.org/10.5194/egusphere-egu24-5426, 2024.

Carbon cycle models used to interpret the IntCal20 compilation of atmospheric Δ¹⁴C have so far neglected a key aspect of the millennial-scale variability connected with the thermal bipolar seesaw: changes in the strength of the Atlantic meridional overturning circulation (AMOC) related to Dansgaard/Oeschger and Heinrich events. Here we implement such AMOC changes in the carbon cycle box model BICYCLE-SE to investigate how model performance over the last 55 kyr is affected, in particular with respect to available ¹⁴C and CO₂ data. Constraints from deep ocean ¹⁴C suggest that the AMOC in the model during Heinrich stadial 1 needs to be highly reduced or even completely shutdown. Ocean circulation and sea ice coverage combined are the processes that almost completely explain modelled changes in deep ocean ¹⁴C age, and these are also responsible for a glacial drawdown of ~60 ppm of atmospheric CO₂. A further CO₂ drawdown of ~25 ppm is caused by the colder ocean surface at the last glacial maximum. We find that the implementation of AMOC changes in the model setup that was previously used for the calculation of the non-polar mean surface marine reservoir age, Marine20, leads to differences of less than ±100 ¹⁴C years. The representation of AMOC changes therefore appears to be of minor importance for deriving mean ocean radiocarbon calibration products such as Marine20, where atmospheric carbon cycle variables are forced by reconstructions. However, simulated atmospheric CO₂ exhibits minima during AMOC reductions in Heinrich stadials, in disagreement with ice core data. This mismatch supports previous suggestions that millennial-scale changes in CO₂ were probably mainly driven by biological and physical processes in the Southern Ocean. By modifying the ¹⁴C production rate (Q), between one that varies so as to fit simulated atmospheric ∆14C to IntCal20 and an alternative constant Q, we can furthermore show that in our model setup the variability in deep ocean 14C age, especially during the Bølling/Allerød—Younger Dryas—Early Holocene climate transition, has its root cause in the carbon cycle, while a Q that achieves agreement with the IntCal20 atmospheric ∆14C record only enhances deep ocean age anomalies and thus optimizes agreement with the benthic 14C data.

How to cite: Köhler, P., Skinner, L., and Adolphi, F.: Simulated radiocarbon cycle revisited by considering the bipolar seesaw and benthic 14C data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5549, https://doi.org/10.5194/egusphere-egu24-5549, 2024.

The Last Glacial Maximum (LGM) was defined based on the low stand sea-level records from the most recent period when global ice sheets reached their maximum volume, between 26,500 and 19,000 years before present. The end of this cold period was the last glacial termination (T1), occurred between 20 and 11.7 ka BP marking the transition to the current interglacial. During T1, the sea level rise responded to a variety of processes although the melting of the world widely distributed ice sheets was initially the main contributor and responsible for abrupt relative sea level rises known as meltwater pulses (MWPs) that deeply changed the Earth’s physiography. MWPs are short-lived global acceleration in sea-level rise resulting from intense glacial melting, surge of large ice streams into oceans and intense iceberg discharge during ice sheet disintegration. Nowadays, the main concerns related to the present fast global climate change is the possibility that sudden drastic ice loss from the Greenland and/or in the West Antarctic Ice Sheet would lead to a new abrupt acceleration of the relative sea level with consequent inundation of vast coastal areas and/or to cause an abrupt slowdown of the Atlantic Meridional Overturning Circulation (i.e. Golledge et al., 2019). To better understand the dynamics and risks associated with the onset of those events, their impact on thermohaline ocean circulation and climate it is pivotal the study of the well-preserved polar marine sediment records of the events occurred during the T1. Here, we present the results of a high-resolution sedimentological, micropaleontological and geochemical investigation of 3 sediment cores collected on the western margin of Svalbard and eastern side of the Fram Strait (Artic). The sediment cores were collected between 1322 m and 1725 m of water depth, in correspondence of the southern IODP sites that will be drilled during the IODP Exp-403 (June-August 2024).

How to cite: Gois Smith, F. S., Lucchi, R. G., Bini, M., Morigi, C., Ferretti, P., Bronzo, L., and Douss, N.: High-resolution sedimentological and palaeoceanographic investigation of the Last Glacial Termination (T1) recorded on the western margin of the Svalbard (Arctic), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6271, https://doi.org/10.5194/egusphere-egu24-6271, 2024.

Paleo-data and models show that reductions in the strength of the Atlantic meridional overturning circulation (AMOC) lead to significant subsurface warming in the western tropical North Atlantic. The thermal response at the sea surface is less constrained due to the competing nature of the atmospheric and oceanic processes that produce opposite signs of temperature change. Here, we used alkenone unsaturation in sediments to reconstruct sea surface temperature (SST) evolution in the southeastern Caribbean (core MD99-2198, 1330 m water depth) during the last glacial-interglacial cycle, including Heinrich Stadial 11, which was a period of intense AMOC weakening. Our data show a 1 °C SST warming associated with the onset of Heinrich Stadial 11, and a 1 °C cooling during the late Heinrich, followed by a gradual 1 °C warming during the early last interglacial. Although stadial events are generally associated with wind-induced surface cooling in the tropical North Atlantic, the positive Caribbean SST anomaly during Heinrich Stadial 11 is consistent with previous findings. It likely originates from the upwelling of subsurface water that warmed in response to the initial AMOC weakening. Reduction in the Caribbean SST during the late Heinrich, associated with a particularly weak AMOC strength as suggested by our benthic d13C values, can indicate that the subsurface warming has diminished in the tropical North Atlantic possibly due to a general cooling in the source region (i.e., the subtropical gyre). A two-phased Heinrich is supported by the planktic foraminifera assemblage data, indicating that cooling occurred in the late Heinrich. In addition, this late phase is characterized by coarser sediments, which can be due to a strongly reduced outflow of the Orinoco and a particularly southern position of the intertropical convergence zone. For the last interglacial, our alkenone-derived SST record suggests stable conditions. However, the obtained interglacial values are characterized by very high alkenone unsaturation indexes that can incorporate large measurement and calibration errors due to the lack of Caribbean sediment traps and core-top data. These results, therefore, emphasize the need to better quantify the effectiveness of alkenones in reconstructing interglacial SST history in the Caribbean.

How to cite: Zhuravleva, A., Fahl, K., and Bauch, H. A.: A two-phased Heinrich Stadial 11 as revealed by alkenone-based temperature record from the western tropical North Atlantic , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6599, https://doi.org/10.5194/egusphere-egu24-6599, 2024.

Understanding the impact of freshwater discharge from the late Pleistocene Laurentide Ice Sheet (LIS) to the North Atlantic has been considered pivotal due to its direct regulating influence on the climate of the surrounding continents. Numerous studies using indirect paleo-proxies for iceberg discharge and fine-grained sediment supply have reconstructed the instabilities of the LIS. This study employs direct proxies for iceberg discharge and fine-grained sediment supply using the ice-rafted detritus (IRD) and X-ray fluorescence (XRF) scan combined with published X-ray diffraction (XRD) data from the same samples of the Integrated Ocean Drilling Program (IODP) Site U1313 (41°N; 32.57°W). Prominent Heinrich IRD events (H-events) of the last glacial cycle were accompanied by Ti/Ca and Fe/Ca peaks, consistent with the dolomite and calcite peaks, suggesting their Ordovician and Silurian carbonate rocks source that floor the Hudson Bay and Hudson Strait. However, despite the lack of an IRD/g peak, Ti/Ca and Fe/Ca peaks in H-event 3 suggest the arrival of fine-grained sediments in the southern edge of the IRD belt, most likely by sediment plume. In contrast to the last glacial cycle, IRD/g and Ti/Ca and Fe/Ca peaks, often assigned as Heinrich-like events, were only identified during the cold marine isotope stage (MIS) 6, 8, 10, and 12. The IRD/g, Ti/Ca, and Fe/Ca peaks, in addition to the dolomite and calcite peaks during the MIS 7, suggest a fundamentally different configuration of the LIS compared to the other warm MISs of the last 500 ka. Our data suggest that the LIS-sourced icebergs impacted the northern edge of the subtropical gyre (STG) by directly injecting meltwater and modifying the upper water masses, which most likely resulted in the southward movements of the Polar and Arctic fronts. These frontal movements were accompanied by frequent encroachment of the subpolar to transitional water masses to the STG. The polar water-dwelling planktonic foraminifera Neogloboquadrina pachyderma coupled to the IRD/g or Fe/Ca and Ti/Ca peaks support this hypothesis. The new sedimentological and micropaleontological data suggest that the instability and configuration of the LIS were not uniform during all the warm MISs of the last 500 ka.

How to cite: Rashid, H., Zeng, M., and Menke, M.: Impact of the Laurentide Ice Sheet instabilities on the mid-latitude North Atlantic and subtropical gyre during the last five glacial cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6815, https://doi.org/10.5194/egusphere-egu24-6815, 2024.

The critical role of the Southern Ocean in controlling the Pleistocene atmospheric CO₂ oscillations is widely acknowledged. However, owing to sampling difficulties surrounding Antarctica, the underlying mechanism and associated pathway of ocean-atmosphere CO₂ exchange in the Antarctic Zone (AZ) of the Southern Ocean remains mysterious. Here, we present a new planktonic δ¹¹B record from sediment core PS1506 (68.73°S, 5.85°W) that tracks the pH and surface pCO₂ of the AZ over the last 8 glacial cycles. These data are complemented by benthic B/Ca and carbonate preservation indices; due to the location of this core on the continental margin of the eastern Weddell Sea, these data allow us to track the source CO₂ chemistry of the dense Antarctic waters that feed the ocean’s lower overturing cell. We find coherent CO₂ change between surface and deep waters, indicating persistent formation of AABW that transfers Antarctic surface water signals to depth. Critically, we discover abrupt AZ CO₂ decline during glacial onset conditions, coinciding with initial atmospheric CO₂ drawdown, highlighting the AZ’s key control on glacial-interglacial CO₂ change. After assessing proposed drivers, our findings implicate shifts in Southern Ocean circulation linked to changes in sea ice and/or the Southern Hemisphere westerlies in this glacial onset CO₂ change, while productivity, solubility, and sea ice 'lid' effects appear insignificant or counterproductive in this region and time interval. Overall, these reconstructed CO₂ system dynamics provide critical insights into Southern Ocean carbon cycling and the associated influence on the atmosphere.

How to cite: Xu, C., Crumpton-Banks, J., Shankle, M., Pelly, M., Jurikova, H., Yu, J., Opdyke, B., Hillenbrand, C.-D., Burke, A., and Rae, J.: The Southern Ocean’s role in the global carbon cycle over the last 800 kyr constrained using reconstructions of the CO2 system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7296, https://doi.org/10.5194/egusphere-egu24-7296, 2024.

Global sea-level changes are significantly associated with variations in Northern Hemisphere ice sheets (NHISs) during the last glacial cycle. However, their responses to glacial millennial-scale climate variability (also known as Dansgaard - Oeschger (DO) cycles), especially during the Marine Isotope Stage 3 (MIS3, ~30-65ka), remains poorly studied, in addition to the contrast lines of geological evidence regarding paleo-sea level changes. Instead of applying Glacial Index Method which overlooks potential tempo-spatial heterogeneity of temperature and precipitation in the northern high latitudes, in this study, we conducted transient PISM ice sheet modeling by imposing full climate forcing derived from fully coupled climate model experiments which are characterized by spontaneous millennial variability. Our results show that control factors of ice volume changes in Laurentide and Eurasian ice sheets are different due to spatially heterogenous climate forcing. During stadial periods, North American Ice sheets is growing because of increased precipitation especially along the margins of the ice sheets, despite spatially heterogenous but trivial changes in the surface air temperature. Meanwhile, dramatic cooling on the southern regions of Eurasian Ice sheets effectively reduces ice loss and hence promote the overall ice growth. In brief, NHIS ice volume grows during stadials while declines during interstadials. We hence propose that stadial-to-interstadial duration ratio is the key to the net change in NHIS volume in a signal DO cycle, providing dynamic understanding of accelerated sea level drop during 40-30ka.

How to cite: Zhang, Y. and Zhang, X.: Millennial-scale Northern Hemisphere ice sheet growth controlled by stadial-versus-interstadial duration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7339, https://doi.org/10.5194/egusphere-egu24-7339, 2024.

In the course of glacial terminations, the increases in greenhouse gas concentrations, summer insolation and the ice sheet demise can trigger episodes of millennial-scale variability. Such variability was observed during the last deglaciation, between 19 ka BP (thousand years ago) and 8 ka BP, in the form of  the abrupt North Atlantic temperature shifts of the Bølling–Allerød Warming (14.5 ka BP) and Younger Dryas (12.900 ka BP).

In some climate models, abrupt climate changes are generated by modifications to the boundary conditions and freshwater discharge. Despite much study, the sensitivity of climate simulations to ice sheet geometry and meltwater is complex and not fully understood, which is a caveat when considering the impact of the rapid demise of the Northern Hemisphere ice sheets during the last deglaciation. In a new set of last glacial maximum HadCM3 simulations that can produce millennial-scale variability, we studied the influence of two ice sheet reconstructions, ICE-6G_C and GLAC-1D, and their associated deglacial meltwater history, on the simulated chain of events of the last deglaciation.

In this experiment, our simulations using the GLAC-1D ice sheet reconstruction produced abrupt climate changes. Triggered by freshwater released close to the Nordic Seas and Iceland Basin deep water formation sites, these simulations display abrupt shifts in the Atlantic Meridional Overturning Circulation (AMOC) that are decoupled from the meltwater flux. In contrast, the reconstructed ICE-6_G ice sheet modifies the North Atlantic wind patterns in the model, preventing convection in the Nordic Seas and intensifying the Iceland Basin deep water formation. As a result, no abrupt climate changes are simulated with ICE-6G_C ice sheets and the AMOC decreases almost linearly with the introduction of freshwater.

The simulations do not capture the timing of the last deglaciation chain of events, but the modelled abrupt changes replicate the main Northern Hemisphere characteristics of the Bølling Warming/Younger Dryas transitions, and are very similar to Dansgaard-Oeschger events.

How to cite: Ivanovic, R., Rome, Y., Gregoire, L., Snoll, B., Pollard, O., and Perez, J.: Abrupt climate changes triggered with GLAC-1D ice sheet, but not with ICE-6G_C, in simulations of the Last Glacial Maximum/Deglaciation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8676, https://doi.org/10.5194/egusphere-egu24-8676, 2024.

The addition of meltwater from continental ice sheets to the North Atlantic is thought to have played a pivotal role in the reorganization of climate and ocean circulation over the last deglaciation as well as during Heinrich events. This is supported by recent analysis of PMIP and CMIP results, which shows that meltwater addition into the North Atlantic can largely alter global climate, and remains a key uncertainty for both reconstruction and climate projections. 

To date, most model studies of freshwater “hosing” assume a relatively uniform distribution and apply meltwater to a large portion of the North Atlantic basin. However, AMOC weakening is sensitive to the actual input position of the typically cold and non-saline meltwater perturbation, and, on a centennial-millennial timescale, the resulting temperature and salt anomaly will only partially disperse over the entire North Atlantic surface ocean. In contrast, most proxy data sensitive to meltwater record the signal at a specific location. It is unclear if spatial heterogeneity of the ocean’s distribution of the meltwater anomaly may contribute to disagreements between freshwater proxy records and model simulations with freshwater additions tuned to reproduce the record of past AMOC weakenings.

To enhance understanding of the spatial distribution of meltwater anomalies during deglaciations, we present the results of a model sensitivity study using HadCM3 and artificial dye tracers to track the fate of meltwater originating from different Northern ice sheet sectors. We consider different meltwater scenarios consistent with Heinrich Stadial 1 ice sheet reconstructions and compare the results under different AMOC states. The results confirm that, on a centennial timescale, meltwater distribution is not uniform over the North Atlantic Ocean. The emerging patterns expose that the efficiency of a meltwater injection to produce a surface ocean anomaly (in, e.g., salinity or δ¹⁸O_sw) at a given proxy location differs between different ice sheet sectors by orders of magnitudes. Further, besides the direct effect of meltwater, the sensitivity of climate indicators, such as temperature, to changes in AMOC strength also shows regional discrepancies. 

How to cite: Endres, L., Ivanovic, R., Romé, Y., Tindall, J., and Stoll, H.: Tracking the fate of meltwater from different Northern ice sheet sectors over Heinrich Stadial 1, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8715, https://doi.org/10.5194/egusphere-egu24-8715, 2024.

Ice-core measurements show diverse atmospheric CO₂ variations – increasing, decreasing or remaining stable – during millennial-scale North Atlantic cold periods called stadials. The reasons for these contrasting trends remain elusive. Ventilation of carbon-rich deep oceans can profoundly affect atmospheric CO₂, but its millennial-scale history is poorly constrained. In this study, I will show a high-resolution deep-water acidity record from the Iberian Margin in the North Atlantic, a unique setting that allows us to construct a robust chronology for confident comparisons between marine and ice-core records. The new data combined with ice-core CO₂ records reveal multiple ocean ventilation modes involving an interplay of the two polar regions, rather than by the Southern Ocean alone. These modes governed past deep-sea carbon storage and thereby atmospheric CO₂ variations on millennial timescales. Overall, our record suggests a bipolar control on millennial atmospheric CO₂ changes during the past glacial cycle.

How to cite: Yu, J., Anderson, R., Jin, Z., Ji, X., Thornalley, D., Wu, L., Thouveny, N., Cai, Y., Tan, L., Zhang, F., Menviel, L., Tian, J., Xie, X., Rohling, E., and McManus, J.: Bipolar control on millennial atmospheric CO2 changes over the past glacial cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9143, https://doi.org/10.5194/egusphere-egu24-9143, 2024.

The last deglaciation, spanning approximately 23 to 6 thousand years before present (ky BP), represents the most recent period in which Earth’s climate underwent large-scale reorganizations comparable (albeit not strictly analogous) to those projected under future climate changes. However, the precise sequence of events – in particular, the timing and spatial manifestation of the initial warming – remains uncertain. Here we present a new method using Gaussian Mixture Model clustering to objectively decompose a model and proxy-based climate reconstruction (LGMR; Osman et al., 2021) into four patterns of temperature change across the last deglaciation. Broadly speaking, the patterns allow us to delineate the impact of retreating Northern Hemisphere ice sheets, the rise in greenhouse gases, and the influence of the bipolar seesaw. Crucially, our analysis reveals that the high latitudes of the Southern Hemisphere exhibited the earliest signs of warming onset around 21 kyr BP, coincident with a retreat of sea ice across the Southern Ocean. A similar pattern is observed when decomposing a solely model-based climate reconstruction (TraCE-21k; He et al., 2013).  Using a combination of both highly-simplified energy balance-type models and fully-coupled climate models forced with insolation alone, we show that the early warming and sea ice retreat was likely linked to an initial rise in high latitude summertime energy that is dominated by enhanced obliquity-driven forcing. Our findings collectively suggest that insolation dynamics in the Southern Hemisphere were a critical trigger of the Last Deglacial onset and, further, may represent one of the key prerequisites for glacial terminations during the late Pleistocene.

How to cite: Zheng, P., Osman, M., and Bauska, T.: An Early Warming Over the Southern Ocean During the Last Deglaciation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9411, https://doi.org/10.5194/egusphere-egu24-9411, 2024.

Atmospheric carbon dioxide concentrations (pCO₂) have increases by approximately  from the Last Glacial Maximum (LGM) to the late Holocene (last deglaciation). These changes in atmospheric greenhouse gases are recognized as climate system responses to gradual changes in insolation. Previous modeling studies have suggested that the deglacial increases in atmospheric pCO₂ are primarily attributed to the release of CO₂ from the ocean. In addition, it has been suggested that abrupt changes in the Atlantic Meridional Overturning Circulation (AMOC) and associated interhemispheric climate changes are involved in the release of CO₂. However, there is still limited understanding in oceanic circulation changes, factors responsible for changes in chemical tracers in the ocean of the last deglaciation and its impact on atmospheric pCO₂.

In this study, we investigate the evolution of the ocean carbon cycle during the last deglaciation (21 to 11 ka BP) using three-dimensional ocean fields from the transient simulation of the MIROC 4m climate model, which exhibits abrupt AMOC changes as in reconstructions. We validate the simulated ocean carbon cycle changes and discuss possible biases and missing or underestimated processes in the model by comparing simulated carbon isotope ratios with sediment core data.

The qualitative changes in atmospheric pCO₂ are consistent with ice core records: during Heinrich Stadial 1 (HS1), atmospheric  increases by . This is followed by a decrease of  during the Bølling–Allerød (BA) and an increase of  during the Younger Dryas (YD). However, the model underestimates the changes in atmospheric  during these events compared to ice core data. Radiocarbon and stable isotope signatures ( and ) indicate that the model underestimates the activated deep ocean ventilation and reduced efficiency of biological carbon export in the Southern Ocean, and active ventilation in the North Pacific Intermediate Water during HS1. The relatively small changes in simulated atmospheric  changes during HS1 may be attributed to these underestimations of ocean circulation changes. The changes in  associated with strengthening and weakening in the AMOC during the BA and YD are generally consistent with the sediment core record. On the other hand, while the data show a continuous  increase in the deep ocean throughout the YD, the model shows the opposite trend. This suggests that the model simulates excessive weakening of the AMOC during the YD, or limited representations in geochemical processes in the model including marine ecosystem responses and terrestrial carbon storage.

Decomposing the factors behind changes in ocean  reveals that changes in temperature and alkalinity have the main effects on atmospheric  changes. The compensation of the effects of temperature and alkalinity suggests the AMOC changes and associated bipolar climate changes contribute to a slight decrease or increase in atmospheric  during the BA and YD periods, respectively.

How to cite: Kobayashi, H., Oka, A., Obase, T., and Abe-Ouchi, A.: Assessing transient changes in the ocean carbon cycle during the last deglaciation through carbon isotope modeling , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9419, https://doi.org/10.5194/egusphere-egu24-9419, 2024.

Be10 in ice cores provides a uniquely well resolved indication of past radionuclide production rates, with a direct bearing on past radiocarbon production.  In the absence of past carbon cycle perturbations (e.g. involving ocean-atmosphere carbon exchange), Be10-based radiocarbon production rate anomalies should correlate directly with atmospheric radiocarbon anomalies, as confirmed by models.  Over the past ~30ka, Be10-inferred radiocarbon production rates and atmospheric radiocarbon (i.e. Intcal20) both exhibit recurrent millennial anomalies, typically of ~5ka duration.  A correlation between these anomalies breaks down during the deglaciation.  This is intriguing and suggests a mix of millennial carbon cycle and radionuclide production influences. Here, global compilations of marine carbon isotope data (radiocarbon and 𝛿¹³C) are used to assess the potential contribution of ocean circulation and air-sea gas exchange to the apparent millennial component of variability in Intcal20, and atmospheric CO₂. We find that existing marine 𝛿¹³C data provide strong support for a marine influence on atmospheric radiocarbon. Support from marine radiocarbon data is more complex, due to the influence of ‘attenuation biases’ (arising from radiocarbon production changes), and due to a distinct regionalism in the ocean’s impact on atmospheric radiocarbon, versus atmospheric CO₂, with air-sea gas-exchange playing a significant role. Major differences in the long-term evolution of radiocarbon and 𝛿¹³C across the last deglaciation further point to distinct and independent controls on these isotopes systems, providing clues as to the nature and timing of different carbon cycle processes during deglaciation.

How to cite: Skinner, L.: Globally resolved marine carbon isotope data spanning the last 25ka: what do they tell us about the drivers of atmospheric radiocarbon and CO2 on millennial and deglacial timescales? , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9678, https://doi.org/10.5194/egusphere-egu24-9678, 2024.

Pleistocene glacial-interglacial variability is still under debate, as the many hypotheses proposed are subject to the models used and assumptions made. The longer time scales involved in glacial cycles make it difficult to use comprehensive climate models because of its large computational cost. In this context, conceptual models are built to mimic complex processes in a simpler and more computationally efficient way. Here we present a conceptual climate-ice sheet model that aims to represent the state-of-the-art physical processes affecting glacial-interglacial variability. Our model was constructed using linear equations that explicitly represent ice-sheet modeling approaches. Preliminary results are consistent with Late Pleistocene variability and point to the existence of nonlinearities related to both ice dynamics and ice aging that determine the timing and shape of deglaciations.

How to cite: Pérez-Montero, S., Alvarez-Solas, J., Montoya, M., and Robinson, A.: Glacial-interglacial variability using a low-complexity, physically based model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9708, https://doi.org/10.5194/egusphere-egu24-9708, 2024.

Glacial Terminations represent the largest amplitude climate changes of the last several million years.  Over ~ 10 ky timescale, large northern hemisphere ice sheets retreat and sea level rises, and atmospheric CO₂ and global temperatures make a full transition from glacial to interglacial levels.  Several possible orbital-insolation triggers have been described to initiate and sustain glacial Terminations, and feedbacks between ice sheet retreat, ocean circulation and ocean carbon storage are invoked to explain the unstoppable progression. 

Because of the availability of radiocarbon dating, the most recent termination (TI) has been extensively characterized. Yet, it is widely discussed whether this sequence of feedbacks and millennial events, and rate of warming is recurrent over previous Terminations or is unique.  Beyond the limit of radiocarbon dating, the chronologies of climate records from ice and marine cores are often developed by tuning to orbital parameters which limits their use in understanding climate dynamics, particularly the response to orbital forcing.

Speleothems provide absolute age control and high-resolution proxy measurements. This archive therefore provides unique records of climate change across Terminations, and additionally may provide the opportunity to tune ice and marine core archives.  However, speleothem climate signals are encoded in a number of proxies. Unlike proxies in other archives like ice or marine cores, the climatic interpretation of a given proxy can vary quite significantly among different regions.

In this study, we

• synthesize the available speleothem records providing climate information for Terminations: TII, TIII, TIV and TV.
• present the records based on the aspect of climate encoded in the available records.
• examine the effects of different ice volume corrections on the final climate proxy record.
• evaluate whether there are leads and lags in the manifestation of Terminations across different aspects of the climate systems and different regions.
• we speculate on suitable tuning targets among marine and ice core proxies, and discuss what model outputs maybe most suitable for comparison.

How to cite: Kaushal, N., Stoll, H., and Pérez-Mejías, C.: Perspective on ice age Terminations from absolute chronologies provided by global speleothem records, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10190, https://doi.org/10.5194/egusphere-egu24-10190, 2024.

The evolution of the northern hemispheric climate during the last glacial period was shaped by two prominent signals of glacial climate variability known as Dansgaard-Oeschger cycles and Heinrich events. Dansgaard- Oeschger cycles are characterised by a period of rapid, decadal warming of up to 14°C in the high northern latitudes, followed by a more gradual cooling spanning several centuries. Temperature reconstructions from ice cores indicate a dominant recurrence interval of ∼1,500 years for Dansgaard-Oeschger cycles. Heinrich events are quasi-episodic iceberg discharge events from the Laurentide ice sheet into the North Atlantic. The paleo record places most Heinrich events into the cold phase of the millennial-scale Dansgaard-Oeschger cycles. However, not every Dansgaard-Oeschger cycle is accompanied by a Heinrich event, revealing a complex interplay between the two prominent modes of glacial variability that remains poorly understood to this day. Here, we present simulations with a coupled ice sheet-solid earth model to introduce a new mechanism that explains the synchronicity between Heinrich events and the cooling phase of the Dansgaard-Oeschger cycles. Unlike earlier studies, our proposed mechanism does not require a trigger mechanism during the cooling phase. Instead, the atmospheric warming signal associated with the interstadial phase of the Dansgaard-Oeschger cycle causes enhanced ice stream thickening such that a critical ice thickenss and temperature threshold is reached faster, triggering the Heinrich event during the early cooling phase of the Dansgaard-Oeschger cycle. An advantage of our mechanism in comparison to previous theories is that it is not restricted to marine-terminating ice streams, but applies equally to land-terminating ice streams that only become marine-terminating during the actual Heinrich event. Our simulations demonstrate that this mechanism is able to reproduce the Heinrich event characteristics as known from the paleo record under a wide range of forcing scenarios and provides a simple explanation for the observational evidence of synchronous Heinrich events from different ice streams within the Laurentide ice sheet.

How to cite: Schannwell, C., Mikolajewicz, U., Kapsch, M.-L., and Ziemen, F.: A mechanism for reconciling the synchronisation of Heinrich events and Dansgaard-Oeschger cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10579, https://doi.org/10.5194/egusphere-egu24-10579, 2024.

Despite decades of research, the cause of glacial-interglacial CO₂ cycles is not fully understood, leaving a critical gap in our understanding of Earth’s climate system. One hypothesis is that shoaling of the boundary between Northern Source Water (NSW) and Southern Source Water (SSW) enhanced oceanic carbon sequestration during glacial intervals, resulting in lower atmospheric pCO₂. To test this hypothesis, we generated vertical profiles of [CO₃^2-], δ¹³C, and δ¹⁸O using a depth transect of cores from the Brazil Margin, focusing on the two major drops in atmospheric pCO₂ during the last glacial cycle at ~115 ka and ~70 ka. Given that [CO₃^2-] is inversely related to the concentration of dissolved inorganic carbon, [CO₃^2-] should decrease if the Atlantic sequestered CO₂. We observe no significant change in the [CO₃^2-] across the first decrease in atmospheric pCO₂ and no evidence for watermass boundary shoaling in the δ¹³C and δ¹⁸O profiles.  [CO₃^2-] decreased only at ~3600 m, the core site most influenced by SSW.  During the second pCO₂ decline at ~70 ka, [CO₃^2-] decreased by ~30 µmol/kg below 2000 m water depth, coincident with marked shoaling in the δ¹³C and δ¹⁸O profiles. The lack of evidence for shoaling and deep Atlantic carbon sequestration at ~115 ka, a time of intermediate ice sheet extent and moderate global cooling, but the clear evidence for shoaling and carbon sequestration at ~70 ka, a time of near glacial maximum ice sheet extent, implies that the deep Atlantic’s capacity to store carbon depends on the Earth’s mean climate state. Our results highlight that distinct mechanisms are necessary to explain the two major drops in atmospheric pCO₂ of the last glacial cycle. 

How to cite: Garity, M. and Lund, D.: Investigating oceanic carbon sequestration during glacial inception using vertical profiles of [CO32-], d13C, and d18O from the Southwest Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12112, https://doi.org/10.5194/egusphere-egu24-12112, 2024.

Global mean surface temperature (GMST) is a fundamental measure of climate evolution in both past and present and a key quantity to evaluate climate simulations. However, for paleoclimate periods, its reconstruction hinges on uncertain and indirect observations which are distributed sparsely and non-uniformly in both space and time. Large datasets of homogenised proxy records help to reduce the sparsity. Then, the records can be aggregated in an algorithm retrieving the GMST signal. Here, we build on the algorithm designed in Snyder 2016, and on a recent database of ocean temperature proxy records to reconstruct the GMST evolution over the last glacial cycle (the last 130 thousand years). First, we evaluate the algorithm and quantify the sources of uncertainty. This analysis draws on pseudo-proxy experiments using a range of simulations of the last glacial cycle. We find that the over-representation of some regions (e.g. coasts, the Atlantic), to the detriment of others (e.g. the central Pacific) significantly impacts the reconstructed temperature anomaly and its variations. Additionally, millennial and shorter timescale variability cannot be reconstructed by the algorithm, due to bioturbation and age uncertainty. However, these experiments also demonstrate the ability of our algorithm to reconstruct the amplitude and timing of GMST variations occurring at orbital timescale (>10.000 years). Second, we reconstruct the GMST evolution during the last glacial cycle. We compare our result to previous studies, and discuss the improvements coming from the use of the recent proxy database. The high number of proxy records allow us to additionally investigate smaller regions (e.g. hemisphere) and overall further our understanding of the driver of orbital-scale GMST variability.

How to cite: Baudouin, J.-P., Weitzel, N., Jonkers, L., Dolman, A. M., and Rehfeld, K.: Reconstructing the global mean surface temperature of the last 130 thousand years, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12199, https://doi.org/10.5194/egusphere-egu24-12199, 2024.

Sea-ice formation in the Southern Ocean can generate supercooled waters, which can even remain below the in-situ freezing point at depths below 1,000 m. These water masses can play an important role in carbon transport to the abyssal ocean and may have therefore also played an important role in glacial-interglacial CO2 cycles.

To address this question, we examined model outputs from the transient 3 Ma simulation conducted with the CESM1.2 model (Community Earth System Model version 1.2, ~3.75 horizontal resolution. This simulation was driven by time-varying orbital forcing and estimates of atmospheric greenhouse gas concentrations and northern hemispheric ice-sheet orography and albedo. Our analysis shows the presence of large swaths of supercooled glacial deep waters mainly in the northern Pacific. This water is originally formed in the seasonal sea-ice formation regions in the subarctic North Pacific during periods of brine release and rapid mixed layer deepening. During interglacial periods, the volume of supercooled water decreases, which may hint towards a possible positive climate-carbon cycle feedback.

In climate models the freezing condition is usually only applied at the surface. Hence, they are incapable of simulating brinicles – vertical sea-ice structures that can extend from the surface to shallower depths, sometimes even reaching the ocean floor. In my presentation, I will address whether such structures may have played a more prominent role during glacial periods, and whether localized deep ocean freezing may have been a possibility.

How to cite: Ishizu, M., Timmermann, A., and Yun, K.-S.: Super-cooled glacial deep waters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13226, https://doi.org/10.5194/egusphere-egu24-13226, 2024.

Erosion of continental rocks controls nutrient and sediment supply, soil formation and global climate. Intensity of this land-surface process is driven by both climatic (runoff, and temperature) and non-climatic (vegetation, lithology and basin slope) factors. Additionally, climatic-driven fluctuations in sea-level may also influence the exposed land-area, which is available for weathering. The coupling between exposed shelf sediments and weathering, however, has received limited attention. In this contribution, geochemical and Sr-Nd isotopic compositions of a sediment core (VM29-17PC) from the western Bay of Bengal have been investigated to reconstruct weathering and climate interaction during last glacial-interglacial cycle. Radiocarbon dating of foraminifera samples establishes that the core preserves a continuous erosional record for last 35 kyr.  Average Sr-Nd isotopic data for the decarbonated sediments confirm dominant sediment supply from the Higher Himalaya to the core site, with sub-ordinate input from the Deccan region. Temporal changes in the isotopic data hint at a sudden increase in the Himalayan source around 15 kyr BP, which is synchronous with the Bølling-Allerød (B/A) warm phase and the strengthening of the south-west (SW) monsoon. Downcore variation of Chemical Index of Alteration (CIA) and K/Al ratios indicates intensification of chemical weathering around 25 kyr BP. This change in weathering intensity is synchronous to dropping of sea level due to onset of glaciation. This sea-level regression and sudden rise in CaCO₃ concentration during this period point to weathering of additional surface exposed in the shelf regions. This enhanced weathering of the shelf sediments may have contributed to the atmospheric CO₂ level during the glacial period.

How to cite: Tripathy, G. R., Negi, P., Rout, R. K., and Bhushan, R.: Weathering of shelf sediments exposed during a glacial period: Evidence from geochemistry and Sr-Nd isotopes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14346, https://doi.org/10.5194/egusphere-egu24-14346, 2024.

Measurements of the air trapped in Antarctic ice cores reveal that atmospheric CO₂ concentration (pCO₂) during the Last Glacial Maximum (LGM) was about 80 ppmv lower than that recorded during the current Holocene interglacial (Bereiter et al., 2015). Studies also show a strong link between pCO₂, ice volume and Antarctic temperature, suggesting pCO₂ as a forcing or amplifying factor behind glacial/interglacial cycles (Petit et al., 1999; Parrenin et al., 2013). Despite such importance in the global climate changes, mechanisms behind rapid variations in pre-anthropic pCO₂ remain elusive. Numerical models emphasized the crucial role of exported marine productivity P_exp, (namely, the Soft Tissue Pump) in such changes. In particular, they feature marine productivity patterns from the Southern Ocean and show that a decrease in P_exp in the Sub-Antarctic zone, linked to a reduction in iron inputs from aeolian dusts, could have increased pCO₂ by 20 to 50 ppmv (Köhler and Fischer, 2006; Martínez-Garcia et al., 2009; Lambert et al., 2012). However, these studies are usually compared to proxy data from the Atlantic sector of the Subantarctic Zone i.e., an area under the direct influence of wind fields that makes it possible to test the “Fe-hypothesis” (Martin et al., 1990) but that is not necessarily representative of the entire ocean (e.g. Lambert et al., 2015). Due to a lack of recent P_exp data compilation but also of direct comparisons with model outputs integrating marine biogeochemistry­­, it remains difficult to understand the role marine biological productivity exerted on the carbon cycle and more specifically on the low pCO₂ during the LGM.

The aim of this study is to explore P_exp patterns during the LGM compared to the pre-industrial Holocene and understand the mechanisms driving their global changes, in order to try and estimate the contribution of marine productivity to the pCO₂ signalbased on (i) a new compilation of P_exp proxy data using the strategy previously proposed by Kohfeld et al. (2005) after Bopp et al., (2003), and (ii) a comparison of these data to outputs from the iLOVECLIM intermediate complexity.

Proxy data show that P_exp is generally higher during the LGM compared to the pre-industrial Holocene. This is particularly the case in the sub-Antarctic and sub-Arctic areas, in the equatorial Atlantic Ocean and in coastal upwelling settings i.e., regions that usually witness higher nutrient content due to revigorated ocean circulation and/or intensified surface winds. Simulations generally confirm such features except from the coastal upwelling and the Southern Ocean, due to a lack of spatial resolution and of aeolian inputs in the model, respectively. However, preliminary results from sensitivity tests show (i) net marine productivity fronts around ~40°N and 45°S due to extended sea ice cover and reduced global temperature, (ii) a decreased P_exp in the Pacific Ocean due to an overall thermohaline circulation slow down and (iii) an increase of P_exp in areas where fertilization by iron-rich dusts is expected (Lambert et al., 2021).

How to cite: Depuydt, P., Duchamp-Alphonse, S., Bouttes, N., Guarnieri, C., Karsenti, A., Yang, J.-W., Peterschmitt, J.-Y., and Landais, A.: Impact of marine productivity on atmospheric pCO2 during the Last Glacial Maximum: a model-data comparison, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14882, https://doi.org/10.5194/egusphere-egu24-14882, 2024.

The deep Southern Ocean (SO) circulation is of major significance for the understanding of the ocean´s impact on Earth’s climate as uptake and release of CO₂ strongly depend on the redistribution of well and poorly ventilated water masses.

Neodymium isotopes (εNd) preserved in deep sea sediment have proven useful to study the Deep Ocean Circulation and water mass provenance and are of special interest over major climate changes as the Mid Pleistocene Transition (MPT). The MPT marks the change from a 41 ka to a 100 ka glacial-interglacial cyclicity and goes along with a significant intrusion of southern sourced waters (SSW) in the deep North Atlantic.

Here, we present the first millennial resolved authigenic εNd data in the Southern Atlantic spanning across  the MPT of a deep sea sediment core positioned at the polar front. The pre-MPT εNd values of ODP 1093 show a small variability of approx. 2 ε-units around the modern AABW signature of -8. In contrast, the post-MPT εNd variability increases to 6 ε-units with glacial extremes of around -3 – εNd values that can not be found in any Atlantic sourced water mass today!

This supports not only the exsiting hypotesis of stonger SSW export to the North, but rather advocates for a radiogenic  watermass influencing the flow regime in the Atlantic south of the polar front. Increasing ice volume during post-MPT glacials has been argued to lead to a reduced AABW production. Due to continuity of flow, this opens up the possiblity of glacial intrusion through the Drake passage of a water masses likely originating in the Pacific, which would generate  the strongly radiogenic glacial εNd values. At present Pacific deep waters are enriched with respired carbon. Assuming this to hold true in the past, the intrusion of such carbon rich water masses into the deep South Atlantic could further reinforce the strong glacials and the overall global cooling trend after the MPT as suggested previously.

Hence, the SO south of the polar front played a leading role in  reinjecting respired CO₂ into the deep Atlantic Ocean and the Atmosphere during climate transitions. 

How to cite: Rückert, E. M. and Frank, N.: Significant change in the flow regime in the deep Southern Ocean through the MPT, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14929, https://doi.org/10.5194/egusphere-egu24-14929, 2024.

Dansgaard-Oeschger (DO) and Heinrich (H) events are ubiquitous features of glacial climates involving abrupt and large changes in climate over the North Atlantic region, extending also to the Southern Hemisphere through the bipolar seesaw mechanism. Ice core data also indicate that the DO and H events are accompanied by pronounced changes in atmospheric CO₂ concentration, but their origin remains uncertain. Here, we use simulations with the fast Earth system model CLIMBER-X, which produces self-sustained DO events as internal variability, to explore the processes involved in the atmospheric CO₂ response. While the DO events are internally generated in the model, the Heinrich events are mimicked by adding a freshwater flux of 0.05 Sv over 1000 years in the latitudinal belt between 40°N and 60°N in the North Atlantic.
The simulated Greenland temperature varies by ~7-8°C between stadials and interstadials, with only small differences between H and DO stadials, while Antarctic temperature responds substantially stronger to H than to DO events, broadly in agreement with observations. In the CLIMBER-X simulations, atmospheric CO₂ varies by ~5 ppm during DO events, but by ~15 ppm during H events, comparable with ice core data. The peak in CO₂ concentrations is delayed by several centuries relative to both the stadial-interstadial transition and the peak in Antarctic temperature. The CO₂ rise during the H stadial is driven by ocean outgassing. In contrast, the rapid CO₂ increase after the transition to the interstadial results from soil carbon release from high NH latitudes originating from substantial warming.

How to cite: Willeit, M., Dalmonech, D., Liu, B., Ilyina, T., and Ganopolski, A.: Exploring the differing CO2 response to Dansgaard-Oeschger and Heinrich events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15214, https://doi.org/10.5194/egusphere-egu24-15214, 2024.

Evidence from both marine and ice cores strongly indicates that surface ocean processes influencing air-sea gas exchange of the Southern Ocean played a crucial role in the transition from a glacial to interglacial climate state. However, few archives have been able to reconstruct how high latitude surface ocean processes affected the biogeochemical changes occurring in nutrient utilization, primary productivity, and their effects on carbon sequestering in ecosystems. An opportunity to explore these processes is provided by accumulated snow petrel (Pagodroma nivea) stomach oil deposits, defensively regurgitated by snow petrels at their nest sites. These deposits provide a record of biogeochemical processes in the austral summer, at a high trophic level and integrated over a relatively wide area defined by snow petrel foraging range. Here, we present a joint carbon and nitrogen stable isotope record from stomach oil deposits from the Lake Untersee nunataks in Dronning Maud Land (DML) integrating data from a coastal area of 65-70°S. Our results show a 3‰ offset in δ¹³C and 4‰ offset in δ¹⁵N between LGM and Holocene, indicating that the coastal high latitudes underwent large changes over the deglaciation. The δ¹⁵N depletion into the Holocene shows strong similarity to changes occurring in nutrient utilization along the margin of the polar front, indicating that the Southern Ocean high latitudes were not an isolated oasis during the LGM but biogeochemically connected to the surface ocean beyond the summer sea-ice margin. In addition, the presence of stomach oil deposits indicates that open water was present in summer along the coast of DML over both the LGM and Holocene. Such highly productive, open water areas were potentially an important factor in the air-sea gas exchange contributing to the deglacial atmospheric CO₂ -rise.

How to cite: Damm-Johnsen, T., Bentley, M. J., Gröcke, D. R., Hodgson, D., and McClymont, E. L.: Carbon and nitrogen stable isotopes across the last deglaciation: perspectives from snow petrel stomach oil deposits, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15672, https://doi.org/10.5194/egusphere-egu24-15672, 2024.

The last glacial maximum (LGM) is the most recent time period in Earth’s history with a climate that was much colder than the present. Robust temperature reconstructions from this period are needed to improve estimates of Earth's climate sensitivity and aid in future climate change projections. However, reconstructing sea surface temperatures (SSTs) during this period can be challenging due to the various limitations with the commonly used proxies. Here, we present new SST estimates from the Alboran Sea in the Western Mediterranean, an area where existing SST records for the LGM (derived from UK37, TEX86, planktic foraminiferal Mg/Ca) show large disagreements. Our new SST estimates are based on clumped isotope analyses of planktic foraminifera (G. bulloides), the same species as used for the Mg/Ca measurements in this area. Due to the insensitivity of the clumped isotope thermometer to changes in seawater chemistry, our results offer new independent constraints on the range of temperature shifts between glacial and interglacial periods in this area. Our findings are evaluated against existing SST estimates, highlighting the benefits and limitations of different proxy estimates. We find that while all proxies agree on the general millennial scale temperature trends during the period of deglaciation, they diverge in the magnitude of these temperature changes. Temperature reconstructions derived from clumped isotopes align more closely with those based on alkenone and Mg/Ca proxies than with those from TEX86, which show large differences. Our research demonstrates that clumped isotopes are a potentially effective tool to improve the accuracy of climate reconstructions from the LGM and the subsequent deglacial period.

How to cite: Fernandez, A., Rodríguez-Sanz, L., Taylor, V., Meckler, N., and Martínez-Ruiz, F.: Bridging Proxy Discrepancies: SST Reconstructions from the Alboran Sea During the Last Glacial Maximum and Deglaciation. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16591, https://doi.org/10.5194/egusphere-egu24-16591, 2024.

The ocean contained a larger carbon content at the Last Glacial Maximum (LGM, ~21kyr before present) compared to the late Holocene, making a considerable contribution to the deglacial atmospheric CO₂ rise of about 90 ppm. Yet, there’s no consensus on the mechanisms controlling the glacial-interglacial changes in oceanic carbon storage due to uncertainties and sparseness of proxy data. Numerical simulations have been widely used to quantify the impact of key factors, such as changes in sea surface temperatures, ocean circulation and biological production, on glacial ocean carbon sequestration. However, the robustness of these findings is subject to further testing due to the differences in process representation, parameterization, model architecture, or external forcing employed by models.

Towards further constraining the LGM ocean carbon cycle, we conducted a multi-model comparison with three comprehensive Earth System Models (Alfred Wegener Institute Earth System Model, AWI-ESM; Community Earth System Model, CESM; Max Planck Institute Earth System Model, MPI-ESM) and one Earth system Model of Intermediate Complexity (CLIMBER-X). We carried out three coordinated experiments with each model: 1) PI (the pre-industrial control simulation), 2) LGM-PMIP (following PMIP4 LGM protocol) and 3) LGM-LowCO2 (as LGM-PMIP, but with boosted alkalinity inventory to lower atmospheric CO₂ to about 190 ppm. All experiments were conducted with the prognostic CO₂ for the carbon cycle, considering only the atmosphere and ocean reservoirs, and prescribed CO₂ for radiative forcing.

All models consistently show that applying the PMIP4 LGM boundary conditions alone leads to only a 5-40 ppm decrease in atmospheric CO₂. Globally, the glacial CO₂ drawdown in LGM-PMIP is mainly controlled by the enhanced solubility pump. The spatial distribution of the increased glacial DIC depends on the ocean circulation state in each model. In MPI-ESM and CLIMBER-X, the shallower and weaker AMOC facilitates carbon storage in the deep Atlantic. An LGM atmospheric CO₂ of 190 ppm can be achieved by boosting alkalinity by 5-8% in scenario LGM-LowCO2. In all models, boosting LGM alkalinity inventory increases DIC in the bottom water. However, comparison to proxy data reveals that the models lack respired carbon, particularly in the deep Pacific. This suggests a need to enhance the glacial biological carbon pump in the models.

How to cite: Liu, B., Ilyina, T., Brovkin, V., Willeit, M., Ye, Y., Völker, C., Köhler, P., Heinemann, M., Kurahashi-Nakamura, T., Paul, A., Schulz, M., Merkel, U., and Lhardy, F.: Constraining glacial ocean carbon cycle – A multi-model study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17501, https://doi.org/10.5194/egusphere-egu24-17501, 2024.

The ability of the deep ocean to store and exchange large quantities of CO₂ with the atmosphere on relatively short timescales means that it is thought to play a key role in dictating glacial-interglacial changes in atmospheric CO₂, however records of deep ocean carbon storage and release remain sparse. The Pacific Ocean contains the largest store of carbon in the ocean-atmosphere system. As a result, changes in its circulation dynamics and biogeochemistry have the potential to significantly impact global climate. Despite this, changes in Pacific conditions and carbon storage over the last glacial cycle are poorly constrained.

Here we present new geochemical proxy records from abyssal, deep, and intermediate depths in the Southwestern Pacific to determine the changes in deep ocean carbon storage over the last glacial cycle and the mechanisms involved in driving these changes. Foraminiferal trace element and stable isotope data indicate that increased carbon storage occurred over the course of the last glaciation, promoting a drawdown in atmospheric CO₂. The processes involved in driving glacial ocean carbon storage are debated, however proxy data from these sites indicate that changes in circulation dynamics promoting the isolation and expansion of deep Pacific waters was likely a key process involved. Comparison of δ¹³C data to box model and Earth system model output provides further insight into the physical as well as biogeochemical mechanisms involved and their relative contributions at different stages over the last glacial cycle. This includes the role of Southern Ocean sea-ice expansion, reduced ocean temperatures, and increased Southern Ocean stratification and biological productivity. We find that physical processes dominate the early in the glacial cycle, with biological processes promoting further drawdown as glacial conditions intensify. These results help to improve the understanding of deep ocean carbon cycling over the last glacial cycle and provide a new framework with which to interpret proxy δ¹³C data.

How to cite: Pelly, M., Shankle, M., Trudgill, M., Millet, B., Xu, C., Owens, G., Owen, H., Foreman, A., Bauska, T., Ridgwell, A., Michel, E., Gray, W., Burke, A., and Rae, J.: Physical and biological controls on deep Pacific carbon storage over the last glacial cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17778, https://doi.org/10.5194/egusphere-egu24-17778, 2024.

Reduced ice volume during interglacials is hypothesized to amplify volcanic activity because ice-mass removal reduces pressure on magma chambers (Huybers & Langmuir, 2009). There is some evidence for this process occurring on regional (Maclennan et al., 2002) and perhaps semi-global scales (Kutterolf et al., 2019), but there is a lack of globally representative tephra production records. Therefore, our understanding of the global relationship between glacial-interglacial cycles and volcanism uncertain. As a result, we do not know whether deglaciation directly drives enhanced volcanism, or if the feedbacks are more complex. In this work we use a database of visible tephra layers in marine sediments, and a weighted bootstrap resampling method to develop a record of global tephra (the products of explosive volcanism) production which covers the past million years.

Our results show an intensification of global tephra production around 420 to 400 thousand years ago (ka), which coincides with Marine Isotope Stage (MIS) 11 – the warmest interglacial of the past million years. MIS11 was a period of high sea level (up to 10 m above present) and low ice cover, with Greenland likely largely ice free. We suggest the low ice levels drove enhanced volcanism, and consequently enhanced volcanic carbon dioxide degassing, which in turn drove further ice sheet ablation. This positive feedback may the explain this warmth, and in turn, the Mid-Brunhes transition, which heralded the arrival of generally warmer interglacials after 400 ka. Further, after 400 ka we begin to see cyclicity in the tephra record, mirroring eccentricity forcing seen in ice volume records. More pronounced ice-volcano feedbacks may therefore explain the stronger interglacials of the past 400,000 years.

References

Huybers, P., & Langmuir, C. (2009). Feedback between deglaciation, volcanism, and atmospheric CO2. Earth and Planetary Science Letters, 286(3–4), 479–491.

Kutterolf, S., Schindlbeck, J. C., Jegen, M., Freundt, A., & Straub, S. M. (2019). Milankovitch frequencies in tephra records at volcanic arcs: The relation of kyr-scale cyclic variations in volcanism to global climate changes. Quaternary Science Reviews, 204, 1–16.

Maclennan, J., Jull, M., McKenzie, D., Slater, L., & Grönvold, K. (2002). The link between volcanism and deglaciation in Iceland. Geochemistry, Geophysics, Geosystems, 3(11), 1–25.

How to cite: Longman, J., Gernon, T. M., Hincks, T. K., Panitz, S., and Palmer, M. R.: A million-year reconstruction of global volcanism intensity: How does it link to glaciation?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17827, https://doi.org/10.5194/egusphere-egu24-17827, 2024.

The ocean plays an essential role in the rise of atmospheric CO₂ by about 90 ppmv during the last deglaciation. The deglacial oceanic CO₂ outgassing is jointly controlled by the physical, biological and geochemical processes, which affect the variations in ocean circulation, biological carbon pump and alkalinity inventory. Transient simulations of climate-carbon feedback, particularly using the comprehensive Earth System Models, are instrumental tools to quantify the contribution of different processes and their interactions. Nonetheless, knowledge gaps still exist in the deglacial variations of oceanic carbon and nutrient cycling because considerable model uncertainties arise from the choices of model processes and parameters, and the proxy data is too sparse to fully constrain the model outcome.

We conduct transient simulations for the last deglaciation with the Max Planck Institute Earth System Model (MPI-ESM) and examine the impact of different model tuning of the global ocean biogeochemistry component and a sediment module on the deglacial CO₂ outgassing. The atmospheric CO₂ is prognostically computed for the carbon cycle, considering only the atmosphere and ocean compartments, and it is prescribed for radiation computation. We force the model with reconstructions of atmospheric greenhouse gas concentrations, orbital parameters, ice sheet and dust deposition. In line with the physical ocean component, we account for the automatic adjustment of marine biogeochemical tracers in response to changing bathymetry and coastlines related to deglacial meltwater discharge and isostatic adjustment.

We find the deglacial CO₂ outgassing is mainly driven by the sea surface warming in MPI-ESM, whereas variations in surface alkalinity and DIC have a relatively small contribution (~18%). Furthermore, the parameterisation of organic debris remineralisation considerably affects the deglacial increase in the global NPP due to different recycling rates of nutrients in the upper ocean. When a longer lifetime of dissolved organic matter is prescribed, the dissolved organic carbon pool in the glacial ocean increases, further facilitating the glacial ocean carbon sequestration. Including an interactive sediment module strongly impacts surface alkalinity due to input-sedimentation imbalance, affecting air-ocean CO₂ flux. Thus, attention has to be given to tuning and adjustments regarding the input-sedimentation imbalance of alkalinity in ESMs to better represent proxy data and the deglacial oceanic CO₂ outgassing.

How to cite: Liu, B. and Ilyina, T.: Quantifying the role of ocean biogeochemistry on the deglacial atmospheric CO2 rise using transient simulations with MPI-ESM, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18082, https://doi.org/10.5194/egusphere-egu24-18082, 2024.

Understanding the evolution of deep ocean circulation and chemistry over the last glacial cycle is key to elucidating the ocean’s role in modulating atmospheric CO₂ changes on millennial and orbital timescales. MIS 4 is a key paleoclimatic interval of the last glacial inception for assessing the role of the deep-ocean carbon storage in driving atmospheric CO₂ levels, because it is characterized by a large decrease of air temperature and a rapid atmospheric CO₂ drop of ~40 ppmv, and includes several millennial climatic events, for example Heinrich Stadial 6. Although various paleo proxy records suggest a weakened Atlantic overturning during MIS 4, and particularly HS 6, changes in AMOC strength and the geometric extent of NADW shoaling remain poorly understood. Here, we present deep-water temperature reconstructions based on infaunal benthic foraminiferal Mg/Ca ratios and bottom water oxygen concentration reconstructions using redox-sensitive foraminiferal U/Ca, from the deep North (~2.65km) and South (~3.8km) Atlantic to assess the changes in deep water hydrography and by extension circulation.

Our reconstructed deep-water temperature changes from the Iberian Margin (~2.65 km water depth) suggest a stronger influence of colder southern sourced waters during MIS 4 and particularly during HS 6; and a clear subsurface warming during MIS 5a stadials. Meanwhile, changes in deep-water temperatures in the Atlantic Sector of the Southern Ocean (SO) closely follow variations in Antarctic temperature, atmospheric CO₂ and the mean ocean temperature, likely mediated by buoyancy forcing in the SO, which is in turn likely linked to sea-ice expansion at the MIS 5a/4 transition. Together with (arguably smaller) contributions from reduced air-sea gas exchange efficiency in the SO, these combined changes would have lowered atmospheric CO₂through more efficient carbon sequestration in an expanded deep Atlantic reservoir during MIS 4, through their impact on the solubility- and soft tissue “pumps” (i.e. the ocean’s disequilibrium and respired carbon budgets). Indeed, bottom water oxygenation reconstructions from the South Atlantic support the conclusion that the Southern Ocean appears to have represented a significant reservoir for sequestering CO₂ away from the atmosphere during MIS 4.

How to cite: Radionovskaya, S., Gottschalk, J., Thornalley, D., Greaves, M., and Skinner, L.: Mechanisms of atmospheric CO2 drawdown during Marine Isotope Stage 4 based on Atlantic deep-water temperature and bottom-water oxygenation reconstructions , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18786, https://doi.org/10.5194/egusphere-egu24-18786, 2024.

The Pacific Ocean equatorial upwelling region is of great interest to understand climate dynamics within the context of current global change. It plays a key role in global biogeochemical cycles, especially in the carbon cycle, as it stands for being one of the areas with largest CO₂ fluxes from the ocean to the atmosphere. Moreover, tropical regions play a key role in regulating global climate, since they control the transfer of thermal energy from low to high latitudes. In this context, and with the aim of reconstructing paleoclimate conditions at glacial-interglacial time scales in this region, we analysed selected molecular biomarkers in the marine sediment core ODP 1240, at the easternmost region of the Eastern Equatorial Pacific (EEP), covering the last 160 kyr. We focused on long-chain alkenones, glycerol dialkyl glycerol tetraethers (GDGTs) and long-chain alkyl diols (LCDs). Upon quantification of these lipids, we calculated the U^K'₃₇, TEX^H₈₆ and LDI indices, and discussed their suitability as paleotemperature proxies to reconstruct sea surface conditions in the study region. We found that U^K'₃₇ and TEX^H₈₆ derived-temperatures track the warming and cooling trends typical of glacial-interglacial variations. However, while they provide similar temperatures during the last two interglacial maxima, they disagree during glacial periods, when the TEX^H₈₆-based estimations display significantly cooler temperatures. The LDI-derived record also shows similar temperatures to those from the U^K'₃₇ and TEX^H₈₆during the more recent interglacial but, for the last glacial-interglacial period, LDI-derived temperatures remain colder than those of the U^K’₃₇ and even colder than those of the TEX^H₈₆ at some periods. Multiple factors could be behind this variability and disagreement between the three paleothermometers: depth dwelling, production or exportation of the different biological producers of each lipid, seasonality, diagenetic processes and changes in biogeochemistry conditions of the studied marine region, amongst others. In this presentation, the factors that we believe are most important in the study region will be presented and discussed, to improve our understanding of the biological dynamics of the precursors of each proxy and of their reconstructed marine temperatures in the EEP.

How to cite: Calvo, E., Quirós-Collazos, L., Rodrigo, M., Schouten, S., Sinninghe-Damsté, J., Pena, L., Cacho, I., and Pelejero, C.: Sea surface temperature variations in the Eastern Equatorial Pacific (ODP Site 1240) over the last 160 kyr from three lipid paleothermometers (UK'37, TEXH86 and LDI), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19515, https://doi.org/10.5194/egusphere-egu24-19515, 2024.

During the last deglaciation large proglacial lakes formed at the base of the retreating northern hemisphere ice sheets. We assess the effect of these ice-contact lakes on regional climate and on the ice sheet surface mass balance components of the adjacent  Laurentide (LIS) and Fennoscandian (FIS) ice sheets,  using an atmosphere general circulation model with a novel extension for proglacial lakes in combination with a surface mass balance scheme for ice sheets, which, for the first time, allows to estimate the effect of the cold surface of these extensive lakes on the surface mass balance of the adjacent ice sheets. In a set of simulations inspired by the  Allerød interstadial around 13000 years before present, we demonstrate that the presence of proglacial lakes significantly reduces summer air temperatures in a larger area around the proglacial lakes and leads to reduced precipitation with increased snow/rain ratio. In consequence surface ablation reduces by 39% over the FIS and 28% over the LIS while accumulation only changes slightly by 1% and -3%  respectively. About one quarter of the response in surface ablation is related to the perennially cold surface of the proglacial lakes.

How to cite: Krebs-Kanzow, U., Sijbrandij, L., Knorr, G., Ackermann, L., Niu, L., and Lohmann, G.: The influence of proglacial lakes on climate and surface mass balance of retreating ice sheets: A study of the Laurentide and Fennoscandian ice sheets at 13 ka BP, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19780, https://doi.org/10.5194/egusphere-egu24-19780, 2024.

Geothermal heat flow (GHF) is the dominant factor affecting the basal thermal regime of ice sheet dynamics. But it is poorly defined for the Antarctic ice sheet. We compare basal thermal state of the Totten Glacier catchment as simulated by eight different GHF datasets. We use a basal energy and water flow model coupled with a 3D full-Stokes ice dynamics model to estimate the basal temperature, basal friction heat and basal melting rate. In addition to the location of subglacial lakes, we use specularity content of the airborne radar returns as a two-sided constraint to discriminate between local wet or dry basal conditions and compare them with the basal state simulations with different GHF. Two medium magnitude GHF distribution maps derived from seismic modelling rank well at simulating both cold and warm bed regions, the GHFs from Shen et al. (2020) and Shapiro and Ritzwoller (2004). The best-fit simulated result shows that most of the inland bed area is frozen. Only the central inland subglacial canyon, co-located with high specularity content, reaches pressure-melting point consistently in all the eight GHFs. Modelled basal melting rates in the slow-flowing region are generally 0-5 mm yr^-1 but with local maxima of 10 mm yr^-1 at the central inland subglacial canyon. The fast-flowing grounded glaciers close to Totten ice shelf are lubricating their bases with melt water at rates of 10-400 mm yr^-1.

How to cite: Zhao, L., Huang, Y., Wolovick, M., Ma, L., and Moore, J.: Using specularity content to evaluate eight geothermal heat flow maps of Totten Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2403, https://doi.org/10.5194/egusphere-egu24-2403, 2024.

The influence of supraglacial debris cover on glacier dynamics in the Karakoram is noteworthy. However, the investigation of how debris cover affects the seasonal and long-term variations in glacier mass balance through alterations in the glacier's energy budget is scarce. The present study applied an energy-mass balance model coupling heat conduction within debris layers on Batura Glacier in Hunza valley, renowned as the most representative debris-covered glacier in the Karakoram, to demonstrate the influence of debris cover on glacial surface energy and mass exchanges. The mass balance of Batura Glacier is estimated to be -0.262 ± 0.561 m w.e. yr-1, with debris cover accounting for 45% of the mass balance variation. Due to the presence of debris cover, a significant portion of the energy income is utilized for heat conduction within the debris layer, reducing the melt latent heat at the glacier surface. We found that the mass balance reveals a pronounced arch-shaped structure along the elevation gradient, which primarily attributes to the distribution of debris thickness and the impact of debris cover on the energy structure within various elevation zones. Through a comprehensive analysis of the energy transfer within each debris layer, we have demonstrated that the primary impact of debris cover lies in its ability to modify the energy reaching the surface of the glacier. Thicker debris cover results in a smaller decrease in temperature between debris layers and the ice-contact zone, consequently reducing heat conduction. Over the past two decades, Batura Glacier has maintained a relatively small negative mass balance, owing to the protective effect of debris cover. The glacier exhibits a tendency towards a smaller negative mass balance, with diminishing dominance of ablation at the glacier terminus on glacier mass changes. 

How to cite: Zhu, Y., Liu, S., Brock, B. W., Xie, F., and Yi, Y.: Controls on the relatively slow thinning rate of a debris-covered glacier in the Karakoram over the past 20 years: evidence from mass and energy budget modelling of Batura Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2585, https://doi.org/10.5194/egusphere-egu24-2585, 2024.

The drainage catchments of the neighbouring Thwaites and Pine Island Glaciers, situated in the Amundson Sea Embayment, West Antarctica, contain sufficient ice to raise global mean sea level by a meter. In recent years, significant scientific attention has been given to the potential for sustained retreat of these glaciers as a possible pathway towards widespread deglaciation of the marine-based West Antarctic Ice Sheet. Some recent studies have demonstrated that the Thwaites Ice Shelf provides only limited buttressing to the upstream grounded ice, suggesting limited sensitivity to the melt-driven loss of the ice shelf.

We use the BISICLES ice sheet model to perform a series of 1000-year model experiments on the Amundson Sea domain. A synthetic sub-shelf melt rate is selectively applied to the Pine Island, Thwaites and Crosson/Dotson basins or combinations of those basins. We find that over millennial timescales, Thwaites is relatively insensitive to melt-driven thinning of its ice shelf, with its grounding line rapidly restabilising ~60km upstream of its current location. The same melt forcing applied to Pine Island Glacier leads to widespread deglaciation of the Pine Island catchment and significant retreat in the neighbouring Thwaites catchment despite the lack of melting there. Applying melting simultaneously in the Thwaites and Crosson/Dotson basins leads to widespread deglaciation that is much greater than the sum of its parts. This retreat is driven by a feedback between the ice fluxes crossing the basin boundary.

We also conduct further experiments to determine the melt rates or additional processes required to trigger retreat of Thwaites Glacier in isolation. The results of our experiments support the suggestion that the Thwaites ice shelf provides limited buttressing, while also demonstrating that Thwaites is still vulnerable to retreat via other pathways.

How to cite: Trevers, M., Payne, A., Cornford, S., and Gasson, E.: Retreat of Thwaites Glacier, West Antarctica, triggered by its neighbours., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3996, https://doi.org/10.5194/egusphere-egu24-3996, 2024.

In recent decades glaciers in the Amundsen Sea Embayment in West Antarctica have undergone substantial changes, including widespread retreat and acceleration. The subsequent mass loss caused the largest contribution to sea level rise from the entire Antarctic Ice Sheet. These changes have led to concerns about the stability of the region and the implications of future climate change. Recent modelling results show that one of the largest and fastest flowing of these glaciers, Pine Island Glacier (PIG), has already undergone an unstable and irreversible retreat in its recent history, when it detached from a subglacial ridge between the 1940s and 1970s.

Here we use the ice-flow model Úa to study the sensitivity of this retreat to changes in basal melting. We show that an intermittent increase in basal melting would have been sufficient to force PIG into a retreat from its stable position on the ridge. Once high melting begins upstream of the ridge, only near-zero melt rates can stop the retreat. Our results suggest that unstable and irreversible responses to warm anomalies are possible, and this can lead to substantial changes in ice flux over relatively short periods of only a few decades.

How to cite: Reed, B., Green, M., Jenkins, A., and Gudmundsson, H.: Melt sensitivity of irreversible retreat of Pine Island Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4001, https://doi.org/10.5194/egusphere-egu24-4001, 2024.

State-of-the-art ice sheet model simulations used in the Ice Sheet Model Intercomparison Project (ISMIP) show a mismatch with recent observations of dynamic ice sheet change. In particular, the difference between the modeled and observed cumulative mass balance trend over the last several decades calls into question the accuracy of current projections of ice sheet contribution to sea level rise. Here, we use one of these models, the Ice-sheet and Sea-level System Model, to investigate how transient calibration may improve model hindcasts of ice dynamics and impact projections. Transient calibration is a relatively new capability in ice flow models; it uses a time series of observations to invert for uncertain model parameters, such as basal friction and ice rheology. With more observational constraints than the common snapshot inversion method, transient calibration has been shown to better capture trends and to have the ability to estimate how parameters evolve through time. We apply this method to Northwest Greenland, a region undergoing rapid changes that also has high-resolution, high-accuracy data for bed topography, ice surface velocity, and ice front positions. We find that transient calibration brings hindcast simulations of cumulative mass balance to within observational error. We also find that, when the basal friction parameter is allowed to vary, transient calibration can help mimic the impacts of subglacial hydrology and reproduce observations of seasonal velocity variability. Future simulations to 2100 using the ISMIP6 protocols show that the use of transient calibration leads to greater mass loss and, in the near term out to 2050, has a greater impact on mass balance than the choice of climate forcing scenario.

How to cite: Badgeley, J., Seroussi, H., and Morlighem, M.: Improving modeled ice dynamics in Northwest Greenland with transient calibration: From multi-decadal trends to seasonal cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4155, https://doi.org/10.5194/egusphere-egu24-4155, 2024.

Debris-covered glaciers are found in most glaciated areas in the world and often represent an important water resource for downstream areas. The dynamics of coupled debris and glacier interactions are not fully understood, which is why there has been an increasing effort in recent years to use numerical modelling to gain a better understanding thereof.

As process understanding is quite limited, implementations of the debris-glacier system vary widely. Here we model the glacier in the along-flow dimension and set the focus on debris transport and tracking debris within and on the ice. We examine feasible implementations of involved processes and their coupled effects on glacier dynamics in a transient climate and that allows to vary the location and rate of debris input into the system.

We perform a sensitivity analysis on this model and conduct experiments of increasing complexity, varying both climate forcing and debris deposition and on both simple synthetic and realistic bedrock topographies. Our modelling corroborates the earlier finding from earlier simpler models (without internal debris tracking) of strongly delayed retreat that only sets in after stagnation of the tongue. Our results show beyond that after retreat following warming, debris covered glaciers show a long-term re-advance effect, even when the absolute debris entrainment rate stays the same. We explain this by the increase of the debris-ice ratio in the debris deposition zone. Interestingly, results also show that – when accompanied with a permanent, regular supply of debris input– single large deposition events can have a sustainable growth effect on the glacier, even after the debris from that event has exited the system. In experiments with below century scale fluctuations in climate and/or debris input the glacier length does not really respond. We conclude that this insensitivity and the response of debris covered glacier in general is not only influenced by debris insulation on the tongue, but is also affected by the long time-scale (centuries) involved in transporting the debris through the glacier system.

How to cite: Hardmeier, F., Ferguson, J. C., and Vieli, A.: Modelling the complex response of debris covered glaciers on variations in climate and debris input , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4943, https://doi.org/10.5194/egusphere-egu24-4943, 2024.

The representation of ice shelf calving in numerical ice models is a new and emerging field in cryospheric modelling. As yet, there has been no systematic, in-depth study of how this process is implemented and whether the results can be trusted. Calving MIP is an ongoing model intercomparison project that seeks to address this issue by providing a common framework for model simulations of ice shelf calving, so that results between different models and approaches can be compared. We find it helpful to distinguish between a calving algorithm, the numerical implementation in a model of how ice is removed due to calving, and a calving law, a law with some physical basis that determines how much ice needs to be removed due to calving. The first phase of Calving MIP experiments are primarily interested in comparing different calving algorithms, whilst future experiments are planned to investigate different calving laws as well as compare simulated results with real world observations.

We present here results from across the cryospheric modelling community from the first phase of Calving MIP experiments investigating calving algorithms as well as future plans for further experiments.

How to cite: Jordan, J.: Calving MIP: Results and conclusions from the first phase of a model intercomparison project into ice shelf calving, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5370, https://doi.org/10.5194/egusphere-egu24-5370, 2024.

The West Antarctic Ice Sheet (WAIS) is losing ice and its annual contribution to sea level is increasing. The future behaviour of WAIS will impact societies worldwide, yet deep uncertainty remains in the expected rate of ice loss. High impact low likelihood scenarios of sea level rise are needed by risk-averse stakeholders but are particularly difficult to constrain. Here we combine traditional model simulations of the Amundsen Sea sector of WAIS with Gaussian process emulation to show that ice-sheet models capable of resolving kilometre-scale basal topography will be needed to assess the probability of extreme scenarios of sea level rise. This resolution exceeds many state-of-the-art continent-scale simulations. Our model simulations show that lower resolutions tend to overestimate future sea level contribution and inflate the tails of the distribution. We therefore caution against relying purely upon low resolution simulations when assessing the potential for societally important high impact sea level rise.

How to cite: Williams, C. R., Thodoroff, P., Arthern, R. J., Byrne, J., Hosking, J. S., Kaiser, M., Lawrence, N. D., and Kazlauskaite, I.: Calculating exposure to extreme sea level risk will require high resolution ice sheet models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8114, https://doi.org/10.5194/egusphere-egu24-8114, 2024.

The observed rapid thinning, speed-up and retreat of the ice in West Antarctica’s Amundsen Sea Embayment might indicate an early stage of a marine ice sheet instability (MISI), potentially leading to the disintegration of the West Antarctic Ice Sheet (WAIS). In general, the stability of a marine ice sheet is strongly linked to the dynamics of its buttressing ice shelves which act as a regulator of the ice discharge into the ocean. Existing numerical modeling studies usually simulated MISI-type WAIS retreat either under prescribed fixed present-day calving front positions (associated with very strong ice-shelf buttressing) or in the absence of ice shelves (neglecting ice-shelf buttressing). These approaches represent extreme cases of realizing ice-shelf buttressing in simulations of a WAIS retreat and comparison between the study results are difficult due to the use of different numerical models and experimental designs. Here we aim to investigate the influence of time-evolving calving fronts and associated buttressing changes in the course of an unfolding WAIS disintegration, based on simulations with the Parallel Ice Sheet Model (PISM). One focus will be on how ice-shelf calving affects MISI retreat rates and the extent of a potential WAIS collapse, i.e., the time evolution and magnitude of the associated sea-level contribution.

How to cite: Feldmann, J., Reese, R., and Winkelmann, R.: Simulated influence of ice-shelf calving on the evolution of a potential West Antarctic Ice Sheet instability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8524, https://doi.org/10.5194/egusphere-egu24-8524, 2024.

We present the concepts and capabilities of IGM (https://github.com/jouvetg/igm), a fast and accessible Python model that simulates the evolution of glaciers at any scale by coupling ice thermomechanics, surface mass balance, and mass conservation. IGM models the ice flow by physics-informed deep learning. Specifically, we use a convolutional neural network, which is trained to minimise the energy associated with high-order ice flow physics. Based on the Tensorflow library, IGM performs a suite of fast, vectorised, and differentiable operations, which can be accelerated with a graphics processing unit (GPU). In turn, this allows fully-parallelised implementations of key model components in glacier modelling applications such as the positive degree day surface mass balance scheme, the enthalpy scheme for modelling the thermal regime of ice, or the integration of a large amount of particle trajectories for modelling debris transportation. As a result, IGM combines coding simplicity and modularity, high computational efficiency, state-of-the-art thermomechanical modelling, and efficient data assimilation thanks to underlying automatic differentiation tools. We demonstrate the capability of IGM for two different applications. First, we present a complete workflow (including OGGM-based data preprocessing, inverse and forward modelling, rendering of results) that allows us to model any mountain glacier in the world within a few minutes requiring only its Randolph Glacier Inventory (RGI) ID. Second, we present an application in paleo glacier modelling by simulating the entire European Alpine ice field (about 800 km long) in high resolution (200 m) during the Last Glacial Maximum.

How to cite: Jouvet, G., Cordonnier, G., Maussion, F., Cook, S., Finley, B., Henz, A., Herrmann, O., Kamleitner, S., Leger, T., Lleshi, K., Mey, J., Scherler, D., and Welty, E.: Capabilities of IGM, a thermo-mechanical glacier evolution model accelerated by deep-learning and GPU, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8997, https://doi.org/10.5194/egusphere-egu24-8997, 2024.

Many numerical models used to simulate ice streams require the specification of control fields representing the slipperiness of the ice/bed interface and local deviations in the assumed rheological properties of the ice. These poorly constrained components of the system are often found by solving an inverse problem given observations of model state variables - typically ice flow speed. However, these inverse problems are generally ill-posed, resulting in degenerate or error-dominated solutions. The clearest way to improve this is to take advantage of additional prior information regarding the control fields. 

In this study, we investigate two ways of using maps of surface fracture, derived from Sentinel-1 satellite imagery, to provide prior information to the inverse problem. We first consider a prior that assumes values of effective viscosity significantly different from Glen's flow law are, for the most part, due to observable fractures. Using Pine Island Glacier as a case study, we investigate the solutions and conditioning of this data-informed inverse problem and compare with a typical heuristic regularisation technique. We find that the inclusion of fracture data results in softness fields that resemble fracture features on floating ice. On grounded ice, despite the prevalence of surface crevassing, the softness fields look no more plausible when fracture data is included - suggesting that the presence of surface fracture is not the largest contribution to our uncertainty in the ice rheology. We go on to investigate the use of timeseries of fracture maps to constrain the evolution of the softness field on ice shelves through time, making the assumption that changes to ice rheology occurring on annual timescales are dominated by the fracturing of ice. We show that this method can result in softness fields that visually mimic fracture patterns on floating ice without significantly affecting the quality of the misfit. Such softness fields could be used to constrain evolution equations in isotropic damage models.

How to cite: Surawy-Stepney, T., Cornford, S. L., and Hogg, A. E.: Using observations of surface fracture to address ill-posed ice softness estimation over Pine Island Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9861, https://doi.org/10.5194/egusphere-egu24-9861, 2024.

It is important that modellers be able to make reasonable projections of ice-sheet loss over the next 50-100 years so that costal planners can make informed decisions. Despite many innovations in modelling and satellite observing, several recent studies show that the agreement between models and the observational record remains poor -- raising concerns about their ability to predict responses to changes in climate on decadal to centennial time scales. A common means to address model-data misfit is via assimilation of satellite data, in which poorly constrained parameters are chosen in a way to minimize this misfit. Data assimilation has been employed extensively, including by many of the models participating in the ISMIP6 intercomparison. However, they are limited to observations at a single point in time (a "snapshot"). Such inversions do not take advantage of the time series of velocity and altimetry observations currently available -- largely due to the complexity and computational expense. The use of Automatic Differentiation makes such approaches possible. The method -- termed "transient assimilation" or "transient calibration" -- provides a physically consistent, time-dependent model which agrees with time-resolved observations.

But with such a development, questions arise: how does transient calibration impact future modelled behaviour? Which types of observations most strongly constrain models? Are results consistent across different models? Here we apply transient calibration to the Amundsen Sea Embayment using two independent models, the Ice-sheet and Sea-level System Model (ISSM) and the MITgcm STREAMICE model, using time-resolved velocities and surface altimetry from 2004 to 2017. We assess the performance of transient compared to snapshot calibrations in terms of capturing past and current trends in speed change, thinning, and grounded ice loss; and we additionally run 50-year projections using the calibrated models. While overall 50-year mass loss is not strongly dependent on assimilation strategy, the rates of mass loss vary greatly, suggesting greater differences on the century time scale or longer. Moreover, we see that the runs calibrated with altimetry: (i) agree best with recent mass loss rates; (ii) show the greatest conformity between models; and (iii) show the largest mass loss rates at the end of the 50-year runs. The results likely have implications for optimal data needs and assimilation strategies in the next generation of ice-sheet models.

How to cite: Goldberg, D. and Mathieu, M.: Transient calibration of the Amundsen Sea Embayment: a model and methodology comparison, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10305, https://doi.org/10.5194/egusphere-egu24-10305, 2024.

There are many uncertainties associated with natural processes governing the evolution of glaciers and ice sheets. Unknown parameters, such as basal drag or surface mass balance, can be estimated through data assimilation workflows coupled with physics-based models of ice flow. The multi-scale nature of ice dynamics and significant spatial and temporal variations in physical properties challenges accurate estimations of distributed fields of unknown parameters. High-performance computing and modern computational architectures such as graphics processing units (GPUs) enable efficient and scalable solvers for the ice flow.

In this work, we introduce a novel GPU-accelerated inversion framework to enable a point-wise reconstruction of unknown parameter fields at high resolution. The inversion framework is based on the adjoint sensitivity method combined to a gradient-based optimisation. The derivation of the adjoint problem often represents a tedious task which limits the applicability of adjoint-based inversions to simplified ice flow models and hinders fast development. To address these limitations we use differentiable programming and the Julia language which permit automatic differentiation (AD) of arbitrary GPU code. Our GPU-based inversion procedure combines an automatically generated adjoint solver by the Enzyme.jl package using AD and a forward solver to retrieve the point-wise gradient we further use to minimise a cost-function.

We demonstrate the capabilities of our inversion framework by developing a forward solver, based on shallow ice approximation (SIA), and several inverse models, utilising different assumptions about the ice flow. One inversion model assumes that the glacier is in a steady-state, which requires iterative solution of SIA equations. The inversion procedure estimates distributions of sliding coefficient, matching the observed ice thickness, glacier outline, and surface velocities. Another inversion model is based on a "snapshot" approach, in which the surface elevation is fixed from observations, and the sliding coefficient is solved to only match observed surface velocities. These two models represent two end members of the spectrum of data assimilation approaches, which will serve as building blocks for more complex workflows, such as transient evolution of glaciers.

The feasibility of our inversion algorithms is validated through extensive testing on synthetic glaciers. Then we consider the application of our inversion approach to glaciers in the European Alps using remote sensing data. A map of sliding coefficients is reconstructed by matching the observed ice surface velocity and elevation. The successful application to real glaciers confirms that our inversion models are well suited for large scale and high-resolution simulations. We also present the performance testing results demonstrating close-to-optimal performance of forward and inverse models on NVIDIA GPUs.

How to cite: Chen, Y., Utkin, I., Räss, L., and Werder, M.: Constraining the basal sliding of alpine glaciers using adjoint-based inversions and automatic differentiation on GPUs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10817, https://doi.org/10.5194/egusphere-egu24-10817, 2024.

High-end estimates of sea-level change from Antarctica have been derived from simulations using upper-end forcing scenarios and ice-cliff height dependent calving laws. Those have been hypothesised to cause collapse of glaciers in West Antarctica through marine ice cliff instability (MICI). However, some previously published high-end estimate are based on results from a limited number of ice-sheet models, or even only a single ice-flow modelling study. There is, furthermore, low agreement on the implications of some of those calving laws for the West Antarctic Ice Sheet, and limited evidence of MICI having occurred in the past. Here we investigate the dynamic response of West Antarctic glaciers to high-end calving laws using the Úa ice-sheet model. Specifically, we conduct ice-shelf collapse experiments as defined in ABUMIP (Sun et al., 2020) with and without cliff failure mechanism in transient simulations conduced over centennial time scales. We find that the ice-cliff height dependent calving laws can cause glaciers to retreat and collapse from both fast and slow flowing regions. Furthermore, we find that the results are sensitive to numerical resolution near the grounding line. We suggest therefore that ice-sheet modellers always conduct convergence studies when implementing high-end calving laws.

How to cite: Sun, S. and Gudmundsson, G. H.: Revisiting the implications of cliff-height dependent calving law on West Antarctic glaciers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10845, https://doi.org/10.5194/egusphere-egu24-10845, 2024.

Marine ice sheets terminate in the ocean where they form floating ice shelves or calve icebergs.  They can significantly influence sea level because of the potential for rapid transfer of grounded ice (with thickness greater than floatation) to floating ice shelves or icebergs.  Most models of marine ice sheet evolution assume that the bed elevation stays constant, or responds isostatically to the weight of the ice sheet.  However, it is known that there is sediment deformation beneath the ice sheet (which is in part what enables the ice to move), and that deposition of this sediment in the vicinity of the grounding line can result in the formation of a grounding-zone wedge.  Although it is widely recognised that such a wedge can influence the evolution of the grounding line (where the ice becomes afloat), there is incomplete knowledge about the interaction of the ice and sediment/bed dynamics.

In this study, we build on idealised two-dimensional (flow-line) models of a marine ice sheet to investigate the influence of a deforming sediment layer at the bed.  We examine how different conditions lead to the development of a grounding zone wedge, and how this impacts the possible steady states of the model under given climate forcing, and under different assumptions about the sediment dynamics.  We then examine how the sediment dynamics, and the presence of the grounding-zone wedge, influence the stability of the system.

How to cite: Hewitt, I. and Herpain, E.: Evolution of marine ice sheets with bed sedimentation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10934, https://doi.org/10.5194/egusphere-egu24-10934, 2024.

Ice sheets have a memory that is stored within both the geometry and thermal properties of the ice. The current Greenland Ice Sheet is thus not in equilibrium with present-day climate, but is in fact affected by a complex product of past changes that occurred over millennial timescales. Therefore, simulating the late-Pleistocene evolution of the Greenland Ice Sheet accurately is important when running future projections using paleo model initialization procedures. Using a novel model-data comparison procedure, we ran an experiment that aimed to produce numerical model simulations that fit available empirical data on the extent and timing of the grounded margin evolution of the Greenland Ice Sheet from the global LGM (24 kyr BP) to 1850 AD. Given the numerous uncertain parameters and boundary conditions required by numerical ice sheet models, finding simulations which adequately replicate empirical data on past grounded ice extent is a challenging task. In an attempt to address this challenge, we ran a perturbed parameter ensemble of 100 ice-sheet-wide simulations at 5 km spatial resolution using the Parallel Ice Sheet Model. Our simulations are forced by the latest transient paleo-climate and ocean simulations of the isotope-enabled Community Earth System Model (iCESM 1.2 and 1.3). Using quantitative model-data comparison tools and the newly developed, Greenland-wide PaleoGrIS 1.0 isochrone reconstruction of former ice extent, each ensemble simulation’s fit with empirical data was assessed quantitatively across both space and time. Using our best-scoring simulations, we here present new insights into the former Greenland Ice Sheet’s likely response to transitional climatic phases throughout the last deglaciation. Secondly, our results suggest ice temperature, geometry, and glacial isostatic adjustment-induced mechanisms of centennial to millennial-scale inertia in ice-extent response to past climatic forcing, with potential implications for the future evolution of the ice sheet. Thirdly, our results show that different parameter combinations produce a better model-data fit during different time periods and for different regions of the ice sheet – i.e. parameter values that work well at one place or time, produce worse fit at others. We hypothesise that better paleo model initializations may be achieved using time- and space-dependent parameter configurations. Finally, after extending several past ensemble simulations to the end of the 21st century under CMIP6-derived forcing, we find that accounting for the past modifies projections of the future. Using a steady-state contemporary ice sheet as an initial state leads to vastly different projected sea level contributions when compared to simulations that perform well at recreating past glacial history.

How to cite: Leger, T., Ely, J., Clark, C., Bradley, S., Archer, R., and Zhu, J.: Insights into the LGM-to-present evolution of the Greenland Ice Sheet from a data evaluated ensemble of numerical model simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11040, https://doi.org/10.5194/egusphere-egu24-11040, 2024.

The force balance of an ice steam determines its velocity, and along with cross sectional area, influences total flux of glacial ice to the ocean. Satellite datasets provide us strong time series velocity data, while radar, seismics, and geophysical inversion methods yield width and depth estimates within an ice column. However, should an ice stream widen or narrow, the flux of ice to the ocean could change perceptibly. 
Thwaites Glacier’s eastern shear margin is not topographically bounded, but rather arcs across a shallow subglacial rise of intermittent hills and valleys. To determine the stability of the margin it is imperative to understand the force balance and total energy of the glacier system along the shear zone. Driving forces are balanced by normal and shear stresses along the bed, and longitudinal shearing in the margin. The resistance (or lack thereof) creates deformational (frictional-sliding) heating which add energy to the system altering rate factor and meltwater generation, which in turn alter the viscosity and slip factors, making a complex feedback system.
To analyze this system, we develop a 3D full-Stokes flow model in the Elmer/ICE finite element software. The model resolves at 500 m horizontally over realistic surface and bed topography from BedMachinev3. Model domains cover key data acquisition sites from the International Thwaites Glacier Collaboration, Thwaites Interdisciplinary shear Margin Evolution (ITGC TIME) seismic and radar field studies. To determine energy balance, we employ the enthalpy field equations which efficiently solve the thermal field, solve for water content generation, and couple nicely with variable rate factors. Models are initialized by a suite of 1D thermal profiles, converted to enthalpy values, derived from quartile statistics of RACMO2.3p1 surface specific mass balance data, and then advected to steady state flow. 
These models are then run with a flow-coupled glacier drainage system (GlaDS) and enthalpy relation to determine temperate ice distribution, and basal water production. Non-linear Coulomb and Weertman sliding laws are tested between scenarios of natural melt generation, through full drainage piracy of the upper Pine Island catchment, which will determine the effect of spatiotemporal variation in effective pressure (N) on shear margin stability.
Through the suite of spin up models and scenarios, we aim to determine the stability of Thwaites Glacier’s eastern shear margin from perturbations in enthalpy from both sliding friction, and viscous heating from temperate ice generation over non-idealized bed topography and within the shear margin itself. Results will help inform catchment scale transient flow models which aid in determining sea level contribution and West Antarctic Ice Sheet stability.  

How to cite: Martin, C. and Hehlen, M.: An Enthalpy-Hydrology Coupled 3D full-Stokes Flow Model of Thwaites’ Eastern Shear Margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11319, https://doi.org/10.5194/egusphere-egu24-11319, 2024.

Basal shear stress on hard-bedded glaciers results from normal stress against bed roughness, which depends on basal water pressure and cavity size. These quantities are related in a steady state but are expected to behave differently under rapid changes in water input, which may lead to a transient frictional response not captured by existing friction laws. Here, we investigate transient friction using GPS vertical displacement and horizontal velocity observations, basal water pressure measurements, and cavitation model predictions during rain-induced speed-up events at Glacier d'Argentière, French Alps. We observe up to a threefold increase in horizontal surface velocity, spatially migrating at rates consistent with subglacial flow drainage, and associated with surface uplift and increased water pressure. We show that frictional changes are mainly driven by changes in water pressure at nearly constant cavity size. We propose a generalized friction law capable of capturing observations in both the transient and steady-state regimes.

How to cite: Togaibekov, A., Gimbert, F., Gilbert, A., and Walpersdorf, A.: Observing and modeling short-term changes in basal friction during rain-induced speed-ups on an Alpine glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11836, https://doi.org/10.5194/egusphere-egu24-11836, 2024.

Deep learning-based surrogate models have emerged as computationally inexpensive tools for simulating glacier dynamic systems defined by complex, nonlinear partial differential equations. Despite the potential, the application of physics-informed neural networks  (PINNS) in glacier modelling is sparse. Thus, this study explores the potential of  NVIDIA Modulus-Sym, a PyTorch-based framework, in simulating glacier velocities. The framework NVIDIA Modulus-Sym provides ground for building, training and fine-tuning physics-based surrogate models targeting computational fluid problems. This study presents the pipeline to generate glacier velocities using the physics-constraint approach that incorporates the physics regularisation term within the loss function to enhance generalisation performance. The study further emphasises the challenges and limitations of tools in glaciological research. 

Keywords: Deep learning, Surrogate Models, Glacier Dynamics,  Glaciology

How to cite: K C, M., Köstler, H., and Fürst, J.: Exploring physics-informed neural networks for glacier flow., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12564, https://doi.org/10.5194/egusphere-egu24-12564, 2024.

Calving is a key process in the dynamics of marine-terminating glaciers with large ice shelves, such as those in West Antarctica. However, this process is currently not included in most predictive models, due to its difficulty to implement in a general form which can reliably reproduce rates of calving over a range of scenarios. We set out to investigate how important it is to develop such representation of calving for future modelling.

In this study, we quantify the sensitivity of modelled future mass loss to ice front retreat in the Amundsen Sea Embayment, including Pine Island and Thwaites Glaciers. We find that prescribing constant frontal retreat rates from 0.1 to 1 km a_­­^-1 progressively increases the contribution to sea level rise when compared to experiments with a fixed ice front. The result is up to 80% more loss of ice by 2100, and more than triple the ice loss in projections beyond 2200 with the higher rates of retreat. The spatial pattern of ice loss is non-uniformly distributed, with some regions thinning and others thickening as an initial response to the calving front retreat. We identify specific thresholds in the geometry of the system, which have clear effects on the ice flow and are reached at different times depending on the retreat rate.

We compare variability in the range of our results using different retreat rates to that in the range of ISMIP6 ocean forcing products, as ocean-induced melt is known to be a major factor in determining the future evolution of the Antarctic ice sheet. We find that the variability due to these two factors is initially similar, and that variability due to ice front retreat becomes comparatively greater over time. Our results demonstrate the high importance of accurately representing calving processes in models, showing that they are at least as important as ocean forcing and deserve a similar amount of attention in future model development work.

How to cite: Barnes, J., Gudmundsson, G. H., Goldberg, D., and Sun, S.: The importance of calving in ice sheet models: A sensitivity study of ice front retreat in the Amundsen Sea Embayment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12685, https://doi.org/10.5194/egusphere-egu24-12685, 2024.

Antarctic sea ice extent reached a record minimum in 2023. Whilst the buttressing resistance provided by ice shelves has been quantified through past numerical studies, the degree to which sea ice can buttress and regulate upstream ice flow is not known. If significant, a future decline in sea ice extent would lead to increased ice discharge rates and a higher global mean sea level.

The January 2022 disintegration of landfast sea ice in the Larsen B embayment was closely followed by a significant increase in ice flow velocities and retreat rates of numerous outlet glaciers in the region. Notably, Crane glacier saw an initial ~8km retreat over six weeks, during which time a 5% increase in velocity was observed. Afterwards, the full evacuation of ambient sea ice between October and November was accompanied by the most significant monthly increase in velocities.

We use the numerical ice flow model, Ua, to investigate the buttressing effect of sea ice to Crane glacier. The ice-sheet model was initialised with sea ice included and constrained with observational velocity and geometry data sets. We conducted perturbation experiments on sea ice properties to explore its impact on the glacier. The results suggest that sea ice provided significant buttressing to the glacier before its collapse.

How to cite: Parsons, R., Sun, S., and Gudmundsson, H.: Quantifying the Buttressing Contribution of Sea Ice to Crane Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12813, https://doi.org/10.5194/egusphere-egu24-12813, 2024.

Ice fabrics – the alignment of crystal orientations - can cause the ice viscosity to vary by an order of magnitude, consequently having a strong impact on the large-scale flow of ice sheets and glaciers. Because of this, there is a need for fabric models which are computationally efficient enough to be included in large-scale ice sheet models. We examine a range of existing models in this class and show they can be combined into a common equation which is a function of 2-3 parameters. By comparing with observations from the Greenland ice sheet, we get the best model predictions by assuming the ice deforms close to the Sachs hypothesis – that all grains experience the same stress. As these fabric predictions also depend on the flow law used, we provide a test of competing anisotropic flow laws for the first time, making a step towards reliably incorporating the effect of fabric and viscous anisotropy in ice sheet flow models.

How to cite: Richards, D., Mantelli, E., Pegler, S., and Piazolo, S.: Unifying and comparing different models of viscous anisotropy to be included in ice sheet models., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13210, https://doi.org/10.5194/egusphere-egu24-13210, 2024.

We present a physical description of the ice-sheet model Nix v1.0, an open-source project intended for collaborative development. Nix is a 2D thermomechanical model written in C/C++ that simultaneously solves for the momentum balance equations, mass conservation and temperature evolution. Nix's velocity solver includes a hierarchy of Stokes approximations: Blatter-Pattyn, depth-integrated higher order, shallow-shelf and shallow-ice. The grounding-line position is explicitly solved by a moving coordinate system that avoids further interpolations. The model can be easily forced with any external boundary conditions, including those of stochastic nature. Nix has been verified for standard test problems. Here we show results for a number of benchmark tests from standard intercomparison projects and assess grounding-line migration with an overdeepened bed geometry. Lastly, we further exploit the thermomechanical coupling by designing a suite of experiments where the forcing is a physical variable, unlike previously idealised forcing scenarios where ice temperatures are implicitly fixed via an ice rate factor. Namely, we use atmospheric temperatures and oceanic temperature anomalies to assess model hysteresis behaviour with active thermodynamics. Our results show that hysteresis in an overdeepened bed geometry is similar for atmospheric and oceanic forcings. We find that not only the particular sub-shelf melting parametrisation determines the temperature anomaly at which the ice sheet retreats, but also the particular value of calibrated heat exchange velocities. Notably, the classical hysteresis loop is narrowed for both forcing scenarios (i.e., atmospheric and oceanic) if the ice sheet is thermomechanically active as a results of the internal feedback among ice temperature, stress balance and viscosity. In summary, Nix combines rapid computational capabilities with a Blatter-Pattyn stress balance fully coupled to a thermomechanical solver, not only validating against established benchmarks but also offering a powerful tool for advancing our insight on ice dynamics and grounding line stability.

How to cite: Moreno-Parada, D., Robinson, A., Montoya, M., and Alvarez-Solas, J.: Description and validation of the ice sheet model Nix v1.0, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13290, https://doi.org/10.5194/egusphere-egu24-13290, 2024.

We have implemented a new framework for simulating the dynamic evolution of mountain glaciers in the Community Ice Sheet Model (CISM), a 3D, higher-order ice sheet model that serves as the ice dynamics component of the Community Earth System Model. We have used CISM to simulate all the glaciers of the European Alps at a resolution of 100 m. We describe the modeling framework and present results for the third phase of the GlacierMIP project (GlacierMIP3), which aims to determine the equilibrium area and volume of all glaciers outside the ice sheets, if global mean temperatures were to stabilize at present-day or various warmer levels. Compared to other glacier models, CISM is relatively sensitive to warming. We project that Alpine glaciers will lose a majority of their area and volume under present-day temperatures, with nearly complete ice loss under warmer scenarios. We are extending this framework to other glacier regions and will show preliminary result.

How to cite: Leguy, G., Lipscomb, W., and Minallah, S.: Simulating glacier evolution with a 3D ice sheet model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13830, https://doi.org/10.5194/egusphere-egu24-13830, 2024.

Simulating mass changes and ice dynamics for mountain glaciers using Earth System Models (ESMs) is challenging due to their small size, sheer number, and spatial discontinuities in the ground ice coverage. This has resulted in a knowledge and representational gap in ESMs. However, there is a need for scaling ESMs from global to regional domains for comprehensive glacio-hydrological and hydroclimatic assessments.

We introduce new developments for simulating the mass balance and dynamic evolution of mountain glaciers within the Community Earth System Model (CESM). We provide an overview of this work across two spatiotemporal scales related to: (1) the dynamic evolution of the Central European glaciers under the GlacierMIP3 protocol using the Community Ice Sheet Model (CISM) and (2) the energy and water balance of the Upper Indus glaciated basins at daily-monthly timescales using the Hillslope Hydrology configuration of the Community Land Model (CLM).

How to cite: Minallah, S., Lipscomb, W., Swenson, S., and Leguy, G.: Simulating Mass Balance and Dynamics of Mountain Glaciers within an Earth System Modeling Framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14128, https://doi.org/10.5194/egusphere-egu24-14128, 2024.

Subglaical hydrology significantly influences the basal sliding that controls how fast ice sheets transport ice from land to oceans. The absence of hydrologic systems in ice sheet models is therefore a notable source of uncertainty in projected ice-mass loss and its subsequent impact on sea-level rise. Specifically, the uncertainty associated with the representation of effective pressure (the difference between subglacial water pressure and ice overburden pressure) in basal sliding lacks comprehensive investigation in Antarctic sea-level rise projections. Here we use Elmer/Ice ice-sheet model setups to examine how different approaches to determining effective pressure in the regularised Coulomb sliding law impact the projected ice mass loss pre-2300 under both continental and basin scales. Our results reveal basin-specific responses to the representation of effective pressure in basal sliding, significantly influencing projected ice-mass loss and the timing of the passing of tipping points. We find that the ongoing interactions between ice dynamics and the hydrologic system render the grounding line much more mobile than in models with no such interaction. Notably, for the entire Antarctic Ice Sheet, grounding line flux is more than doubled by 2300 when employing a smoothly decreasing effective pressure near the grounding line, compared to constant pressure. Remarkably, Thwaites Glacier shows a tenfold increase in its grounding line flux by 2300. These findings underscore the critical need to better understand the interactions between ice dynamic evolution and the subglacial hydrologic system. Explicitly modelling the hydrologic system in a coupled ice sheet-subglacial hydrology models is crucial to make more robust predictions of Antarctica's future ice-mass loss, thereby reducing uncertainty in sea-level rise projections. 

How to cite: Zhao, C., Gladstone, R., Zwinger, T., Gillet-Chaulet, F., Wang, Y., Caillet, J., Mathiot, P., Saraste, L., Galton-Fenzi, B., Christoffersen, P., and King, M.: Subglacial Water Pressure Reshapes projected Antarctic Sea-Level Rise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14499, https://doi.org/10.5194/egusphere-egu24-14499, 2024.

The basal friction parameterization is often mentioned as key source of uncertainty when using ice sheet models to project future evolution of the ice sheet. Previous work suggests that parameterizations with an exponential relationship between friction and basal velocity (power laws) predict lower sea level rise than ‘Coulomb-style’ friction laws. For Coulomb laws, the basal friction asymptotes for high velocities and is effectively independent of velocity for fast-flowing ice. We use the Community Ice Sheet Model (CISM) for two kinds of simulations: one with present-day climate forcing, including sub-shelf ocean temperatures kept constant and one with 1-degree ocean warming in the Ross Sea, both matching the current rate of ice thickness changes. In the constant scenario, Thwaites Glacier and Pine Island Glacier collapse, creating a huge, laterally bounded ice shelf. In the scenario with Ross Sea warming, a large part of the Ross Ice Shelf disappears, allowing Siple Coast glaciers to flow freely into the ocean. For Thwaites and Pine Island Glaciers, there are competing processes causing increases or decreases in ice flux across the grounding line, ice shelf thickness, buttressing, and ice velocities, once the glaciers are collapsing. These processes work in the opposite direction of the differences caused by choosing different basal friction parameterizations. Therefore, in our model runs, the choice of basal friction parameterization has little effect on the collapse of Thwaites and Pine Island glacier. In the unbuttressed Siple Coast case, we confirm earlier results: Coulomb friction leads to more ice mass loss and sea level rise. We conclude that unbuttressed glaciers are more sensitive to the choice of basal friction parameterizations than are heavily buttressed glaciers, and that the presence of a large buttressing ice shelf decreases the sensitivity of glacier dynamics to different basal friction parameterizations. 

How to cite: van den Akker, T., Lipscomb, W. H., Leguy, G. R., van de Berg, W. J., and van de Wal, R. S. W.: Modelled ice sheet sensitivity to basal friction parameterizations is controlled by the amount of buttressing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15275, https://doi.org/10.5194/egusphere-egu24-15275, 2024.

The Antarctic Ice Sheet (AIS) is the largest ice sheet and hence the potentially largest contributor to future sea-level rise. However, the AIS represents also the largest source of uncertainty regarding future projections. One of the main sources for this uncertainty are the floating ice shelves. While these ice shelves do not directly contribute to sea-level rise, they play a major role in the dynamics of the AIS. By transmitting resistive stress to the grounding line, they are capable of slowing down inland ice. If ice shelves disintegrate, this buttressing effect disappears, promoting the flow of inland ice into the ocean. Thus, the assessment of ice shelf stability in future scenarios becomes crucial for accurate predictions.

One key element which is often overlooked is the formation of ice fractures. Satellite images display increased crevasse formation on Antarctic ice shelves and grounded ice near the grounding line over the past decade. These fractures, referred to as damage, impact the ice flow by reducing its viscosity. Reduced viscosity enhances ice flow, leading to higher strain rates which further promotes more damage formation. However, despite its known effect, its application has been only done on idealized domains so far.

Here we will assess the damage sensitivity of a three-dimensional ice-sheet-shelf model in a simplified, symmetric case (MISMIP+ domain) and a complex real-world scenario such as the Amundsen-Sea Embayment (ASE). For this we will test three different damage formulations from literature which account for explicit crevasse formation. In addition, we will also test a new regularization approximation in our viscosity formulation. This approximation ensures that if no damage is applied, then the effective yield strength of our model cannot exceed the failure strength of ice.

Our findings reveal that incorporating damage or viscosity regularization into future projections of the ASE results in higher sea-level contribution and faster grounding-line migration. This underscores the critical need to enhance our understanding of damage and its implications for future sea-level rise, since current projections do not account for this process.

How to cite: Blasco, J., Li, Y., Coulon, V., and Pattyn, F.: The effect of ice damage on future Antarctic projections, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15478, https://doi.org/10.5194/egusphere-egu24-15478, 2024.

The Subglacial Drainage System model (GlaDS) is one of the most widely used advanced glacier drainage models, with implementations in several ice sheet models. Here we present a new version of this model capable of execution on graphics processing units (GPUs) programmed in Julia. The aim is for the model to run on meshes larger than 10,000² grid points, which would allow, for instance, to simulate Antarctica at 500m resolution. Unlike the original GlaDS implementation, this is based on a finite difference scheme on a structured grid. Together with a matrix-free solver, this allows us to leverage the full performance capabilities of GPUs. We present model runs of the SHMIP test cases, show the model's scalability and provide an outlook towards higher-resolution continental-scale applications and inversion schemes.

How to cite: Pohle, A., Utkin, I., Räss, L., and Werder, M.: Modelling subglacial drainage with GlaDS on GPUs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16256, https://doi.org/10.5194/egusphere-egu24-16256, 2024.

Efficient modeling of ice sheets involves considering multiple coupled physical processes, including thermomechanical interactions. While using a Full-Stokes model for ice flow in Greenland and Antarctica provides most accurate results, it is can be extremely costly on a large scale with existing software, justifying the use of various reduced models.

Some important features of ice sheets, such as ice streams, are inherently three-dimensional. Accurate stress distribution, particularly around topography features comparable to ice thickness and near a grounding line, can only be achieved with a full stress tensor. In addition, a reference Full-Stokes solver for regional to ice sheet scale simulations can be a valuable tool for calibrating reduced models.

We introduce FastIce, a novel ice flow model for massively parallel architectures, written in Julia. Leveraging GPUs (Nvidia, AMD) and supporting distributed computing, FastIce includes a thermo-mechanically coupled Full-Stokes ice flow model and a novel conservative energy formulation for describing thermal effects. FastIce is written to be easily extensible, and its core is fully differentiable, enabling data assimilation pipelines using adjoint sensitivities and automatic differentiation (AD).

We validate FastIce through ISMIP-HOM benchmark tests and assess the coupled thermomechanical solver using the method of manufactured solutions. Our results showcase the thermo-mechanical instability arising from the non-linear interaction between temperature-dependent viscosity of ice and shear heating, reproducing existing analytical results. We present the performance testing of FastIce in single-node and distributed scaling benchmarks on LUMI, the largest European supercomputer.

How to cite: Utkin, I., Räss, L., Quarenghi, F., and Werder, M.: Benchmarking FastIce, a new massively parallel thermomechanical ice flow solver, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16675, https://doi.org/10.5194/egusphere-egu24-16675, 2024.

Mass loss from the Antarctic Ice Sheet is increasing, accelerating its contribution to global sea level rise. Projecting the future evolution of the Antarctic Ice Sheet but also better understanding the processes at play is therefore of major importance for the mitigation/adaptation of/to sea level rise.  

Despite considerable advancements in the initialization of ice sheet models over the last decade, challenges persist in reproducing the observed trend in global Antarctic mass loss. This discrepancy between models and reality reflects in the large range of sea level projections in the recent Ice Sheet Model Intercomparison Project (ISMIP6). As part of the European H2020 project, PROTECT, we conducted Antarctic Ice Sheet simulations with six European ice-sheet models until 2150, focusing on the ability of the model to reproduce observations. These simulations were driven by a range of ocean and atmospheric forcings derived from Earth System models or downscaled by regional climate models under various Shared Socioeconomic Pathways (SSPs). Our experimental design enables us  to sample climate forcing as well as model and parametric uncertainties, ensuring a comprehensive exploration of the future evolution of the Antarctic System and its contribution to sea level rise

Our simulations confirm that, regardless of the model used, the Amundsen sector is the region that will most likely dominate mass loss in the decades to come. In high emission scenarios (SSP5-8.5), a large increase in surface mass balance is also expected to temporarily overshadow acceleration in mass loss caused by ice-shelf basal melting. All the models show an acceleration in mass loss from the middle of the 22th century, following the significant increase in surface melting from the end of the 21st century for the SSP5-8.5 scenario. This emphasizes the pivotal role of surface melt in the long-term evolution of the Antarctic ice sheet and its contribution to sea level rise.

How to cite: Mosbeux, C., Durand, G., Jourdain, N., Gillet-Chaulet, F., Caillet, J., Coulon, V., Pattyn, F., Schoell, S., Klose, A. K., Winkelman, R., Cornford, S., Bevan, S., Berends, T., van de Wal, R., Goelzer, H., Edwards, T., Turner, F., Amory, C., Kittel, C., and van den Broeke, M. and the PROTECT: Assessing Antarctic Ice Sheet Dynamics and Sea Level Rise: Insights from PROTECT Model Intercomparison, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17095, https://doi.org/10.5194/egusphere-egu24-17095, 2024.

Despite constituting 80% of the total number of glaciers in mid- to low-mountain range catchments, the attention paid to very small glaciers (< 0.5 km²) in glacier research remains relatively low. However, glaciers of this size category are expected to undergo dramatic changes. Within Switzerland, more than half are predicted to disappear within the next two decades. As these glaciers shrink, they lose their firn cover, a crucial latent heat source through refreezing meltwater. Simultaneously, reduced glacier dynamics result in less ice deformation and decreased frictional heating at the base. Various studies suggest that such conditions can promote cooling, possibly enabling a transition from temperate to polythermal or cold states. Polythermal glaciers, especially those with partly frozen glacier beds, have been found to accumulate excessive meltwater, significantly increasing their hazard potential. In this study we present a new enthalpy-based englacial temperature model (IceT) to investigate the potential transition of very small Swiss glaciers from temperate to polythermal or cold conditions. The study focuses on identifying key parameters influencing glacier thermal transitions through a sensitivity analysis. Furthermore, we apply the model on a subset of 20 very small Swiss glaciers and compare our findings against previously generated model results of the Glacier Evolution Runoff Model (GERM). Our results indicate that mass balance and the liquid water content are the most significant factors for predicting glacier thermal states. The influence of mass balance works in two ways: (1) Highly negative mass balances hinder the development of a polythermal structure by allowing surface melt to surpass the propagation of the cold-temperate transition surface (CTS). (2) Less negative mass balances combined with limited snowfall, induce a transition to polythermal conditions by enabling the CTS propagation to outpace surface melt. Ultimately, the liquid water content (φ) appears as the most critical parameter in predicting ice temperatures. A mere increase of φ by 1% could reduce the maximum CTS depth by 165.07 m and lower the annual CTS propagation rate by 13.85 m a^-1. Significant differences emerge between GERM and IceT findings. GERM suggests that the majority of all very small Swiss glaciers exhibit polythermal conditions, while in the subset of 20 glaciers modeled with IceT, only 15% show indications of a polythermal regime. However, the considerable impact of liquid water on predicting ice temperatures, coupled with the incomplete knowledge regarding its distribution within glaciers, leads to substantial uncertainties in the presented model outcomes.

How to cite: Beer, J., Jacquemart, M., Utkin, I., Huss, M., Vieli, A., and Farinotti, D.: Determining the englacial temperature evolution of very small glaciers in the Swiss Alps: An enthalpy-based modelling approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17427, https://doi.org/10.5194/egusphere-egu24-17427, 2024.

Projections for Antarctica's contribution to global sea-level rise until 2100 range from a positive contribution due to increased ice loss, caused by an increase in surface melt and in dynamic loss of grounded ice, to a negative contribution due to increased snowfall. The high uncertainties in projections can be attributed to different sources, including emission trajectories, climate forcings from Global Circulation Models (GCMs) and Regional Climate Models (RCMs), as well as inter- and intra-ice-model differences.
Here, we present an ensemble of future projections based on simulations with the Parallel Ice Sheet Model (PISM), driven by multiple climate forcings. These are based on several initial states and ice-sheet trajectories over the historical period, consistent with observations.
We assess the influence of the initial states on the spread in projected sea-level change and compare these to the uncertainties arising from climatic forcings, to compare the sources of uncertainty in future sea-level projections until 2100 and beyond.

How to cite: Schöll, S., Klose, A. K., Reese, R., Jourdain, N., and Winkelmann, R.: Effect of initial states on the uncertainty in sea-level rise projections until 2100 and beyond, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17606, https://doi.org/10.5194/egusphere-egu24-17606, 2024.

The vast majority of ice-sheet modelling studies rely on simplified representations of the Glacial Isostatic Adjustment (GIA), which, among other limitations, do not account for lateral variations of the lithospheric thickness and upper-mantle viscosity. In studies using 3D GIA models, this has however been shown to have major impacts on the dynamics of marine-based sectors of Antarctica, which are likely to be the greatest contributors to sea-level rise in the coming centuries. This gap in comprehensiveness is explained by the fact that 3D GIA models are computationally expensive, seldomly open-source and require the implementation of an iterative coupling scheme to converge with the history of the ice-sheet model. To close this gap between "best" and "tractable" GIA models, we here propose FastIsostasy, a regional GIA model capturing lateral variations of the lithospheric thickness and mantle viscosity. By means of Fast-Fourier transforms and a hybrid collocation scheme to solve its underlying partial differential equation, FastIsostasy can simulate 100,000 years of high-resolution bedrock displacement in only minutes of single-CPU computation, including the changes in sea-surface height due to mass redistribution. Despite its 2D grid, FastIsostasy parametrises the depth-dependent viscosity in a physically meaningful way and therefore represents the depth dimension to a certain extent. FastIsostasy is here benchmarked against analytical, 1D and 3D GIA solutions and shows very good agreement with them. It is fully open-source, documented with many examples and provides a straight-forward interface for coupling to an ice-sheet model. The model is benchmarked here based on its implementation in Julia, while a Fortran version is also provided to allow for compatibility with most existing ice-sheet models. The Julia version provides additional features, including a vast library of time-stepping methods and GPU support.

How to cite: Swierczek-Jereczek, J., Montoya, M., Latychev, K., Robinson, A., Alvarez-Solas, J., and Mitrovica, J.: FastIsostasy - An accelerated regional GIA model for coupled ice-sheet/solid-Earth simulations with laterally-variable solid-Earth structures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19141, https://doi.org/10.5194/egusphere-egu24-19141, 2024.

We present detailed modelling of ice flow over a synthetic topography using the full-Stokes ice flow model ELMER-ICE. Our results indicate that landforms/obstacles under 1000 m wavelength contribute importantly to basal drag, implying that predictive ice sheet models that are initialised using static parameterisations of basal drag will greatly underestimate the possible mediating effects of bedrock topography. We conducted numerous simulations using a 10 m resolution, 40 x 22 km model domain with a uniform ice thickness of 1000 m and with sliding restricted to a 20 km-wide central corridor to negate ice leaving the lateral margins. Basal slipperiness (i.e. skin drag) in all simulations used the value obtained during an initial simulation using an entirely flat bed and an imposed surface velocity of 150 m a^-1. Subsequent simulations used a synthetic bed with wavelength 5 km, amplitude 200 m, and randomised superimposed smaller-scale roughness. Because ice sheet beds are bumpy at a range of scales - from landforms reflective of km-scale patterns of glacial bedrock erosion down to m-scale obstacles characteristic of bedrock structure – roughness was introduced gradually into the simulations by stepwise reduction of the degree of smoothing applied to the synthetic topography using a band-pass filter. Our results demonstrated that around two-thirds of observed surface velocity was by sliding, and that mean sliding velocity (and thus surface velocity) declined rapidly when introducing roughness with length scale smaller than 1000 m. Further, the observed decline appeared broadly exponential in relation to obstacle size as smaller roughness length scales were added, down to the smallest length scale (10 m) permitted by present model resolution. The results therefore highlight the potential importance of form drag provided by sub-km scale bed roughness in stabilising ice flow, including flow in grounding line locations that are critical to marine ice sheet stability. The results also have implications for predictive ice sheet models, which typically use static fields of basal drag derived from inversions of present-day surface observations, and do not distinguish between form and skin drag. As such, current models could imprecisely predict ice discharge and grounding line behaviour in regions of evolving bedrock or sedimentary landforms, which are ubiquitous to ice sheet beds.

How to cite: Swift, D., Martin, C., and Ely, J.: The importance of bed roughness on ice sheet flow investigated using a full-Stokes ice flow model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19220, https://doi.org/10.5194/egusphere-egu24-19220, 2024.

Many model studies show that a shutdown of the Atlantic meridional overturning circulation (AMOC) causes reduced northward heat transport into the North Atlantic and a warming Southern Ocean in addition to shifts in large-scale atmospheric circulations. How these changing climate conditions could influence the present-day state of the Antarctic Ice Sheet is little studied even though observational data of AMOC strength show a slowdown trend over the last decades. The ocean current as well as the Antarctic Ice Sheet might reach climate tipping points triggering irreversible processes with consequences already on human time-scales. It's unclear whether increasing Southern Ocean temperatures due to a AMOC shutdown could accelerate basal melting rates, the critical parameter which in turn may induce tipping of the West Antarctic Ice Sheet.

Here, a freshwater hosing that forces the shutdown of the AMOC is applied to the North Atlantic in a global climate model with an interactive ice sheet model for Antarctica. This model framework consists of the Parallel Ice Sheet Model (PISM) that is coupled to the CM2Mc global Earth system model via the ice shelf cavity model PICO (Potsdam Ice-shelf Cavity mOdel). PISM is interactively coupled to the ocean module in order to investigate feedbacks at the ice-ocean boundary, while the atmospheric forcing is prescribed. Preliminary results show that an AMOC shutdown results in warming sea surface temperatures in the southern hemisphere along with a small shift in the mid-latitude westerlies due to reduced northward heat transport, which is in line with previous studies. Antarctic marginal temperatures decrease, however, resulting in a reduction of Antarctic mass through increased calving and decreased basal melting.

How to cite: Höse, A., Kreuzer, M., Huiskamp, W., Albrecht, T., Petri, S., Winkelmann, R., and Feulner, G.: Simulating the impact of an AMOC weakening on the Antarctic Ice Sheet using a coupled climate and ice sheet model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-926, https://doi.org/10.5194/egusphere-egu24-926, 2024.

The Last Interglacial period (LIG) (130 - 116 kaBP), characterized by higher global mean temperature and sea levels compared to the present-day due to the Earth’s orbit configuration, has been well-studied as a recent example of a climate period warmer than today. There is particular interest in studying the ice sheet-climate interactions in view of our current climate change. However, the extent of the ice sheet and its contribution to the rise of sea levels during the LIG remain debatable as different approaches suggest a wide range of estimations. In order to cover such a long period, some processes are simplified in the modeling approach by using prescribed forcings, simple surface mass balance (SMB) schemes, or equilibrium simulations, which all affect the numerical estimation of ice sheet evolution. 

In our work, to perform transient simulations, we use an Earth system model of intermediate complexity (iLOVECLIM), which has been widely used to study various long-timescale periods. Additionally, we use a physically-based energy and mass balance model with 15 vertical snow layers BESSI (BErgen Snow Simulator) to account for the effect of insolation changes as well as snow-albedo feedback. The climate forcings of the snow model are obtained by running iLOVECLIM transiently from 135 to 115 kaBP, downscaled over the Northern Polar region. Using the SMB computed by BESSI, we then simulate the ice sheet evolution during the LIG with GRISLI - the ice sheet model in the iLOVECLIM framework. 

To assess the benefits of using a physically-based SMB model in the ice sheets simulation, the outputs of GRISLI-BESSI are compared to the current SMB scheme of iLOVECLIM, a simple parametrization called ITM (Insolation Temperature Melt). The Greenland ice sheet volume simulated by the two SMB models reaches the minimum value at 127.5 kaBP, around 500 years after the peak of global mean temperature. The magnitude of ice sheet retreat and its contribution to the sea level in ITM simulations are significantly higher than in BESSI due to an overestimation of the zones of ablation. 

The findings suggest that, compared to a parameterization, we have more confidence in the ice sheet estimation with a physically-based SMB model. Further works with fully interactive ice sheet modeling that takes into account the melt-elevation feedback can improve the simulation of the ice sheet-climate interactions of long-time scales. 

How to cite: Hoang, T. K. D., Quiquet, A., Dumas, C., Born, A., and Roche, D. M.: Greenland Ice Sheet evolution during the Last Interglacial with an improved surface mass balance modeling approach , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-966, https://doi.org/10.5194/egusphere-egu24-966, 2024.

The Antarctic contribution to sea-level rise in the coming centuries remains very uncertain, due to the possible triggering of instabilities such as the Marine Ice Sheet Instability (MISI) and Marine Ice Cliff Instability (MICI). These instabilities are mainly linked to the evolution of the floating ice shelves, which usually buttress the ice flow from the ice-sheet to the ocean. However, these are currently thinning. Better understanding the evolution of ice shelves in the next decades to centuries is therefore important and crucial to better anticipate the evolution of sea-level rise.

In this study, we investigate the viability of ice shelves for a number of climate models and scenarios. This is estimated from the emulation of the surface and basal mass balance of MAR and NEMO respectively, and from high-end dynamical ice flows obtained through Elmer/Ice. We then use a Bayesian calibration to give weight to members closer to observations. We find that large uncertainties remain, mainly because of the uncertainty in basal melt, and that viability limits vary largely depending on the ice-shelf location.

How to cite: Burgard, C., Jourdain, N. C., Kittel, C., Mosbeux, C., Caillet, J., and Mathiot, P.: When will the Antarctic ice shelves not be viable anymore?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1991, https://doi.org/10.5194/egusphere-egu24-1991, 2024.

The Antarctic Ice Sheet (AIS) is currently undergoing accelerated mass loss, significantly contributing to rising sea levels (SLR). Despite numerous observations, uncertainties persist in understanding the drivers and dynamic responses of AIS mass loss. Climate variability strongly influences AIS dynamics, but limited observational data hinders precise attribution to climate change or natural variability. This study addresses this gap by employing advanced modeling techniques to assess the extent to which observed and future AIS mass loss can be attributed to climate change versus variability. Utilizing a unique "initialization method" with the ISSM model, we approximate the AIS state circa 1850, a period minimally affected by anthropogenic forces. From this baseline, we project AIS development using UKESM1 forcing, comparing scenarios with and without anthropogenic influence. This investigation aims to enhance our understanding of the impact of climate change on the AIS and its implications for future SLR.

How to cite: Beckmann, J., Seroussi, H., Bird, L., Caillet, J., Jourdain, N., McCormack, F., and Mackintosh, A.: Deciphering Antarctic Ice Sheet Mass Loss: A Modeling Approach to Distinguish Climate Change from Natural Variability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3666, https://doi.org/10.5194/egusphere-egu24-3666, 2024.

During the last glacial period, the climate went through rapid fluctuations together with changes in ocean circulation and ice sheets volume accompanied by iceberg discharges. These rapid climate variations, namely Dansgaard-Oeschger events, are still not fully explained. This study’s aim is to contribute to their better understanding, focusing on interactions between ice sheets and ocean circulation. To this end, we use the iLOVECLIM-GRISLI coupled climate-ice sheet model and run two different perturbation experiments related to the ice sheet and ocean components. Starting from a quasi equilibrium corresponding to 40 ky B.P. greenhouse gas concentration, incoming solar radiation and ice sheet volume, the first experiment consists in imposing either constant or amplified sub-shelf melt rates in comparison with the control simulation. In the second experiment, we focus on the interface between the ice sheets and the bedrock. The basal friction coefficient values are imposed following the same procedure. These two experiments are similar to freshwater hosing experiments but here the water comes directly from the interactively computed ice sheets change. For each experiment, the perturbation is imposed for 500 years before returning to the unperturbed conditions for one thousand years and its impacts on the climate system are investigated. Our results highlight feedbacks that may help to explain the abrupt nature of the climate transitions observed during the last glacial period. 

How to cite: Abot, L., Waelbroeck, C., Quiquet, A., Delavergne, C., and Bouttes, N.: Interactions between ocean circulation and the Northern Hemisphere ice sheets at 40 ky B.P. in an Earth System Model (iLOVECLIM-GRISLI), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4093, https://doi.org/10.5194/egusphere-egu24-4093, 2024.

How to cite: Sergienko, O., Harrison, M., Huth, A., and Schlegel, N.: A synchronously coupled global model iOM4: a new modeling tool for simulations of the ocean-cryosphere interactions , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4802, https://doi.org/10.5194/egusphere-egu24-4802, 2024.

Unravelling the main drivers of the mid-Pleistocene transition (MPT; around 1.2–0.8 million years ago) remains a significant challenge in paleoclimate research. Noteworthy changes that occurred in the climate system during that time include a pronounced shift from 41-kyr to 100-kyr periodicity of glacial cycles and the emergence of much larger ice sheets. While a number of studies have focused on the interplay between the climate system and northern hemispheric ice sheets during the MPT, the role of Antarctica in driving and responding to climate change at that time remains largely unknown. This is particularly relevant as, consequently, the response of Antarctica’s vast ice sheets to a major transition in Quaternary climate, and their potential role in shaping the transition, remain uncertain. 

How to cite: Wirths, C., Hermant, A., Stepanek, C., Sutter, J., and Stocker, T.: Simulating Antarctic Ice Sheet evolution through the mid-Pleistocene transition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5104, https://doi.org/10.5194/egusphere-egu24-5104, 2024.

Sublimation is the most important ablation term in the Antarctic Surface Mass Balance (SMB) (Agosta et al., 2019), while it is currently negligible for both Greenland and mountain glaciers (prevailing surface melt). Since simple parameterized SMB models are usually developed for Greenland and Alpine glaciers, they mostly misrepresent sublimation. To face this problem, we developed EBAL, a new parameterized Energy SMB model for Antarctica based on SEMIC (Krapp et al., 2017), which is an Energy SMB model developed for Greenland whose main innovations are a sinusoidal parameterization for the diurnal cycle to assess melt and refreezing and an albedo dependence on snow depth. EBAL was calibrated with both MAR (Kittel et al., 2022) and RACMO (Wessem et al., 2018) outputs for the period 1979-2000 and for the period 2075-2099 under the SSP5-8.5. EBAL can reproduce the statistical properties of MAR and RACMO sublimation time series and spatial distribution even if it uses a coarse time step (1 day). However, our final aim is to use EBAL for paleoclimate simulations, for which the temporal resolution of the inputs is even coarser, as often only monthly data is available. Thus, we have tested the idea of superimposing the present day-to-day variability on the MAR monthly atmospheric forcing of SSP5-8.5. Simulated SMB with EBAL forced with MAR original daily SSP5-8.5 inputs leads to a 210 Gt/yr sublimation, and to a 1425 Gt/yr melt. When forcing EBAL with monthly means only (linearly interpolated), we obtain a 113 Gt/yr sublimation and a 620 Gt/yr melt. When adding present-day variability to linearly interpolated monthly inputs, EBAL computes a 175 Gt/yr sublimation and a 1386 Gt/yr melt. Those latter numbers are very similar to those obtained when forcing with daily inputs. We propose to use this method to test EBAL for paleoclimate applications.

References

• Agosta, C. et al., (2019). “Estimation of the Antarctic surface mass balance using the regional climate model MAR (1979–2015) and identification of dominant processes”. The Cryosphere. 13,  pp. 281-296. 10.5194/tc-13-281-2019. 
• Kittel, C. et al., (2022). “Clouds drive differences in future surface melt over the Antarctic ice shelves”. The Cryosphere. 16, pp. 2655-2669. 10.5194/tc-16-2655-2022.
• Krapp, M et al., (July 2017). “SEMIC: an efficient surface energy and mass balance model applied to the Greenland ice sheet”. The Cryosphere 11.4, pp. 1519–1535. 10.5194/tc-11-1519-2017
• Wessem, J. M. et al., (Apr. 2018). “Modelling the climate and surface mass balance of polar ice sheets using RACMO2 – Part 2: Antarctica (1979–2016)”. The Cryosphere 12, pp. 1479–1498. 10.5194/tc-12-1479-2018

How to cite: Maiero, E., Colleoni, F., Agosta, C., Barbante, C., and Stenni, B.: Modeling the Antarctic Surface Mass Balance with a coarse temporal resolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5525, https://doi.org/10.5194/egusphere-egu24-5525, 2024.

Estimates of future Greenland ice sheet (GrIS) melt are mostly based on regional climate modelling for a fixed GrIS topography or on ice sheet modelling with forcing from climate models. This prevents the modelling of climate and GrIS feedbacks and other types of interaction. Here we examine a set of multi-century simulations with the Community Earth System Model featuring an interactive GrIS to explore future relationship between global climate change and ice sheet change. To this end, we compare a set of coupled CESM-CISM 1% CO₂ increase simulations until stabilization at two, two and a half, three and four times pre-industrial CO₂ levels to examine the sensitivity of the GrIS to emission mitigation. Here we find a large role of ocean circulation weakening and associated regional climate changes on GrIS melt for moderate emission scenarios and large melt differences between the three times and four times CO₂ stabilization scenarios. In addition, we examine the role of feedbacks on ice sheet evolution by comparing a 1% to 4xCO₂ coupled simulation with a simulation where the GrIS topography and meltwater fluxes to the ocean are prescribed as pre-industrial. Finally, we explore the effects on GrIS melt rates of a fast 5% CO₂ reduction from four times to pre-industrial levels, with a focus on restoration of high latitude climate, GrIS albedo, surface energy fluxes and refreezing capacity.  

How to cite: Vizcaino, M., Feenstra, T., Petrini, M., Sellevold, R., Sotiria, G., Thayer-Calder, K., Lipscomb, W., and Rudlang, J.: Future Greenland melt in coupled ice sheet-climate CESM simulations: feedbacks, thresholds, reversibility, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5584, https://doi.org/10.5194/egusphere-egu24-5584, 2024.

Using the BISICLES ice sheet model, we compare the Antarctic ice sheet’s response over the 22nd century in a scenario where idealised large scale, instantaneous geoengineering is implemented in 2100 or 2050 (geoengineering), with scenarios where the climate forcing is held constant in the same year (stabilisation). Results are highly climate model dependent, with larger differences between models than between geoengineering and stabilisation scenarios, but show that geoengineering cannot prevent significant losses from Antarctica over the next two centuries. If implemented in 2050, sea level contributions under geoengineering are lower than under stabilisation scenarios. If implemented in 2100, under high emissions, geoengineering produces higher sea level than stabilisation scenarios, as increased surface mass balance in the warmer stabilisation scenarios offsets some of the dynamic losses. Despite this, dynamic losses appear to accelerate and may eventually negate this initial offset, indicating that beyond 2200, geoengineering could eventually be more effective.

How to cite: Adhikari, M., Martin, D., Edwards, T., Payne, A., O'Neill, J., and Irvine, P.: Geoengineering's role in reducing future Antarctic mass loss is unclear, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5698, https://doi.org/10.5194/egusphere-egu24-5698, 2024.

Slow climate feedbacks that operate on timescales of more than a century are currently underrepresented in model assessments of climate sensitivity, and this continues to hinder efforts to accurately predict future climate change beyond the end of the 21^st Century. As such, the magnitude of multi-centennial and millennial climate feedbacks are still poorly constrained. We utilise recent reconstructions of Earth’s Energy Imbalance (EEI) to estimate both the total climate feedback parameter and the ice-sheet albedo feedback since the Last Glacial Maximum. This new proxy-based record of EEI facilitates the first opportunity to simultaneously calculate both the magnitude and timescale of Earth’s climate feedback over the most recent deglaciation using a purely proxy data-driven approach, and without the need for simulated reconstructions. We find the ice-sheet albedo feedback to have been an amplifying feedback reaching an equilibrium magnitude of 0.55 Wm^-2K^-1, with a 66% confidence interval of 0.45 Wm^-2K^-1 to 0.63 Wm^-2K^-1. The timescale for the ice-sheet albedo feedback to reach equilibrium is estimated as 3.61Kyrs, with a 66% confidence interval of 1.88Kyrs to 5.48Kyrs. These results provide new evidence for the timescale and magnitude of the amplifying ice-sheet albedo feedback that will continue to drive anthropogenic warming for millennia to come, further increasing the urgency for an effective climate change mitigation strategy to avoid serious long-term consequences for our planet and its ecosystems.

How to cite: Booth, A., Goodwin, P., and Cael, B.: Long term ice-sheet albedo feedback constrained by most recent deglaciation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6140, https://doi.org/10.5194/egusphere-egu24-6140, 2024.

Earth's climate will likely exceed a warming of 1.5°C in the coming decades. Maintaining such warming levels for a longer period of time may pose a considerable risk of crossing critical thresholds in Antarctica and, thereby, triggering self-sustained, potentially irreversible ice loss, even if the forcing is reduced in a temperature overshoot. Due to the complex interplay of several amplifying and dampening feedbacks at play in Antarctica, the duration and amplitude of such warming overshoots as well as their eventual 'landing' climate will determine the long-term evolution of the ice sheet.

Using the Parallel Ice Sheet Model, we systematically test for the reversibility of committed large-scale ice-sheet changes triggered by warming projected over the next centuries, and thereby explore (1) the stability regimes of the Antarctic Ice Sheet and (2) the potential for safe overshoots of critical thresholds in Antarctica.

We demonstrate crucial features of the Antarctic Ice Sheet's stability landscape for its long-term trajectory in response to future human actions: Given ice-sheet inertia, an early reversal of climate may allow for avoiding self-sustained ice loss that would otherwise be irreversible (for the same reduction in warming) due to multistability of the ice sheet at the basin- and continental scale. While we show that such safe overshoots of critical thresholds in Antarctica may be possible, it is also clear that limiting global warming is the only viable option to evade the risk of widespread ice loss in the long term.

How to cite: Klose, A. K. and Winkelmann, R.: Stability regimes and safe overshoots in West and East Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7415, https://doi.org/10.5194/egusphere-egu24-7415, 2024.

Coupled climate-ice sheet models can capture important interactions between the ice sheets and the climate that can help us better understand an ice sheet's response to changes in forcings. In this respect, they are a useful tool for simulating future ice sheet and sea level changes as a result of climate change. However, such models have large uncertainties related to the choice of climate and ice sheet parameters used. The same processes that operate today, also occurred in glacial times, and previous work has shown that simulating the North American ice sheet at the Last Glacial Maximum (LGM; ~21 ka BP) provides a strong benchmark for testing coupled climate-ice sheet models and recalibrating uncertain parameters that control surface mass balance and ice flow (Gandy et al., 2023).

Here, we build on this work by performing the first coupled FAMOUS-BISICLES simulations of the last two glacial maxima, including all Northern Hemisphere ice sheets interactively. The ice sheet component of this model is capable of efficiently simulating marine ice sheets, such as the Eurasian ice sheet, despite the high computational cost of higher order physics. We simulate and compare both the LGM and the Penultimate Glacial Maximum (PGM; ~140 ka BP), since both periods displayed major differences in the distribution of ice between Eurasia and North America. Uncertainty is explored by running ensembles of 120 simulations, randomly varying the uncertain parameters controlling ice sheet dynamics and climate through Latin Hypercube Sampling. We also work on improving the representation of ice streams in the model through performing internal ice temperature spin ups and sensitivity tests varying till water drainage properties. The ensemble members are evaluated against empirical data on ice sheet extent and ice stream location to find combinations of parameters that produce reasonable simulations of the North American and Eurasian ice sheets for both periods. We determine the impact of the uncertainty in these parameters on the result and whether both ice sheets show similar sensitivities to the model parameters. These simulations will provide a starting point for analysing some of the interactions between the climate and the ice sheets during glacial periods and how they may have led to different ice sheet evolutions.

How to cite: Patterson, V., Gregoire, L., Ivanovic, R., Gandy, N., Cornford, S., and Sherriff-Tadano, S.: Coupled ensemble simulations of the Northern Hemisphere ice sheets at last two glacial maxima , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8333, https://doi.org/10.5194/egusphere-egu24-8333, 2024.

The dynamics of the ice sheets on glacial-interglacial time scales are highly controlled by interactions with the solid Earth, i.e., glacial isostatic adjustment (GIA). Particularly at marine ice sheets, competing feedback mechanisms govern the migration of the ice sheet’s grounding line and hence the ice sheet stability.

In this study, we run coupled ice sheet–solid Earth simulations over the last two glacial cycles. For the ice sheet dynamics we apply the Parallel Ice Sheet Model PISM and for the load response of the solid Earth we use the three-dimensional viscoelastic Earth in view of sea-level and vertical displacement changes we apply the Viscoelastic Lithosphere and Mantle Model VILMA.

With our coupling setup we evaluate the relevance of feedback mechanisms for the glaciation anddeglaciation phases in Antarctica considering different 3D Earth structures resulting in a range of load-response time scales. For rather long time scales, in a glacial climate associated with far-field sea level low stand, we find grounding line advance up to the edge of the continental shelf mainly in West Antarctica, dominated by a self-amplifying GIA feedback, which we call the ‘forebulge feedback’. For the much shorter time scale of deglaciation, dominated by the Marine Ice Sheet Instability, our simulations suggest that the stabilizing GIA feedback can significantly slow-down grounding line retreat in the Ross sector, which is dominated by a very weak Earth structure (i.e. low mantle viscosity and thin lithosphere).

The described coupled framework, PISM-VILMA, allows for defining restart states to which to run multiple sensitivity simulations. It can be easily implemented in Earth System Models (ESMs) and provides the tools to gain a better understanding of ice sheet stability on glacial time scales as wellas in a warmer future climate.

How to cite: Albrecht, T., Bagge, M., and Klemann, V.: Feedback mechanisms controlling Antarctic glacial cycle dynamics simulated with a coupled ice sheet–solid Earth model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9032, https://doi.org/10.5194/egusphere-egu24-9032, 2024.

Recent progress in parameterizations of surface and atmospheric processes have led to the development of a major update of the polar version of the Regional Atmospheric Climate Model (RACMO2.4.1). Here, we present a new high-resolution climate and surface mass balance product by applying RACMO2.4.1 to the Antarctic and Greenland ice sheet for the historical period (starting in 1960 and 1945, respectively). In addition, RACMO output is now available for the first time on a pan-Arctic domain, starting in 1980. We assess these products by comparing model output of the surface mass balance and its components and the near-surface climate with in-situ and remote sensing observations, and study differences with the previously operational RACMO iteration, RACMO2.3p2. 

Among other changes, RACMO2.4.1 includes new and updated parameterizations related to surface and atmospheric processes. Most major updates are part of the physics package of cycle 47r1 of the Integrated Forecast System (IFS) of the European Center for Medium-Range Weather Forecasts (ECMWF), which is embedded in RACMO2.4.1. This includes updates to the cloud, radiation, convection, turbulence, aerosol and lake scheme. Other major changes are directly related to the cryosphere, such as the introduction of a new spectral albedo and radiative transfer scheme for glaciated snow, fixes to the snow drift scheme, a new multilayer snow scheme for seasonal snow and an updated ice mask. These updates lead to changes in the near-surface climate. For example, the horizontal transport of snow that is present in the atmosphere leads to a redistribution of snowfall. Furthermore, the spatial resolution for the Antarctic domain is increased to 11 km, which is also used for the pan-Arctic domain, while 5.5 km is used for Greenland. Here, we also discuss the impact that aforementioned changes have on the climate of the polar regions and the surface mass balance and its components of the ice sheets.

How to cite: van Dalum, C., van de Berg, W. J., Nagarada Gadde, S., and van den Broeke, M.: A new climate and surface mass balance product for the Antarctic and Greenland ice sheet using RACMO2.4.1, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10162, https://doi.org/10.5194/egusphere-egu24-10162, 2024.

The Parallel Ice Sheet Model (PISM) is used to build up a glacial Greenland ice sheet, simulate the evolution of the Greenland ice sheet through glacial terminations I and II and investigate the evolution during previous warmer climates, the Eemian and the Holocene thermal maximum. During the Holocene, surface elevation changes derived from ice cores suggest a large thinning in the North, suggesting that the Greenland ice sheet was connected to the North American ice sheet in Canada during the last glacial. By including Canada in the modelling domain this thinning in the early Holocene as the connecting ice bridge broke up will be investigated. 

How to cite: Eckert, M. K., Lauritzen, M., Rathmann, N., Solgaard, A., and Hvidberg, C.: Reconstructing the Greenland ice Sheet during the last two deglaciations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10256, https://doi.org/10.5194/egusphere-egu24-10256, 2024.

Representing the interactions between ice sheets and climate is essential for more accurate prediction of climate change and sea level rise. Ice sheets interact with the overlying atmosphere via the accumulation of snow and its compaction into firn, then ice, as well as the melting of surface snow and ice and the creation of runoff water. Getting an adequate representation of heat transfer, compaction, and melting processes is essential for an accurate representation of snow on land ice in global climate models. We are implementing an improved snow model on top of land ice as part of an effort to couple the NASA GISS climate model with the PISM ice sheet model. The new snow model includes additional layers and processes that are not currently incorporated (e.g., liquid water retention, percolation and refreezing, and snow densification), and mass and energy transfer methods that are consistent with both static ice sheets (with implicit iceberg fluxes) and interactive ice sheets (with explicit dynamics). We are tuning the densification scheme of this snow model with temperature and density data from common FirnCover and SumUp observations at locations in the accumulation zone of Greenland, and we compare the resulting density profiles to other SumUp density profiles in Greenland and Antarctica. We will assess the impact of this new snow model in climate model simulations with a static ice sheet compared with the previous (simpler) 2-layer snow model. Finally, we aim to use the non-coupled simulations as a baseline to assess the impact of dynamic coupling with an interactive ice sheet model.

How to cite: Ringeisen, D., Alexander, P., Roach, L., Mankoff, K., and Aleinov, I.: Improved treatment of snow over ice sheets in the NASA GISS climate model: towards ice sheet–climate coupling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12773, https://doi.org/10.5194/egusphere-egu24-12773, 2024.

During the Last Interglacial (LIG), approximately 130-118 thousand years ago (ka), the Arctic experienced relative warmth and global sea levels considerably higher than modern.  While this interval is thus considered key for understanding long-term ice–climate feedbacks under warm-state climate conditions, large uncertainties remain surrounding i. the magnitude and spatial expression of LIG global temperature change, ii. the relative contributions of the Antarctic vs. Greenlandic Ice Sheets (GrIS) to LIG sea level rise, and iii. the sensitivity of the GrIS to centennial- to millennial-scale ocean-atmospheric forcing.  Here, we present, to our knowledge, a first attempt at reconstructing the coupled GrIS–climate evolution during the LIG using an internally consistent offline “paleoclimate data assimilation” approach.  Our methodology combines a newly compiled database of nearly 400 chronologically consistent marine geochemical and ice sheet-derived climate-proxy records (spanning 250 sites globally) with recently developed, state-of-the-art transient simulations of the LIG using the coupled Community Earth System Model v2 featuring an interactive Community Ice Sheet Model v2 (CESM2-CISM2).  Our preliminary assimilations suggest LIG peak global mean surface warming of +0.1-0.5˚C (±2 range) above the pre-industrial state, arising from enhanced and widespread (>2-5˚C) high Arctic warming.  Leveraging our CESM2-coupled CISM2 results, we further identify a max GrIS contribution of 2.0 (±0.6) meters of sea level rise equivalent at around 125 ka, nearly ~two millennia after peak LIG climate forcing.  These initial results provide a new proxy-model integration framework for reconciling past GrIS contributions to global sea level rise and benchmark the potential long-term sensitivity of the GrIS to ongoing Arctic warming.

How to cite: Osman, M., Tierney, J., and Lofverstrom, M.: Reconstructing the coupled Greenland Ice Sheet–climate evolution during the Last Interglacial warm period, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13618, https://doi.org/10.5194/egusphere-egu24-13618, 2024.

Mass loss from ice sheets under the ongoing anthropogenic warming episode is a major source for sea-level rise. Due to the slow responses of ice sheets to changes in atmospheric and oceanic boundary conditions, ice sheets are projected to undergo further retreat as the climate reaches a new equilibrium, producing a long-term commitment to future sea-level rise that is fulfilled on multi-millennial scale. Future projections of ice sheets beyond 2100 have routinely employed end-of-the-century atmosphere-ocean conditions from climate model output under specified emission scenarios. This approach, however, does not account for long-term responses of the climate system to external forcings. Here we analyze the long-term atmospheric and oceanic responses to a variety of emission scenarios in several climate models and show that polar climates may see substantial changes after the atmospheric CO₂ level stabilizes. With a 3-D ice sheet model, we demonstrate that the long-term climate responses are crucial for evaluating ice sheets' commitment to future sea-level rise.

How to cite: Li, D.: Effects of long-term climate responses on ice sheets' commitment to future sea-level rise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15160, https://doi.org/10.5194/egusphere-egu24-15160, 2024.

Surface mass balance (SMB) forcing for projections of the future evolution of the Greenland ice sheet with stand-alone modeling approaches is commonly produced on a fixed ice sheet geometry. As changes of ice sheet geometry become significant over longer time scales, conducting projections for the long-term evolution and stability of the Greenland ice sheet usually requires a coupled climate-ice sheet modeling setup. In this study we use an SMB remapping procedure to capture the first order feedbacks of a coupled climate-ice sheet system with a stand-alone modeling approach. Following a remapping procedure originally developed to apply SMB forcing to a range of initial ice sheet geometries (Goelzer et al., 2020), we produce SMB forcing that adapts to the changing ice sheet geometry as it evolves over time. SMB forcing from a regional climate model is translated from a function of absolute location to a function of surface elevation depending on 25 regional drainage basins, thereby reducing biases that would arise by applying the SMB derived from a fixed ice sheet geometry. We use forcing for different emission scenarios from the CMIP6 archive to compare results from the remapping approach with results from commonly used methods of parameterizing the SMB-height feedback, as well as with results from a semi-coupled climate-ice sheet simulation.

How to cite: Rahlves, C., Goelzer, H., and Petrini, M.: Investigating the evolution and stability of the Greenland ice sheet using remapped surface mass balance forcing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15323, https://doi.org/10.5194/egusphere-egu24-15323, 2024.