Content:

CR – Cryospheric Sciences

CR1.1 – The Antarctic Ice Sheet: past, present and future contributions towards global sea level

EGU21-9256 | vPICO presentations | CR1.1

Antarctic ice dynamics amplified by Northern Hemisphere sea level forcing

Natalya Gomez, Michael Weber, Peter Clark, Jerry Mitrovica, and Holly Han

A longstanding hypothesis for near-synchronous evolution of global ice sheets over ice-age cycles invokes an interhemispheric sea-level forcing whereby sea-level rise due to ice loss in the Northern Hemisphere in response to insolation and greenhouse gas forcing causes grounding-line retreat of marine-based sectors of the Antarctic Ice Sheet (AIS). Recent studies have shown that the AIS experienced substantial millennial-scale variability during and after the last deglaciation, with several times of recorded increased iceberg flux and grounding line retreat coinciding, within uncertainty, with well documented global sea-level rise events, providing further evidence of this sea-level forcing. However, the sea level changes associated with ice sheet mass loss are strongly nonuniform due to gravitational, deformational and Earth rotational effects, suggesting that the response of the AIS to Northern Hemisphere sea-level forcing is more complicated than previously modelled.

We adopt an ice-sheet model coupled to a global sea-level model to show that a large or rapid Northern Hemisphere sea-level forcing enhances grounding-line advance and associated mass gain of the AIS during glaciation, and grounding-line retreat and AIS mass loss during deglaciation. Relative to models without these interactions, including the Northern Hemisphere sea-level forcing leads to a larger AIS volume during the Last Glacial Maximum (about 26,000 to 20,000 years ago), subsequent earlier grounding-line retreat and millennial-scale AIS variability throughout the last deglaciation. These findings are consistent with geologic reconstructions of the extent of the AIS during the Last Glacial Maximum and subsequent ice-sheet retreat, and with relative sea-level change in Antarctica. 

How to cite: Gomez, N., Weber, M., Clark, P., Mitrovica, J., and Han, H.: Antarctic ice dynamics amplified by Northern Hemisphere sea level forcing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9256, https://doi.org/10.5194/egusphere-egu21-9256, 2021.

EGU21-13669 | vPICO presentations | CR1.1 | Highlight

Redating the Global Abrupt Sea-Level Rise during Meltwater Pulse-1A and Implications for Global Ice Mass Loss

Christian Turney, Nicholas Golledge, Paula Reimer, Tim Heaton, Alan Hogg, Zoë Thomas, Lorena Belcerra-Valdivia, Maarten Blaauw, Haidee Cadd, Heather Haines, Matthew Harris, Christopher Marjo, and Jonathan Palmer
Model-based projections of ice-sheet thresholds and global sea-level rise are severely constrained by instrumental observations being only decadal to century-long. As we improve our understanding of these processes, projections just a few years old are now considered conservative, raising concerns about our ability to successfully plan for abrupt future change. Past periods of abrupt and extreme warming offer ‘process analogues’ that can provide new insights into the future rate of response of polar ice sheets to warming of the Earth system. The Last Termination (20,000-10,000 years ago or 20-10 ka BP) in the North Atlantic region was characterised by a series of abrupt climatic changes including rapid warming at 14.7 ka BP (the start of the “Bølling”, or GI-1 in the Greenland ice-core isotope stratigraphy) which was accompanied by an Antarctic Cold Reversal (ACR) in the south. Potentially important, during the onset of GI-1, warming persisted in the south for some 256±133 calendar years before the ACR, providing a period of time during which both polar regions experienced increasing temperatures. Sometime around the onset of GI-1 and the ACR, Meltwater Pulse 1A (MWP-1A) formed an abrupt sea level rise of ~15 metres, and was coincident with a period of enhanced iceberg flux in the Southern Ocean. It seems likely the majority of the sea level rise came from the Northern Hemisphere – up to 5-6 metres from the Laurentide Ice Sheet – though the timing remains uncertain. The contribution of Antarctic Ice Sheets (AIS) to global mean sea level (GMSL) rise during MWP-1A range from ‘high-end’ scenarios (>10 m contributing over half of the total GMSL rise), to ‘low-end’ (scenarios with little to no contribution). Here we report the results of a multidisciplinary study, with refined age and Antarctic ice-sheet modelling of the MWP-1A sea-level rise. With the recently released international radiocarbon calibration curve (IntCal20), our Bayesian age modelling of terrestrial ages from flooded mangrove swamps suggests global sea level rose across a mean age range of 14.58 ka BP to 14.42 ka BP, with a mean rate of sea-level rise of 0.94 metres per decade (14.97 metres over 160 years). Because the calibrated age range at 95% confidence overlaps in this age model, it is possible the 15 metre rise during MWP1A could have taken place essentially instantaneously. Even the most conservative age modelling we have undertaken indicates an extraordinary rapid rate of sea-level rise; two orders of magnitude larger than the mean rate of global sea level rise since 1993 (0.03±0.003 metres per decade). Our ice-sheet modelling suggests a substantial and rapid loss of Antarctic ice mass (mostly from the Weddell Sea Embayment and the Antarctic Peninsula), synchronous with warming and ice loss in the North Atlantic. The drivers and mechanisms of the observed near-synchronous interhemispheric changes will be discussed, with implications for the future.

How to cite: Turney, C., Golledge, N., Reimer, P., Heaton, T., Hogg, A., Thomas, Z., Belcerra-Valdivia, L., Blaauw, M., Cadd, H., Haines, H., Harris, M., Marjo, C., and Palmer, J.: Redating the Global Abrupt Sea-Level Rise during Meltwater Pulse-1A and Implications for Global Ice Mass Loss, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13669, https://doi.org/10.5194/egusphere-egu21-13669, 2021.

EGU21-9151 | vPICO presentations | CR1.1

U-Pb zircon geochronology of dropstones and IRD in the Amundsen Sea, applied to the question of bedrock provenance and Miocene-Pliocene ice sheet extent in West Antarctica

Christine Siddoway, Stuart Thomson, Sidney Hemming, Hannah Buchband, Cade Quigley, Heather Furlong, Robin Hilderman, Delaney Robinson, Connor Watkins, Stephen Cox, and Kathy Licht and the IODP Expedition 379 Scientists and Expedition 382 Scientists

IODP Expedition 379 to the Amundsen Sea continental rise recovered latest Miocene-Holocene sediments from two sites on a drift in water depths >3900m. Sediments are dominated by clay and silty clay with coarser-grained intervals and ice-rafted detritus (IRD) (Gohl et al. 2021, doi:10.14379/iodp.proc.379.2021). Cobble-sized dropstones appear as fall-in, in cores recovered from sediments >5.3 Ma.  We consider that abundant IRD and the sparse dropstones melted out of icebergs formed due to Antarctic ice-sheet calving events. We are using petrological and age characteristics of the clasts from the Exp379 sites to fingerprint their bedrock provenance. The results may aid in reconstruction of past changes in icesheet extent and extend knowledge of subglacial bedrock.

Mapped onshore geology shows pronounced distinctions in bedrock age between tectonic provinces of West or East Antarctica (e.g. Cox et al. 2020, doi:10.21420/7SH7-6K05; Jordan et al. 2020, doi.org/10.1038/s43017-019-0013-6). This allows us to use geochronology and thermochronology of rock clasts and minerals for tracing their provenance, and ascertain whether IRD deposited at IODP379 drillsites originated from proximal or distal Antarctic sources. We here report zircon and apatite U-Pb dates from four sand samples and five dropstones taken from latest Miocene, early Pliocene, and Plio-Pleistocene-boundary sediments. Additional Hf isotope data, and apatite fission track and 40Ar/39Ar Kfeldspar ages for some of the same samples help to strengthen provenance interpretations.

The study revealed three distinct zircon age populations at ca. 100, 175, and 250 Ma. Using Kolmogorov-Smirnov (K-S) statistical tests to compare our new igneous and detrital zircon (DZ) U-Pb results with previously published data, we found strong similarities to West Antarctic bedrock, but low correspondence to prospective sources in East Antarctica, implying a role for icebergs calved from the West Antarctic Ice Sheet (WAIS). The ~100 Ma age resembles plutonic ages from Marie Byrd Land and islands in Pine Island Bay.  The ~250 and 175 Ma populations match published mineral dates from shelf sediments in the eastern Amundsen Sea Embayment as well as granite ages from the Antarctic Peninsula and the Ellsworth-Whitmore Mountains (EWM). The different derivation of coarse sediment sources requires changes in iceberg origin through the latest Miocene, early Pliocene, and Plio/Pleistocene, likely the result of changes in WAIS extent.

One unique dropstone recovered from Exp379 Site U1533B is green quartz arenite, which yielded mostly 500-625 Ma detrital zircons. In visual appearance and dominant U-Pb age population, it resembles a sandstone dropstone recovered from Exp382 Site U1536 in the Scotia Sea (Hemming et al. 2020, https://gsa.confex.com/gsa/2020AM/meetingapp.cgi/Paper/357276). K-S tests yield high values (P ≥ 0.6), suggesting a common provenance for both dropstones recovered from late Miocene to Pliocene sediments, despite the 3270 km distance separating the sites. Comparisons to published data, in progress, narrow the group of potential on-land sources to exposures in the EWM or isolated ranges at far south latitudes in the Antarctic interior.  If both dropstones originated from the same source area, they could signify dramatic shifts in the WAIS grounding line position, and the possibility of the periodic opening of a seaway connecting the Amundsen and Weddell Seas.

How to cite: Siddoway, C., Thomson, S., Hemming, S., Buchband, H., Quigley, C., Furlong, H., Hilderman, R., Robinson, D., Watkins, C., Cox, S., and Licht, K. and the IODP Expedition 379 Scientists and Expedition 382 Scientists: U-Pb zircon geochronology of dropstones and IRD in the Amundsen Sea, applied to the question of bedrock provenance and Miocene-Pliocene ice sheet extent in West Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9151, https://doi.org/10.5194/egusphere-egu21-9151, 2021.

EGU21-7680 | vPICO presentations | CR1.1

Simulating the contribution of the Antarctic ice sheet to Miocene benthic δ18O variability

Lennert B. Stap, Roderik S. W. van de Wal, Johannes Sutter, Gregor Knorr, and Gerrit Lohmann

Large benthic δ18O fluctuations, which are caused by deep-ocean temperature and ice-volume changes, are shown on multiple time scales during the early to mid-Miocene (23-14 Myr ago). To understand how these signals are related to orbital changes, it is necessary to disentangle them. Here, we approach this problem by simulating how the Antarctic ice sheet (AIS) responds to typical CO2 changes during this period. We use the 3D thermodynamical model PISM, forced by climate model output, to conduct both transient and steady-state experiments. Our results indicate that even if equilibrium differences are relatively large (~40 m.s.l.e.), transient AIS variability on orbital time scales (20-400 kyr) still has a much smaller amplitude due to the slow ice-volume response to climatic changes. We analyse our results further using a conceptual model, based on the notion that at any CO2 level an ice sheet will grow (shrink) by a specific rate towards its smaller (larger) equilibrium size. We show that phases of concurrent ice volume increase and rising CO2 levels are possible, even though the equilibrium ice volume decreases monotonically with CO2. When the AIS volume is out of equilibrium with the forcing climate, the ice sheet can still be adapting to a relatively large equilibrium size, although CO2 is rising after a phase of decrease. A delayed response of Antarctic ice volume to in-sync solar insolation and CO2 changes can cause discrepancies between Miocene solar insolation and benthic δ18O variability.

How to cite: Stap, L. B., van de Wal, R. S. W., Sutter, J., Knorr, G., and Lohmann, G.: Simulating the contribution of the Antarctic ice sheet to Miocene benthic δ18O variability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7680, https://doi.org/10.5194/egusphere-egu21-7680, 2021.

EGU21-4076 | vPICO presentations | CR1.1

Sensitivity of the Antarctic ice sheets to the warming of MIS11c

Martim Mas e Braga, Jorge Bernales, Matthias Prange, Arjen P. Stroeven, and Irina Rogozhina

The Marine Isotope Substage 11c (MIS11c) interglacial (425 – 395 thousand years before present) is a useful analogue to climate conditions that can be expected in the near future, and can provide insights on the natural response of the Antarctic ice sheets to a moderate, yet long lasting warming period. However, its response to the warming of MIS11c and consequent contribution to global sea level rise still remains unclear. We explore the dynamics of the Antarctic ice sheets during this period using a numerical ice-sheet model forced by MIS11c climate conditions derived from climate model outputs scaled by three ice core and one sedimentary proxy records of ice volume. We identify a tipping point beyond which oceanic warming becomes the dominant forcing of ice-sheet retreat, and where collapse of the West Antarctic Ice Sheet is attained when a threshold of 0.4 oC oceanic warming relative to Pre-Industrial levels is sustained for at least 4 thousand years. Conversely, its eastern counterpart remains relatively stable, as it is mostly grounded above sea level. Our results suggest a total sea level contribution from the East and West Antarctic ice sheets of 4.0 – 8.2 m during MIS11c. In the case of a West Antarctic Ice Sheet collapse, which is the most probable scenario according to far-field sea-level reconstructions, this range is reduced to 6.7 – 8.2 m, and mostly reflects uncertainties regarding the initial configuration of the East Antarctic Ice Sheet.

How to cite: Mas e Braga, M., Bernales, J., Prange, M., Stroeven, A. P., and Rogozhina, I.: Sensitivity of the Antarctic ice sheets to the warming of MIS11c, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4076, https://doi.org/10.5194/egusphere-egu21-4076, 2021.

EGU21-1321 | vPICO presentations | CR1.1

The unique behavior of stable water isotopes profiles during interglacial periods at Talos Dome, Antarctica

Ilaria Crotti, Amaelle Landais, Barbara Stenni, Massimo Frezzotti, Aurélien Quiquet, Frédéric Prié, Bénédicte Minster, Giuliano Dreossi, and Carlo Barbante

The growth and decay of marine ice sheets act as important controls on regional and global climate, in particular, the behavior of the ice sheets is a key uncertainty in predicting sea-level rise during and beyond this century. The East Antarctic Ice Sheet (EAIS), which contains deep subglacial basins with reverse-sloping, is considered to be susceptible to ice loss caused by marine ice sheet instability. Sediment core offshore Wilkes Subglacial Basin reveals oscillations in the provenance of detrital sediment that have been interpreted to reflect an erosion of Wilkes Basin during interglacial periods MIS 5, MIS 7, and MIS 9 greater than Holocene period (Wilson et al., 2018). The aim of our study is to investigate past climate and environmental changes in the coastal area of the East Antarctic Ice Sheet during MIS 7.5 and 9.3 with the help of a new high-resolution water isotopes record of the TALDICE ice core.

Here we present new δ18O and δD high resolution (5 cm) records covering the oldest portion of the TALDICE ice core. MIS 7.5 and 9.3 isotopic signal reveals a unique feature, already observed for MIS 5.5, that has not been spotted in other Antarctic ice cores (Masson-Delmotte et al., 2011). Interglacial periods at TALDICE are characterized by a first peak, observed in correspondence to the culmination of the deglaciation event as for all Antarctic cores, followed by a less pronounced isotopic peak (for MIS 5.5 and 9.3) or a plateau (for MIS 7.5) prior to the glacial inception. Several factors might drive this peculiar behavior of the water stable isotopes record, as an increase in temperatures due to a drop in surface elevation or changes in moisture sources.

The new δ18O and δD high-resolution records for the TALDICE ice core reveal a unique pattern that characterizes interglacial periods at Talos Dome. Taking into account the coastal position of the core and its vicinity to the Wilkes Subglacial Basin we intend to investigate the possible decrease in surface elevation, through the application of the GRISLI ice sheet model (Quiquet et al., 2018), and changes in moisture sources, traceable from the d-excess record.

How to cite: Crotti, I., Landais, A., Stenni, B., Frezzotti, M., Quiquet, A., Prié, F., Minster, B., Dreossi, G., and Barbante, C.: The unique behavior of stable water isotopes profiles during interglacial periods at Talos Dome, Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1321, https://doi.org/10.5194/egusphere-egu21-1321, 2021.

EGU21-9957 | vPICO presentations | CR1.1

Post-Last Glacial Maximum ice thinning and glacier dynamics in the Hurd Peninsula ice cap (Livingston Island, South Shetland Islands, Antarctic Peninsula)

José M. Fernández-Fernández, Marc Oliva, David Palacios, Julia García-Oteyza, Francisco Navarro, and Irene Schimmelpfennig

In the Antarctic Peninsula (AP), the small ice caps distributed across its periphery and surrounding islands have recorded important ice volume changes since the end of the Last Glacial Cycle. These volume changes have occurred in the form of surface extent shrinking and ice thinning. The latter has been investigated only at a reduced number of locations. In this context, nunataks constitute key spots to assess the environmental evolution of deglaciated areas as they offer the opportunity to track the deglaciation history and reconstruct past ice losses by using Cosmic-Ray Exposure (CRE) dating. Indeed, nunataks are supposed to have played a prominent role in the vegetal and animal colonization of Antarctica.

The South Shetland Islands archipelago is one of the AP areas where past ice thinning has been least investigated, with only one study conducted in King George Island. In order to shed some light on the last deglaciation and its associated ice thinning, we apply 10Be CRE dating to vertical sequences of glacially polished outcrops on two palaeonunataks and one nunatak distributed across the ice-cap covering part of the Hurd Peninsula (SW of Livingston Island): Reina Sofía Peak (62°40'8" S, 60°22'51" W, 273 m a.s.l.), Moores Peak (62°41'21" S, 60°20'42" W, 407 m a.s.l.) and Napier Peak (62°40'18"S, 60°19'31" W, 382 m a.s.l.).

Most of the resulting exposure ages provided a logical chronological sequence and allowed reconstructing past vertical changes of the ice surface. The uppermost surfaces of the Moores and Reina Sofía peaks became deglaciated during the Last Glacial Maximum (LGM), between ~24 ka and ~20 ka. Following the LGM, between ~20 and ~14 ka (Termination-1), a massive deglaciation occurred. This trend was especially exacerbated at around ~14 ka, triggering the onset of the deglaciation at other nunataks, such as the Napier Peak, in good agreement with the coetaneous global melt-water pulse 1a. From our results, we infer that ice shrinking during the Holocene must have been very limited compared to the post-LGM period.

Nevertheless, some of the exposure ages were either anomalously old or inconsistent, such as those found at the summits of the Reina Sofía and Moores peaks or at the base of the Napier nunatak. These artifacts suggest the occurrence of nuclide inheritance and are indicative of the conservation of previously exposed surfaces. These ages allow to qualitatively infer cold-based regimes characterized by basal ice frozen to bed, with slow mobility and inefficient subglacial erosion due to the gentle slope gradient, not capable of removing inherited nuclides accumulated during former exposure periods. But, as a whole, the dataset adds valuable knowledge on the polythermal character of the Hurd Peninsula Ice cap.

 

This paper was supported by the project NUNANTAR (02/SAICT/2017 – 32002; Fundação para a Ciência e a Tecnologia, Portugal) and the College on Polar and Extreme Environments (University of Lisbon).

How to cite: Fernández-Fernández, J. M., Oliva, M., Palacios, D., García-Oteyza, J., Navarro, F., and Schimmelpfennig, I.: Post-Last Glacial Maximum ice thinning and glacier dynamics in the Hurd Peninsula ice cap (Livingston Island, South Shetland Islands, Antarctic Peninsula), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9957, https://doi.org/10.5194/egusphere-egu21-9957, 2021.

EGU21-3385 | vPICO presentations | CR1.1 | Highlight

Decadal-scale onset and termination of Antarctic ice-mass loss during the last deglaciation

Michael E. Weber, Nicholas R. Golledge, Christopher J. Fogwill, Chris S.M. Turney, and Zoë A. Thomas

Emerging evidence suggests retreat of the Antarctic Ice Sheet (AIS) can persist considerably longer than the duration of the forcing. Unfortunately, the short observational record cannot resolve the tipping points, rate of change, and responses on century and longer timescales. New data from Iceberg Alley identifies eight retreat phases after the last Ice Age that de-stabilized the AIS within a decade, contributing to global sea-level rise for centuries to a millennium, which subsequently stabilized equally rapidly. New blue ice records and independent ice-sheet modeling demonstrate the dynamic response of the AIS included a step-wise retreat of up to 400 km across the Ross Sea, accompanied by ice elevation drawdown of the West Antarctic Ice Sheet (>600 m). Together, these long time series support studies that propose the recent acceleration of AIS mass loss may mark the beginning of a prolonged period of ice sheet retreat, associated with substantial global sea level rise.

How to cite: Weber, M. E., Golledge, N. R., Fogwill, C. J., Turney, C. S. M., and Thomas, Z. A.: Decadal-scale onset and termination of Antarctic ice-mass loss during the last deglaciation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3385, https://doi.org/10.5194/egusphere-egu21-3385, 2021.

EGU21-11743 | vPICO presentations | CR1.1

Regional climate and ice shelf melt captured in an Antarctic Peninsula ice core

Daniel Emanuelsson and Elizabeth R. Thomas

In this study, we present the stable water isotope record (δ18O) from an ice core drilled in Palmer Land, the southern Antarctic Peninsula (AP). This unique record, records changes in eastern AP ice shelf melt on the Larsen ice shelves. We show that warm years recorded in the ice core δ18O record are associated northeasterly winds that pass over the peninsula and subsequently result in foehn-induced surface warming and melt events on the Larsen Ice shelves on the eastern coast. The recent strengthening of westerly winds that circumference Antarctica (positive trend in SAM) and the deepening of the Amundsen Sea Low drives these strong northeasterly winds. We reconstruct the number of yearly melt days on the Larsen B ice shelf using melt days estimates from the published QSCAT/ASCAT dataset. Our record shows that melting on the Larsen B ice shelf since the late 1990s was higher than at any time during the past 388 years. However, periods with a high number of melt days have occurred in the past during the latter parts of the 17th and 19th centuries, as well as more recently during the 1940s, which may indicate past foehn-induced ice shelf melting.

How to cite: Emanuelsson, D. and Thomas, E. R.: Regional climate and ice shelf melt captured in an Antarctic Peninsula ice core, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11743, https://doi.org/10.5194/egusphere-egu21-11743, 2021.

EGU21-9225 | vPICO presentations | CR1.1

Reconstructing atmospheric circulation and sea-ice extent in the West Antarctic over the past 200 years using data assimilation 

Quentin Dalaiden, Hugues Goosse, Jeanne Rezsohazy, and Elizabeth R. Thomas

Ocean and ice sheet in the West Antarctic sector have witnessed large climate changes during the second half of the 20th century including a strong and widespread continental warming, important regional changes in sea-ice extent and snow accumulation, as well as a major mass loss from the melting of some ice shelves. However, the potential links between those observed changes are still unclear and instrumental data do not allow determining if they are part of a long-term evolution or specific to the recent decades. In this study, we analyze the climate variability of the past two centuries in the West Antarctic sector by reconstructing the key atmospheric variables (atmospheric circulation, near-surface air temperature and snow accumulation) as well as the sea-ice extent at the annual timescale using a data assimilation approach. To this end, information from Antarctic ice core records (snow accumulation and δ18O) and tree-ring width sites located in the mid-latitudes of the Southern Hemisphere are combined with the physics of climate models using a data assimilation method. This ultimately provides a complete spatial reconstruction over the west Antarctic region. Our reconstruction reproduces well the main characteristics of the observed changes over the instrumental period. We show that the observed sea-ice reduction in the Bellingshausen-Amundsen Sea sector over the satellite era is part of a long-term trend, starting at around 1850 CE, while the sea-ice expansion in the Ross Sea sector has only started around 1950 CE. Furthermore, according to our reconstruction, the Amundsen Sea Low pressure (ASL) displays no significant linear trend in its strength or position over 1850-1950 CE but becomes stronger and shifts eastward afterwards. The year-to-year sea-ice variations in the Ross Sea sector are strongly related to the ASL variability over the past two centuries, including the recent trends. By contrast, the link between ASL and sea ice the Bellingshausen-Amundsen Sea sector changes with time, being stronger in recent decades than before, Our reconstruction also suggests that the continental response to the variability of the ASL may not be stationary over time, being significantly affected by modification of the mean circulation. Finally, we show that the widespread warming since 1958 CE in West Antarctica is unusual in the context of past 200 years and is explained by both the deeper ASL and the positive phase of the Southern Annular Mode.

How to cite: Dalaiden, Q., Goosse, H., Rezsohazy, J., and Thomas, E. R.: Reconstructing atmospheric circulation and sea-ice extent in the West Antarctic over the past 200 years using data assimilation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9225, https://doi.org/10.5194/egusphere-egu21-9225, 2021.

EGU21-8714 | vPICO presentations | CR1.1

Antarctic Surface Mass Balance from 1980 to 2017

Nicolaj Hansen, Peter L. Langen, Fredrik Boberg, Rene Forsberg, Sebastian B. Simonsen, Peter Thejll, Baptiste Vandercrux, and Ruth Mottram

The regional climate model HIRHAM5 developed for Greenland ice sheet applications has now been updated to also simulate Antarctic conditions. The outputs of the Antarctic runs have been used to force an offline subsurface model, to give estimates of the Antarctic surface mass balance (SMB) from 1980 to 2017.  Here, we compare two different versions of this offline subsurface model and evaluate how they simulate the physical properties of the uppermost part of the Antarctic firn pack. We find that the total calculated SMB of Antarctica is sensitive to the subsurface model variant. One model version uses an Eulerian framework, meaning that mass is advected through layers of fixed mass. When snowfall occurs at the surface, it is added to the first layer and an equal mass from that layer is shifted to the underlying layer. The same goes for each layer in the model column, and vice versa for mass loss. The other model version uses a Lagrangian framework for the layer development. Layers evolve through splitting and merging dynamically based on a number of weighted criteria.

The model simulations are validated against in situ observations of firn temperature and subsurface density. We find a mean temperature bias of 0.42-0.52 ℃  and a mean bias in modelled density of -24.0±18.4 kg m⁻³ and  -8.2±15.3 kg m⁻³ for layers less than 550 kg m⁻³ for the Eulerian and Lagrangian framework, respectively. For layers with a density above 550 kg m⁻³ the bais is -31.7±23.4 kg m⁻³ and -35.0±23.7 kg m⁻³  for the Eulerian and Lagrangian framework, respectively. The modelling framework also  affects the resulting  SMB. The Lagrangian framework,  estimates a total SMB  of 2473.5±114.4 Gt yr⁻¹ while the Eulerian framework results in slightly higher modelled SMB of  2564.8±113.7 Gt yr⁻¹. The majority for this difference in modelled SMB is pinpointed to the  ice shelves (the SMB over grounded ice only  differs  30 Gt yr⁻¹) and  demonstrates the importance of firn modelling in areas with substantial melt. Both the Eulerian and the Lagrangian SMB estimates are within each other's uncertainties and within range of other SMB studies. However, the Lagrangian version has the best statistics for modelling the densities. Given the importance of precipitation to Antarctic SMB, climate models must accurately simulate regional circulation patterns that modulate precipitation rates. We therefore investigate the relationship between SMB in individual drainage basins and the southern annular mode (SAM),  using Monte Carlo simulations. This shows a robust relationship between SAM and SMB in half of the basins (13 out of 27). In general, when SAM is positive there is a lower SMB over the Plateau and a higher SMB on the westerly side of the Antarctic Peninsula, and vice versa when the SAM is negative.

How to cite: Hansen, N., Langen, P. L., Boberg, F., Forsberg, R., Simonsen, S. B., Thejll, P., Vandercrux, B., and Mottram, R.: Antarctic Surface Mass Balance from 1980 to 2017, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8714, https://doi.org/10.5194/egusphere-egu21-8714, 2021.

Input-Output method (IOM) is a common method for estimating ice sheet mass balance, which shows ice dynamics in mass loss to analyze the response of ice sheet to climate change. However, compared with the altimetry method and the gravity method, the mass balance estimation using IOM has relatively large uncertainty. Assessing the impact of the uncertainties of each component in IOM on the mass balance estimation is conducive to effectively lowering uncertainty in the Antarctic mass budget estimate but of which there has been little quantitative analysis. We assess the uncertainty in the mass balance due to methodological differences in IOM, compare the differences of surface mass balance (SMB, input) in diverse versions and at different spatial scales, and evaluate the uncertainty in ice discharge (FG, output) due to data uncertainty in ice thickness, ice velocity and grounding line. Results showed that the SMBs at different scales are more divergent than that in different versions, resulting in a variation of 216.7 Gt yr-1 in Antarctica, of which the Antarctic peninsula accounts for 55.1%, followed by East Antarctica. The largest variation in FG due to uncertainty in the location of the grounding line is observed, where a 1 km retreat and a 1 km advance of the Antarctic grounding line would respectively result in FG reductions of 82.8 Gt yr-1 and 272.7 Gt yr-1, which are significant in all regions, with the FG corresponding to a 1 km retreat of grounding line in the islands being closer to the multi-year average SMB of the islands. The difference in Antarctic FG due to different ice thickness products is 124.4 Gt yr-1, consistent with the trend in the thickness of ice shelves, and that due to different ice velocity products is only 18.7 Gt yr-1. Within the same margin of error, systematic errors in ice thickness and ice velocity result in an order of magnitude higher difference of FG than random errors.

How to cite: Lin, Y. and Liu, Y.: Uncertainties in Mass Balance Estimation of the Antarctic Ice Sheet Using Input-output Method, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5589, https://doi.org/10.5194/egusphere-egu21-5589, 2021.

EGU21-6252 | vPICO presentations | CR1.1

Towards investigating the race of two Marine Ice instabilities: Sheet vs. Cliff

Tanja Schlemm and Anders Levermann

Due to ocean warming in the Amundsen sea, pine island glacier and thwaites glacier could lose their buttressing ice shelves in the near future. This would lead to glacier retreat through the marine ice sheet instability and could be accelerated by additional cliff calving (marine ice cliff instability). Using the Parallel Ice Sheet Model (PISM-PIK) we investigate this in a regional setup of the West Antarctic Ice Sheet. We remove floating ice in the Amundsen sea and investigate the resulting glacier retreat without additional cliff calving and with cliff calving with a range of maximum calving rates. We find that without additional cliff calving, the removal of the ice shelves in the Amundsen sea leads to a glacier retreat that is equivalent to 0.4-0.6m of sea level rise in 100 years, consistent with earlier simulations of other models (ABUMIP and LARMIP-2). Cliff calving can more than double this number.

How to cite: Schlemm, T. and Levermann, A.: Towards investigating the race of two Marine Ice instabilities: Sheet vs. Cliff, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6252, https://doi.org/10.5194/egusphere-egu21-6252, 2021.

EGU21-5388 | vPICO presentations | CR1.1

The influence of the solid Earth on the contribution of marine sections of the Antarctic ice sheet to future sea level change

Maryam Yousefi, Jeannette Wang, Linda Pan, Natalya Gomez, Konstantin Latychev, Jerry Mitrovica, and David Pollard

The future retreat of marine-based sectors of the Antarctic Ice Sheet (AIS) and its consequent global mean sea level (GMSL) rise is driven by various climatic and non-climatic feedbacks between ice, ocean, atmosphere, and solid Earth. The primary mode of ice loss in marine sectors of the AIS is dynamic flow of ice across the grounding line into the ocean. The flux of ice across the grounding line is strongly sensitive to the thickness of ice there, which is in turn proportional to the water depth (sea level) such that sea level rise enhances ice loss and grounding line retreat while sea level fall acts to slow or stop migration of the grounding line. In response to the unloading from removal of ice mass, the underlying bedrock deforms isostatically leading to lower local sea surface which promotes stabilization of the grounding line. In addition to its effect on AIS evolution, solid Earth deformation also alters the shape and size of the ocean basin areas that are exposed as marine areas of ice retreat and influences the amount of meltwater that leaves Antarctica and contributes to global sea-level rise. The solid Earth deformational response to surface loading changes, in terms of both magnitude and timescales, depends on Earth rheology. Seismic tomography models indicate that the interior structure of the Earth is highly variable over the Antarctica with anomalously low shallow mantle viscosities across the western section of the AIS. An improved projection of the contribution from AIS to sea level change requires a consideration of this complexity in Earth structure. Here we adopt a state-of-the-art seismic velocity model to build a high-resolution 3D viscoelastic structure model beneath Antarctica. We incorporate this structure into a high spatiotemporal resolution sea-level model to simulate the influence of solid Earth deformation on contributions of the AIS evolution to future sea-level change. Our sea-level model is coupled with the dynamics of PSU ice sheet model and our calculations are based on a range of future climate forcings. We show that the influence of applying a spatially variable Earth structure is significant, particularly in the regions of West Antarctica where upper mantle viscosities are lower and the elastic lithosphere is thinned.

How to cite: Yousefi, M., Wang, J., Pan, L., Gomez, N., Latychev, K., Mitrovica, J., and Pollard, D.: The influence of the solid Earth on the contribution of marine sections of the Antarctic ice sheet to future sea level change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5388, https://doi.org/10.5194/egusphere-egu21-5388, 2021.

EGU21-6722 | vPICO presentations | CR1.1

ISMIP6-based projections of ocean-forced Antarctic ice loss using the Community Ice Sheet Model 

William Lipscomb, Gunter Leguy, Nicolas Jourdain, Xylar Asay-Davis, Hélène Seroussi, and Sophie Nowicki

The future retreat rate for marine-based regions of the Antarctic Ice Sheet is one of the largest uncertainties in sea-level projections. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) aims to improve projections and quantify uncertainties by running an ensemble of ice sheet models with forcing derived from global climate models. Here, the Community Ice Sheet Model (CISM) is used to run ISMIP6-based projections of ocean-forced Antarctic Ice Sheet evolution. Using several combinations of sub-ice-shelf melt schemes, CISM is spun up to steady state over many millennia. During the spin-up, basal-friction and thermal-forcing parameters are adjusted to optimize agreement with the observed ice thickness. The model is then run forward to year 2500, applying ocean thermal forcing anomalies from six climate models. In all simulations, ocean warming triggers long-term retreat of the West Antarctic Ice Sheet, especially in the Filchner-Ronne and Ross sectors. The ocean-forced sea-level rise in 2500 varies from about 150 mm to 1300 mm, depending on the melt scheme and ocean forcing applied. Further experiments show relatively high sensitivity to the basal friction law, and moderate sensitivity to grid resolution and the prescribed collapse of small ice shelves. The Amundsen sector exhibits threshold behavior, with modest retreat under many parameter settings, but complete collapse under some combinations of low basal friction and high thermal-forcing anomalies. Large uncertainties remain, as a result of parameterized sub-shelf melt rates, simplified treatments of calving and basal friction, and the lack of ice–ocean coupling.

How to cite: Lipscomb, W., Leguy, G., Jourdain, N., Asay-Davis, X., Seroussi, H., and Nowicki, S.: ISMIP6-based projections of ocean-forced Antarctic ice loss using the Community Ice Sheet Model , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6722, https://doi.org/10.5194/egusphere-egu21-6722, 2021.

CR1.2 – Integrating models and observations for the estimation of ice sheet mass balance and sea level, incorporating ISMASS/ISMIP6

EGU21-3103 | vPICO presentations | CR1.2

Trends in ice sheet mass balance

Andrew Shepherd and Erik Ivins and the IMBIE Team

The Ice Sheet Mass Balance Inter-Comparison Exercise (IMBIE) is a community effort supported by ESA and NASA that aims to provide a consensus estimate of ice sheet mass balance. In its first phase, IMBIE showed that estimates of ice sheet mass balance derived from satellite gravimetry, altimetry and the mass budget method could be reconciled within their respective uncertainties. In its second phase, IMBIE showed that rates of ice loss from Antarctica and Greenland have increased by a factor 6 during the satellite era and are tracking the high-end (worst-case) projections reported in the IPCC’s fifth assessment report (AR5). The project now involves 96 individual participants based in 50 institutes from 13 nations and includes 26 satellite estimates of ice sheet mass balance, 11 models of glacial isostatic adjustment, and 10 models of surface mass balance. IMBIE has now begun its third phase, and the objectives are to (i) include measurements from new satellite missions, (ii) to report annual assessments, (iii) to partition changes in mass due to ice dynamics and surface mass balance, (iv) to produce regional assessments in areas of imbalance, and to (v) explore remaining biases between the various geodetic techniques involved. Participation is open to the full community, and the quality and consistency of submissions is regulated through a series of data standards and documentation requirements. This paper will introduce the objectives of IMBIE-3 and present the latest assessment of ice sheet mass balance. which has been updated for the IPCC's sixth assessment report.

How to cite: Shepherd, A. and Ivins, E. and the IMBIE Team: Trends in ice sheet mass balance, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3103, https://doi.org/10.5194/egusphere-egu21-3103, 2021.

EGU21-12825 | vPICO presentations | CR1.2

Historic simulations of the Antarctic Ice Sheet with the Parallel Ice Sheet Model

Ronja Reese, Adrian Jenkins, Christopher Bull, Hartmut Hellmer, and Ricarda Winkelmann

Large uncertainties in Antarctic sea level projections are related to ocean-driven melting (Seroussi et al., 2020; Jourdain et al., 2020; Reese et al., 2020; Edwards et al., in press) and the marine ice sheet instability (Robel et al., 2019). ‘Hindcasting’ simulations that follow the trajectory of the Antarctic Ice Sheet from pre-industrial conditions to present-day, are a useful tool to better constrain such uncertainties. We here perform historic simulations with the Parallel Ice Sheet Model. The simulations are forced by changes in the ocean and atmosphere from GCM output of CMIP5 as selected for ISMIP6 (Barthel et al., 2020). Sub-shelf melting is modeled using PICO (Olbers & Hellmer, 2010; Reese et al., 2018), with careful consideration of PICO’s parameters: the parameters for heat exchange across the ice ocean interface as well as the overturning strength are fitted with estimates of the melt sensitivity based on observations (Jenkins et al., 2018). Present-day observation of sub-shelf melting and mass loss inform parameter selection using an ensemble approach (Albrecht et al., 2020; Reese et al., 2020). The historic simulations provide an important basis to assess the future evolution and stability of Antarctic grounding lines. This work is done in the framework of the H2020 TiPACCs project.

How to cite: Reese, R., Jenkins, A., Bull, C., Hellmer, H., and Winkelmann, R.: Historic simulations of the Antarctic Ice Sheet with the Parallel Ice Sheet Model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12825, https://doi.org/10.5194/egusphere-egu21-12825, 2021.

EGU21-7476 | vPICO presentations | CR1.2

Predicting the Antarctic sea level contribution to sea level rise with emulation

Fiona Turner and Tamsin Edwards and the ISMIP6 team and others

The Antarctic ice sheet has the potential to be a major contributor to future global sea level rise, but this has been difficult to predict, in part due to the combination of expected ice mass loss and snowfall accumulation. A great deal of uncertainty arises from the large variation of atmospheric and oceanic changes across climate models, and sensitivity to ocean changes across ice sheet models, but these uncertainties cannot be fully sampled because the models are too computationally expensive.

Here we make projections of Antarctica’s contribution to global sea level rise based on the simulations of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). Using a Gaussian process emulator, a statistical approximation of expensive computer models, we estimate probability distributions by sampling uncertainties in future climate and ice sheet sensitivity to ocean warming far more thoroughly than the original ISMIP6 ensemble could. We find a sea level contribution of 4 cm (5th-95th percentile range -5 to 14 cm) sea level equivalent by 2100 under current emissions policies, increasing to 21 cm (5th-95th percentile range 7 to 43 cm) if we use the subset of climate models, ice sheet models and ice sheet/ocean sensitivity values that lead to the highest sea level contributions.

We then compare the output from this emulator to a linear mixed model emulator, which  incorporates a random effect to represent the variation arising from different ice sheet models. We do this for all three Antarctic regions (West and East Antarctica, and the Peninsula) under two greenhouse emissions scenarios (SSP1-26 and SSP5-85). Both methods produce similar probability distributions of sea level contribution in 2100, demonstrating that differences in statistical models are not dominating the results.

How to cite: Turner, F. and Edwards, T. and the ISMIP6 team and others: Predicting the Antarctic sea level contribution to sea level rise with emulation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7476, https://doi.org/10.5194/egusphere-egu21-7476, 2021.

EGU21-11823 | vPICO presentations | CR1.2

Antarctic ice sheet response to upper-bound scenarios

Sainan Sun and Frank Pattyn

Mass loss of the Antarctic ice sheet contributes the largest uncertainty of future sea-level rise projections. Ice-sheet model predictions are limited by uncertainties in climate forcing and poor understanding of processes such as ice viscosity. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) has investigated the 'end-member' scenario, i.e., a total and sustained removal of buttressing from all Antarctic ice shelves, which can be regarded as the upper-bound physical possible, but implausible contribution of sea-level rise due to ice-shelf loss. In this study, we add successive layers of ‘realism’ to the ABUMIP scenario by considering sustained regional ice-shelf collapse and by introducing ice-shelf regrowth after collapse with the inclusion of ice-sheet and ice-shelf damage (Sun et al., 2017). Ice shelf regrowth has the ability to stabilize grounding lines, while ice shelf damage may reinforce ice loss. In combination with uncertainties from basal sliding and ice rheology, a more realistic physical upperbound to ice loss is sought. Results are compared in the light of other proposed mechanisms, such as MICI due to ice cliff collapse.

How to cite: Sun, S. and Pattyn, F.: Antarctic ice sheet response to upper-bound scenarios, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11823, https://doi.org/10.5194/egusphere-egu21-11823, 2021.

EGU21-2160 | vPICO presentations | CR1.2

Diverging future surface mass balance between the Antarctic ice shelves and grounded ice sheet

Christoph Kittel, Charles Amory, Cécile Agosta, Nicolas C Jourdain, Stefan Hofer, Alison Delhasse, Sébastien Doutreloup, Pierre-Vincent Huot, Charlotte Lang, Thiery Fichefet, and Xavier Fettweis

The future surface mass balance (SMB) will influence the ice dynamics and the contribution of the Antarctic ice sheet (AIS) to the sea-level rise. Most of recent Antarctic SMB projections were based on the 5th phase of the Coupled Model Intercomparison Project (CMIP5). However, new CMIP6 results have revealed a +1.3°C higher mean Antarctic near-surface temperature than in CMIP5 at the end of the 21st century enabling estimations of future SMB in warmer climates. Here, we investigate the AIS sensitivity to different warmings with an ensemble of four simulations performed with the polar regional climate model MAR forced by two CMIP5 and two CMIP6 models over 1981--2100. Statistical extrapolation allows us to expand our results to the whole CMIP5 and CMIP6 ensembles. Our results highlight a contrasting effect on the future grounded ice sheet and the ice shelves. The SMB over grounded ice is projected to increase as a response to stronger snowfall, only partly offset by enhanced meltwater runoff. This leads to a cumulated sea-level rise mitigation (i.e. an increase in surface mass) of the grounded Antarctic surface by 5.1 ± 1.9 cm sea-level equivalent (SLE) in CMIP5-RCP8.5 and 6.3 ± 2.0 cm SLE in CMIP6-ssp585. Additionally, the CMIP6 low-emission ssp126 and intermediate-emission ssp245 scenarios project a stabilised surface mass gain resulting in a lower mitigation to sea-level rise than in ssp585. Over the ice shelves, the strong runoff increase associated with higher temperature is projected to lower the SMB with a stronger decrease in CMIP6-ssp585 compared to CMIP5-RCP8.5. Ice shelves are however predict to have a close-to-present-equilibrium stable SMB under CMIP6 ssp126 and ssp245 scenarios. Future uncertainties are mainly due to the sensitivity to anthropogenic forcing and the timing of the projected warming. Furthermore,  we compare the MAR projected SMB to the ISMIP6-derived SMB, revealing large local and integrated differences between MAR and the respective forcing ESM highlighting the need of additional projections relying on more models including both RCMs and ESMs. While ice shelves should remain at a close-to-equilibrium stable SMB under the Paris Agreements, MAR projects strong SMB decrease for an Antarctic near-surface warming above +2.5°C limiting the warming range before potential irreversible damages on the ice-shelves. Finally, our results reveal the existence of a potential threshold (+7.5°C) that leads to a lower grounded SMB increase. This however has to be confirmed in following studies using more extreme or longer future scenarios.

How to cite: Kittel, C., Amory, C., Agosta, C., Jourdain, N. C., Hofer, S., Delhasse, A., Doutreloup, S., Huot, P.-V., Lang, C., Fichefet, T., and Fettweis, X.: Diverging future surface mass balance between the Antarctic ice shelves and grounded ice sheet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2160, https://doi.org/10.5194/egusphere-egu21-2160, 2021.

EGU21-13754 | vPICO presentations | CR1.2

Some future projections from coupling the U.K. Earth System Model to the Antarctic ice sheets

Antony Siahaan, Robin Smith, Paul Holland, Adrian Jenkins, and Colin Jones

A UKESM climate model which is coupled annually to the BISICLES ice sheet model to enable a two way interactions in Antarctica has been developed 
and run through a small ensemble of four SSP1-1.9 & SSP5-8.5 scenario members. Under the extreme anthropogenic forcing, all the initial condition 
ensemble members develop strong melting under the cold & large Ross and Filchner-Ronne ice-shelves, where it starts after the first half of simulation 
period for the former and in the last decade of the run for the latter. Despite that, during the 85 years timescale of these scenario runs, the stronger radiative forcing has positive effects on the ice-sheet mass gain through increasing precipitation on grounded ice regions which offsets the impact of basal melting in ice discharge across the grounding lines.

How to cite: Siahaan, A., Smith, R., Holland, P., Jenkins, A., and Jones, C.: Some future projections from coupling the U.K. Earth System Model to the Antarctic ice sheets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13754, https://doi.org/10.5194/egusphere-egu21-13754, 2021.

EGU21-140 | vPICO presentations | CR1.2

Uncertainty in East Antarctic firn thickness constrained using a model ensemble approach

Vincent Verjans, Amber Leeson, Malcolm McMillan, Max Stevens, Jan Melchior van Wessem, Willem Jan van de Berg, Michiel van den Broeke, Christoph Kittel, Charles Amory, Xavier Fettweis, Nicolaj Hansen, Fredrik Boberg, and Ruth Mottram

Mass balance assessments of the East Antarctic ice sheet are highly sensitive to changes in firn thickness resulting from variability in firn compaction rates and surface mass fluxes (snowfall, sublimation, melt). To better constrain uncertainty in firn thickness and in the underlying processes, we develop a model-based ensemble of firn evolution scenarios over 1992-2017. We combine statistical emulation of nine firn-densification models, climatic output from three regional climate models and different assumptions about surface snow density to generate a comprehensive set of 54 model scenarios. The ensemble agrees that firn thickness changes in the interior are minor, but there are pronounced thickening and thinning patterns in coastal areas.  At basin level, model uncertainty in firn thickness change ranges between 0.2–1.0 cm yr-1 (15–300%). Statistical analysis of the ensemble uncertainty demonstrates that climatic forcing is the primary contributor of model spread on firn thickness estimates. However, in basins characterised by warmer temperatures, high snowfall or increasing snowfall, the contributions of firn compaction and surface snow density can account for up to 46 and 28% of the spread, respectively.

By comparing the ensemble scenarios with satellite measurements of elevation changes over the same 1992-2017 period, we find that these estimates are consistent over a majority of basins. Nonetheless, we identify several basins where model estimates of firn thickness change do not match altimetry measurements. These discrepancies can be explained by different causes: (1) the model ensemble may fail to represent the real firn thickness change over our period of interest, (2) the uncertainty range associated with the altimetry data may not capture the true signal and (3) a component of the elevation change signal may be related to ice dynamical imbalance. As such, our analysis serves to highlight specific areas where further focus on potential sources of errors in model and altimetry results is needed in order to better constrain mass balance assessments in East Antarctica.

How to cite: Verjans, V., Leeson, A., McMillan, M., Stevens, M., van Wessem, J. M., van de Berg, W. J., van den Broeke, M., Kittel, C., Amory, C., Fettweis, X., Hansen, N., Boberg, F., and Mottram, R.: Uncertainty in East Antarctic firn thickness constrained using a model ensemble approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-140, https://doi.org/10.5194/egusphere-egu21-140, 2021.

Ice Sheet Models are a powerful tool to project the evolution of the Greenland and Antarctic Ice Sheets, and thus their future contribution to global sea-level changes. Probing the fitness of ice-sheet models to reproduce ongoing and past changes of the Greenland and Antarctic ice cover is a fundamental part of every modelling effort. However, benchmarking ice-sheet model data against real-world observations is a non-trivial process, as observational data comes with spatio-temporal gaps in coverage. Here, we present a new approach to assess the ability of ice-sheet models which makes use of the internal layering of the Antarctic Ice Sheet. We simulate observed isochrone elevations within the Antarctic Ice Sheet via passive Lagrangian tracers, highlighting that a good fit of the model to two dimensional datasets does not guarantee a good match against the three dimensional architecture of the ice-sheet and thus correct evolution over time. We show, that paleoclimate forcing schemes commonly used to drive ice-sheet models work well in the interior of the Antarctic Ice Sheet and especially along ice divides, but fail towards the ice-sheet margin. The comparison to isochronal horizons attempted here reveals, that simple heuristics of basal drag can lead to an overestimation of the vertical interior ice sheet flow especially over subglacial basins. Our model-observation intercomparison approach opens a new avenue to the improvement and tuning of current ice-sheet models via a more rigid constraint on model parameterisations and climate forcing which will benefit model-based estimates of future and past ice-sheet changes.

How to cite: Sutter, J., Fischer, H., and Eisen, O.: Investigating the internal structure of the Antarctic Ice Sheet: the utility of isochrones for spatio-temporal ice sheet model calibration, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9446, https://doi.org/10.5194/egusphere-egu21-9446, 2021.

EGU21-2107 | vPICO presentations | CR1.2

Polarimetric radar-sounding to infer and quantify shear margin ice fabric anisotropy

Tun Jan Young, Thomas M Jordan, Carlos Martín, Dustin M Schroeder, Poul Christoffersen, Slawek M Tulaczyk, Riley Culberg, and Nicole L Bienert

Glaciers and ice streams channel the majority of ice mass discharge into the ocean, and are modulated by basal slip at the ice-bed interface, deformation within the ice interior, and lateral shear at the margins separating fast- and slow-moving ice. The anisotropy of glacier ice (i.e. ice that deforms preferentially in certain modes and directions) at shear margins greatly facilitates streaming ice, however it is still poorly understood due to a lack of in-situ measurements and is usually incorporated into models as a simple scalar enhancement factor. The resurgence of polarimetric radar techniques to detect bulk fabric anisotropy through exploiting the birefringence of ice crystals has greatly aided quantification of the ice crystal orientation fabric (COF) across the Antarctic Ice Sheet. In our study, we invert these techniques to infer the azimuthal fabric strength at the Eastern Shear Margin of Thwaites Glacier from non-polarimetric airborne radargrams collected during the 2018-19 field season. From these results, we infer the evolution of the crystal orientation fabric across the shear margin, where ice is subjected to varying levels of both pure and simple shear. Our findings suggest the potential of the upper reaches of the ESM having undergone recent inward migration. Together with compatible ground-based polarimetric radar experiments, our study highlights the potential of radar sounding to observe and infer variations in fabric strength from regions of complex flow at multiple spatial scales. Because the bulk COF of ice sheets records the past history of ice sheet deformation and influences present-day ice flow dynamics, accurate measurements of ice fabric strength and orientation not only places constraints on present and past ice flow history, but also aids in the incorporation of anisotropic rheology in ice flow models.

How to cite: Young, T. J., Jordan, T. M., Martín, C., Schroeder, D. M., Christoffersen, P., Tulaczyk, S. M., Culberg, R., and Bienert, N. L.: Polarimetric radar-sounding to infer and quantify shear margin ice fabric anisotropy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2107, https://doi.org/10.5194/egusphere-egu21-2107, 2021.

EGU21-3366 | vPICO presentations | CR1.2

Englacial stratigraphy in Ellsworth Subglacial Highlands, West Antarctica

Felipe Napoleoni, Neil Ross, Michael J. Bentley, Stewart S.R. Jamieson, Andrew M. Smith, José-Andrés Uribe, Rodrigo Zamora, and Alex M. Brisbourne

Airborne ice-penetrating radar surveys around the Ellsworth Subglacial Highlands (ESH) have mapped and dated englacial ice sheet layers, hereafter referred to as ‘Internal Reflection Horizons’ (IRHs). The geometry and internal structure of IRHs can reveal the cumulative effects of surface mass balance, strain, basal melt and ice dynamics, to improve understanding of the glacial history of West Antarctic Ice Sheet (WAIS). Despite the airborne-surveyed IRHs however, international efforts to develop a continental-wide scale coverage of IRHs (i.e. AntArchitecture), are limited by a lack of data in the critical regions between the upper reach of Pine Island Glacier (PIG), Rutford Ice Stream (RIS) and Institute Ice Stream (IIS). This region is important because any significant collapse of WAIS or reorganisation of ice flow would likely be felt in the ESH because it hosts deep subglacial troughs (Ellsworth Trough and CECs Trough), that represent a potential connection between the Weddell and Amundsen Seas. Using an extensive ground-based ice radar dataset acquired by Centro de Estudios Científicos (CECs) we bridge this regional gap by mapping IRHs across the Amundsen-Weddell divide of the WAIS. This work links airborne-derived IRH datasets across PIG and IIS, to develop an extensive layer characterisation across a large area of West Antarctica. We present the regional internal structure of the ice sheet, gridded paleo ice surfaces, and identify areas with complex IRH structures, and evaluate the possible glaciological processes responsible. We then compare our results with modelled outputs of ice sheet geometry and outline our current understanding of the past ice flow behaviour of the ESH, and the implications for WAIS glacial history. We consider our results in the context of the characterisation of ‘old-ice’ in WAIS and in relation to the upcoming plans for accessing subglacial Lake CECs in order to determine its history.

How to cite: Napoleoni, F., Ross, N., Bentley, M. J., Jamieson, S. S. R., Smith, A. M., Uribe, J.-A., Zamora, R., and Brisbourne, A. M.: Englacial stratigraphy in Ellsworth Subglacial Highlands, West Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3366, https://doi.org/10.5194/egusphere-egu21-3366, 2021.

Dome A is the summit of the East Antarctic Ice Sheet (EAIS), underlain by the rugged Gamburtsev Subglacial Mountains (GSM).  The rugged basal topography produces a complex hydrological system featuring basal melt, water transport and storage, and freeze-on.  Here, we present the results of an inverse model used to infer the spatial distributions of geothermal heat flow (GHF) and accumulation rate that best fit a variety of observational constraints.  Our model agrees well with the observed water bodies and freeze-on structures, while also predicting a significant amount of unobserved water and suggesting a change in stratigraphic interpretation that reduces the volume of the freeze-on units.  Our model stratigraphy agrees well with observations, and we predict that there will be two distinct patches of ice up to 1.5 Ma suitable for ice coring underneath the divide.  Past divide migration could have interrupted stratigraphic continuity at the old ice patches, but various indirect lines of evidence suggest that the divide has been stable for about the last one and a half glacial cycles, which is a hopeful but by no means definitive sign for stability in the longer term.  Finally, our GHF estimate is higher than previous estimates for this region, but consistent with possible heterogeneity in crustal heat production.     

How to cite: Wolovick, M., Moore, J., and Zhao, L.: Joint Inversion for Surface Accumulation and Geothermal Heat Flow from Ice-Penetrating Radar Observations at Dome A, East Antarctica. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13492, https://doi.org/10.5194/egusphere-egu21-13492, 2021.

The Greenland ice sheet (GrIS) is one of the largest contributors to global mean sea-level rise today and is expected to continue losing mass in the future under increasing Arctic warming. Mass loss in the future is caused by the thinning and retreat of marine-terminating outlet glaciers and to a larger extent by decreasing surface mass balance (SMB) due to increased surface meltwater runoff. In this paper we study the relative importance of changes in SMB and outlet glacier retreat by means of model simulations that have been performed as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). The effect of the two forcing mechanisms can be separated based on a comparison between full projections and single forcing experiments up to year 2100 for a number of ice sheet models, driving General Circulation Models and two forcing scenarios (RCP2.6 and RCP8.5). We can confirm earlier findings for the high forcing scenario that a compensation between the two processes renders the sea-level contribution from the full experiment lower than the sum of the single forcing experiments.

How to cite: Goelzer, H. and the The ISMIP6 team: Relative importance of surface mass balance and outlet glacier forcing in ISMIP6 Greenland ice sheet sea-level projections, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11177, https://doi.org/10.5194/egusphere-egu21-11177, 2021.

Mass loss from the Greenland Ice Sheet (GrIS) can be partitioned between surface mass balance (SMB) and discharge due to ice dynamics through its marine-terminating outlet glaciers. A perturbation to a glacier terminus (e.g. a calving event) results in an instantaneous response in velocity and mass loss, but also a diffusive response due to the evolution of ice thickness over time. This diffusive response means the total impact of a retreat event can take decades to be fully realised. Here we model the committed response of the GrIS to recent observed changes in terminus position, neglecting any future climate perturbations. Our simulations quantify the sea level contribution that is locked in due to the slow dynamic response of the ice. Using the Ice Sheet System Model (ISSM), we run forward simulations starting from an initial state representative of the 2007 ice sheet. We apply perturbations to the marine-terminating glacier termini that represent recent observed changes, and simulate the response over the 21st Century, holding the climate forcing constant. The sensitivity of the ice sheet response to model parameter uncertainty is explored with in an ensemble framework, and GRACE data is used to constrain the results. We find that terminus retreat observed between 2007 and 2015 results in approximately 6 mm of sea level rise by 2100, with retreat having a lasting impact on velocity and mass loss. Our results complement the ISMIP6 projections, which report the ice sheet response to future forcing, excluding the background committed response. In this way, we can obtain estimates of Greenland’s total contribution to sea level rise by 2100.

How to cite: Nias, I., Nowicki, S., and Felikson, D.: Recent retreat of Greenland's marine terminating glaciers has a lasting impact on velocity and mass loss during the 21st Century, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9908, https://doi.org/10.5194/egusphere-egu21-9908, 2021.

EGU21-444 | vPICO presentations | CR1.2

Long-term future projections for the Greenland and Antarctic ice sheets with the model SICOPOLIS

Ralf Greve, Christopher Chambers, Reinhard Calov, Takashi Obase, Fuyuki Saito, Kaho Harada, and Ayako Abe-Ouchi

The Coupled Model Intercomparison Project Phase 6 (CMIP6) is a major international climate modelling initiative. As part of it, the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) was devised to assess the likely sea-level-rise contribution from the Greenland and Antarctic ice sheets until the year 2100. This was achieved by defining a set of future climate scenarios by evaluating results of CMIP5 and CMIP6 global climate models (GCMs, including MIROC) over and surrounding the Greenland and Antarctic ice sheets. These scenarios were used as forcings for a variety of ice-sheet models operated by different working groups worldwide (Goelzer et al. 2020, doi: 10.5194/tc-14-3071-2020; Seroussi et al. 2020, doi: 10.5194/tc-14-3033-2020).

Here, we use the model SICOPOLIS to carry out extended versions of the ISMIP6 future climate experiments for the Greenland and Antarctic ice sheets until the year 3000. For the atmospheric forcing (anomalies of surface mass balance and temperature) beyond 2100, we sample randomly the ten-year interval 2091-2100, while the oceanic forcing beyond 2100 is kept fixed at 2100 conditions. We conduct experiments for the pessimistic, "business as usual" pathway RCP8.5 (CMIP5) / SSP5-8.5 (CMIP6), and for the optimistic RCP2.6 (CMIP5) / SSP1-2.6 (CMIP6) pathway that represents substantial emissions reductions. For the unforced, constant-climate control runs, both ice sheets are stable until the year 3000. For RCP8.5/SSP5-8.5, they suffer massive mass losses: For Greenland, ~1.7 m SLE (sea-level equivalent) for the 12-experiment mean, and ~3.5 m SLE for the most sensitive experiment. For Antarctica, ~3.3 m SLE for the 14-experiment mean, and ~5.3 m SLE for the most sensitive experiment. For RCP2.6/SSP1-2.6, the mass losses are limited to a two-experiment mean of ~0.26 m SLE for Greenland, and a three-experiment mean of ~0.25 m SLE for Antarctica. Climate-change mitigation during the next decades will therefore be an efficient means for limiting the contribution of the ice sheets to sea-level rise in the long term.

How to cite: Greve, R., Chambers, C., Calov, R., Obase, T., Saito, F., Harada, K., and Abe-Ouchi, A.: Long-term future projections for the Greenland and Antarctic ice sheets with the model SICOPOLIS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-444, https://doi.org/10.5194/egusphere-egu21-444, 2021.

EGU21-9540 | vPICO presentations | CR1.2

Projecting 21st century GrIS surface melt using artificial neural networks

Raymond Sellevold and Miren Vizcaino

Accelerated surface melt of the Greenland ice sheet (GrIS) is currently a large contributor to sea level rise, and the primary process of GrIS mass loss. Projections of future GrIS melt are limited by the lack of explicit melt calculations within most global climate models and the high computational cost of dynamical downscaling with regional models. To translate global climate evolution to GrIS surface melt, we train artificial neural networks (ANNs) with the output of the explicit melt calculation of the Community Earth System Model 2.1 (CESM2). ANNs are well suited for this task, as they are capable of learning complex, non-linear relationships, and they are fast to run.

Our results show that the ANNs accurately project GrIS surface melt when evaluated against regional climate simulations. Further, the ANNs recognize patterns already established in litterature as important for surface melt, and use bases the projections on these patterns. Using the global climate simulations from the CMIP6 archive, the ANNs project a GrIS surface melt increase ranging from 414 Gt yr-1 to 1,378 Gt yr-1 by the end of the 21st century. The main source of projection uncertainty throughout the 21st century is due to the spread in the models’ climate sensitivity.

How to cite: Sellevold, R. and Vizcaino, M.: Projecting 21st century GrIS surface melt using artificial neural networks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9540, https://doi.org/10.5194/egusphere-egu21-9540, 2021.

EGU21-15672 | vPICO presentations | CR1.2

Timing, thresholds and processes for complete future Greenland deglaciation

Miren Vizcaino, Michele Petrini, Raymond Sellevold, Sotiria Georgiou, Laura Muntjewerf, William Lipscomb, and Gunter Leguy

The Greenland ice sheet is currently losing mass at a rate of 0.8 mm of global mean sea level rise (SLR) per year. Here, we simulate its future evolution under an idealized scenario of high greenhouse gas forcing (1% increase per year until four times pre-industrial CO2).  To this end, we use the newly, bi-directionally coupled Community Earth System Model version 2 and Community Ice Sheet Model version 2 (CESM2-CISM2, Muntjewerf et al, GRL, 2020), that includes an advanced calculation of the surface mass balance in the land component with elevation classes downscaling to CISM. Deglaciation rates increase from 2 mm SLR per year by simulation year 140 (or time of CO2 stabilization) to 7 mm SLR per year two centuries later as the ablation areas expand and net solar radiation and turbulent (latent, sensible) heat fluxes become the dominant energy sources for melt. The ice sheet retreats to an ice cap in the interior of the northern half of Greenland, that melts completely by simulation year 1,700. We compare the Greenland climate evolution with a CESM2 simulation with fixed topography, and evaluate the role of vegetation, clouds, precipitation, and surface energy fluxes on the relatively fast decay of the ice sheet. In addition, we use a set of CISM2 simulations forced with CESM2 SMB to estimate the global warming/forcing threshold for complete deglaciation.

How to cite: Vizcaino, M., Petrini, M., Sellevold, R., Georgiou, S., Muntjewerf, L., Lipscomb, W., and Leguy, G.: Timing, thresholds and processes for complete future Greenland deglaciation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15672, https://doi.org/10.5194/egusphere-egu21-15672, 2021.

EGU21-5752 | vPICO presentations | CR1.2

Data assimilation and ensemble method applied to Upernavik Isstrom

Eliot Jager, Fabien Gillet-Chaulet, and Jérémie Mouginot

Lack of observation is one of the main limitations for improving model prediction in glaciology. However, over the past few years, the amount of observations from satellites has increased at a phenomenal rate. Hopefully, this amount of data will allow to validate the models and their parameterizations. In addition, data assimilation seems to be an optimal method to combine the model and these frequent observations, allowing to reduce the uncertainties of the model and thus potentially improve the projections. While inverse methods are now common in glaciology to infer uncertain parameters from observed surface velocities acquired at a given date, transient data assimilation algorithms are still under development. Recently, the performance of an Ensemble Kalman Filter has been studied on a synthetic case. Here, the goal of this study is to investigate the feasibility of applying this assimilation scheme on a real case : evolution of Upernavik Isstrøm since 1985 using the open source finite element software Elmer/Ice. To do so, we first need to generate an ensemble of simulations that sample the model uncertainties and to evaluate this ensemble against available observations.

We first assemble a set of observations that will serve for model setup and validation. In this sense, we have collected ice velocity measurements, from optical and radar source, surface elevation and bed topography, ice front position and surface mass balance that give us a fairly good a priori knowledge of the evolution of Upernavik Isstrøm between 1985 and 2020. These datasets are divided into two parts : one is used to better characterize and set up the initial state of the system, and the other is used to evaluate model outputs.

Uncertainties in the model comes from different sources: (i) the model parameters, (ii) the initial topography as the surface elevation in 1985 is only partially known, and (iii) the forcings (i.e. the surface mass balance, the ice front position).
For the model parameters we take into account uncertainties in the ice rheology by perturbing the Glen’s enhancement factor and by generating an ensemble of friction coefficients for different friction laws using a set of inversions that has been performed for the whole Greenland using present day observations. Using these perturbed parameters and a set of surface mass balance representative of the period we generate and evaluate an ensemble of initial topographies for 1985.


With this ensemble of initial states, we perform transient simulations where the position of glacier terminus and a set of perturbed SMB are prescribed each year. Each simulation is scored with specifically designed metrics in terms of dynamics and geometry using the observations described previously. This analysis allows to evaluate the impact of different sources of uncertainty on the transient simulation. Using the results of this study, we will discuss the capacity of Elmer/Ice to reconstruct the trend of the evolution of Upernavik Isstrøm and the possibility to perform transient data assimilation.

How to cite: Jager, E., Gillet-Chaulet, F., and Mouginot, J.: Data assimilation and ensemble method applied to Upernavik Isstrom, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5752, https://doi.org/10.5194/egusphere-egu21-5752, 2021.

EGU21-4672 | vPICO presentations | CR1.2

Modeling of the Russell glacier's basal conditions at seasonal time scale using the satellite observations of surface ice speed

Anna Derkacheva, Fabien Gillet-Chaulet, and Jeremie Mouginot

Greenland’s future response to climate change will be determined partly by various phenomena controlling ice flow. For the land-terminating sectors, the water lubricating the glacier's base is considered as a major control on the ice motion. For instance, the seasonal modulations of water input induced by summer melt can cause glacier speed-up up to +200-300% compared to the winter mean. Thus, a comprehensive understanding of variations in the basal conditions, which are at the origin of the glacier flow fluctuations, plays a key role for the climate projections.

While the in-situ measurements stay a local and hard approach to investigate the basal conditions, ice flow modeling offers the possibility to invert for them over the large area based on observations of surface glacier speed and topography. During the last decade, the number of available satellite observations has increased significantly, allowing for far more frequent measurements of the glacier speed and precise reconstruction of the seasonal fluctuations. Here, we investigate the possibility of applying this satellite-derived time-series of surface ice velocity to reconstruct the annual behavior of the basal conditions with 2 weeks temporal resolution using an ice flow model.

The area of this study is Russell glacier located on the southwest coast of Greenland. A time series of surface velocity dataset was created by merging measurements from Sentinel-1&2 and Landsat-8, covering an area up to 100 km inland with 150 m/pix spatial resolution and 2-weeks temporal resolution (Derkacheva et al. 2020). The 3D Full-Stokes ice flow model Elmer/Ice is used to invert for the effective basal friction coefficient for each time step.  Usage of a friction law that has been derived for hard beds (Gagliardini et al., 2007) allows to constrain the variation of the basal effective pressure. Overall, the results from the model inversions give access to the evolution of the basal ice speed, friction, effective and water pressure, floatation fraction throughout a complete year. The results are compared with in-situ measurements in terms of absolute values and show a good agreement. The impact of the flow model setup, regularization, assumptions for the ice rheology, and the impact of noise in the speed data are also examined and compared with in-situ measurements.

How to cite: Derkacheva, A., Gillet-Chaulet, F., and Mouginot, J.: Modeling of the Russell glacier's basal conditions at seasonal time scale using the satellite observations of surface ice speed, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4672, https://doi.org/10.5194/egusphere-egu21-4672, 2021.

EGU21-13450 | vPICO presentations | CR1.2

Heat flux and the North East Greenland Ice Stream

Paul D. Bons, Tamara de Riese, Steven Franke, Maria-Gema Llorens, Till Sachau, Nicolas Stoll, Ilka Weikusat, and Yu Zhang

The prominent North East Greenland Ice Stream (NEGIS) is an exceptionally large ice stream in the Greenland Ice sheet. It is over 500 km long, originates almost at the central ice divide, and contributes significantly to overall ice drainage from the Greenland Ice sheet. Surface velocities in the inland part of the ice stream are several times higher inside NEGIS than in the adjacent ice sheet. Modelling NEGIS is still a challenge as it remains unclear what actually causes and controls the ice stream.

An elevated geothermal heat flux is one of the factors that are being considered to trigger or drive the fast flow inside NEGIS. Unfortunately, the geothermal heat flux below NEGIS and its upstream area is poorly constrained and estimates vary from close to the global average for continental crust (ca. 60 mW/m2) to values as high as almost 1000 mW/m2. The latter would cause about 10 cm/yr of melting at the base of the ice sheet.

We present a brief survey of global geothermal heat flux data, especially from known hotspots, such as Iceland and Yellowstone. Heat fluxes in these areas that are known to be among the hottest on Earth rarely, if ever, exceed 300 mW/m2. A plume hotspot or its trail can therefore not cause heat fluxes at the high end of the suggested range. Other potential factors, such as hydrothermal fluid flow and radiogenic heat, also cannot raise the heat flux significantly. We conclude that the heat flux at NEGIS is very unlikely to exceed 100-150 mW/m2, and future modelling studies on NEGIS should thus be mindful of implementing realistic geothermal heat flux values. If NEGIS is not the result of an exceptionally high heat flux, we are left with the exciting challenge to find the true trigger of this fascinating structure.

How to cite: Bons, P. D., de Riese, T., Franke, S., Llorens, M.-G., Sachau, T., Stoll, N., Weikusat, I., and Zhang, Y.: Heat flux and the North East Greenland Ice Stream, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13450, https://doi.org/10.5194/egusphere-egu21-13450, 2021.

EGU21-3506 | vPICO presentations | CR1.2

Assimilating sparse data in glaciological inverse problems

Daniel Shapero and Reuben Nixon-Hill

Most of the existing work on solving inverse problems in glaciology has assumed that the observational data used to constrain the model are spatially dense. This assumption is very convenient because it means that the model-data misfit term in the objective functional can be written as an integral. In many scenarios, however, the computational mesh can locally be much finer than the observational grid, or the observations can have large patches of missing data. Moreover, pretending as if the observations are a globally-defined continuous field obscures valuable information about the number of independent measurements we have. It is then impossible to apply a posteriori sanity checks on the expected model-data misfit from regression theory. Here we'll describe some recent work we've done on assimilating sparse point data into ice flow models and how this allows us to be more rigorous about the statistical interpretation of our results. For now we are focusing on the kinds of inverse problems that have been solved in the glaciology literature for a long time -- inferring rheology and basal friction from surface velocities. But these developments open up the possibility of assimilating new sources of data, such as measurements from strain gauges or ice cores.

How to cite: Shapero, D. and Nixon-Hill, R.: Assimilating sparse data in glaciological inverse problems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3506, https://doi.org/10.5194/egusphere-egu21-3506, 2021.

CR1.4 – Glaciers and Ice Caps under Climate Change

EGU21-1539 | vPICO presentations | CR1.4

Recent, rapid and profound changes to glacier morphology and dynamics, Juneau Icefield, Alaska

Bethan Davies, Jacob Bendle, Robert McNabb, Jonathan Carrivick, Christopher McNeil, Seth Campbell, and Mauri Pelto

The Alaskan region (comprising glaciers in Alaska, British Columbia and Yukon) contains the third largest ice volume outside of the Greenland and Antarctic ice sheets, and contributes more to global sea level rise than any other glacierised region defined by the Randolph Glacier Inventory. However, ice loss in this area is not linear, but in part controlled by glacier hypsometry as valley and outlet glaciers are at risk of becoming detached from their accumulation areas during thinning. Plateau icefields, such as Juneau Icefield in Alaska, are very sensitive to changes in Equilibrium Line Altitude (ELA) as this can result in rapidly shrinking accumulation areas. Here, we present detailed geomorphological mapping around Juneau Icefield and use this data to reconstruct the icefield during the “Little Ice Age”. We use topographic maps, archival aerial photographs, high-resolution satellite imagery and digital elevation models to map glacier lake and glacier area and volume change from the Little Ice Age to the present day (1770, 1948, 1979, 1990, 2005, 2015 and 2019 AD). Structural glaciological mapping (1979 and 2019) highlights structural and topographic controls on non-linear glacier recession.  Our data shows pronounced glacier thinning and recession in response to widespread detachment of outlet glaciers from their plateau accumulation areas. Glacier detachments became common after 2005, and occurred with increasing frequency since then. Total summed rates of area change increased eightfold from 1770-1948 (-6.14 km2 a-1) to 2015-2019 (-45.23 km2 a-1). Total rates of recession were consistent from 1770 to 1990 AD, and grew increasingly rapid after 2005, in line with regional warming.

How to cite: Davies, B., Bendle, J., McNabb, R., Carrivick, J., McNeil, C., Campbell, S., and Pelto, M.: Recent, rapid and profound changes to glacier morphology and dynamics, Juneau Icefield, Alaska, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1539, https://doi.org/10.5194/egusphere-egu21-1539, 2021.

EGU21-59 | vPICO presentations | CR1.4

Coupling the delta-h parametrization with melt beneath a supraglacial debris cover: an evaluation across 54 glaciers in the southern European Alps

Francesco Avanzi, Simone Gabellani, Edoardo Cremonese, Umberto Morra di Cella, and Matthias Huss

Glacier mass balance is an essential component of the water budget of high-elevation and high-latitude regions, and yet this process is rather oversimplified in most hydrological models. This oversimplification is particularly relevant when it comes to representing two mechanisms: ice flow dynamics and melt beneath a supraglacial debris cover. In 2010, Huss et al. proposed a parsimonious approach to account for  glacier dynamics in hydrological models without solving complex equations of three-dimensional ice flow, the so-called delta-h parametrization. On the other hand, accounting for melt of debris-covered ice is still challenging as  estimates of debris thickness are rare. 

Here, we leveraged a distributed dataset of glacier-thickness change to derive a glacier-specific delta-h parametrization for 54 glaciers across the Aosta Valley (Italy), as well as  develop a novel approach for modeling melt beneath supraglacial debris based on residuals between locally observed change in thickness and that expected by regional elevation gradients. This approach does not require any on-the-ground data on debris cover, and as such it is particularly suited for ungauged regions where remote sensing is the only, feasible source of information for modeling. 

We found an expected, significant variability in both the delta-h parametrization and residuals over debris-covered ice across glaciers, with somewhat steeper orographic gradients in the former compared to the curves originally proposed by Huss et al. for Swiss glaciers. At a regional scale, the glacier mass balance showed a clear transition between a regime dominated by active glacier flow above 2,300 m ASL and a debris-dominated regime below this elevation threshold, which makes accounting for melt in the debris-covered area essential to correctly capture the future fate of low-elevation glaciers. Implementing the delta-h parametrization and our proposed approach to melt beneath supraglacial debris into S3M, a distributed cryospheric model, yielded an improved realism in estimates of future changes in glacier geometry  compared to assuming non-dynamic downwasting.

How to cite: Avanzi, F., Gabellani, S., Cremonese, E., Morra di Cella, U., and Huss, M.: Coupling the delta-h parametrization with melt beneath a supraglacial debris cover: an evaluation across 54 glaciers in the southern European Alps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-59, https://doi.org/10.5194/egusphere-egu21-59, 2021.

EGU21-9990 | vPICO presentations | CR1.4

Tree-ring and 14C dates of moraines of the Greater Azau Glacier (Baksan valley, Northern Caucasus)

Olga Solomina, Irina Bushueva, Ekaterina Dolgova, Natalya Volodicheva, Alexandr Alexandrovskiy, and Elya Zazovskaya

The age of moraines of the Greater Azau Glacier was identified by tree-ring analysis of more than 150 Scots pines, by historical and cartographic data, remote sensing, lichenometric and radiocarbon dating. We determined the limits of the area covered by the glacier tongue at the end of the 19th century. We also discuss the controversial issue of the position of the moraine of 1849 CE, which was described by H. Abich [1]. The highest and most clearly shaped lateral moraine, conventionally called the "17th century moraine", was formed earlier than the end of the 16th century (tree-ring minimum age). The oldest tree in the valley (1598 CE) was found at the "forested island" end moraine (2294 m asl). Judging by the size of the lichens Rhizocarpon geographicum (120-130 mm) on this surface the moraine may be several centuries older. We re-examined the trunk of a pine which was discovered in the 1960s buried in the fluvio-glacial sediments presumably formed in 1880s (historical descriptions). It was dated earlier by radiocarbon (140 +/- 75 BP [2] (calibrated date - 1650-1960 CE). According to the ring width cross-dating, the most probable dates of the buried tree are 1759-1883 CE, however, the second likely dates are 1826-1950 CE. Suppressions of pine growth at the forefields of the Greater Azau in the 1640s, 1710s, 1800s, 1840s-1860s CE are synchronous with the advances of the Bosson, Mer de Glace and Grindelwald glaciers in the Alps [2]. Three soil horizons buried in the moraine of the Greater Azau glacier were identified in the artificial outcrop on the left side of the valley (N43.26583, E42.4767, 2370 m asl). The uppermost horizon located 0.6 m below the surface of the moraine is a thin layer of loam developed in a short time interval (130±20 BP (IGAN ams - 6826) 1680-1939cal BP (charcoal). Two lower thicker horizons (buried 13 and 15 m below the surface) indicate longer periods of continuous soil formation lasting for about 720 years (between 774-89 CE and 1496-1641 CE) and for 1750 years (between ca 3 ka BP and 7-8 centuries CE), respectively. They both are well developed soils formed within the loam layers without detrital material, containing a thick dark humus horizon with a high content of soil organic matter, as well as fragments of charcoal and tree bark. During these three periods, the glacier was relatively small.

References

1. Abich H., Geologische Beobachtungen auf Reisen im Kaukasus um Jahre 1873. Moskau, 1875. 138 p.

2. Nussbaumer S., Zumbühl H. The Little Ice Age history of the Glacier des Bossons (Mont Blanc massif, France): A new high-resolution glacier length curve based on historical documents. Climatic Change, 111, 2012. 301-334 pp.

How to cite: Solomina, O., Bushueva, I., Dolgova, E., Volodicheva, N., Alexandrovskiy, A., and Zazovskaya, E.: Tree-ring and 14C dates of moraines of the Greater Azau Glacier (Baksan valley, Northern Caucasus), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9990, https://doi.org/10.5194/egusphere-egu21-9990, 2021.

EGU21-16020 | vPICO presentations | CR1.4

Surface velocity variations of glaciers on Kenai Peninsula, Alaska, 2014-2019

Ruitang Yang, Regine Hock, Shichang Kang, Donghui Shangguan, and Wanqin Guo

We characterize the spatiotemporal variations surface velocity of glaciers on the Kenai Peninsula, Alaska, using intensity offset tracking on a set of repeat-pass Sentinel-1 data and TerraSAR-X data. We derived 92 velocity fields and generated time-averaged annual and seasonal surface velocity maps for the period October 2014 to December 2019, as well as time series surface velocity profiles along centerlines for individual glaciers. We find considerable spatial and seasonal variations in surface velocity in the study area, especially a pronounced average spring speedup of 50% averagely compared to annual mean velocity. Ice velocities varied systematically between glaciers with different terminus types. Generally, the pixel-averaged velocity of tidewater and lake-terminating glaciers are up to 2 and 1.5 times greater than those of the land-terminating glaciers, respectively. For Bear glacier, with the analysis of surface velocity profile and the terminus change, we state this glacier retreat and accelerate. While the time-series result shows the velocity speed-up of the Bear glacier synchronizes well with the ice-damaged lake outburst flood (GLOF) events.

How to cite: Yang, R., Hock, R., Kang, S., Shangguan, D., and Guo, W.: Surface velocity variations of glaciers on Kenai Peninsula, Alaska, 2014-2019, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16020, https://doi.org/10.5194/egusphere-egu21-16020, 2021.

Proglacial lakes are becoming ubiquitous at the termini of many glaciers worldwide, leading to increased glacier mass loss and terminus retreat due to the influence such lakes are having upon ice dynamics. However, despite the highly dynamic nature and relative insensitivity to climate of many lake-terminating glaciers, an understanding of the key processes forcing their behaviour is lacking. As a result, it is difficult at present to accurately assess and predict the future response of these glaciers to continued warming. In addition, current methods of investigating lake-terminating glacier dynamics primarily involve the use of satellite remote sensing, which despite its clear importance in cryospheric studies does suffer from important limitations. A novel alternative is the use of repeat unmanned aerial vehicle (UAV) imagery, which can provide high resolution (cm-scale) imagery of the ice surface at varying spatial and temporal scales, depending on the needs of the researcher. As a result, this study utilised ultra-high resolution repeat UAV imagery to provide insights into the changing dynamics of Fjallsjökull, a lake-terminating glacier in southeast Iceland, over two periods during the 2019 summer melt season. The findings indicate that the overall dynamics of the glacier are controlled by the ~120 m deep subglacial channel under the study region, which is causing the glacier to flow faster as it enters deeper water, leading to increased ice acceleration, thinning and retreat. Such a correspondence between ice velocity and surface thinning suggests the implementation of the positive feedback mechanism “dynamic thinning” in this region of Fjallsjökull, with such heightened rates of surface thinning and frontal retreat continuing in future until the glacier recedes out of the subglacial channel into shallower water. Within this overall pattern, however, more localised, short-term changes in glacier dynamics are also observed which are likely to be forced primarily by subaqueous melting at the waterline, rather than being solely influenced by the basal topography. Although further work is required to add additional support to these findings, they clearly indicate the complex nature of the calving process and the dynamics of calving glaciers in general, highlighting the need for continued monitoring of lake-terminating glaciers at varying spatial and temporal scales.

How to cite: Baurley, N. and Hart, J.: Insights into the seasonal dynamics of the lake-terminating glacier Fjallsjökull, south-east Iceland, inferred using ultra-high resolution repeat UAV imagery, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-677, https://doi.org/10.5194/egusphere-egu21-677, 2021.

EGU21-13311 | vPICO presentations | CR1.4

Proglacial Lakes Elevate Glacier Surface Velocities in the Himalayan Region

Jan Bouke Pronk, Tobias Bolch, Owen King, Bert Wouters, and Douglas Benn

Meltwater from Himalayan glaciers sustains the flow of rivers such as the Ganges and Brahmaputra on which over half a billion people depend for day-to-day needs. Upstream areas are likely to be affected substantially by climate change, and changes in the magnitude and timing of meltwater supply are likely to occur in coming decades. About 10 % of the Himalayan glacier population terminates into pro-glacial lakes and such lake-terminating glaciers are known to be capable of accelerating total mass losses. However, relatively little is known about the mechanisms driving exacerbated ice loss from lake-terminating glaciers in the Himalaya. Here we examine a 2017-2019 glacier surface velocity dataset, derived from Sentinel 2 imagery, covering most of the Central and Eastern Himalayan glaciers larger than 3 km2. We find that centre flow line velocities of lake-terminating glaciers are more than double those of land-terminating glaciers (18.8 vs 8.24 m yr-1) and show substantially more heterogeneity around glacier termini. We attribute this large heterogeneity to the varying influence of lakes on glacier dynamics, resulting in differential rates of dynamic thinning, which effects about half of the clean-ice lake-terminating glacier population. Also, numerical ice-flow model experiments suggest that changes at the frontal boundary condition can play a key role in accelerating the glacier flow at the front. With continued warming new lake development is likely to happen and will further accelerate future ice mass losses, a scenario not currently considered in regional projections. 

How to cite: Pronk, J. B., Bolch, T., King, O., Wouters, B., and Benn, D.: Proglacial Lakes Elevate Glacier Surface Velocities in the Himalayan Region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13311, https://doi.org/10.5194/egusphere-egu21-13311, 2021.

Glaciers are iconic features of mountain landscapes with significant cultural, environmental, scientific, and economic value. While we know that glaciers are sensitive to changes in their local climate, the extent to which cloud cover will amplify or reduce the melting of a glacier in response to future atmospheric warming is uncertain. Clouds alter the solar and infrared radiation available for glacier melt and can enhance or dampen the influence of surface meteorology, albedo feedbacks and subsurface processes (e.g. refreezing) on melt. How these processes interact in different mountain glacier environments and climate regimes has not been well established. To address this knowledge gap, published surface energy and mass balance datasets from 15 mountain glacier sites around the world have been collated and analysed in a common framework. The framework seeks to reveal how melt rate is altered by cloud cover in each environment and which processes are more important for determining how cloud cover modifies melt. For example, does a decrease in incoming solar radiation dominate the effect of clouds on melt, or does covariance between clouds and other meteorological forcing moderate this effect in different environments? By unravelling the interacting effects of clouds and other atmospheric processes on glacier melt in diverse mountain locations, we hope to add fundamental understanding of the processes determining mountain glacier response to climate change.

How to cite: Conway, J.: Cloud forcing of glacier surface energy balance in diverse mountain environments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6902, https://doi.org/10.5194/egusphere-egu21-6902, 2021.

Processes controlling the glacier wastage in the Himalaya are still poorly understood. In the present study, a surface energy-mass balance model is applied to reconstruct the long-term mass balances over 1979-2020 on two benchmark glaciers, Dokriani and Chhota Shigri, located in different climatic regimes. The model is forced with ERA5 reanalysis data and calibrated using field-observed point mass balances. The model is validated against available glacier-wide mass balances. Dokriani and Chhota Shigri glaciers show moderate wastage with a mean value of –0.28 and –0.34 m w.e. a-1, respectively over 1979-2020. The mean winter and summer glacier-wide mass balances are 0.44 and –0.72 m w.e. a-1 for Dokriani Glacier and 0.53 and –0.85 m w.e. a-1 for Chhota Shigri Glacier, respectively, showing a higher mass turn over on Chhota Shigri Glacier. Net radiation flux is the major component of surface energy balance followed by sensible and latent heat fluxes on both the glaciers. The losses through sublimation is around 10% to the total ablation. Surface albedo is one of the most important drivers controlling the annual mass balance of both Dokriani and Chhota Shigri glacier. Summer mass balance (0.76, p<0.05) mainly controls the annual glacier-wide mass balance on Dokriani Glacier whereas the summer (0.91, p<0.05) and winter (0.78, p<0.05) mass balances together control the annual glacier-wide mass balance on Chhota Shigri Glacier.

How to cite: Srivastava, S. and Azam, M. F.: Modelling mass changes of Dokriani (Central Himalaya) and Chhota Shigri (Western Himalaya) glaciers, India using energy balance approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15945, https://doi.org/10.5194/egusphere-egu21-15945, 2021.

EGU21-8663 | vPICO presentations | CR1.4

Combining distributed glacier mass balance and ice flow models to improve projections of mass change for debris-covered Khumbu Glacier, Nepal

Anya Schlich-Davies, Ann Rowan, Duncan Quincey, Andrew Ross, and David Egholm

Debris-covered glaciers in the Himalaya are losing mass more rapidly than expected. Quantifying and understanding the behaviour of these glaciers under climate change requires the use of numerical glacier models that represent the important feedbacks between debris transport, ice flow, and mass balance. However, these approaches have, so far, lacked a robust representation of the distributed mass balance forcing that is critical for making accurate simulations of ice volume change. This study forces a 3D higher-order ice flow model, with the outputs from an ensemble of distributed models of present day and future mass balance of Khumbu Glacier, Nepal. Distributed mass balance modelling, using the open access COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY) model (Sauter et al., 2020), was forced by three statistically downscaled climate models from the Coordinated Regional Climate Downscaling Experiment (CORDEX) project.

Climate models were selected based on their ability to reproduce observed present-day seasonality and to account for several future climate and monsoon scenarios, the latter being of particular importance for these summer-accumulation type glaciers. Two emission scenarios, RCP4.5 and RCP8.5, were also chosen to simulate glacier change to 2100. Statistical downscaling involved Quantile Mapping and Generalized Analog Regression Downscaling, and the efficacy of these approaches was informed by present day mass balance sensitivity studies. Downscaled daily climate data were trained with data from two weather stations to aid disaggregation to an hourly resolution.

The integration of the mass balance and ice flow models posed some interesting challenges. The COSIPY model was run as if Khumbu Glacier were a clean-ice glacier (with no supraglacial debris) with sub-debris ablation resolved in the ice flow model. The value of using distributed mass balance forcing is seen in the simulated present-day velocities in the Khumbu icefall, which give a better fit to remote-sensing observations than previous simulations using a simple elevation-dependent mass balance forcing. The simulated present-day glacier extent is considerably smaller than the existing glacier outline. The debris-covered tongue, known to be losing mass at an accelerating rate, is virtually absent from these results, and is indicative of a stagnant tongue that is now or very soon to be dynamically disconnected from the active upper reaches of Khumbu Glacier.

How to cite: Schlich-Davies, A., Rowan, A., Quincey, D., Ross, A., and Egholm, D.: Combining distributed glacier mass balance and ice flow models to improve projections of mass change for debris-covered Khumbu Glacier, Nepal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8663, https://doi.org/10.5194/egusphere-egu21-8663, 2021.

EGU21-10205 | vPICO presentations | CR1.4

Long-term mass balance and firn modelling for Abramov glacier, Pamir Alay

Marlene Kronenberg, Horst Machguth, Ward van Pelt, and Martin Hoelzle

The application of a coupled energy balance-subsurface model allows studying the mass balance evolution of mountain glaciers and thereby assessing the role of subsurface processes in the accumulation area. Such model simulations are scarce for glaciers in High Mountain Asia where meteorological and glaciological calibration data are poorly available. Uncertainties in mass balance estimates are therefore high and questions regarding changes in accumulation and ablation regimes remain open.

Here, we run a distributed energy balance model coupled to a multi-layer snow model for Abramov glacier (Pamir Alay, 39.60°N 71.55° E) over the time period 1968 to present. A unique set of meteorological and glaciological data measured from 1968-99 is used to forceand calibrate the coupled model. The modelling period is extended to present using gridded precipitation data and recent measurements from an automatic weather station installed in 2012. We use repeated firn profiles from the 1970s and 2018 to evaluate modelled evolution of snow and firn conditions.

Preliminary modelling results show that the mass balance of Abramov glacier has been predominantly negative since 1969. However, also periods with increasing mass balance trends have been found since then. For the period of historical measurements (1968-98), our results suggest an increase of net accumulation in the accumulation area. This result points towards a steepening of the mass balance gradient, which may cause increased dynamics.

How to cite: Kronenberg, M., Machguth, H., van Pelt, W., and Hoelzle, M.: Long-term mass balance and firn modelling for Abramov glacier, Pamir Alay, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10205, https://doi.org/10.5194/egusphere-egu21-10205, 2021.

EGU21-8686 | vPICO presentations | CR1.4

Eastern Alpine summit mass balances as complementary indicators of local climate change 

Andrea Fischer, Pascal Bohleber, and Martin Stocker-Waldhuber

Eastern Alpine Mountain Glaciers are threatened by current climate change, for which they are visible and prominent indicators. This makes them an important part of climate communication pushing our commitment for mitigation efforts. At the same time, this requires the scientific community to thoroughly understand and communicate the ongoing processes.

From a scientific viewpoint, the link between classical in-situ mass balance data and the climate and environmental records potentially preserved in the so-called cold “miniature ice caps” sparks novel research perspectives. Summit stake measurements and ice core drillings are both rare, although the comparison of today’s stake mass balance records with the variance of annual accumulation preserved in ice cores offers an intriguing hub to unravelling past processes.

We implemented summit stake mass balance measurements on two summits in the Austrian Alps, Weißseespitze (3500 m) in Ötztal Alps and Großvenediger (3600 m) in Hohe Tauern National Park. At Weißseespitze summit ice cap, two ice cores were drilled recently to bedrock and subsequently micro-radiocarbon dated. A stake network is complemented by a continuous monitoring of point thickness changes and a time lapse cam to monitor patterns of snow cover distribution. An energy balance station offers information on wind, air and ice temperatures and radiation.

The results from the first two years of monitoring at Weißseespitze indicate that the remaining ice cap of about 10 m thickness will be gone within two decades even under current conditions. In view of present melt rates of about 0.6 m/year, a dated ice core record could eventually shed light on the question if similar conditions as today have occurred earlier in the past 6000 years of glacier cover at the summit. Learning more about (sub)seasonal patterns of accumulation is extremely import for the interpretation of these ice cores, as main accumulation takes place during early and late accumulation season, whereas the accumulation during colder periods is lost by wind erosion. The so far rarely studied miniature ice caps therefore open windows to complementary climate information, different from summer temperatures and winter precipitation which are widely accepted to be represented in total glacier mass balances.

How to cite: Fischer, A., Bohleber, P., and Stocker-Waldhuber, M.: Eastern Alpine summit mass balances as complementary indicators of local climate change , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8686, https://doi.org/10.5194/egusphere-egu21-8686, 2021.

EGU21-3274 | vPICO presentations | CR1.4

Firn changes at Colle Gnifetti revealed with a high-resolution process-based physical model approach

Enrico Mattea, Horst Machguth, Marlene Kronenberg, Ward van Pelt, Manuela Bassi, and Martin Hoelzle

Cold firn is progressively transitioning to a temperate state under a changing climate. This process is expected to affect ice core records and the mass balance of cold and polythermal glaciers. Thus there is a need to gain better understanding of this transition and develop quantitative, physical models, to predict cold firn evolution under a range of climate scenarios.

Here we present the application of a distributed, fully coupled energy balance and sub-surface model, to simulate high-alpine cold firn at Colle Gnifetti over the period 2003–2018. For the first time, we force such a model with high-resolution, long-term, quality-checked meteorological data measured in closest vicinity of the firn site, at the highest weather station in Europe (Capanna Margherita, 4560 m a.s.l.). The model includes the spatial variability of snow accumulation rates, and is calibrated using several, partly unpublished high-altitude measurements from the Monte Rosa area.

Overall, the simulated firn temperature profiles reach a very good agreement in comparison with a large archive of borehole measurements. Our results show a 20 m-depth firn warming rate of 0.44 °C per decade. Moreover, we find that surface melt over the glaciated saddle is increasing by 3–4 mm w.e. yr-2 (+29–36 % in 16 years) depending on the location, although with a large inter-annual variability. The simulation also indicates that atmospheric humidity is a prominent control over melt occurrence, with considerable amounts of sublimation taking place in dry conditions. Hourly-resolution analysis of the melt dynamics reveals a marked tendency towards frequent, small melt events (< 4 mm w.e.): these collectively represent a significant fraction of the total amounts.

How to cite: Mattea, E., Machguth, H., Kronenberg, M., van Pelt, W., Bassi, M., and Hoelzle, M.: Firn changes at Colle Gnifetti revealed with a high-resolution process-based physical model approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3274, https://doi.org/10.5194/egusphere-egu21-3274, 2021.

EGU21-12879 | vPICO presentations | CR1.4

Spatio-temporal variability of snow accumulation on the Biafo and Hispar glaciers in the central Karakoram

Alexander Raphael Groos, Christoph Mayer, Astrid Lambrecht, Sabrina Erlwein, and Margit Schwikowski

The Karakoram is an extensively glacierised mountain range in the western part of High Mountain Asia and constitutes an important source of fresh water for millions of people in the Indus Basin. Over the last years, the Karakoram has attracted increasing attention due to an anomalous glacier stability, which contrasts the progressing ice mass loss across the Himalaya. Decreasing summer temperatures and increasing winter precipitation have been proposed as potential causes for the anomaly. However, the lack of snow accumulation studies and long-term meteorological measurements above 3,000 m a.s.l. hampers the corroboration of this hypothesis. To quantify the spatial and temporal variability of snow accumulation in the central Karakoram, we followed the track of a Canadian research expedition from 1986. We reinvestigated eight sites between ca. 4,400 and 5,200 m a.s.l. in the connected accumulation zone of the Biafo and Hispar glaciers in 2019. Density measurements were performed in each snow pit down to the summer horizon of the previous year to quantify the elevation-dependent amount of annually accumulated snow. In addition, snow samples were collected from three selected pits for the analysis of rare earth elements and stable water isotopes to constrain the origin and seasonality of the deposited snow. Finally, we compared our recent measurements with the 30-year-old results from the Canadian research expedition as well as independent meteorological data.  In doing so we aim to evaluate the hypothesised increase in winter precipitation in this region.

How to cite: Groos, A. R., Mayer, C., Lambrecht, A., Erlwein, S., and Schwikowski, M.: Spatio-temporal variability of snow accumulation on the Biafo and Hispar glaciers in the central Karakoram, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12879, https://doi.org/10.5194/egusphere-egu21-12879, 2021.

EGU21-14976 | vPICO presentations | CR1.4

Reconstructing the runoff and mass changes of a maritime Tibetan glacier since 1975

Achille Jouberton, Thomas E. Shaw, Evan Miles, Shaoting Ren, Wei Yang, Chuanxi Zhao, Michael McCarthy, Stefan Fugger, Amaury Dehecq, and Francesca Pellicciotti

Glaciers are key components of the water towers of Asia and as such are relied upon by large downstream communities for domestic, agricultural and industrial uses. They have experienced considerable shrinking over the last decades, with some of the highest rates of mass loss observed in the south-eastern part of the Tibetan Plateau, where mass loss is also accelerating.  Despite these rapid changes, Tibetan glaciers’ changing role in catchment hydrology remains largely unknown. Parlung No.4 Glacier is considered as a benchmark glacier in this region, since its meteorology, surface energy fluxes and mass-balance have been examined since 2006. It is a maritime glacier with a spring (April-May) accumulation regime , which is followed by a period of ablation during the Indian Summer Monsoon (typically June-September). Here, we conduct a glacio-hydrological study over a period of five decades (1978-2018) using a fully distributed model for glacier mass balance and runoff simulation (TOPKAPI-ETH). We force the model with ERA5-Land and China Meteorological Forcing Dataset (CMFD) climate reanalysis downscaled to a local weather station to reconstruct meteorological time series at an hourly resolution. TOPKAPI-ETH is calibrated and validated with automatic weather station data, discharge measurements, geodetic mass balance, stake measurements and snow cover data from MODIS. We find a very clear acceleration in mass loss from 2000 onwards, which is mostly explained by an increase in temperature. This influence however was initially compensated by an increase in precipitation until the 2000’s, which attenuated the negative trend. Our results also indicate that the increase in the liquid-solid precipitation ratio has reduced the amount of seasonal accumulation, exacerbating annual mass loss. We demonstrate that the southern westerlies and the associated spring precipitation have as much influence on the glacier mass balance and catchment discharge as the Indian Summer Monsoon, by controlling seasonal snowpack development, which simultaneously provides mass to the glacier and protects it from melting in the early stage of the monsoon.

How to cite: Jouberton, A., Shaw, T. E., Miles, E., Ren, S., Yang, W., Zhao, C., McCarthy, M., Fugger, S., Dehecq, A., and Pellicciotti, F.: Reconstructing the runoff and mass changes of a maritime Tibetan glacier since 1975, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14976, https://doi.org/10.5194/egusphere-egu21-14976, 2021.

EGU21-6422 | vPICO presentations | CR1.4

Future surface mass balance of the Elbrus Glacial Complex under climate change

Oleg Rybak, Taisya Dymova, Irina Korneva, Stanislav Kutuzov, Ivan Lavrentiev, Elena Rybak, and Pavel Toropov

The evolution of the Elbrus glacier complex, consisting of two dozen of glaciers, in the last two decades of the 20th century and at the beginning of the 21st century generally corresponded to the trend of a decrease in the glaciated area of ​​the whole Caucasus. Over the period 1960-2014, the area of ​​Elbrus glaciation decreased by approximately 15%, and over two decades 1997-2017 - by almost 11%. As of 2017, the area of ​​Elbrus glaciation was estimated to ca. 112 sq. km, its volume exceeded 5 cub. km. Elbrus glaciation contributes significantly to the formation of the hydrological regime in the region, and, therefore, may be considered as a major challenge ti the regional socio-economic development. The latter circumstance requires an accurate assessment of the glacial runoff, and, consequently, the calculation of the surface mass balance of the glacial complex. We use an energy balance model to calculate the current and future surface mass balance. The series of observations at the Terskol meteorological station, located fifteen kilometers from the southern spurs of Elbrus, and the Mestia meteorological station, located somewhat further, on the territory of Georgia on the southern slope of the Main Caucasian ridge, as well as data from automatic weather stations on Elbrus slopes and on Djankuat glacier a few tens of kilometers from Elbrus, were applied for model forcing to reproduce present surface mass balance. The modeling results were validated by comparison with the measured surfave mass balance components on Garabashi glacier, one of the glaciers on the southern slope of Elbrus. Climate projections until the end of the 21st century for the Elbrus region were composed on the basis of multi-model results of regional climate modeling within the CORDEX project for various scenarios.

We demonstrate that simultaneous surface air temperature and insolation growth accompanied by decrease in precipitation, predicted by multi-model regional climate modeling and downscaled to the Central Caucasus area, will cause essential lifting of the equilibrium line altitude and shrinking of accumulation area. As a result, we must expect an accelerated degradation of Elbrus glaciation in forthcoming decades.   

The reported study was funded by RFBR and RS, project number 21-55-100003

How to cite: Rybak, O., Dymova, T., Korneva, I., Kutuzov, S., Lavrentiev, I., Rybak, E., and Toropov, P.: Future surface mass balance of the Elbrus Glacial Complex under climate change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6422, https://doi.org/10.5194/egusphere-egu21-6422, 2021.

EGU21-15063 | vPICO presentations | CR1.4

Occurrence and impacts of heat waves events in a glacierized basin in the subtropical Andes

Claudio Bravo, Pablo Paredes, Nicolás Donoso, and Sebastián Cisternas

Subtropical Andean glaciers are losing mass in response to the long-term atmospheric warming and precipitation decrease. Extreme events as heat waves, however, seems to potentially play a key role in the sustained ice loss detected in the last decades. Increased frequency of heat wave events have been detected in the central valley of Chile, however, the occurrence and impact of these events on the Andean cryosphere remain unknown. The main reason is associated with the lack of meteorological observations at higher elevations in the Andes. 

In filling this gap, we present an assessment of the occurrence of heat waves in the glacierized Río Olivares basin (33°S), which comprise an elevation range between ~1500  and ~6000 m a.s.l. and where a strong ice loss has been detected during the last decades. The main aim is to analyse the correspondence of heat waves events occurred with those in the nearby city of Santiago located in the central valley of Chile and to assess the potential impacts of these events on the glaciers located in this basin. Using meteorological observations in Río Olivares basin and in Santiago between the years 2013 and 2020, heat wave events were determined. We estimated the heat wave events using the monthly 90th percentile and the adjustment of a harmonic function. An additional adjustment relative to the climate period 1981-2010 was also introduced. The results determined 66 events in the Río Olivares basin while in Santiago were 53 events. These results reveal high spatial variability in the occurrences of heat waves as only 49% of the events in Santiago were detected in the Río Olivares basin. Ongoing work is focused on analysing the impacts of these events over the glaciers of the basin. Here, through the use of the computed basin-scale 0°C isotherm, the relation between glacier area under melt (i.e. glacier area located below the 0°C isotherm) and the heat wave events will be shown. The findings of this works reinforce the need for more observational efforts over high elevations in the Andes in order to robustly assess and at a basin scale, the impact of extreme events on the Andean cryosphere.

How to cite: Bravo, C., Paredes, P., Donoso, N., and Cisternas, S.: Occurrence and impacts of heat waves events in a glacierized basin in the subtropical Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15063, https://doi.org/10.5194/egusphere-egu21-15063, 2021.

CR1.5 – Glaciation and climate change in the Andean Cordillera

EGU21-7633 | vPICO presentations | CR1.5

Environmental drivers of planform change in the glacially-fed Rio Chubut, Argentina (42°S)

Grace Skirrow, Rachel Smedley, Richard Chiverrell, and Janet Hooke

The eastern margin of the former Patagonian Ice Sheet was drained by large and dynamic river systems, which remain largely unstudied. New geomorphological mapping and luminescence chronology of the glacially-fed Rio Chubut reveal the preservation of large gravel outwash terraces up to 50 m above the modern river channel that previously acted as glacial spillways during the last glaciation. Also discovered is a gradual shift from a braided to a meandering planform between 12.3 ± 1.0 ka and 9.4 ± 0.8 ka, where the braided system experienced a decrease in energy and subsequent abandonment, transitioning into the meandering system that persists today. The coincidence of a new luminescence age from the innermost ice lobe in the Epuyen area (18.1 ± 2.2 ka), palaeoenvironmental records (Moreno et al. 2018, Whitlock et al. 2007, Iglesias et al. 2016) and the PATICE ice sheet reconstruction (Davies et al, 2020) suggest that the abandonment of the Rio Chubut braided planform was not a product of the river decoupling from the ice sheet. Alternatively, it was a response to the reduced water supply likely linked with the weakening and southward shift in the mid-latitude storm tracks and westerlies ~11.3 ka (Moreno et al. 2018). These findings contradict the widely reported process of planform change in glacially-fed river systems whereby a river decoupled from a glacier experiences a loss in sediment supply, which leads to incision and the river confining to a single channel. Here at the Rio Chubut, braiding is sustained in a paraglacial landscape for ~5 ka after the ice had retreated into the Andean mountains. A reduction in water supply related to precipitation changes in the early Holocene is identified as the key driver of planform change.

References

Davies, B.J., Darvill, C.M., Lovell, H., Bendle, J.M., Dowdeswell, J.A., Fabel, D., García, J.L., Geiger, A., Glasser, N.F., Gheorghiu, D.M. and Harrison, S., 2020. The evolution of the Patagonian Ice Sheet from 35 ka to the present day (PATICE). Earth-Science Reviews, p.103152.

Iglesias, V., Markgraf, V. and Whitlock, C., 2016. 17,000 years of vegetation, fire and climate change in the eastern foothills of the Andes (lat. 44 S). Palaeogeography, Palaeoclimatology, Palaeoecology, 457, pp.195-208.

Moreno, P.I., Videla, J., Valero-Garcés, B., Alloway, B.V. and Heusser, L.E., 2018. A continuous record of vegetation, fire-regime and climatic changes in northwestern Patagonia spanning the last 25,000 years. Quaternary Science Reviews, 198, pp.15-36.

Whitlock, C., Moreno, P.I. and Bartlein, P., 2007. Climatic controls of Holocene fire patterns in southern South America. Quaternary Research, 68(1), pp.28-36.

How to cite: Skirrow, G., Smedley, R., Chiverrell, R., and Hooke, J.: Environmental drivers of planform change in the glacially-fed Rio Chubut, Argentina (42°S), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7633, https://doi.org/10.5194/egusphere-egu21-7633, 2021.

EGU21-2820 | vPICO presentations | CR1.5

A detailed Pleistocene cosmogenic nuclide chronology of Patagonian Ice-Sheet expansions in north-eastern Patagonia (43°S)

Tancrede Leger, Andrew Hein, Robert Bingham, Ángel Rodes, and Derek Fabel

The former Patagonian Ice Sheet was the most extensive Quaternary ice sheet of the southern hemisphere outside of Antarctica. Against a background of Northern Hemisphere-dominated ice volumes, it is essential to document how the Patagonian Ice Sheet and its outlet glaciers fluctuated throughout the Quaternary. This information can help us investigate the climate forcing mechanisms responsible for ice sheet fluctuations and provide insight on the causes of Quaternary glacial cycles at the southern mid-latitudes. Patagonia is part of the only continental landmass that fully intersects the precipitation-bearing Southern Westerly Winds and is thus uniquely positioned to study past climatic fluctuations in the southern mid-latitudes. While Patagonian palaeoglaciological investigations have increased, there remains few published studies investigating glacial deposits from the north-eastern sector of the former ice sheet, between latitudes 41°S and 46°S. Palaeoglaciological reconstructions from this region are required to understand the timing of Pleistocene glacial expansion and retreat, and to understand the causes behind potential latitudinal asynchronies in glacial advances throughout Patagonia. Here, we reconstruct the glacial history and chronology of a previously unstudied region of north-eastern Patagonia that formerly hosted the Río Corcovado (43°S, 71°W) palaeo ice-lobe. Here we present a new set of cosmogenic 10Be exposure ages from presumed pre-LGM moraine boulder and glaciofluvial outwash surface cobble samples, establishing for the first time a comprehensive chronology for pre-LGM glacial margins of the Río Corcovado palaeo-glacier. This new dataset completes our effort to date the entire preserved moraine record of the Río Corcovado valley: which captures at least seven distinct Pleistocene glacial events. Our results allow answering questions on the timing of the maximum local ice extent of the last glacial cycle as well as older, pre-last glacial cycle glaciations, for which few robust glacier chronologies exist in the Southern Hemisphere. The most informative cosmogenic nuclide-derived glacial chronologies with the capacity to resolve questions on interhemispheric phasing of climate change require unambiguous dating of glacial margins spanning the entirety of the last glacial cycle and ideally earlier glacial cycles. Therefore, our findings have significant implications for understanding past climate fluctuations at the southern mid-latitudes, former Southern Westerly Winds behaviour and interhemispheric climate linkages throughout the Pleistocene. They also provide further evidence supporting the proposed latitudinal asynchrony in the timing of Patagonian Ice Sheet expansion during the last glacial cycle and enable novel glacio-geomorphological interpretations for the studied region.

How to cite: Leger, T., Hein, A., Bingham, R., Rodes, Á., and Fabel, D.: A detailed Pleistocene cosmogenic nuclide chronology of Patagonian Ice-Sheet expansions in north-eastern Patagonia (43°S), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2820, https://doi.org/10.5194/egusphere-egu21-2820, 2021.

EGU21-13184 | vPICO presentations | CR1.5

The Glacial Geomorphology of central-Patagonia (44 – 46°S): glacier dynamics within and beyond the austral Andes

Emma-Louise Cooper, Varyl Thorndycraft, Bethan Davies, Adrian Palmer, and Juan-Luis García

The former Patagonian Ice Sheet (PIS, 38 – 56°S) was one of the largest ice masses to develop in the Southern Hemisphere. Its formation was uniquely influenced by the Southern Westerly Winds (SWWs) colliding with the Andean Cordillera, generating a marked West-East precipitation gradient. Variability in the strength and position of the SWWs is thought to have played a significant role in ice sheet dynamics. In particular, understanding of the timing of palaeo-glacier fluctuations is required to elucidate the role of these regional climate drivers on ice retreat. However, in order to fully understand the structure and pace of deglacial ice fluctuations, detailed glacial geomorphological reconstructions must be completed.

During deglaciation, as the PIS retreated from local Last Glacial Maxima positions, large proglacial lakes formed east of the austral Andes, ice-dammed by the Andean Cordillera. In central-Patagonia (44 – 46°S) during the final stages of deglaciation, these ice-dammed lakes drained to the west, through the Andean Cordillera, opening new drainage corridors towards the Pacific Ocean. As a result, the floors of these valleys are now exposed subaerially, preserving a complex suite of glacial and glaciolacustrine landform assemblages. Moreover, as most of the region is now ice-free, excluding smaller mountain ice caps such as Queulat (44.4°S, ~2000 m a.s.l) more recent Holocene geomorphology has also been exposed. These landforms possess the potential to yield new insights into the style and manner of regional ice retreat, during the transition from large terrestrial ice-lobes, to smaller mountain glaciers and ice caps.

We mapped seven terrestrial palaeo-ice lobes of the PIS: the Río Pico (~44.2°S), Río Cisnes (~44.6°S), Lago Plata-Fontana (~44.8°S), Río El Toqui (~45°S), Lago Coyt/Río Ñirehuao (~45.3°S), Simpson/Paso Coyhaique (~45.5°S) and Balmaceda (~46°S) lobes. Mapping was then extended west, into the Andean Cordillera. Landforms were mapped using ESRI™ DigitalGlobe World (1-2 m) and Sentinel-2 (10 m) imagery, verified with field surveys. These new data build on previous work in the area. To date, over 60,000 ice-marginal, ice-contact, subglacial, glaciolacustrine and glaciofluvial landforms have been mapped across a ~70,000km2 area of the Andean Cordillera and adjacent valleys. When combined with robust geochronological reconstructions, these data possess the potential to inform on the role of the SWWs, versus local topography, and ice-marginal processes in regulating the structure and rate of regional deglaciation.

How to cite: Cooper, E.-L., Thorndycraft, V., Davies, B., Palmer, A., and García, J.-L.: The Glacial Geomorphology of central-Patagonia (44 – 46°S): glacier dynamics within and beyond the austral Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13184, https://doi.org/10.5194/egusphere-egu21-13184, 2021.

EGU21-10973 | vPICO presentations | CR1.5

Projected increases in surface melt and ice loss and their potential feedbacks for the Northern and Southern Patagonian Icefields 

Claudio Bravo, Deniz Bozkurt, Andrew N. Ross, and Duncan J. Quincey

Patagonia (40°S-55°S) includes two large icefields, the Northern and Southern Patagonian Icefields (NPI and SPI). Most of the glaciers within these icefields are shrinking rapidly, raising concerns about their contribution to sea-level rise in the face of ongoing climatic change. This ice volume loss has led to rapid changes that remain imprinted on the Patagonia landscapes. In view of the local, regional and worldwide impacts of glacier retreat in Patagonia, an assessment of the potential future surface mass balance (SMB) and ice loss of the icefields, is critical. We seek to provide this assessment by modelling the SMB between 1976 and 2050 for both icefields, using regional climate model data (RegCM4.6) and a range of emission scenarios at a spatial resolution of 10 km. Additionally, using meteorological observations during strong drought conditions which occurred in Patagonia in 2016, key meteorological and glaciological characteristics are described, quantified and analysed in order to assess possible future conditions.

For the NPI, a reduction between 1.51 m w.e.  (RCP2.6) and 1.88 m w.e. (RCP8.5) was projected, suggesting that negative SMB will prevail well into future decades. For the SPI the projected reduction was within the range of 1.12 m w.e. (RCP2.6) to 1.45 m w.e. (RCP8.5), which implies positive SMB will dominate, albeit at a lower rate than the current observed. However, if it is assumed that the recent frontal ablation rates tend to continue into future decades, ice loss and sea-level contributions will increase for both Icefields. The trend towards lower SMB is explained by an increase in melt, and to a lesser extent by a reduction in snow accumulation.

Several mechanisms not accounted for our modelling approach could act as positive feedbacks in the magnitude of the ice loss. We summarise these feedbacks in a conceptual framework based on a combination of our own meteorological observations as well as on the recent research findings. This framework highlights the diversity of meteorological and glaciological conditions that can prevail even between nearby glaciers. Importantly, more frequent thermal inversion events and increased meltwater availability are likely to trigger ice dynamics changes and potential increases in ablation. Together, these plus other factors make the prediction of future glacier response and evolution in Patagonia a very complex and challenging task.

How to cite: Bravo, C., Bozkurt, D., Ross, A. N., and Quincey, D. J.: Projected increases in surface melt and ice loss and their potential feedbacks for the Northern and Southern Patagonian Icefields , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10973, https://doi.org/10.5194/egusphere-egu21-10973, 2021.

EGU21-6185 | vPICO presentations | CR1.5

Glacial isostatic adjustment near the center of the former Patagonian Ice Sheet (48°S) during the last 16.5 kyr

Matthias Troch, Sebastien Bertrand, Carina B. Lange, Paola Cardenas, Helge Arz, Ricardo De Pol-Holz, and Rolf Kilian

Our understanding of glacial isostatic rebound across Patagonia is highly limited, despite its importance to constrain past ice volume estimates and better comprehend relative sea-level variations. With this in mind, our research objective is to reconstruct the magnitude and rate of Late Glacial to Holocene glacial isostatic adjustment near the center of the former Patagonian Ice Sheet. We focus on Larenas Bay (48°S; 1.26 km2), which is connected to Baker Channel through a shallow (ca. 7.4 m) and narrow (ca. 150 m across) inlet, and hence has the potential to record periods of basin isolation and marine ingression. The paleoenvironmental evolution of the bay was investigated through a sedimentological analysis of a 9.2 m long, radiocarbon-dated, sediment core covering the last 16.8 cal. kyr BP. Salinity indicators, including diatom paleoecology, alkenone concentrations and CaCO3 content, were used to reconstruct the bay’s connectivity to the fjord. Results indicate that Larenas Bay was a marine environment before 16.5 cal. kyr BP and after 9.1 cal. kyr BP, but that it was disconnected from Baker Channel in-between. We infer that glacial isostatic adjustment outpaced global sea-level rise between 16.5 – 9.1 cal. kyr BP. During the Late Glacial - Holocene transition, the center of the former Patagonian Ice Sheet rose ca. 96 m, at an average rate of 1.30 cm/year. During the remainder of the Holocene, glacial isostatic adjustment continued (ca. 19.5 m), but at a slower average pace of 0.21 cm/year. Comparisons between multi-centennial variations in the salinity indicators and existing records of global sea-level rise suggest that the glacial isostatic adjustment rate fluctuated during these time intervals, in agreement with local glacier dynamics. More specifically, most of the glacial isostatic adjustment registered between 16.5 – 9.1 cal. kyr BP seems to have occurred before meltwater pulse 1A (14.5 – 14.0 kyr BP). Likewise, it appears that the highest Holocene glacial isostatic rebound rates occurred during the last 1.4 kyr, most likely in response to glacier recession from Neoglacial maxima. This implies a relatively rapid response of the local solid earth to ice unloading, which agrees with independent modelling studies investigating contemporary uplift. We conclude that the center of the former Patagonian Ice Sheet experienced a glacial isostatic adjustment of ca. 115 m over the last 16.5 kyr, and that >80% occurred during the Late Glacial and early Holocene.

How to cite: Troch, M., Bertrand, S., Lange, C. B., Cardenas, P., Arz, H., De Pol-Holz, R., and Kilian, R.: Glacial isostatic adjustment near the center of the former Patagonian Ice Sheet (48°S) during the last 16.5 kyr, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6185, https://doi.org/10.5194/egusphere-egu21-6185, 2021.

EGU21-10265 | vPICO presentations | CR1.5

Southern Patagonia Icefield freshwater calving glaciers recent collapses into deep lake waters 

Andres Rivera, Francisca Bown, Andres Castillo, Jonathan Oberreuter, María Gabriela Lenzano, and Luis Lenzano

The Patagonian Icefields are among the biggest worldwide glaciers contributors to sea level rise. In spite of ongoing deglaciation in Patagonia, climatic models are estimating that the icefields surface mass balances during at least the last 4 decades has been neutral or even positive. The main mass losses are therefore, mainly related to frontal ablation, namely surface ablation, calving and subaquatic melting. These are the predominant factors in almost every single calving glacier in the region, especially among the eastern glaciers of the Southern Patagonia Icefield that are ending into deep lakes. The only and most remarkable exception to this trend on the eastern side of the SPI is the well-known stable and even advancing state of glaciar Perito Moreno. In spite of the relatively benign surface mass balances modelled for the last 4 decades, during the 2010’s several freshwater calving glaciers experienced strong retreats, and in some cases, the collapse of the whole ice fronts with losses mounting several square kilometers of ice in single events or during a series of huge calving events.   In order to study the glacier-lake interactions in the area, a collaborative research program was initiated in 2013 by Chilean and Argentinean scientists allowing the installation of a network of Automatic Weather Stations, fixed photographic cameras, water level pressure sensors and GPS stations at both sides of the international border. Since 2013 several field campaigns were conducted to the area including the survey of lake waters nearby several retreating glaciers. In most of the studied cases were detected very deep bathymetries (up to 600 m in places), and in some cases, a vertical structure of the lake water indicating a highly stratified condition that we estimate is responsible for very low subaquatic melting favoring the presence of glacier foots extending tens or even few hundreds of meters beyond the subaerial ice walls. The most remarkable recent collapses took place at glaciares O’Higgins and Viedma, whilst the rest or our studied glaciers (Chico, Upsala and Dickson) also experienced retreats with smaller rates. In this presentation we will show novel data collected in the main freshwater calving glaciers of the SPI and will discuss the local conditions explaining the recent glacier behavior.

How to cite: Rivera, A., Bown, F., Castillo, A., Oberreuter, J., Lenzano, M. G., and Lenzano, L.: Southern Patagonia Icefield freshwater calving glaciers recent collapses into deep lake waters , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10265, https://doi.org/10.5194/egusphere-egu21-10265, 2021.

EGU21-4193 | vPICO presentations | CR1.5

Long-lasting impacts of a glacial lake outburst flood on the hydrology of a fjord-river system (Pascua River, Chilean Patagonia)

Loic Piret, Sebastien Bertrand, Nhut Nguyen, Jon Hawkings, Cristian Rodrigo, and Jemma Wadham

Glacial Lake Outburst Floods (GLOFs) are an increasing threat to Patagonian environments and communities. Here, we investigate the geomorphological and hydrological impact of a recent GLOF from Pascua River, which discharges at the head of Baker Fjord (Chile, 48°S). To do so, a sediment core was taken ~4 km offshore of the Pascua River mouth at a water depth of 248 m. The coring site is located on the flank of a submarine channel incised trough the subaquatic delta of Pascua River, 30 m above the bottom of the channel. The sediment physical and chemical properties were analysed at high resolution with X-ray CT, MSCL and XRF core scanning, in combination with lower resolution grain-size and bulk organic geochemistry measurements, and a core chronology was established using downcore variations in 137Cs activity. In addition, historical maps and satellite imagery of the past century were examined in combination with multibeam bathymetry of Baker Fjord to aid the interpretation of the sediment record.

Results show that the sediments are composed of two distinct units separated by a 5-cm thick event deposit dated 1945±9 CE. Below the event, the sediment consists of coarse silt and fine sand, likely representing sediment deposition from turbidity currents. Above it, it consists of very fine silts, likely representing settling from the surficial sediment plume. Historical evidence shows that the event deposit corresponds to a ~256 106 m3 GLOF from Bergues Lake, the proglacial lake of Lucia Glacier that discharges directly into Pascua River. Before 1945, historical information shows that Pascua River drained via two active river branches that were most likely connected to the two submarine channels visible in the bathymetry of the subaquatic delta. After 1945, only the western river branch appears active, which likely caused the abandonment of the eastern submarine channel near which the sediment core was taken. Therefore, we hypothesize that the 1945 Bergues Lake GLOF caused the abandonment of the eastern river branch and submarine channel, which explains the absence of coarse-grained sediments in our sediment record after 1945±9 CE.

This study provides the first report of a GLOF from the northeastern part of the Southern Patagonian Icefield, and it demonstrates that GLOFs can have long-term impacts on the hydrology of fjord-river systems.

How to cite: Piret, L., Bertrand, S., Nguyen, N., Hawkings, J., Rodrigo, C., and Wadham, J.: Long-lasting impacts of a glacial lake outburst flood on the hydrology of a fjord-river system (Pascua River, Chilean Patagonia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4193, https://doi.org/10.5194/egusphere-egu21-4193, 2021.

EGU21-14687 | vPICO presentations | CR1.5

Neoglacial increase in high-magnitude Glacial Lake Outburst Flood frequency (Baker River, Patagonia, 47°S)

Sebastien Bertrand, Elke Vandekerkhove, Dmitri Mauquoy, Dave McWethy, Brian Reid, Sarah Stammen, Krystyna Saunders, and Fernando Torrejon

Glacial Lake Outburst Floods (GLOFs) constitute a major hazard in periglacial environments. Despite a recent increase in the size and number of glacial lakes worldwide, there is only limited evidence that climate change is affecting GLOF frequency. In Patagonia, GLOFs are particularly common in the Baker River watershed (47°S), where 21 GLOFs occurred between 2008 and 2017 due to the drainage of Cachet 2 Lake into the Colonia River, a tributary of the Baker River. During these GLOFs, the increased discharge from the Colonia River blocks the regular flow of the Baker River, resulting in the inundation of the Valle Grande floodplain, which is located approximately 4 km upstream of the confluence. To assess the possible long-term relationship between GLOF frequency, glacier behavior, and climate variability, four sediment cores collected in the Valle Grande floodplain were analyzed. Their geophysical and sedimentological properties were examined, and radiocarbon-based age-depth models were constructed. All cores consist of dense, fine-grained, organic-poor material alternating with low-density organic-rich deposits. The percentage of lithogenic particles, which were most likely deposited during high-magnitude GLOFs, was used to reconstruct the flood history of the last 2.75 kyr. Results show increased flood activity between 2.57 and 2.17 cal kyr BP, and between 0.75 and 0 cal kyr BP. These two periods coincide with glacier advances during the Neoglaciation. Our results suggest that GLOFs are not a new phenomenon in the region. Although rapid glacier retreat is likely responsible for high GLOF frequency in the 21st century, high-magnitude GLOFs seem to occur more frequently when glaciers are larger and thicker.

How to cite: Bertrand, S., Vandekerkhove, E., Mauquoy, D., McWethy, D., Reid, B., Stammen, S., Saunders, K., and Torrejon, F.: Neoglacial increase in high-magnitude Glacial Lake Outburst Flood frequency (Baker River, Patagonia, 47°S), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14687, https://doi.org/10.5194/egusphere-egu21-14687, 2021.

EGU21-12809 | vPICO presentations | CR1.5

Moisture control on high-altitude cooling during the Last Glacial Maximum

Guillaume Leduc, Etienne Legrain, Pierre-Henri Blard, and Julien Charreau

Reconstructing the spatial and temporal variabilities of the vertical atmospheric temperature gradient (lapse rate, LR) is key to predict the evolution of glaciers in a changing climate. Variations in this parameter may amplify or mitigate the future warming at high elevation, implying contrasted impacts on the stability of glaciers. Several regional studies suggested that the tropical LR was steeper than today during the last glacial maximum (LGM) (Loomis et al., 2017; Blard et al.,  2007), while another study concluded that the LGM lapse rate was similar than today (Tripati et al., 2014).

Here we combine published LGM sea surface temperatures (SSTs) data and LGM moraines dated by cosmogenic nuclides to reconstruct the lapse rate along the American Cordillera. To do so, we combined paleo-Equilibrium Line Altitudes (ELAs) of glaciers with independent precipitation proxies to derive high latitude atmospheric temperatures. The whole dataset includes 34 paleo-glaciated sites along a North-South transect in the American Cordillera, ranging in latitude from 40°N to 36°S. Our reconstruction indicates that the lapse rate (LR) was steeper than today in the tropical American Cordillera (20°N – 11°S). The average ΔLR (LGM – Modern) for this Tropical Andes region (20°N – 11°S) is ~-1.5 °C.km-1 (20 sites). At higher latitude, in both hemispheres (Central Andes, 15°S – 35°S (8 sites); Sierra Nevada and San Bernardino mountains (40°N – 34°N) (6 sites), the LR was constant during the LGM. 

 Our results show that a drier climate during the LGM is systematically associated with a steeper LR. Modification of LR during LGM was already observed from other tropical regions, in Hawaii-Central Pacific (Blard et al 2007), and in Eastern Africa (Loomis et al., 2017). Similarly, in these regions, precipitation did not increase during the LGM. With this multi-site exhaustive synthesis, we make a case that drier Tropical LGM conditions induce a steeper LR. This corresponds to an amplification of cooling at high altitude during the LGM. These results highlight the necessity to consider LR variations in modelling future climate. In a warmer and wetter Earth, temperature increase may be amplified at high elevation, due to smoother LR. If valid, this mechanism implies that tropical glaciers are more vulnerable than predicted by current climate modelling.

 

References

Blard, P.-H., Lavé, J., Pik, R., Wagnon, P., & Bourlès, D. (2007). Persistence of full glacial conditions in the central Pacific until 15,000 years ago. Nature, 449(7162), 591.

Loomis, S. E., Russell, J. M., Verschuren, D., Morrill, C., De Cort, G., Damsté, J. S. S., … & Kelly, M. A. (2017). The tropical lapse rate steepened during the Last Glacial Maximum. Science advances, 3(1), e1600815.

Tripati, A. K., Sahany, S., Pittman, D., Eagle, R. A., Neelin, J. D., Mitchell, J. L., & Beaufort, L. (2014). Modern and glacial tropical snowlines controlled by sea surface temperature and atmospheric mixing. Nature Geoscience, 7(3), 205.

How to cite: Leduc, G., Legrain, E., Blard, P.-H., and Charreau, J.: Moisture control on high-altitude cooling during the Last Glacial Maximum, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12809, https://doi.org/10.5194/egusphere-egu21-12809, 2021.

EGU21-13819 | vPICO presentations | CR1.5

Last Glacial Maximum to near present 10Be chronology of the Universidad glacier fluctuations in the Subtropical Chilean Andes (34° S): paleoclimate implications  

Hans Fernández, Juan-Luis García, Samuel U. Nussbaumer, Alessa Geiger, Isabelle Gärtner-Roer, Dmitry Tikhomirov, and Markus Egli

The geochronological and geomorphological reconstruction of glacier fluctuations is required to assess the timing and structure of climate changes of the last glacial cycle in the subtropical Andes of Chile. The scarcity of data in this region limits the knowledge related to the timing of glacial landscape changes during this long-term period. To provide a new framework to better understand the climate history of the semiarid Andes of Chile, we have reconstructed the glacial history of the Universidad glacier (34° S).

Our mapping shows the existence of four moraine belts (UNI I to UNI IV, from outer to inner) that are spatially unequally distributed along the 13 km of the valley between ~2500 and ~1400 m a.s.l. We applied 10Be cosmogenic surface exposure dating to 26 granodioritic boulders on moraines and determined the age of the associated glacial advances. UNI I moraine represents the distal glacier advance between 20.8±0.8 and 17.8±0.8 kyr ago (number of 10Be samples = 11). Other two significative glacier advances terminated one and four km up-valley from the UNI I moraine, respectively, formed 16.1±0.9 kyr (n=1) (UNI II) and 14.6±1 to 10±0.5 kyr ago (n=3) (UNI III). A sequence of six distinct and smaller moraine ridges has been identified in the proglacial area. They are part of last significative glacier advances labeled as UNI IV. The four distal ridges have been dated to between 645-150 years ago (n=11), while the most proximal moraines coincide with mid-20th century and 1997 aerial photographs.

The results indicate that the Universidad glacier advanced during the Last Glacial Maximum (LGM) (UNI I). Deglaciation was punctuated by glacier readvances during the Late Glacial when the UNI II and UNI III moraines were deposited. Finally, UNI IV moraine shows six glacier fluctuations developed between the 14th and 20th centuries.

Our data suggest that the glacier advances by the Universidad glacier were triggered by intensified southern westerly winds bringing colder and wetter conditions to subtropical latitudes in the SE Pacific. Moreover, our data indicate that more or less in-phase Late-Glacial advances along the tropical and extratropical Andes occurred. We discuss different climate forcings that explain these glacier changes. Finally, we illustrate the influence of the “Little Ice Age” in the Semiarid Andes.

How to cite: Fernández, H., García, J.-L., Nussbaumer, S. U., Geiger, A., Gärtner-Roer, I., Tikhomirov, D., and Egli, M.: Last Glacial Maximum to near present 10Be chronology of the Universidad glacier fluctuations in the Subtropical Chilean Andes (34° S): paleoclimate implications  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13819, https://doi.org/10.5194/egusphere-egu21-13819, 2021.

EGU21-6795 | vPICO presentations | CR1.5

Influence of Enso in Perú's Cordillera Blanca Glaciers

Lihan Del Rocio Hoyos Zarzosa, Ibeth Celia Rojas Macedo, Christian German Garcia Rojas, Luzmila Dávila Roller, and Pedro Tapia Ormeño

In areas located over 2000 m.a.s.l., the warm phase of ENSO (El Niño) is characterized by a decrease in precipitation and an increase in temperature which can reach values above the annual average, while in the cold phase of ENSO (La Niña), precipitation increases and temperature decreases compared to the annual average. In both cases ENSO has an influence on the glacier evolution of the Andes.

The objective of the present investigation is to determine the influence of ENSO in the Cordillera Blanca through satellite images (glacier coverage delimitation) and climatic proxy (ice core) in the Shallap and Artesonraju glaciers respectively for the hydrological years between 2009/2010 to 2018/2019.

The climate analysis in both glaciers showed higher annual temperatures and lower precipitation, revealing the influence of the 2015/2016 El Niño on the studied glaciers. There was a prominent reduction in glacier coverage in Shallap, which is supported by the ice core record extracted from Artesonraju, presenting an equivalent accumulated water decrease and an 18O enrichment for this period. These findings point out the influence of the 2015/2016 El Niño that significantly reduced the glacier coverage in both studied areas. On the other hand, the 2011/2012 La Niña event displayed the opposite effect, that is, colder temperatures, less glacier coverage reduction, an increase in the volume of accumulated water and an impoverishment of 18O.

Given the results, it can be affirmed that during an El Niño year the loss of glacier coverage is greater, causing less equivalent water accumulation and an enrichment of 18O; inversely for a La Niña year. These results support previous findings shown in research about glaciers in Peru.

How to cite: Hoyos Zarzosa, L. D. R., Rojas Macedo, I. C., Garcia Rojas, C. G., Dávila Roller, L., and Tapia Ormeño, P.: Influence of Enso in Perú's Cordillera Blanca Glaciers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6795, https://doi.org/10.5194/egusphere-egu21-6795, 2021.

EGU21-7524 | vPICO presentations | CR1.5

Quantifying the controls of Peruvian glacier response to climate

Catriona L. Fyffe, Emily Potter, Stefan Fugger, Andrew Orr, Simone Fatichi, Katy Medina, Robert Å. Hellström, Thomas E. Shaw, Maud Bernat, Alan Llacza, Gerardo Jacome, Caroline Aubry-Wake, Wolfgang Gurgiser, L. Baker Perry, Wilson Suarez, Duncan J. Quincey, Edwin Loarte, and Francesca Pellicciotti

Peruvian glaciers are important contributors to dry season runoff for agriculture and hydropower, but they are at risk of disappearing due to climate warming. Their energy balance and ablation characteristics have previously been studied only for individual glaciers, with no comparisons between regions. We applied the physically-based, energy balance melt component of the model Tethys-Chloris at five on-glacier meteorological stations: three in the Cordillera Blanca near Huaraz (with glaciers above ~4300 m a.s.l.), and two in the Cordillera Vilcanota east of Cusco (with glaciers above ~ 4800 m). The climate of these regions is strongly seasonal, with an austral summer wet season and winter dry season. 

Our results revealed that at most sites the energy available for melt is greatest in the wet season. This is a consequence of the dry season energy losses from the latent heat flux and net longwave radiation which counter-balance the high dry season net shortwave radiation, which otherwise dominates the energy balance. The sensible heat flux is a relatively small contributor to melt energy in both seasons. Comparison of the five sites suggests that there is more energy available for melt at a given elevation in the Cordillera Vilcanota compared to the Cordillera Blanca. At three of the sites the wet season snowpack was discontinuous, forming and melting within a daily to weekly timescale. Albedo and melt are thus highly variable in the wet season and closely related to the precipitation dynamics. At the highest site, in the accumulation zone of the Quelccaya Ice Cap, 81% of ablation was from sublimation. Sublimation was less important at the lower sites, but it reduces dry season melt. 

Correlation of the NOAA Oceanic El Niño Index (ONI) to the outputs of the two sites with the longest records revealed that the warmer wet season temperatures characteristic of a positive ONI were associated with a decreased albedo, greater net shortwave radiation, a more positive sensible heat flux and increased melt rates.  Air temperature and precipitation inputs were also perturbed at all five sites to understand their sensitivity to climate change. Enhanced mass loss was predicted with a static increase of 2°C or more, even with a +30% precipitation increase, with the lower elevation Cordillera Blanca sites at risk of the greatest mass loss due to warming.

How to cite: Fyffe, C. L., Potter, E., Fugger, S., Orr, A., Fatichi, S., Medina, K., Hellström, R. Å., Shaw, T. E., Bernat, M., Llacza, A., Jacome, G., Aubry-Wake, C., Gurgiser, W., Perry, L. B., Suarez, W., Quincey, D. J., Loarte, E., and Pellicciotti, F.: Quantifying the controls of Peruvian glacier response to climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7524, https://doi.org/10.5194/egusphere-egu21-7524, 2021.

EGU21-7580 | vPICO presentations | CR1.5

Palaeoglaciation in the low latitude, low elevation tropical Andes, northern Peru

Ethan Lee, Neil Ross, Andrew Henderson, Andrew Russell, Stewart Jamieson, and Derek Fabel

Palaeo-glaciological studies of former ice thickness and extent within the tropical Andes have tended to focus on locations where glaciers are currently present, or in high elevation locations where evidence exists of recently deglaciated cirques. Few studies have focussed on low elevation regions due to the presumption that glaciers could not have existed at such low altitudes within the tropics. A latitudinal ‘data gap’ exists between Ecuador and more central and southern Peru where evidence for former glaciation is abundant. To fill this gap we present rare evidence of past glaciation from the Las Huaringas region, northern Peru, located in a relatively low elevation massif (<3900 m).

Within Las Huaringas a large valley glacier existed, extending N-S ~12 km down valley to ~2900 m in elevation while glacial cirques existed exhibiting an E-W orientation on the western facing hillslope of the massif with pronounced moraine complexes and bedrock erosion. We used high-resolution remotely sensed imagery, a 30 m ALOS DEM, and preliminary field observations to identify and map an abundance of geomorphic evidence of glaciation. These include moraines at different stages of preservation and predominance, eroded bedrock surfaces, cirque landforms and overdeepened valleys to develop the first glacial geomorphological map of the region. We performed morphometric analysis (e.g. width, length, altitude, azimuth) of the mapped glacial landforms and cirques along with hypsometric analysis of the main valley of Laguna Shimbe, yielding a hypsometric maxima of 3250 m. Using the geomorphological map, we determine the former extent and thickness of palaeoglaciers in the area and use delineated glacial outlines of their furthest extent to reconstruct Equilibrium Line Altitudes (ELAs) of these ice masses using a combination of ELA estimation techniques.

Ongoing research aims to determine whether the palaeoglacial evidence is consistent with formation by valley glaciers or an icecap and whether the timing of the local Last Glacial Maximum (LGM) was synchronous with the global timing. A set of hypotheses for the timing and drivers of the reconstructed extent of former glaciers in the area will be presented. Our analysis confirms the presence of former glaciers in a low elevation and low latitude region of the tropical Andes. Our ongoing work aims to unveil the timing of the glacial events and the drivers of the glacial and climate history seen within this important region.

How to cite: Lee, E., Ross, N., Henderson, A., Russell, A., Jamieson, S., and Fabel, D.: Palaeoglaciation in the low latitude, low elevation tropical Andes, northern Peru, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7580, https://doi.org/10.5194/egusphere-egu21-7580, 2021.

EGU21-8669 | vPICO presentations | CR1.5

Multi-decadal past and future temperature and precipitation trends in the Peruvian Andes

Emily Potter, Andrew Orr, Catriona Fyffe, Duncan Quincey, Andrew Ross, Helen Burns, Robert Hellström, Katy Medina, Edwin Loarte, Alan Llacza, Gerardo Jacome, Scott Hosking, and Francesca Pellicciotti

The Peruvian Andes contain the vast majority of the world’s tropical glaciers. Warming temperatures due to climate change have caused a dramatic shrinking of these glaciers, posing a threat to water supplies. Two of the most heavily glacierised areas of Peru are the Cordillera Blanca,  which includes the Rio Santa River Basin to the north of Peru, and the Cordilleras Urubamba, Vilcabamba, and Vilcanota towards the south.

Due to the topographic and climatic complexity of the regions, spatial variations in precipitation and temperature are high, and spatially distributed high-resolution climate data can offer a crucial tool to understand those variations, in a way which is not possible from limited, individual ground stations. Here we present a new high-resolution climate dataset over both regions, created by bias-correcting Weather Research and Forecasting (WRF) model output at 4 km spatial resolution against observations. 

The spatial variation in precipitation differs over the two river basins. In the region of the Cordillera Blanca, precipitation mostly increases with elevation and distance upstream. Around the southern cordilleras, there are regions of greater precipitation near the mountains and glaciers which lie further downstream, but the high elevations of the cordillera Vilcanota, further upstream, are much drier. Analysis of the precipitation and temperature trends from 1980 to 2018 demonstrates a clear warming trend in both regions. The precipitation trends are less uniform, with the Rio Santa showing a general trend for increasing precipitation, but with a less clear trend over the higher, glacierised regions of the valley. Around the Cordilleras Urubamba, Vilcabamba and Vilcanota, there is no clear trend in precipitation over recent decades.

Using a range of CMIP5 models, the high-resolution precipitation and temperature datasets are statistically projected into the future, using quantile mapping. Future trends in precipitation and temperature are analysed over both regions, and the inter-model variability in the CMIP5 models is examined.

 

How to cite: Potter, E., Orr, A., Fyffe, C., Quincey, D., Ross, A., Burns, H., Hellström, R., Medina, K., Loarte, E., Llacza, A., Jacome, G., Hosking, S., and Pellicciotti, F.: Multi-decadal past and future temperature and precipitation trends in the Peruvian Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8669, https://doi.org/10.5194/egusphere-egu21-8669, 2021.

EGU21-12241 | vPICO presentations | CR1.5

What’s in a lake? Glacial Lake Outburst Floods in the Peruvian Andes.

Joanne Wood, Stephan Harrison, Ryan Wilson, Neil Glasser, John Reynolds, Alejandro Diaz Moreno, Adam Emmer, Simon Cool, Juan Carlos Torres, Adriana Caballero, Harrinson Jara, Christian Yarleque, Enver Melgarejo, Hilbert Villafane, Julia Araujo, Efrain Turpo, and Tito Tinoco

Climate change is resulting in mass loss and the retreat of glaciers in the Andes, exposing steep valley sides, over-deepened valley bottoms, and creating glacial lakes behind moraine dams. Glacial Lake Outburst Floods (GLOFs) present the biggest risk posed by glacier recession in Peru. Understanding the characteristics of lakes that have failed in the past will provide an aid to identifying those lakes that might fail in the future and narrow down which lakes are of greatest interest for reducing the risks to local vulnerable populations. 

Using a newly created lake inventory for the Peruvian Andes (Wood et al., in review) and a comprehensive GLOF inventory (unpublished) we investigate lakes from which GLOFs have occurred in the past. This is to establish which physical components of the glacial lake systems are common to those lakes that have failed previously and which can be identified remotely, easily and objectively, in order to improve existing methods of hazard assessment.

How to cite: Wood, J., Harrison, S., Wilson, R., Glasser, N., Reynolds, J., Diaz Moreno, A., Emmer, A., Cool, S., Torres, J. C., Caballero, A., Jara, H., Yarleque, C., Melgarejo, E., Villafane, H., Araujo, J., Turpo, E., and Tinoco, T.: What’s in a lake? Glacial Lake Outburst Floods in the Peruvian Andes., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12241, https://doi.org/10.5194/egusphere-egu21-12241, 2021.

EGU21-12951 | vPICO presentations | CR1.5

Antarctic-like temperature variations in the Tropical Andes recorded by glaciers and lake levels during the last deglaciation

Léo Martin, Pierre-Henri Blard, Jérôme Lavé, Vincent Jomelli, Maarten Lupker, Julien Charreau, and Thomas Condom

The climatic reorganizations that occurred in the Southern and Northern hemispheres during the last deglaciation are thought to have affected the continental tropical regions. However, the respective impact of North and Southern climatic changes in the Tropics are still poorly understood. In the Norhtern Tropical Andes, moraines records indicate that the Antarctic Cold Reversal (ACR, 14.3-12.9 ka BP) stage was more represented than the Younger Dryas (12.9-11.7 ka BP) (Jomelli et al., 2014). However, further South, in the Altiplano basin (Bolivia), two cold periods of the North Hemisphere (Heinrich Stadial 1a (16.5-14.5 ka) and Younger Dryas) are synchronous with (i) major advances or stillstands of paleo-glaciers and with (ii) the highstands of the giant palaeo-lakes Tauca and Coipasa (Martin et al., 2018). Therefore, additional geochronological records of paleoglaciers fluctuations are necessary to address the respective impacts of North and South Hemisphere on the glacial dynamics in the region.

We present new Cosmic Ray Exposure (CRE) ages from glacial landforms of the Bolivian Andes that extend pre-existing datasets for four different sites spreading from 16 to 21°S. We reconstruct the Equilibrium Line Altitudes (ELA) associated with each moraine with the AAR method and use them in an inverse algorithm that combines both the palaeo-glaciers and palaeo-lake budgets to derive temperature and precipitation reconstructions. Our temperature reconstruction (ΔT vs. Present) shows a consistent trend through the four glacial sites with a progressive warming from ΔT= -5°C (17 ka BP) to –2.5°C (15-14.5 ka BP, at the end of the Tauca highstand). This is followed by a return to colder conditions, around -4°C, during the ACR (15.5-12.9 ka BP). The Coipasa highstand is coeval with another warming trend followed by ΔT stabilization at the onset of the Holocene (circa 10 ka BP), around -3°C. Precipitation is mainly characterized by increases during the lake highstands, modulated by the distance from the glacial sites to the center of the paleolakes that are moisture sources (recycling processes).

These new results highlight the decorrelation of the glacier dynamics to the temperature signal in regions that are characterized by high precipitation variability. They also provide a theoretical frame to explain how both regional and global forcings can imprint the paleo-glacial records. Our results strongly suggest that during the last deglaciation (20 – 10 ka BP), in the Tropical Andes, atmospheric temperatures follow the Antarctic variability, while precipitation is driven by the changes occurring in the Northern Hemisphere.

References

Jomelli et al., Nature, 2014; Martin et al., Sc. Advances, 2018

How to cite: Martin, L., Blard, P.-H., Lavé, J., Jomelli, V., Lupker, M., Charreau, J., and Condom, T.: Antarctic-like temperature variations in the Tropical Andes recorded by glaciers and lake levels during the last deglaciation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12951, https://doi.org/10.5194/egusphere-egu21-12951, 2021.