Content:

CL – Climate: Past, Present, Future

CL1 – Open Session on Climate: Past, Present and Future

The controversy between the CO2 driving or lagging models is elucidated in a new climate model, that reunites insights from models from other planets, carbon draw down models during earth history as a whole, spores spike related to catastrophic events from the Phanerozoic, late Palaeozoic climate models and carbon dioxide and temperature fluctuations during the Quaternary as shown by Petit et al., (1999).

 

This model advocates that for the natural system orbitally induced insolation maxima (eccentricity in particular) momentarily and erratically trigger ocean degassing and drive temperature rise orbitally while it is otherwise driven by carbon drawdown through photosynthesis leading to cooling.

 

For the natural system high concentrations of particulate organic carbon (fungal spore, pollen, vegetation debris, soot and charcoal) or abiotic dust are forming crystallisation cores that trigger an ephemeral greenhouse effect in the cirrus from the lowermost stratosphere. This happens at the onset of orbital insolation peaks when warming leads to larger crystal sizes. The consecutive warming induces the waxing of the cirrus forming sphere which necessarily has lower concentrations of crystallisation cores and shifts back to the albedo effect.

 

In this model the decrease in CO2 concentration in the atmosphere through photosynthesis regulates temperature and supports the view that temperature lags CO2 concentration, yet in this natural system, the greenhouse effect is briefly triggered by orbital forcing and support the results of Feulner (2017) indicating that both the carbon drawdown and orbital forcing are driving temperature in the natural system. In this model the CO2 gets ping-ponged from the terrestrial to the marine system until both are depleted in CO2.  It indicates that, ultimately, under natural circumstances, spreading rate and tectonic events drive climate. From this model it also follows that the industrial use of organic and inorganic carbon sinks, as they have constantly been replenished during earth history through tectonic activity, will lead to CO2 concentrations as experienced before photosynthesis appeared and concentrations far beyond.

 

The aberrant CO2 and temperature rise in the Anthropocene reflects the tempering of the response system in the lowermost stratosphere because of increasing concentrations of particulate organic carbon and dust by changing land use, lowering of the ground water table by wood cutting, aridification (pyro-cumulonimbi), transport (contrails) and soot emission.

How to cite: Waveren, I.: Midas or Gaia revisited, about anthropogenic tempering with the natural response system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2689, https://doi.org/10.5194/egusphere-egu2020-2689, 2020.

EGU2020-11039 | Displays | CL1

Global temperature response to regional and sectoral air pollutant and greenhouse gas emissions under the Shared Socioeconomic Pathways

Marianne T. Lund, Borgar Aamaas, Camilla W. Stjern, Zbigniew Klimont, Terje K. Berntsen, and Bjørn H. Samset

Achieving the ambition of the Paris Agreement and meeting the Sustainable Development Goals require both near-zero levels of long-lived greenhouse gases and deep cuts in emissions of so-called short-lived climate forcers (SLCFs), including methane and black carbon. Here we present a comprehensive dataset of contributions to future global temperature change from emissions of CO2 and individual SLCFs from 7 economic sectors and 13 source regions, both as they are today and as they are projected to change under the Shared Socioeconomic Pathways (SSPs). Such detailed knowledge about the mix of emissions from individual sources and benefits and trade-offs of reductions is essential for designing efficient mitigation strategies at the national and international levels, as well as for informing policy processes on how to best address linkages between climate, sustainable development and air quality.

Our results demonstrate that the mitigation potential inherent in the present SLCF emissions is highly inhomogeneous across region and sector, and that co-emissions of all species – including CO2 – should be considered in any targeted climate policy. We also reinforce the importance of reducing methane emissions, from agriculture, waste management and energy production, for reducing warming in the near-term. In contrast, in many regions, reducing industry emissions brings air quality benefits but may cause a net additional near-term warming. The spatiotemporal heterogeneity is expected to continue under the SSPs. Most scenarios project a particularly strong increase in aerosol and other SLCF emissions in South Asia and Africa South of the Sahara, suggesting that technology development and air pollution legislation in these regions is a key step in the transition to a low emission future. Moreover, both rapidly increasing and decreasing emissions of SLCFs will play an important role in shaping the regional climate and air quality.

By using an analytical climate model, we build a methodological framework that can be used to estimate the impact of any emission scenarios. Our data set hence provide a toolkit for further studies of implications of mitigation pathways and policy responses, and support assessments of environmental impacts.

How to cite: Lund, M. T., Aamaas, B., Stjern, C. W., Klimont, Z., Berntsen, T. K., and Samset, B. H.: Global temperature response to regional and sectoral air pollutant and greenhouse gas emissions under the Shared Socioeconomic Pathways, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11039, https://doi.org/10.5194/egusphere-egu2020-11039, 2020.

EGU2020-13155 | Displays | CL1

Evaluation of Clouds in the E3SM Atmosphere Model with Satellite Simulators

Yuying Zhang, Shaocheng Xie, Wuyin Lin, Stephen A. Klein, Mark Zelinka, Po-Lun Ma, and Philip J. Rasch

EGU2020-6095 | Displays | CL1

Short-Lived Climate Forcers over the Arctic between 1995 and 2015 as simulated by the GISS modelE2.1

Ulas Im, Kostas Tsigaridis, Cynthia H. Whaley, Gregory S. Faluvegi, Zbigniew Klimont, and Knut von Salzen

The Arctic Monitoring and Assessment Programme (AMAP) is currently assessing the impacts of Short-Lived Climate Forcers (SLCF) on Arctic climate and air quality. In support of the assessment, we used the NASA Goddard Institute of Space Sciences (GISS) Earth System Model (modelE2.1), with prescribed sea surface temperature and sea-ice fraction, to simulate SLCF concentrations globally between 1995 and 2015. Two simulations were conducted, using the One-Moment Aerosol (OMA) and the Multiconfiguration Aerosol TRacker of mIXing state (MATRIX) aerosol modules. OMA is a mass-based scheme in which aerosols are assumed to remain externally mixed and have a prescribed and constant size distribution, while MATRIX is an aerosol microphysics scheme based on the quadrature method of moments, which is able to explicitly simulate the mixing state of aerosols. Anthropogenic emissions from the ECLIPSE v6b emissions database were used, along with emissions from aircrafts and open biomass burning from the Coupled Model Intercomparison Project Phase 6 (CMIP6), while the natural emissions of sea salt, DMS, isoprene and dust are calculated interactively. The simulated monthly surface concentrations of sulfate (SO4), black carbon (BC), organic carbon (OA), and ozone (O3) are compared with observations from a set of Arctic stations, extracted from the EBAS and IMPROVE databases, as well as a few additional locations. Simulated aerosol optical depths (AOD) are also compared with Advanced Very-High Resolution Radiometer (AVHRR). The study will present the evaluation of the modelE2.1 in simulating SLCF levels over the Arctic using different aerosol schemes, along with observed and simulated trends of SLCFs over the Arctic between 1995 and 2015.

 

How to cite: Im, U., Tsigaridis, K., Whaley, C. H., Faluvegi, G. S., Klimont, Z., and von Salzen, K.: Short-Lived Climate Forcers over the Arctic between 1995 and 2015 as simulated by the GISS modelE2.1, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6095, https://doi.org/10.5194/egusphere-egu2020-6095, 2020.

The Turpan basin is one of the most arid and water insecure regions in China. The mountain snowmelt is the primary source of water. To assess the impact of climate change on stream flow, this study examined the long-term trends and change points of hydro-meteorological variables and explored the possible correlation between them at annual and seasonal scales. A set of non-parametric statistical tests including Mann-Kendall, Kendall’s tau, Sen’s slope estimator, and Pettitt test was applied, and change point of the hydro-meteorological variables. This study provided valuable information in understanding the changing properties of the stream flow in the basin and insights for a better integrated water resources management planning.

How to cite: Du, L.: Hydrological Variability and its Response to Climate Change in Turpan basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12545, https://doi.org/10.5194/egusphere-egu2020-12545, 2020.

EGU2020-8357 | Displays | CL1

New records of freshwater ostracoda from the xingyun lake

Manping Xie

This present paper reports eight modern ostracode collected from the bottom of the Xingyun Lake,Yunnan Province, including Candonocypris novaezelandiae (Baird, 1843), mateless cyclocypris Cypridopsis Vidua (O.F.M ller, 1776), star (which really wedge dielectric) Eucypris CF. Cuneata (Tsao, 1959), Cleveland star kraeplini (G.W.M mediated Cypris ller, 1903) Belgium, sheshi (similar) glass dielectric Schellencandona CF. Belgica (Klie, 1937), Fabaeformiscandona subacuta (Yang, 1982), unarmed mobs mediated Cetacella inermis (Martin, 1958), the Yunnan flower (compare kinds) Yunnanicyhere cf.reticulate mediated gen.etsp.nov. the true star (dielectric wedge comparison of three) Eucypris CF. Cuneata (Tsao, 1959), unarmed mobs mediated Cetacella inermis (Martin, 1958) and Yunnan (a comparison of dielectric reticulate flowers) Yunnanicyhere cf.reticulate gen.etsp.nov.  these species are newly recorded from modern lakes.It has enriched the understanding of freshwater ostracoda of the biological communities in China.

Key word  freshwater ostracods; Xingyun Lake; Yunnan Province

How to cite: Xie, M.: New records of freshwater ostracoda from the xingyun lake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8357, https://doi.org/10.5194/egusphere-egu2020-8357, 2020.

In this study, we focus on the relationship between the water vapor source region and the isotopic composition of the precipitation. The change of isotope characteristics of precipitation depends on the moisture source region. Long-term stable isotope (δ18O, δ2H ) measurements of precipitation were performed in Debrecen, Hungary, between 2001 and 2014. The long-term isotope time series and trajectory modeling are suitable for determining moisture source regions. Backward trajectory analysis was carried out using the Lagrangian Raptor model based on ERA5 atmospheric data. Hourly backward trajectories were calculated for Debrecen for the days with precipitation in the period between 2001-2014.

Based on the study three source regions were identified. Of these, 60% represented the Carpathian Basin, which is where most of the moisture evaporated from near the surface. The remaining 40% of the northwest and southwest were represented by moisture source regions. This means that the isotopic composition of precipitation significantly determines the local and continental effects, i.e. the moisture evaporated from the continental surface contributes significantly to the spatial and temporal variation of the precipitation isotope composition.

How to cite: László, E., Palcsu, L., and Leelőssy, Á.: Identification of moisture source region based on trajectory model analysis and isotopic composition of the precipitation in Debrecen, Hungary , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18226, https://doi.org/10.5194/egusphere-egu2020-18226, 2020.

EGU2020-13537 | Displays | CL1

Comparison of noble gas temperature with recent mean annual air and soil temperature in different regions of Hungary

Anita Puskás-Preszner, Carmen Fekete, Elemér László, László Kompár, Andor Hajnakl, and László Palcsu

This paper describes the relation of noble gas temperature (NGT) and mean annual air (MAAT) and soil (MAST) temperature through studying water samples and meteorological data from six Hungarian regions. Alluvial plains, hilly and mountainous regions were studied to investigate the effects of geomorphological, hydrogeological and micro-climatic conditions. Water samples were collected from springs and wells fed from different aquifers. Comparing NGTs derived from these water samples with the MAAT and MAST values of the given region, we identified differences between the sampled areas. In case of the Geresd Hills, Mezőföld, Danube-Tisza Interfluves and Nyírség, the NGTs (13.0 ± 0.9 °C, 12.1 ± 1.1 °C, 12.1 ± 0.6 °C and 12.7 ± 1.6 °C, respectively)  generally reflect MAST, however in karstic Bükk Mts. (6.8 ± 0.6 °C) and Mecsek Mts. (10.7 ± 1.9 °C) they are closer to MAAT. Consequently, it can be concluded that the direct relationship between noble gas temperature and mean annual air temperature is not always as well-defined as it is often assumed. It is shown that MAAT and MAST should be distinguished, especially when using NGT as a paleoclimate proxy.

How to cite: Puskás-Preszner, A., Fekete, C., László, E., Kompár, L., Hajnakl, A., and Palcsu, L.: Comparison of noble gas temperature with recent mean annual air and soil temperature in different regions of Hungary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13537, https://doi.org/10.5194/egusphere-egu2020-13537, 2020.

EGU2020-9276 | Displays | CL1

A synchronous change of mid- to late- Holocene hydroclimate and prehistoric population in coastal East Asia indicated by pollen, XRF and grain size data

Jinheum Park, Jungjae Park, Sangheon Yi, Jin Cheul Kim, Eunmi Lee, Quihong Jin, and Jieun Choi

A relationship between climate change and prehistoric civilizations is a topic of growing interest. Here, we present a 6,000-year-long pollen, X-ray fluorescence (XRF), and grain size data of the core STP18-03 from the southern Korean peninsula, spanning the mid- to late- Holocene. The proxies generally show a synchronous change throughout the core. During dry periods, reduced precipitation indicated by lower sand proportion (river discharge) would have hindered tree growth, which then resulted in increased titanium erosion from nearby hills, and vice versa. The drying trend is remarkable during ca. 4.8, 4.3, 4.0, 3.3, 2.7-2.3 ka BP and corresponds with sudden dropping points of a summed probability distribution (SPD) of archaeological records found in the Korean Peninsula. This implies that ancient civilizations of Korea responded highly sensitively to abrupt climate deterioration. As an underlying mechanism of the change, we suggest a role of the equatorial Pacific Ocean. The temporal pattern of our arboreal pollen proportion closely follows that of sea surface temperature (SST) data from the Western Pacific Warm Pool (WPWP) region. Furthermore, the dry periods indicated by our multiple proxies coincide with strong El Niño–Southern Oscillation (ENSO) activity, when the core region of the warm seawater pool deviated eastward than usual. This supports that the equatorial Pacific Ocean has served as an important factor for modulating mid- to late- Holocene hydroclimate of the Korean Peninsula, where the East Asian Summer Monsoon (EASM) accounts for nearly 70 percent of the total annual precipitation amount.

How to cite: Park, J., Park, J., Yi, S., Kim, J. C., Lee, E., Jin, Q., and Choi, J.: A synchronous change of mid- to late- Holocene hydroclimate and prehistoric population in coastal East Asia indicated by pollen, XRF and grain size data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9276, https://doi.org/10.5194/egusphere-egu2020-9276, 2020.

Temperature cycles with periods > 2000 yr, including peaks of order 6000 yr, has been reported in 14C proxy records in sediments for Fennoscandia (Olsen et al, 2005) and in glacier geochemistry for the Greenland ice-sheet (Mayewski et al, 1997, 2004).  Similar spectral peaks are also seen in 14C and 10Be isotopes in Greenland GRIP ice-cores (Xapsos, 2009); these cycles have been attributed to solar sunspot activity (Solanki et al, 2004). Complicating the question of existence of global millennial cycles, a comparison of d18O data in ice cores for Greenland (NGRIP) and Antarctica (EDML) has shown that for events prior to the Last Glacial Maximum (LGM), variations on the scale of 2-6kyr are markedly stronger in northern hemisphere records, associated with ice dynamics and Dansgaard–Oeschger (D-O) and Heinrich events (EPICA, 2006).

This paper discusses ocean sediment cores from three temperate zone and sub-tropical sites which provide sea-surface temperature (SST) histories using the UK37 proxy.  The available time spans are 20, 70 and 136 ka.  This study restricts the three records to 0-20ka thus avoiding complexities of D-O and Heinrich events, and of the associated phase changes between hemispheres which have been discussed by EPICA (2006).  We apply Lomb-Scargle spectral analysis and find that all three sediment SST records (Okinawa Trough, Murray Canyon south of South Australia, and Iberian Margin) show a high-confidence 6000 yr period spectral peak for the time span 0-20ka; we may conclude that this post-LGM peak is unlikely to be related to glacial-epoch ice dynamics.  The same 6000 yr spectral peak also shows in 0-20ka EDML d18O data from EPICA (2006).

The three SST records also show spectral peaks in the range 1000 to 3500 yr periods. The high-resolution Okinawa Trough shows a clear 2300 yr (Hallstatt) peak and the Iberian Margin similarly.  The peak is visible on southern hemisphere Murray Canyon data but is of doubtful significance.  A unique feature of the Iberian Margin data is a strong 3400 yr spectral peak.  This peak is also visible but much weaker on the other SST records, and on the 0-20ka EPICA d18O data.   We hypothesize the strong peak for the Iberian Margin is a consequence of effects of ocean and ice dynamics in the north Atlantic.

Similar spectral analysis of limited 10Be data from McCracken et al 2013, (available length limited to 0-10ka) supports the hypothesis that millennial cycles in temperature (especially the 6000 yr and 2300 yr periods) are global and associated with cosmic ray/solar magnetic activity.  This is in contrast with the longer Milankovich cycles which are well established as being primarily related to forcing associated with variable solar insolation.

How to cite: Asten, M.: Holocene 6000-yr climate cycles in temperate and sub-tropical SST records – a cosmic ray connection?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7285, https://doi.org/10.5194/egusphere-egu2020-7285, 2020.

EGU2020-12830 | Displays | CL1

Perturbations in Antarctic bottom water formation in the Atlantic sector of the Southern Ocean during the last peak interglacial period

Julia Gottschalk, Robert F. Anderson, Adam P. Hasenfratz, Bärbel Hönisch, Samuel L. Jaccard, Jerry F. McManus, Luke C. Skinner, Claire Waelbroeck, and Gisela Winckler

Interglacial climate conditions are generally characterized by relatively strong and persistent deep-water formation both in the North Atlantic and in the Southern Ocean, and overall ‘stable’ climate conditions. Recent evidence, however, challenges the notion of persistent deep-water formation in both hemispheres during the last interglacial, and points at rapid reductions in convective mixing that may have lasted few centuries to millennia. The spatial pattern of this phenomenon and its driving mechanisms remain poorly constrained. Here we present multi-proxy data for rapid reductions in bottom water oxygen in the central sub-Antarctic Atlantic (sediment core MD07-3077, 44°9.20’S, 14°13.69’W, 3776 m water depth) during the warmer-than-present period of the last interglacial (i.e., 132-116 kyr before present). The first of these “stagnation events”, as they are often denoted, is synchronous, within dating uncertainties, with a similar drop in bottom water oxygenation at a more southern site, ODP Site 1094, south of the Polar Front. Our findings hint at a widespread and significant change in the formation rate and/or end-member pre-formed oxygen levels of Antarctic bottom water (AABW) in the South Atlantic during the last interglacial. The onset of these events closely coincides with increases in sea surface temperatures in the sub-Antarctic Atlantic above average Holocene levels. Although this needs to be further tested at more proximal sites, we argue that stagnation events were likely driven by excess ocean warming, in particular below ice shelves in the Weddell Sea, that may have perturbed AABW formation and/or air-sea gas exchange in that region during the last interglacial. Our findings highlight important feedback mechanisms linking hydrographic conditions at the sea surface, instabilities of the local cryosphere, and the strength of deep water formation in warmer-than-present climate scenarios – the full understanding of which has relevance for assessing the trajectory of future changes in the Southern Ocean.

How to cite: Gottschalk, J., Anderson, R. F., Hasenfratz, A. P., Hönisch, B., Jaccard, S. L., McManus, J. F., Skinner, L. C., Waelbroeck, C., and Winckler, G.: Perturbations in Antarctic bottom water formation in the Atlantic sector of the Southern Ocean during the last peak interglacial period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12830, https://doi.org/10.5194/egusphere-egu2020-12830, 2020.

EGU2020-3496 | Displays | CL1

The Last Glacial Maximum and Holocene along the western Iberian Margin: paleoceanographic and paleoclimatic analyses preliminary results

Carmen Argenio, Pierluigi Palladino, José Abel Flores Villarejo, and Filomena Ornella Amore

During the past 25 ky, the Earth system underwent a series of dramatic climate transitions until the most recent glacial period. It peaked about 21 ky ago during the time interval known as “Last Glacial Maximum” (LGM). This study focuses on the reconstruction of global changes occurred from the LGM to the Holocene.

For this aim coccolithophore assemblages have been studied at Integrated Ocean Drilling Program (IODP) Site U1385 (37°34.285’N, 10°7.562’W, 2578 m below sea level) located on the continental slope of the southwestern Iberian Margin in a timeframe between 25 and 0 ky. Moreover, an integration with isotopic and biogeochemical data and a comparison with other proxies were carried out.

This IODP Site nowadays is influenced by the Portugal Current system (Pérez et al., 2001; Relvas et al., 2007), whose seasonality is driven by migrations of the semi-permanent subtropical Azores High pressure system (Coelho et al., 2002). The study area also undergoes intra-seasonal oscillations mainly related to changes, during winter, of westerly wind prevalence, induced by the North Atlantic Oscillation (Trigo et al., 2004).

Coccolithophore data were carried out by sediments from the first four sections of the core A of the IODP Site U1385. Coccolithophores, haptophyte algae living in the photic zone, are sensitive to some environmental parameters as temperature, salinity, availability of nutrients and sunlight. Thanks to their ecological sensitivity, coccolithophores are able to record paleoceanographic changes and for this reason are considered to be an important proxy to study the climate variability.

The age model was calculated using linear interpolation between 64 tie points based on log (Ca/Ti) records of Site U1385 and MD01-2444 (Hodell et al., 2015; Datema et al., 2019) and on δ18O records of Site MD01-2444 and Greenland (Hodell et al., 2013). About 500 samples were sampled and preliminary results are based on the analysis of samples with a time-resolution of about 0,3 ky.

The preservation of the assemblages is from good to moderate (Flores et al., 2003). For quantitative analyses, a minimum of 300 coccoliths was counted per slide in a varying number of visual fields using a light microscope at 1000x magnification. This allows a 95% level of confidence to be reached for all species present in at least 1% abundance (Patterson and Fishbein, 1989). Absolute abundance (coccoliths per gram of sediment) and nannofossil accumulation rate (NAR; coccoliths cm-2 ka-1) were estimated following Flores and Sierro (1997).

The preliminary results highlight a progressive increase of small Gephyrocapsa and a decrease of Emiliania huxleyi, between 4,26 ky and 0,91 ky. Moreover, most abundant species, in this interval, are Gephyrocapsa oceanica, Umbilicosphaera sibogae and Calcidiscus leptoporus. Furthermore, between 18,40 ky and 14,72 ky a significant increase of E. huxleyi > 4 µm and G. mullerae occurs associated with a decrease of small Gephyrocapsa and E. huxleyi.

How to cite: Argenio, C., Palladino, P., Flores Villarejo, J. A., and Amore, F. O.: The Last Glacial Maximum and Holocene along the western Iberian Margin: paleoceanographic and paleoclimatic analyses preliminary results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3496, https://doi.org/10.5194/egusphere-egu2020-3496, 2020.

Long chain n-alcohols and n-alkanes in core sediments from the northern South China Sea (SCS) were measured to make a comparison during terrestrial vegetation reconstruction from ~42 to ~7 ka. The results showed that terrestrial vegetation record from long chain n-alkanes matched well with previous studies in nearby cores, showing more C4 plants developed during the Last Glacial Maximum (LGM) and C3 plants dominated in the interglacial period. However, these scenarios did not occur during terrestrial vegetation reconstruction using long chain n-alcohols, i.e., showing C3 plant expansion during the LGM. The discrepancy during the interglacial period could be likely attributed to aerobic degradation of functionalized long chain n-alcohols due to the oxygen-rich SCS bottom water, resulting in the weak response of terrestrial vegetation signals. On the other hand, the difference between functionalized n-alcohols and non-functional n-alkanes to record local and distal vegetation signals, respectively might be a potential interpretation for the contradiction during the LGM when the SCS was characterized by low-oxygen deep water. Nevertheless, large variations on n-alkyl lipid compositions in C3/C4 plants could likely play a part in modulating sedimentary long chain n-alcohols and n-alkanes towards different vegetation signals, and caution must be taken in respect to the terrestrial vegetation reconstruction using long chain n-alkanes and long chain n-alcohols.

How to cite: Mao, S., Zhu, X., Sun, Y., Liu, L., and Wu, N.: Last glacial terrestrial vegetation record of leaf wax n-alcohols in the northern South China Sea: Contrast to scenarios from long chain n-alkanes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12293, https://doi.org/10.5194/egusphere-egu2020-12293, 2020.

 

Calcareous stromatolite crusts overgrowing beach gravels and stabilising piles of rocks were observed on shoreline terraces of Lake Lisan along the eastern coast of the Dead Sea. The stromatolite crusts are thick, massive and hard, with a dark-grey or white-grey finely-laminated structure, indicating that they are mostly calcareous organic build-up of cyanobacterial origin. Samples from these stromatolites have been analyzed using Stable Isotopes (δ13C & δ18O), AAS and XRD analysis. The samples range in altitude between -350 m and -19 m, representing the time interval of Lake Lisan (~ 80-19 ka BP) according to our U/Th dating. Since stromatolites grow in shallow water, they are very sensitive to minor shifts in rainfall and evaporation and therefore an excellent tool to track small changes in hydrology, in climate and in paleoenvironmental conditions of the lake basin.

 

Oxygen and carbon isotopic compositions of these stromatolites show a linear covariant trend with a strong positive correlation (r = 0.8) and large ranges of 7.85 and 6.78‰, respectively. This trend is most typical of primary carbonates formed in closed lakes. Isotopes analyses show low negative values of stromatolites from the lake highest stands at -76 m to -19 m, reflecting fresh water conditions of the lake basin at the last interglacial-glacial boundary (80-76 ka BP). The lowest values were derived from stromatolites at -103 to -119 m associated with the transgression of the lake to these high stands between 55 and 33 ka BP. The heaviest values were derived from stromatolites at -137 to -160 m indicating a change to dry climatic conditions in the Eastern Mediterranean that caused a subsequent drop of the lake level during MIS 2 (31-19 ka BP).

 

The Mg/Ca ratio and the XRD analysis of the stromatolites correlate also with transgression-regression phases of the lake. Dominance of calcite in stromatolites at -76 to 0 m and inferred low Mg/Ca ratios of the lake water (i.e. ~2) imply a high fresh water input of the lake during the   highest stands period. A high Mg/Ca ratio of the lake water of >7 inferred from low-level stromatolite at -350 m and the existence of aragonite as the sole mineral reflect low fresh water input and high evaporation rates that caused a lake level regression during H6, ~ 60 ka BP.

 

Inferred low Mg/Ca ratios of stromatolites at -247 to -101 m and the existence of calcite as a main mineral phase indicate wet climatic conditions of the eastern Mediterranean and lake level transgression to higher than -137 during MIS 3. The appearance of more aragonite in stromatolites at -137 to -154 m and the inferred high Mg/Ca ratio of the lake water points to a return to dry climatic conditions that caused a regression of Lake Lisan between 32 to 22 ka BP (MIS 2). However, the change in the mineral composition to pure calcite at -160 m in addition to the inferred low Mg/Ca ratio correlates well with the transgression of the lake to this level by the end of the LGM.

 

 

How to cite: Abu Ghazleh, S. and Kempe, S.: Fluctuations of Lake Lisan (the Dead Sea) during the last glacial: Implications for paleoclimatic changes of the Levant. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12906, https://doi.org/10.5194/egusphere-egu2020-12906, 2020.

EGU2020-13551 | Displays | CL1

Reconstruction of paleoenvironmental changes using geochemical data from South Carpathian Mountains

Katalin Hubay, Mihály Braun, Sándor Harangi, Mihály Molnár, Krisztina Buczkó, and Enikő Magyari

This study applied bulk sediment geochemistry to reconstruct lateglacial and early Holocene climatic changes in a glacial lakes (Lake Brazi, 1740 m a.s.l. and Lake Lia, 1910 m a.s.l.) in the Retezat Mts. (South Carpathians, Romania). We studied how the changes of chemical element concentration in the sediment can indicate environmental changes, climate variations and human effects. Our aim was to develop analytical methods, which may complement the methodology of routinely applied paleoenvironmental methods and can be used to identify environmental changes in the past and help us reconstruct local and regional processes.

            In the Retezat Mts., Southern Carpathians, more than hundred glacial lakes were formed after the last glaciation. These glacial lakes are paleoecologically significant because they are characterized by continuous sedimentation since their origin to the present.

            In 2007 and 2008 continuous undisturbed sediment cores were obtained from Lake Brazi and Lake Lia in the Retezat Mts. (Southern Carpathians, Romania) with Livingstone and modified Kullenberg corers. The lowermost part of the sediment cores, covering the period between 9900 and 15 800 cal yr BP, was used for high resolution bulk analysis of major elements (Al2O3, SiO2, TiO2, CaO, MgO, K2O, Na2O, Fe2O3 and MnO). Linear discriminant analysis (LDA) was used to compare a priori classified main chemical groups. Subsamples from the core were priory ordered to “warm” and “cold” groups respectively, according to their age and evidence of cold and warm events in the record, as suggested by proxy correlation with the lateglacial event stratigraphy of North Greenland Ice Core Project (NGRIP). The discriminant function was calculated using concentration of major elements after log ratio transformation. Loss-on-ignition and silicon concentration were not used for the discriminant analysis, but regarded as comparison proxies for checking up the validity of outputs.

            The calculated discriminant values are good indicators of changes in sediment caused by climate change, as their values give the cold and warm directions. The “a posteriori” groups can be used to determine the period during which local changes differed from the climate changes in the North Atlantic region. The chemical composition of sediments deposited during the “cold” and “warm” periods shows differences in both sediments. The discriminant scores showed strong correlation with the NGRIP d18O data and with the pollen percentage sum of trees and shrubs.

            Discriminant analyses of bulk sediment major oxide chemical data may be a useful tool to identify the impact of climate events upon the nature and composition of materials delivered to a lake basin.

Key words: climate reconstruction, sediment geochemistry, Retezat Mts.

How to cite: Hubay, K., Braun, M., Harangi, S., Molnár, M., Buczkó, K., and Magyari, E.: Reconstruction of paleoenvironmental changes using geochemical data from South Carpathian Mountains, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13551, https://doi.org/10.5194/egusphere-egu2020-13551, 2020.

CL1.4 – Climate Change in the geological record: what can we learn from data and models?

EGU2020-10623 | Displays | CL1.4

Tectonic forcing of global chemical weathering since the mid-Paleozoic

Thomas Gernon, Thea Hincks, Andrew Merdith, Eelco Rohling, Martin Palmer, Gavin Foster, Clement Bataille, and Dietmar Muller

Weathering of the Earth’s surface has commonly been invoked as a driver of global cooling through geologic time. During the Phanerozoic Eon (541–0 million years ago, Ma), for example, the periodic onset of icehouse conditions has variously been attributed to enhanced weathering fluxes associated with mountain building (e.g. the Himalayas) (1), reductions in the global extent of continental arc volcanoes (e.g. the present-day Andes) (2), and uplift of oceanic crust during arc-continent collisions (e.g. present-day Indonesia and New Guinea) (3). These processes, tied to the global plate tectonic cycle, are inextricably linked.  The resulting collinearity (i.e. independent variables are highly correlated) makes it difficult — using conventional statistical techniques — to isolate the contributions of individual geologic processes to global chemical weathering.   An example of this is the Late Cenozoic Ice Age (34–0 Ma) that corresponds both to uplift of the Tibetan Plateau and Himalaya, and a gradual reduction in the extent of the global continental arc system. 

We developed a machine learning framework to analyse the interdependencies between multiple global tectonic and volcanic processes (e.g., continental distribution, extent of volcanic arcs, mid-ocean ridges etc.) and seawater Sr composition (a proxy for weathering flux) over the past 400 million years. We developed a Bayesian network incorporating a novel algorithm that accounts for time lags for each of the predictor variables, and joint conditional dependence (i.e. how variables combine to influence the environmental outcome). Our approach overcomes problems traditionally encountered in geologic time series, such as collinearity and autocorrelation. Our results strongly indicate a first-order role for volcanism in driving chemical weathering fluxes since the mid-Palaeozoic. This is consistent with the strong empirical correlation previously observed between the strontium isotope composition of seawater and continental igneous rocks over the past billion years (4). Our study highlights how geologic processes operate together — not in isolation — to perturb the Earth system over ten to hundred million-year timescales.

References

(1). M. E. Raymo, W. F. Ruddiman, Tectonic forcing of late Cenozoic climate, Nature 359, 117 (1992).

(2). N. R. McKenzie, et al., Continental arc volcanism as the principal driver of icehouse greenhouse variability, Science 352, 444 (2016).

(3). F. A. Macdonald, N. L. Swanson-Hysell, Y. Park, L. Lisiecki, O. Jagoutz, Arc-continent collisions in the tropics set Earth’s climate state, Science 364, 181 (2019).

(4). C. P. Bataille et al., Continental igneous rock composition: A major control of past global chemical weathering, Science Advances 3, e1602183 (2017).  

How to cite: Gernon, T., Hincks, T., Merdith, A., Rohling, E., Palmer, M., Foster, G., Bataille, C., and Muller, D.: Tectonic forcing of global chemical weathering since the mid-Paleozoic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10623, https://doi.org/10.5194/egusphere-egu2020-10623, 2020.

EGU2020-19675 | Displays | CL1.4

The contribution of numerical models to our understanding of the Phanerozoic CO2 history

Yves Godderis and Yannick Donnadieu

Our understanding of the geological regulation of the carbon cycle has been deeply influenced by the contribution of Bob Berner with his well-known model GEOCARB. Here, we will present a fundamentally different carbon cycle model that explicitly accounts for the effect of the paleogeography using physically based climate simulations and using 22 continental configurations spanning the whole Phanerozoic (GEOCLIM, geoclimmodel.wordpress.com). We will show that several key features of the Phanerozoic climate can be simply explained by the modulation of the carbon cycle by continental drift with the notable exception of the Late Paleozoic Ice Age, which is explained by the intense weathering of the Hercynian mountain range. In particular, the continental drift may have strongly impacted the runoff intensity as well as the weathering flux during the transition from the hot Early Cambrian world to the colder Ordovician world. Another fascinating example is the large atmospheric CO2 decrease simulated during the Triassic owing to the northward drift of Pangea exposing large continental area to humid sub-tropics and boosting continental weathering. Conversely, our model fails to reproduce the climatic trend of the last 100 Ma. This is due to the highly dispersed continental configurations of the last 100 Ma that optimize the consumption of CO2 through continental weathering. This discrepancy may be reduced if we account for a larger influence of the Earth degassing flux on the atmospheric CO2 evolution, which could come from the increase contribution of the pelagic component on the oceanic crust on the global carbonate flux and from the many sub-marine LIPs occurring during the Late Cretaceous.

 

How to cite: Godderis, Y. and Donnadieu, Y.: The contribution of numerical models to our understanding of the Phanerozoic CO2 history, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19675, https://doi.org/10.5194/egusphere-egu2020-19675, 2020.

EGU2020-242 | Displays | CL1.4

Temperate rainforests near the South Pole during peak Cretaceous warmth

Johann Philipp Klages, Salzmann Ulrich, Bickert Torsten, Hillenbrand Claus-Dieter, Gohl Karsten, Kuhn Gerhard, Bohaty Steven, Titschack Jürgen, Müller Juliane, Frederichs Thomas, Bauersachs Thorsten, Ehrmann Werner, van de Flierdt Tina, Simões Pereira Patric, Larter Robert, Lohmann Gerrit, Igor Niezgodzki, Uenzelmann-Neben Gabriele, Zundel Maximilian, and Spiegel Cornelia and the Science Team of Expedition PS104

The mid-Cretaceous was one of the warmest intervals of the past 140 million years (Myr) driven by atmospheric COlevels around 1000 ppmv. In the near absence of proximal geological records from south of the Antarctic Circle, it remains disputed whether polar ice could exist under such environmental conditions. Here we present results from a unique sedimentary sequence recovered from the West Antarctic shelf. This by far southernmost Cretaceous record contains an intact ~3 m-long network of in-situ fossil roots. The roots are embedded in a mudstone matrix bearing diverse pollen and spores, indicative of a temperate lowland rainforest environment at a palaeolatitude of ~82°S during the Turonian–Santonian (93–83 Myr). A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric COcontents of 1120–1680 ppmv and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo in high-COclimate worlds.

How to cite: Klages, J. P., Ulrich, S., Torsten, B., Claus-Dieter, H., Karsten, G., Gerhard, K., Steven, B., Jürgen, T., Juliane, M., Thomas, F., Thorsten, B., Werner, E., Tina, V. D. F., Patric, S. P., Robert, L., Gerrit, L., Niezgodzki, I., Gabriele, U.-N., Maximilian, Z., and Cornelia, S. and the Science Team of Expedition PS104: Temperate rainforests near the South Pole during peak Cretaceous warmth, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-242, https://doi.org/10.5194/egusphere-egu2020-242, 2020.

EGU2020-5962 | Displays | CL1.4

A new framework to quantify carbon cycle perturbations using trace metal isotopes

Markus Adloff, Sarah E. Greene, Fanny M. Monteiro, and Andy Ridgwell

Reconstructing the environmental consequences of large carbon additions in the past has the potential to improve our understanding and prediction of how the Earth system will respond to human carbon emissions. However, uncertainties over the scale and timing of external carbon additions during past carbon emission events limit quantitative knowledge gained from the geological record. The metals Sr, Os, Li and Ca are essential proxies for changes in volcanic activity and terrestrial weathering rates, and thus for major causes of pre-industrial carbon emission and sequestration, because their isotopic compositions in old continental crust and Earth’s mantle differ significantly. So far, box models and equilibrium-state equations have been the only method to quantitatively relate weathering-derived and magmatic input fluxes to trace metal concentrations and isotopic ratios preserved in ancient sediments. This approach results most commonly in a first order estimate of emitted carbon or weathering changes, but it does not account for the effect of climate feedbacks on metal sources and sinks and associated variations in the residence time of these metals in the ocean. Particularly during fast carbon emissions (e.g. Cenozoic hyperthermals, Oceanic Anoxic Events), the processes which added isotopically traceable metals to the oceans also enchained environmental changes which would have affected metal cycles and residence times, resulting in significant alterations of the recorded isotopic excursion in marine sediments. To disentangle the signals of causes and consequences of environmental change recorded by trace metal isotopes, we simulated various coupled carbon and metal cycle perturbations in the 3D Earth system model of intermediate complexity cGENIE, now containing the first representation of isotope-enabled trace metal dynamics. Here, we present a resulting extended framework to reconstruct metal and carbon fluxes from the geological trace metal record during periods of environmental change.

How to cite: Adloff, M., Greene, S. E., Monteiro, F. M., and Ridgwell, A.: A new framework to quantify carbon cycle perturbations using trace metal isotopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5962, https://doi.org/10.5194/egusphere-egu2020-5962, 2020.

When it comes to paleoclimate data-model integration, temperature is arguably the most important parameter. Although a range of temperature proxies has been developed over the decades, many of the available methods suffer from large calibration uncertainties, in particular when applied on deep-time intervals. Clumped isotope thermometry is based on thermodynamic principles and therefore can provide accurate temperature constraints for the deeper geological record. Recent analytical developments allow now the analysis of relatively small sample sizes and the application in paleoceanogaphic studies becomes more feasible. I will present new clumped isotope based temperature estimates for the Atlantic deep-sea across the Cenozoic. I will also show that the analysis of small samples now allows us to even resolve seasonal sea surface temperature estimates from high-resolution archives. Deep-sea temperatures as well as seasonally resolved surface temperature estimates are particularly useful for data-model comparison.

How to cite: Ziegler, M.: Cenozoic climate evolution revealed by clumped isotope thermometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20336, https://doi.org/10.5194/egusphere-egu2020-20336, 2020.

A compilation of benthic δ18O from the whole Atlantic and the Southern Ocean (Atlantic sector), shows two major jumps in the interbasinal gradient of d18O (Δδ18O) during the Eocene and the Oligocene: One at ~40 Ma and the second concomitant with the isotopic event of the Eocene-Oligocene transition (EOT), ~33.7 Ma ago. From previously published circulation models, we show that the first Δδ18O jump reflects the thermal isolation of Antarctica associated with the proto-Antarctic circumpolar current (ACC). The second marks the onset of interhemispheric northern-sourced circulation cell, similar to the modern Atlantic meridional overturning circulation (AMOC). The onset of AMOC-like circulation probably slightly preceded (100-300 ky) the EOT, as we show by the high resolution profiles of δ18O and δ13C previously published from DSDP/ODP sites in the Southern Ocean and South Atlantic. We suggest that while the shallow proto-ACC supplied the energy for deep ocean convection in the Southern Hemisphere, the onset of the interhemispheric northern circulation cell was due to the significant EOT intensification of deepwater formation in the North Atlantic driven by the Nordic anti-estuarine circulation. This onset of the interhemispheric northern-sourced circulation cell could have prompted the EOT global cooling.

How to cite: Abelson, M. and Erez, J.: Was the onset of interhemispheric AMOC slightly prior to Antarctic glaciation at the Eocene-Oligocene transition?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2204, https://doi.org/10.5194/egusphere-egu2020-2204, 2020.

EGU2020-18410 | Displays | CL1.4

Reconstructing ocean temperatures using coccolith clumped isotopes

Luz Maria Mejia, Alvaro Fernandez, Hongrui Zhang, Jose Guitian, Stefano Bernasconi, and Heather Stoll

     Reliable temperature reconstructions of the ocean are often difficult to obtain due to the limitations of widely used proxies. The application of clumped isotope thermometry to coccolith calcite, which is geographical and chronological ubiquitously distributed, and whose production is limited to the photic zone, may provide ocean’s temperature information when and where other proxies have been shown inaccurate or not applicable.

     To evaluate the potential of coccolith clumped isotopes in paleoceanography we compare the temperatures derived from the fine fraction (<11µm), a pure mixed coccolith fraction (2-10 µm), and to a fraction of carbonate fragments from unidentified sources (<2 µm), with coeval alkenone sea surface temperatures (SST) from ODP Site 982 in the North Atlantic covering the last 16 Ma. The similarity in magnitudes and trends from the <11 and 2-10 µm size fractions, and trace element analysis of the <2 µm size fraction, suggest that for this site and time interval, exclusion of small unrecognizable fragments is not necessary to obtain reliable temperatures. The warmer values of alkenone SSTs compared to coccolith clumped isotope-derived temperatures cannot be explained by diagenetic processes, but may be related to temperature overestimations by alkenone calibrations, which assume a warm season and/or shallow production of coccolithophores in the study area.           

     Vital effects in coccolith clumped isotopes potentially associated to carbon limitation may also help to explain the differences in cooling magnitudes compared to the alkenone record. To further investigate vital effects in clumped isotopes, we compare calcification temperatures of three pure coccolith size fractions (3-5, 5-8, and 8-10 µm), and relate them to vital effects observed in their δ13C and δ 18O. The analysis of the fine fraction of Holocene sediments (<10 or <8 µm) showing a range of temperature and CO2 concentrations also provide information on the potential effects of carbon availability in coccolith clumped isotopes, and suggests calcification of coccolithophores may occur in deeper habitats than those considered by alkenone calibrations. Our study shows clumped isotope thermometry applied to coccolith calcite as a promising alternative proxy for calcification temperature of coccolithophores.

How to cite: Mejia, L. M., Fernandez, A., Zhang, H., Guitian, J., Bernasconi, S., and Stoll, H.: Reconstructing ocean temperatures using coccolith clumped isotopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18410, https://doi.org/10.5194/egusphere-egu2020-18410, 2020.

EGU2020-3350 | Displays | CL1.4

Resolution-dependent variations of sinking particle trajectories in general circulation models: Implications for data-model comparison in past climate

Peter Nooteboom, Philippe Delandmeter, Peter Bijl, Erik van Sebille, Henk Dijkstra, and Anna von der Heydt

Any type of non-buoyant material in the ocean is transported by currents during its sinking journey. This transport can be far from negligible for typical (plankton) particles with a low sinking velocity. To estimate the lateral transport, the material can be modelled as a set of Lagrangian particles advected by currents that are obtained from Ocean General Circulation Models (OGCMs). State-of-the-art OGCMs are often strongly eddying, providing flow fields with a horizontal resolution of  10km on a daily basis. However, many long term climate modelling studies (e.g. in palaeoclimate) rely on low resolution models that cannot capture mesoscale features. The lower model resolution could influence data-model comparisons using Lagrangian techniques, but this is not properly evaluated yet through a direct comparison.

In this study, we simulate the transport of sinking Lagrangian particles using low (1°; non-eddying)  and high (0.1°; eddying) horizontal resolution OGCMs of the present-day ocean, and evaluate the effect of the two resolutions on particle transport. We find major differences between the transport in the non-eddying versus the eddying OGCM (in terms of the divergence of particle trajectories and their mean trajectory). Addition of stochastic noise to the particle trajectory parameterizes the effect of eddies well in some regions (e.g. in the North Pacific gyre).

We recommend to apply sinking Lagrangian particles only in velocity fields with eddying OGCMs, which basically excludes all paleo-simulations. We are currently simulating the equilibrium Eocene (38Ma) climate using an eddying OGCM, to be able to apply these Lagrangian techniques in an eddying ocean of the past. We expect this to lead towards a better agreement between the OGCM and sedimentary fossil microplankton.

How to cite: Nooteboom, P., Delandmeter, P., Bijl, P., van Sebille, E., Dijkstra, H., and von der Heydt, A.: Resolution-dependent variations of sinking particle trajectories in general circulation models: Implications for data-model comparison in past climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3350, https://doi.org/10.5194/egusphere-egu2020-3350, 2020.

EGU2020-20554 | Displays | CL1.4

Neogene changes in land surface reactivity and implications for Earth system sensitivity to carbon cycle perturbations

Jeremy Caves Rugenstein, Daniel Ibarra, and Friedhelm von Blanckenburg

Long-term cooling, pCO2 decline, and the establishment of permanent, polar ice sheets in the Neogene has frequently been attributed to increased uplift and erosion of mountains and consequent increases in silicate weathering, which removes atmospheric CO2. However, geological records of erosion rates are potentially subject to averaging biases and the magnitude of the increase in weathering fluxes, and even its existence, remain debated. Moreover, a weathering increase scaled to the hypothesized erosional increase would have removed nearly all carbon from the atmosphere, leading to proposals of compensatory carbon fluxes in order to preserve carbon cycle mass balance. In contrast, increasing land surface reactivity—resulting from greater fresh mineral surface area or an increase in the supply of reactive minerals—rather than an increase in the weathering flux, has been proposed to reconcile these disparate views. We develop a parsimonious carbon cycle model that tracks two weathering-sensitive isotopic tracers (stable 7Li/6Li and cosmogenic 10Be/9Be) to show that an increase in land surface reactivity is necessary to simultaneously decrease atmospheric CO2, increase seawater 7Li/6Li, and retain constant seawater 10Be/9Be since 16 Ma. We find that the global silicate weathering flux remained constant, even as the global silicate weathering intensity—the fraction of the total denudation flux derived from silicate weathering—decreased, sustained by an increase in erosion. Thus, long-term cooling during the Neogene reflects a change in the partitioning of denudation into weathering and erosion. Variable partitioning of denudation and consequent changes in silicate weathering intensity reconcile marine isotope and erosion records with the need to maintain mass balance in the carbon cycle and without increases in the silicate weathering flux. These changes in land surface reactivity through time suggest that the Earth system’s response to carbon cycle perturbations is not constant and that today’s Earth can more efficiently remove excess carbon than during analogous perturbations observed in the geologic record. 

How to cite: Caves Rugenstein, J., Ibarra, D., and von Blanckenburg, F.: Neogene changes in land surface reactivity and implications for Earth system sensitivity to carbon cycle perturbations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20554, https://doi.org/10.5194/egusphere-egu2020-20554, 2020.

EGU2020-10864 | Displays | CL1.4

The continental Middle Miocene Climatic Transition in Southern Europe as derived from clumped isotope analyses

Niklas Löffler, Andreas Mulch, Wout Krijgsman, Emilija Krsnik, and Jens Fiebig

Reconstructing Cenozoic terrestrial paleoclimate is frequently limited by temporal resolution and suitable quantitative tools to reliably assess changes in temperature and aridity. The dynamics of ocean temperatures1 and chemistry2, varying pCO23, and faunal assemblages are known to a certain extent, however, terrestrial data on temperatures, which are mostly indirectly derived from fossil assemblages and palynologycal data4 are rare. This study contributes to the understanding of the dynamics and variability of terrestrial temperatures during one of the most extreme Neogene climate changes, the Middle Miocene Climate Transition (MCT). The comparison of pCO2 forecasts for the coming century and reconstructed Mid-Miocene pCO2 levels suggest that the Mid-Miocene is an important time interval for ascertaining suitable model projections of the future anthropogenic impact on climate. In order to establish an appropriate understanding and modeling of the natural variability of the European/Mediterranean climate system, quantitative climate information of the European continental Mid-Miocene is mandatory. This would facilitate the identification of main drivers of climate evolution in an area which is exposed to the present climate change and its subsequent natural hazards.

 

This study presents a profound and well-dated terrestrial clumped isotope (Δ47) paleosoil carbonate dataset from Spain that ranges from 13.0 to 15.1 Ma (100 kyr resolution) and hence covers an interval that was previously classified as the MCT. The Δ47 data is supported by stable carbon and oxygen isotope analyses that are in agreement with previously published continental and oceanic records. A distinct decline in apparent Δ47-based temperatures between 13.7 and 14.1 Ma reveals a substantial drop in continental temperatures and indicates changes in seasonality of pedogenic carbonate formation. The major cooling thereby coincides with a change in Milanković periodicities and can be linked to oceanic isotope records5. While the transition into the MCT shows a high temperature variability indicating varying environmental conditions, calculated oxygen isotopic values of the soil water point to a rather stable moisture source across the MCT in Southern Europe.

 

1: Super, J. R., Thomas, E., Pagani, M., et al. (2018) North Atlantic temperature and pCO2 coupling in the early-middle Miocene. Geology, 46(6), 519-522.

2: Pearson, P. N., and Palmer, M. R. (1999) Middle Eocene seawater pH and atmospheric carbon dioxide concentrations. Science, 284(5421), 1824-1826.

3: Pagani, M., Freeman, K. H., and Arthur, M. A. (1999) Late Miocene atmospheric CO2 concentrations and the expansion of C4 grasses. Science, 285(5429), 876-879.

4: Lewis, A. R., Marchant, D. R., Ashworth, A. C., et al. (2008) Mid-Miocene cooling and the extinction of tundra in continental Antarctica. Proceedings of the National academy of Sciences.

5: Holbourn, A., Kuhnt, W., Clemens, S., et al. (2013) Middle to late Miocene stepwise climate cooling: Evidence from a high resolution deep water isotope curve spanning 8 million years. Paleoceanography, 28(4), 688-699.

How to cite: Löffler, N., Mulch, A., Krijgsman, W., Krsnik, E., and Fiebig, J.: The continental Middle Miocene Climatic Transition in Southern Europe as derived from clumped isotope analyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10864, https://doi.org/10.5194/egusphere-egu2020-10864, 2020.

EGU2020-9756 | Displays | CL1.4

A modeling study of physical and biogeochemical changes occurring in the tropical Indian Ocean during Miocene times.

Anta-Clarisse Sarr, Yannick Donnadieu, Clara Bolton, and Baptiste Suchéras-Marx

The South Asian Monsoon (SAM) is one of the most important climatic features of the Asian continent. Proxy-based reconstructions from continuous records in the Indian Ocean suggest a settlement of modern-like monsoon during the Miocene, with a modern winds distribution and strength potentially reached by ~13 Ma. Concurrent with the SAM intensification, a major reorganization of surface ocean currents occurred in the Indian Ocean. The timing of monsoon strengthening overlaps with changes in Indian Ocean and Indonesian Gateway configurations, Himalayas uplift, global cooling, as well as East Antarctic Ice Sheet expansion. Thus, the respective influence of each factor on SAM evolution and Indian Ocean paleoceanography is still poorly understood owing to the modification of multiple forcing mechanisms.

Here we will use a set of experiments with the IPSL-CM5A2 Earth System Model under early to late Miocene configurations in order to tease apart the effects of paleogeography changes, ice-sheet growth and CO2levels on the Indian Ocean region during the Miocene. We will focus on the impact of increasing SAM winds and precipitation on the oceanographic conditions in the Indian Ocean including not only physical parameters but also biogeochemical ones.

 

How to cite: Sarr, A.-C., Donnadieu, Y., Bolton, C., and Suchéras-Marx, B.: A modeling study of physical and biogeochemical changes occurring in the tropical Indian Ocean during Miocene times. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9756, https://doi.org/10.5194/egusphere-egu2020-9756, 2020.

EGU2020-13972 | Displays | CL1.4

Atmospheric CO2 during the Late Miocene Cooling

Thomas Tanner, José Guitián, Iván Hernández-Almeida, and Heather Stoll

Alkenone sea surface temperature records recently observed suggest a substantial long-term and large-magnitude ocean surface cooling during the Late Miocene. At the same time, starting about seven million years ago, both hemispheres on Earth witnessed synchronous cooling and large areas of the continents experienced drying and enhanced seasonality. Coinciding with this climatic shift were significant changes in ecology, including the rise of C4-photosynthesizing terrestrial plants and the emergence of so-called "vital effects" in oceanic coccolithophores. These changes are collectively hypothesized to be induced by declining atmospheric CO2. However, the sparse proxy data available for this time interval limits our understanding of the link between these changes and atmospheric greenhouse gas fluctuations and has let people to propose a "climate-CO2 decoupling".
In this study, the alkenone based pCO2 proxy is used to reconstruct atmospheric CO2 for the time interval between 4.5 and 8.5 Ma. Estimations are based on the carbon isotopic fractionation during photosynthesis (εp) and a new statistical multilinear regression model based on an analysis of culture and sediment data. Past coccolithophore growth rates are reconstructed using foraminiferal isotopic-based proxies, related to water column structure which favour or limit nutrient supply to the photic zone. A thorough sensitivity analysis of modern and past  εp values and its influencing factors in the Southern Ocean yield to a new, high resolution pCO2 record. Estimated pCO2 concentrations synchronously decline with the observed long-term cooling (5°C) from 6.8 to 5.9 Ma, periodically decreasing to sufficiently low values of <200 ppm, potentially inducing ephemeral Northern Hemisphere glaciation. CO2 concentrations during the Late Miocene Cooling Event are thus successfully reproduced in this study and allow a reasonable interpretation of past conditions as has not yet been previously achieved in the relevant literature. 

How to cite: Tanner, T., Guitián, J., Hernández-Almeida, I., and Stoll, H.: Atmospheric CO2 during the Late Miocene Cooling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13972, https://doi.org/10.5194/egusphere-egu2020-13972, 2020.

EGU2020-13946 | Displays | CL1.4

The linkage of dust cycle dynamics and loess during the Last Glacial Maximum in Europe

Patrick Ludwig, Erik J. Schaffernicht, Yaping Shao, and Joaquim G. Pinto

In this work, we present different aspects of the mineral dust cycle dynamics and the linkage to loess deposits during the Last Glacial Maximum (LGM) in Europe. To this aim, we simulate the LGM dust cycle at high resolution using a regional climate-dust model. The simulated dust deposition rates are found to be comparable with the mass accumulation rates of the loess deposits determined from Loess sites across Europe. In contrast to the present-day prevailing westerlies, easterly wind directions (36 %) and cyclonic regimes (22 %) were dominant circulation patterns over central Europe during the LGM. This supports the hypothesis that recurring east sector winds, dynamically linked with a high-pressure system over the Eurasian ice sheet (EIS), are an important component for the dust transport from the EIS margins towards the central Europe loess belt. Our simulations reveal the occurrence of highest dust emission rates in Europe during summer and autumn, with the highest emission rates located near the southernmost EIS margins corresponding to the present-day German-Polish border region. Coherent with the persistent easterlies, westwards running dust plumes resulted in high deposition rates in western Poland, northern Czechia, the Netherlands, the southern North Sea region and on the North German Plain including adjacent regions in central Germany. Further, a detailed analysis of the characteristics of LGM cyclones shows that they were associated with higher wind speeds and less precipitation than their present-day counterparts. These findings highlight the importance of rapid and cyclic depositions by cyclones for the LGM dust cycle. The agreement between the simulated deposition rates and the mass accumulation rates of the loess deposits corroborates the proposed LGM dust cycle hypothesis for Europe.

How to cite: Ludwig, P., Schaffernicht, E. J., Shao, Y., and Pinto, J. G.: The linkage of dust cycle dynamics and loess during the Last Glacial Maximum in Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13946, https://doi.org/10.5194/egusphere-egu2020-13946, 2020.

EGU2020-5526 | Displays | CL1.4

Antarctic Uncertainty: Learning more about past ice sheet shapes with Bayesian methods

Fiona Turner, Richard Wilkinson, Caitlin Buck, Julie M. Jones, and Louise Sime

Understanding the effect warming has on ice sheets is vital for accurate projections of climate change. A better understanding of how the Antarctic ice sheets have changed size and shape in the past would allow us to improve our predictions of how they may adapt in the future; this is of particular relevance in predicting future global sea level changes. This research makes use of previous reconstructions of the ice sheets, ice core data and Bayesian methods to create a model of the Antarctic ice sheet at the Last Glacial Maximum (LGM). We do this by finding the relationship between the ice sheet shape and water isotope values. 

We developed a prior model which describes the variation between a set of ice sheet reconstructions at the LGM. A set of ice sheet shapes formed using this model was determined by a consultation with experts and run through the general circulation model HadCM3, providing us with paired data sets of ice sheet shapes and water isotope estimates. The relationship between ice sheet shape and water isotopes is explored using a Gaussian process emulator of HadCM3, building a statistical distribution describing the shape of the ice sheets given the isotope values outputted by the climate model. We then use MCMC to sample from the posterior distribution of the ice sheet shape and attempt to find a shape that creates isotopic values matching as closely as possible to the observations collected from ice cores. This allows us to quantify the uncertainty in the shape and incorporate expert beliefs about the Antarctic ice sheet during this time period. Our results suggests that there may have been a thicker West Antarctic ice sheet at the LGM than previously estimated.

How to cite: Turner, F., Wilkinson, R., Buck, C., Jones, J. M., and Sime, L.: Antarctic Uncertainty: Learning more about past ice sheet shapes with Bayesian methods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5526, https://doi.org/10.5194/egusphere-egu2020-5526, 2020.

EGU2020-3988 | Displays | CL1.4

Greenhouse climate forces expansion of peatlands into inland areas

Zhihui Zhang, Chengshan Wang, Dawei Lv, and Tiantian Wang

As a significant terrestrial carbon reservoir, peatland has great potential to affect the global carbon cycle and global climate. However, our understanding of broad-scale mechanisms that control the long-term global peatland expansion and carbon accumulation rates is still limited. Here we present a new data synthesis of global coal deposit location, thickness changes, carbon concentration, and distribution area changes, along with new carbon pool estimates of global peatlands from Devonian through geological time. By identifying orbital cycles in coal seams, we show that the long-term rate of carbon accumulation (LORCA) in peatland calculated from published data is controlled by pO2, pCO2, temperature, precipitation, and total solar irradiance. We use this relationship and latitudinal temperature gradients to reconstruct the equations between LORCA with latitude on different geological time. The results suggest that there are three main sets of high carbon pool and high carbon accumulation rate of global peatlands in Late Paleozoic, Early-Middle Jurassic, and Late-Cretaceous to Early Cenozoic under low tectonic activity and high terrestrial plant diversity background. In addition, we measure the shortest distances between all coal locations and coastlines based on the new Scotese’s paleo-Atlas for the past 400 million years, in order to exhibit the extent of peatland expansion into inland. The result shows the Early-Middle Jurassic period has the longest average distance, which is probably due to the high sea level that minimizes the development of peat swamps on coastal areas and facilitated the moisture to move into deeper inland under the Jurassic Greenhouse climate condition. This study highlights that combining comprehensive coal-related database with paleoclimate, tectonics, and evolution of land plants provides insights into the mechanisms of the long-term behavior of the peatland expansion and carbon reservoir through deep time.

Keywords: Greenhouse climate, Peatland expansion, Carbon pool, Cabon accumulation rates, Coal

This study wasfinancially supported by the National Natural Science Foundation of China (grant No. 41888101), the National Key R&D Plan of China (grant No. 2017YFC0601405) and the National Natural Science Foundation of China (grants 41790450, 41772096).

How to cite: Zhang, Z., Wang, C., Lv, D., and Wang, T.: Greenhouse climate forces expansion of peatlands into inland areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3988, https://doi.org/10.5194/egusphere-egu2020-3988, 2020.

The Neoproterozoic glaciations, referred to as snowball Earth periods, describe the most extreme transition from a very cold climate to a state of strong greenhouse effect. Atmospheric CO2 concentrations are rising during the snowball, due to the shutdown of oceanic and terrestrial carbon sinks, until a tipping point is reached and a rapid deglaciation sets in. Subsequently, a warm and completely ice-free climate under very high CO2 concentrations develops. We show first results of simulations using a coupled atmosphere-ocean general circulation model covering the initiation, as well as the melting of the Marinoan snowball Earth (645 – 635 My ago) and the greenhouse climate in its aftermath. CO2 concentrations are decreased to initiate a global glaciation and then increased again in order to melt the snowball Earth. As soon as a certain CO2 threshold is reached, sea-ice melts rapidly, reaching a completely ice-free ocean after only one hundred years, in our model without land glaciers. The ocean becomes strongly stratified, because at the surface the freshwater from the sea-ice melt is warming up quickly, whereas the deeper ocean remains cold and salty. Ocean surface currents return to their pre-snowball behavior soon after the melt, but destratification is slow. The largest mixed layer depths of up to 500 m are reached in the mid latitudes of the winter hemisphere. We compare the climate before and after the snowball state and estimate the time needed for destratification.

How to cite: Ramme, L. and Marotzke, J.: Ocean dynamics and climate during a Neoproterozoic snowball Earth and its aftermath as simulated in a coupled Earth system model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10320, https://doi.org/10.5194/egusphere-egu2020-10320, 2020.

EGU2020-20746 | Displays | CL1.4

Modeling the impact of oceanic circulation and marine productivity on Cretaceous seafloor anoxia

Yannick Donnadieu, Marie Laugie, Jean-Baptiste Ladant, François Raisson, and Laurent Bopp

Oceanic anoxic events (OAEs) are abrupt events of widespread deposition of organic-rich sediments and extensive seafloor anoxia. Mechanisms usually invoked as drivers of oceanic anoxia are various and still debated today. They include a rise of the CO2 atmospheric level due to increased volcanic activity, a control by the paleogeography, changes in oceanic circulation or enhanced marine productivity. In order to assess the role of these mechanisms, we use an IPCC-class model, the IPSL-CM5A2 Earth System Model, which couples the atmosphere, land surface, and ocean components, this last one including sea ice, physical oceanography and marine biogeochemistry which allows to simulate oceanic oxygen.

We focus here on OAE2, which occurs during the Cretaceous at the Cenomanian-Turonian boundary (93.5 Ma), and is identified as a global event with evidence for seafloor anoxia in the Atlantic and Indian Oceans, the Southwest Tethys Sea and the Equatorial Pacific Ocean. Using a set of simulations from 115 to 70 Ma, we analyze the long-term paleogeographic control on oceanic circulation and consequences on oceanic oxygen concentration and anoxia spreading. Short-term controls such as an increase of pCO2, nutrients, or orbital configurations are also studied with a second set of simulations with a Cenomano-Turonian (90 Ma) paleogeographic configuration. The different simulated maps of oxygen are used to study the evolution of marine productivity and oxygen minimum zones as well as the spreading of seafloor anoxia, in order to unravel the interlocking of the different mechanisms and their specific impact on anoxia through space and time.

How to cite: Donnadieu, Y., Laugie, M., Ladant, J.-B., Raisson, F., and Bopp, L.: Modeling the impact of oceanic circulation and marine productivity on Cretaceous seafloor anoxia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20746, https://doi.org/10.5194/egusphere-egu2020-20746, 2020.

EGU2020-19916 | Displays | CL1.4 | Highlight

The simulated transition from a hard snowball Earth

Philipp de Vrese, Tobias Stacke, Victor Brovkin, and Jeremy Caves Rugenstein

Geological evidence suggests that Earth's past featured periods during which the planet was largely or even entirely covered by ice, a state termed "snowball Earth".  Model based studies confirm that one of Earth's equilibrium states is a fully glaciated planet (hard snowball) but it is not clear how this state could have been left once it had been established. We use simulations with the Max-Planck-Institute for Meteorology's Earth system model to investigate the conditions that enable the transition out of the snowball-state. We show that the high albedo of pure snow would have prevented deglatiation, even for extremely high atmospheric CO2 concentrations. Terminal deglaciation is only triggered for surface albedos corresponding to old, darkened snow or sea-ice. Here, increasing snowfall rates, resulting from the intensification of the hydrological cycle with rising CO2 concentrations, would have prohibited the gradual build-up of dust that leads to a darkening of the surface.  Only when assuming dust deposition fluxes at least similar to present-day fluxes, can the deglation be triggered for plausible atmospheric CO2 concentrations.

How to cite: de Vrese, P., Stacke, T., Brovkin, V., and Caves Rugenstein, J.: The simulated transition from a hard snowball Earth, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19916, https://doi.org/10.5194/egusphere-egu2020-19916, 2020.

EGU2020-15254 | Displays | CL1.4

Role of paleogeography in preconditioning the Late Cretaceous Oceanic Event (OAE2) in a full global circulation Earth System model

Alexander Manning, Paul Valdes, Fanny Monteiro, and Jonny Williams

Ocean anoxic event 2 (OAE2) was a large perturbation in the Earth's ocean carbon system, occurring at approximately 93.5 Ma, and is characterised by widespread black shales deposition in sediment records. This record has been interpreted as evidence of large anoxia in the global ocean for a long period, resulting in large scale extinction of marine life. However, the exact causes of OAE2, and how it initially developed, are not fully understood. We modelled the period leading up to OAE2 using the HadCM3L global climate model with full ocean (HADOCC) and terrestrial carbon cycle (TRIFFID) modules. We compared our results to equivalent simulations using late Cretaceous (Maastrichtian) paleogeographies. This allowed us to analyse the effects of continental configuration on the development to the OAE. Our results show that restricted ocean circulation, caused by the paleobathymetry, is necessary for anoxic conditions to develop but is not sufficient alone. This suggests that continental configuration is highly important in determining the ability of the oceans to develop an OAE and may explain why they only occur during some times during Earth history.

How to cite: Manning, A., Valdes, P., Monteiro, F., and Williams, J.: Role of paleogeography in preconditioning the Late Cretaceous Oceanic Event (OAE2) in a full global circulation Earth System model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15254, https://doi.org/10.5194/egusphere-egu2020-15254, 2020.

EGU2020-9074 | Displays | CL1.4

Exploring Mesozoic Climates - Modeling and Evaluation of Proxy Distributions

Jan Landwehrs, Georg Feulner, Matthias Hofmann, Stefan Petri, Benjamin Sames, and Michael Wagreich

The Mesozoic Era (~252-66 Ma) is a decisive period in Earth’s history. It is marked by a tectonic transition from the Pangea supercontinent towards a modern continental configuration as well as the ecological success of the dinosaurs and the evolution of mammals, flowering plants, stony corals and important groups of planktic calcifiers. The Mesozoic is generally considered as a greenhouse climate period, with especially high global temperatures during the Triassic and the Late Cretaceous. Here, we present novel modeling results on the evolution of global climatic conditions through the Mesozoic.

An ensemble of equilibrium climate states for 40 geological timeslices between 255 and 60 Ma is simulated with the CLIMBER-3α Earth System Model of Intermediate Complexity. The influence of changing paleogeography, sea level, vegetation cover, solar luminosity, orbital configuration and atmospheric CO2 concentration is systematically tested based on constraints from published geological proxy reconstructions and previous modeling work.

Atmospheric pCO2 is found to be the strongest driver of global mean temperatures, which are generally elevated above the present and reach 20°C in the Late Triassic to Early Jurassic and the mid-Cretaceous if a recently published pCO2 proxy compilation is employed. The simulated seasonal latitudinal shift of high precipitation zones exhibits a maximum during the mid-Triassic to Early Jurassic and therefore supports the notion of a “Megamonsoon” during this time. Simulated humid and arid climate zones generally agree well with spatial distributions of geologic climate indicators like coal and evaporites, although some discrepancies exist. The same applies to the correlation of fossil stony coral reef distributions with regions where seawater temperatures would have been suitable for (modern) coral reefs. We will discuss which changes of Earth System parameters throughout the Mesozoic can best explain shifts in these distributions.

How to cite: Landwehrs, J., Feulner, G., Hofmann, M., Petri, S., Sames, B., and Wagreich, M.: Exploring Mesozoic Climates - Modeling and Evaluation of Proxy Distributions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9074, https://doi.org/10.5194/egusphere-egu2020-9074, 2020.

Antarctic bryozoans are important colonial marine invertebrates in terms of their origin, palaeoenvironment and climatic approaches. The changes of the bryozoan fossil records during the last 55 Ma years  are well-defined by their biodiversity, taxonomic composition and colony growth-forms. The late Early Eocene biota from the shallow-marine–estuarine clastic succession of the lower part (Telm1-2) of the La Meseta Formation of Seymour Island are represented by the prolific, spectacular in size, massive multilamellar colonies dominated by the cerioporids as well as diverse ascophorans  cheilostomes (Hara, 2001). The free-living lunilitiform, disc-shaped colonies, which occur in the middle part of the La Meseta Formation (Telm4-Telm5), are characteristic for the warm, shallow-self environment and bottom temperature, which ranges from 10 to 29°C. The presence of the bimineralic skeletons of this fauna (such as Lunulites, Otionellina, and Uharella) with the traces of aragonite is indicative for the temperate shelf environment, sandy and often shifting substrate. Lunulitids are inhabited by the circumpolar to warm-temperate waters, at the present day. Contrary to that, the bryozoans  from the upper part of the LM (Telm6-7) are  represented by the scarce lepraliomorphs accompanied by the crustaceans, brachiopods and gadiform fish remains. The individuality of the Eocene bryozoan assemblages are well-correlated with the EECO, MECO and EOT climatic events, based on the other marine macrofaunal marine fossil records (see also Ivany et al. 2008). The lower Pliocene bryofauna recently described  from the Cockburn Island Formation  is composed of the rich encrusting shallow-water, membraniporiform zoaria (Hara and Crame, in review, 2020). The biota of thePectenConglomerate are indicative of the interglacial conditions during the deposition of the Cockburn Island Formation. At the present day bryozoans with the preponderance of cheilostomes are the most significant marine benthic community, thriving successfully in cool-water Antarctic  conditions.

References,

Hara, U., 2001. Bryozoans from the Eocene of Seymour Island, Antarctic Peninsula, Palaeontogia Polonica , 60:33-155.

Hara, U., Mors, T., Hagstrom, and Reguero M. A., 2018. Eocene bryozoans  assemblages from the La Meseta Formation of Seymour Island. Geological Quarterly, 62: 705-728. 

Hara., U., and Crame, J.A. 2019. Paleobiodiversity of the Lower Pliocene bryozoan  benthic community and its response to interglacial conditions.  Geological Review (in review).

Ivany L.C., Lohmann, K. C. Hasiuk, F., Blake D.B., Glass A., Aronson R.B., and Moody R.M. 2008. Eocene climate record of the high southern latitude continental shelf: Seymour Island, Antarctica. Geological Society of America Bulletin, v. 120, no. 5-6: 659-678.

 

How to cite: Hara, U.: Cenozoic bryozoan biota and their response to climatic changes in Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22540, https://doi.org/10.5194/egusphere-egu2020-22540, 2020.

EGU2020-18748 | Displays | CL1.4

The climate in Antarctica during the Middle Eocene: a modelling perspective

Frederic Fluteau, Delphine Tardif, Guillaume Le Hir, Yannick Donnadieu, Pierre Sepulchre, Jean-Baptiste Ladant, Fernando Poblete, and Guillaume Dupont-Nivet

The Middle Eocene represents the last ice-free period of the Cenozoic. Vegetation proxy data (wood, leaves, palynomorphs) discovered in the Antarctica peninsula and neighbouring islands or hosted in sedimentary sequences deposited on the continental margin reveal the presence of paratropical rain forests which thrived along the Antarctica coast during the Early Eocene. During the Middle and Late Eocene these flora have been progressively replaced by temperate Nothofagus-dominated rainforests (Contreras et al., 2013). Jacques et al. (2012) proposed, using a physiognomic approach (CLAMP), that a warm temperate and wet climate (with a marked summer rainy season) prevails until the middle Eocene (43±2 Ma) on the tip of the Antarctica Peninsula.

            To better constrain the climate in Antarctica and understand processes governing the polar climate during the Middle Eocene, we performed a set of experiments using the IPCC-like Earth System Model (IPSL-CM5A2-VLR) forced with a Middle Eocene (~40 Ma) paleogeography reconstruction and a 4 times pre-industrial atmospheric CO2 level (1120ppm). To highlight the importance of the seasonality, we launched 6 orbital configurations exploring end-members situations. To complete the procedure, simulated sea surface temperatures and sea ice extents were then employed as boundary conditions to force the Atmospheric General circulation model LMDz6 (run at higher spatial resolution) coupled with a soil and vegetation model ORCHIDEE to simulate the corresponding vegetation over Antarctica. The 6 end-members Earth's orbital configuration allows exploring the full climatic spectrum which would have been recorded by proxy data. Simulated changes in atmospheric circulation will be discussed and the simulated climate and vegetation will be confronted to paleoclimatic indicators and vegetation data.

How to cite: Fluteau, F., Tardif, D., Le Hir, G., Donnadieu, Y., Sepulchre, P., Ladant, J.-B., Poblete, F., and Dupont-Nivet, G.: The climate in Antarctica during the Middle Eocene: a modelling perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18748, https://doi.org/10.5194/egusphere-egu2020-18748, 2020.

EGU2020-8370 | Displays | CL1.4

Estimating structural and parametric uncertainties in the simulated early Eocene surface warming

Sebastian Steinig, Fran J. Bragg, Peter J. Irvine, Daniel J. Lunt, and Paul J. Valdes

Simulating the proxy-derived surface warming and reduced meridional temperature gradient of the early Eocene greenhouse climate still represents a challenge for most atmosphere-ocean general circulation models. A profound understanding of uncertainties associated with the respective model results is thereby essential to reliably identify any similarities or misfits to the proxy record. Besides incomplete knowledge of past greenhouse gas concentrations and other boundary conditions, structural and parametric uncertainties are the main factors that determine our confidence in paleoclimate simulation results.

The recent publication of coordinated model experiments that apply identical paleogeographic boundary conditions for key time periods of the early Eocene (DeepMIP) allows a systematic analysis of inter-model differences and therefore of structural uncertainties in the simulated surface warming. Here we additionally explore the parametric uncertainty of the early Eocene climatic optimum (EECO) surface warming within one DeepMIP model. For this we performed perturbed parameter ensemble (PPE) simulations with HadCM3B at different atmospheric CO2 concentrations following the DeepMIP protocol. Twenty-one parameter sets based on changes in six atmospheric parameters, a sea-ice parameter and the ocean background diffusivity were branched off from the respective DeepMIP control simulations and integrated for a further 1500 model years. The selected parameter sets are based on previous results demonstrating their ability to simulate a pre-industrial global-mean surface temperature within ±2 °C of the standard configuration.

Preliminary results indicate a large spread of the simulated low-latitude surface warming in the PPE and therefore significant changes of the large-scale meridional temperature gradient for the EECO. Some ensemble members develop numerical instabilities at CO2 concentrations of 840 ppmv and above, most likely in consequence of high temperatures in the tropical troposphere. We further compare the magnitude of the parametric uncertainty of the HadCM3B perturbation experiments with the structural differences found in the DeepMIP multi-model ensemble and explore the sensitivity of the results to the strength of the applied greenhouse gas forcing. Model skill of the PPE members is tested against the most recent DeepMIP compilations of marine and terrestrial proxy temperatures.

How to cite: Steinig, S., Bragg, F. J., Irvine, P. J., Lunt, D. J., and Valdes, P. J.: Estimating structural and parametric uncertainties in the simulated early Eocene surface warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8370, https://doi.org/10.5194/egusphere-egu2020-8370, 2020.

EGU2020-13450 | Displays | CL1.4

Thermohaline Fingerprints of the Greenland-Scotland Ridge and Fram Strait Subsidence Histories

Akil Hossain, Gregor Knorr, Gerrit Lohmann, Michael Stärz, and Wilfried Jokat

Changes in ocean gateway configuration are known to induce basin-scale rearrangements in ocean characteristics throughout the Cenozoic. However, there is large uncertainty in the relative timing of the subsidence histories of ocean gateways in the northern high latitudes. By using a fully coupled General Circulation Model we investigate the salinity and temperature changes in response to the subsidence of two key ocean gateways in the northern high latitudes during early to middle Miocene. Deepening of the Greenland-Scotland Ridge causes a salinity increase and warming in the Nordic Seas and the Arctic Ocean. While warming this realm, deep water formation takes place at lower temperatures due to a shift of the convection sites to north off Iceland. The associated deep ocean cooling and upwelling of deep waters to the Southern Ocean surface causes a cooling in the southern high latitudes. These characteristic impacts in response to the Greenland-Scotland Ridge deepening are independent of the Fram Strait state. Subsidence of the Fram Strait for a deep Greenland-Scotland Ridge causes less pronounced warming and salinity increase in the Nordic Seas. A stronger salinity increase is detected in the Arctic while temperatures remain unaltered, which further increases the density of the North Atlantic Deep Water. This causes an enhanced contribution of North Atlantic Deep Water to the abyssal ocean and on the expense of the colder southern source water component. These relative changes largely counteract each other and cause little warming in the upwelling regions of the Southern Ocean.

How to cite: Hossain, A., Knorr, G., Lohmann, G., Stärz, M., and Jokat, W.: Thermohaline Fingerprints of the Greenland-Scotland Ridge and Fram Strait Subsidence Histories, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13450, https://doi.org/10.5194/egusphere-egu2020-13450, 2020.

EGU2020-10818 | Displays | CL1.4

Transport of planktic foraminifera by ocean currents in the Uruguayan margin

Anne Kruijt, Andrew Mair, Peter Nooteboom, Anna S. von der Heydt, Martin Ziegler, and Tracy Aze

Fossils of planktic foraminifera are found in marine sediments and are widely used as a proxy for past ocean conditions. The habitat of these unicellular marine zooplankton ranges from tropical to polar regions and is mostly located in the upper mixed layer of the ocean. The foraminifera form a calcium carbonate ’shell’ around their cell during their lifespan. When they die, foraminifera lose their ability to control their buoyancy and their shells sink to the ocean floor. It is often assumed that the proxies which are derived from the shells in sediment cores represent ocean conditions above the location of deposition. However, foraminifera are transported by ocean currents, both during and after their lifespan. Hence, the paleoclimatic conditions recorded from their shells may originate far from the core site, generating large footprints in foraminifera-based paleoclimatic proxies. 

In this project, we quantify the influence of the transport by ocean currents on the proxy signal of foraminifera found at core sites in the Uruguayan margin of the Punta del Este basin. This is a region where two western boundary currents meet: The southward flowing Brazil current and the northward flowing Malvinas current. We use a high resolution (0.1° horizontally) ocean general circulation model to track virtual sinking particles and the local oceanic conditions along their pathways. These model results are compared to proxy- and species analysis from the core sites. We found that offsets in modelled proxy signals due to transport in the Uruguayan margin are strongly linked to the relative position of the core site to the Brazil-Malvinas confluence. These offsets are most pronounced in the tails of the temperature distributions where they can reach up to +/- 7°C at sites located in the confluence zone. Species analysis from core tops taken slightly north of this region show more cold water species than reflected by the modelled temperature distributions, suggesting biological activity and nutrient availability not taken into account in the model play an important additional role in the relative abundances of species.
Our model simulations have provided both a first order insight into the potential proxy-signal offsets in highly dynamic ocean regions and show that understanding of the interplay between transportation effects and the biological activity of foraminifera is crucial for the interpretation of these proxies.

 

How to cite: Kruijt, A., Mair, A., Nooteboom, P., von der Heydt, A. S., Ziegler, M., and Aze, T.: Transport of planktic foraminifera by ocean currents in the Uruguayan margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10818, https://doi.org/10.5194/egusphere-egu2020-10818, 2020.

EGU2020-5974 | Displays | CL1.4

Concurrent Miocene Antarctic ice sheet growth and CO2 increase caused by disequilibrium

Lennert Stap, Gregor Knorr, and Gerrit Lohmann

Geological evidence indicates considerable Antarctic ice volume variations during the early to mid-Miocene. Hitherto, ice modelling studies have mostly used equilibrium simulations to explain this variability. In these simulations, the gain in precipitation due to increased temperatures has to outweigh the loss caused by increased ice melt, to obtain simultaneous ice sheet growth and CO2 level rise. Here, conceptualising ice dynamical model results, we find that this is not a necessary condition for the transiently evolving Miocene Antarctic ice sheet. Instead, ice volume increase when CO2 levels are rising can also be explained as a consequence of disequilibrium between the transiently changing ice volume and forcing climate. This disequilibrium permits a continuation of ice sheet growth after a gradual CO2 decline. When the CO2 level is increased again, the ice sheet is still adapting to a relatively large equilibrium volume. Lowering the periodicity of the forcing leads to a larger disequilibrium, and consequently larger CO2-ice volume phase differences. Furthermore, amplified forcing variability increases ice volume variations, because the growth and decay rates depend on the forcing. It also leads to a reduced average ice volume, which is induced by the growth rate generally being smaller than the decay rate. We therefore submit that retrieval of high resolution proxy-CO2 records covering the Miocene would be very beneficial to constrain ice modelling studies.

How to cite: Stap, L., Knorr, G., and Lohmann, G.: Concurrent Miocene Antarctic ice sheet growth and CO2 increase caused by disequilibrium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5974, https://doi.org/10.5194/egusphere-egu2020-5974, 2020.

The North American Great Plains are characterized by a sharp aridity gradient at around the 100th meridian with a more humid climate to the east and a more arid climate to the west. This aridity gradient shapes the region's agriculture and economy, and recent work suggests that arid conditions on the Great Plains may expand eastward with global warming. The abundant Neogene sediments of the Ogallala Formation in the Great Plains present an opportunity to reconstruct regional hydroclimate conditions at a time when pCO2 and global temperatures were much higher than today, providing insight into the aridity and ecosystem response to warming. We present new paleosol carbonate δ13C and δ18O data (n=366) across 37 sites spanning the Great Plains and compile previously published measurements (n=381) to evaluate the long-term hydroclimatic and ecosystem changes in the region during the late Neogene. This study combines a spatial and temporal analysis of carbon and oxygen isotope data with reactive-transport modeling of oxygen isotopes constrained by climate model output, providing critical constraints on the paleoenvironmental and paleoclimatological evolution of the Neogene Great Plains. Carbonate δ18O demonstrate remarkable similarity between the spatial pattern of paleo-precipitation δ18O and modern precipitation δ18O. Today, modern precipitation δ18O over the Great Plains is set by the mixing between moist, high-δ18O moisture delivered by the Great Plains Low-Level Jet and drier, low-δ18O westerly air masses. Thus, in the absence of countervailing processes, we interpret this similarity between paleo and modern δ18O to indicate that the proportional mixing between these two air masses has been minimally influenced by changes in global climate and that any changes in the position of the 100th meridian aridity gradient has not been forced by dynamical changes in these two synoptic systems. In contrast, prior to the widespread appearance of C4 plants in the landscape of the Great Plains, paleosol carbonate δ13C show a robust east-to-west gradient, with higher values to the west. We interpret this gradient as reflective of lower primary productivity and hence soil respiration to the west. Close comparison with modern primary productivity data indicates that primary productivity has declined and shifted eastward since the late Neogene, likely reflecting declining precipitation and/or a reduction in CO2 fertilization during the late Neogene. Finally, δ13C increases across the Miocene-Pliocene boundary, which, consistent with previous studies, we interpret as a shift from a C3 to a C4 dominated landscape. We conclude that, to first order, the modern aridity gradient and the hydrologic processes that drive it are not strongly sensitive to changes in global climate and any shifts in this aridity gradient in response to rising CO2 will be towards the west, rather than towards the east.

How to cite: Manser, L., Kukla, T., and Caves Rugenstein, J. K.: Long-term stability of large-scale hydroclimate processes in the North American Great Plains revealed by a Neogene stable isotope study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11141, https://doi.org/10.5194/egusphere-egu2020-11141, 2020.

For several decades, the comparison of climate data with results from water isotope-enabled Atmosphere General Circulation Models (AGCMs) significantly helped to a better understanding of the processes ruling the water cycle, which is one of the main drivers of the climate variability. For the modern period, the use of AGCMs nudged with weather forecasts reanalyses is a powerful way to obtain model outputs under the same weather conditions than at the sampling time of the observations.

Here we present new isotopic simulations results from ECHAM6-wiso [1] nudged with the last reanalyses dataset from the European Centre for Medium-Range Weather Forecasts (ECMWF), ERA5 [2], at different spatial resolutions over the period 1979-2018. Model results are evaluated against isotopic data compilations, including GNIP (Global Network of Isotopes in Precipitation [3]), speleothems [4], ice cores datasets and water vapor measurements. To quantify the impact of these reanalyses on our simulations, we also performed nudged simulations with the previous model version ECHAM5-wiso [5] by using ERA5 data and its predecessor ERA-Interim [6].

These new simulation products could be a useful contribution to the isotopic data community for the interpretation of their water isotope records and for the exploration of the mechanisms controlling the variability of the surrounding water isotopic composition.

 

[1] Cauquoin et al., Clim. Past, 15, 1913–1937, https://doi.org/10.5194/cp-15-1913-2019, 2019.

[2] Copernicus Climate Change Service (C3S), 2017.

[3] IAEA, the GNIP Database, available at: https://nucleus.iaea.org/wiser.

[4] Comas-Bru et al., Clim. Past, 15, 1557–1579, https://doi.org/10.5194/cp-15-1557-2019, 2019.

[5] Werner et al., Geosci. Model Dev., 9, 647–670, https://doi.org/10.5194/gmd-9-647-2016, 2016.

[6] Dee et al., Q. J. R. Meteorol. Soc., 137, 553–597, https://doi.org/10.1002/qj.828, 2011.

How to cite: Cauquoin, A. and Werner, M.: High-resolution isotopic simulations from ECHAM6-wiso nudged with ERA5 reanalyses: new products for isotopic model-data comparisons, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12319, https://doi.org/10.5194/egusphere-egu2020-12319, 2020.

EGU2020-12420 | Displays | CL1.4

Investigation of the response of water isotope records to the changes in orbital forcing with the isotope-enabled AGCM MIROC5-iso

Kanon Kino, Atsushi Okazaki, Alexandre Cauquoin, and Kei Yosnimura

It has been well demonstrated that the variations of orbital parameters, known as Milankovitch theory, are one of the most important drivers of the Earth’s climate system. However, the way how the changes in orbital forcing imprint the glacial-interglacial cycles recorded in paleo-proxies, such as stable water isotopes in ice cores and speleothems, is still unclear. One way to progress in this question is to make direct comparisons of isotopic data with simulation results from isotope-enabled General Circulation Models (GCMs). We use here such a model, the Japanese atmospheric GCM MIROC5-iso[1], to perform simulations under different idealized paleoclimate conditions. For that, corresponding orbital parameters and greenhouse gases concentrations are set. Prescribed sea surface temperature and sea ice coverage boundary conditions from the fully coupled atmosphere-ocean GCM MIROC (MIROC-AOGCM) experiments are used, after an adaptation to the MIROC5-iso grid. Because earlier version of MIROC-AOGCM has been widely used for paleoclimate modeling purposes, the climatological mean states of MIROC5-iso under preindustrial conditions are evaluated against simulation results from different versions of MIROC-AOGCM (MIROC4m, which is a slightly updated version of MIROC3.2(med), and MIROC5 [2]). In addition, several interglacial periods and idealized paleoclimate experiments will be investigated and implications for the interpretation of water isotope response to the changes in orbital forcing will be discussed.

[1] Okazaki and Yoshimura, J. Geophys. Res. Atmos, 124, 8972–8993, 2019.

[2] Watanabe et al., J. Climate, 23, 6312–6335, 2010.

How to cite: Kino, K., Okazaki, A., Cauquoin, A., and Yosnimura, K.: Investigation of the response of water isotope records to the changes in orbital forcing with the isotope-enabled AGCM MIROC5-iso, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12420, https://doi.org/10.5194/egusphere-egu2020-12420, 2020.

The hydrological response to radiative forcing is less understood than the thermal one: many climate models have difficulties in simulating seasonal rainfall and its variability. Indeed, future precipitation projections are much more uncertain than those of temperature. However, confident projections of precipitation are of crucial importance, particularly for highly populated regions where agriculture strongly relies on seasonal rainfall, such as South and Central Asia.

Instrumental data from Eurasia show a negative correlation between temperature and precipitation on short timescales (10-3 to 100 years). However, on longer timescales (101 to 103 years), proxy data covering the Holocene show a positive correlation between temperature and precipitation. Climate models in contrast simulate a negative correlation on all timescales. To extend previous estimates to longer time scales, we focus on the last Glacial period, characterized by colder temperature than the Holocene as well as pronounced millennial-scale climate fluctuations in the Northern Hemisphere.

We reconstruct temperature and precipitation from four high resolution pollen records at mid-latitudes in the Northern Hemisphere. The estimates are compared with climate simulations. The chosen proxy sites cover the East and West coasts of both the Eurasian and North American continent. We employ four different statistical reconstruction methods to assess validity and biases of each method. The differences between reconstructed and simulated temperature-precipitation relationships as well as the zonal structure of orbital- and millennial-scale variations are examined. In particular, we explore the thermodynamic and dynamic contributions to the inferred relationships between temperature and precipitation.

How to cite: Sommani, A., Weitzel, N., and Rehfeld, K.: Northern Hemisphere temperature to precipitation relationships during the last Glacial from pollen records and climate simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7293, https://doi.org/10.5194/egusphere-egu2020-7293, 2020.

The project PalMod II is the second phase of Germany’s national paleoclimate modelling initiative (www.palmod.de) whose aim is to model the transient climate evolution from the last interglacial to the anthropocene with state of the art earth system models. The second phase more precisely wants to perform simulations for the last glacial inception, the marine isotope stage 3, and the last deglaciation. It further plans to compile paleo-observational proxy data over the full glacial cycle from about 130,000 years before present until today. Models of differing complexity (fully-coupled earth system models and models of intermediate complexity) will be used to assess the scientific questions posed in PalMod II. Model output will be combined with the compiled paleo-proxy data for validation purposes. The sheer data amount in excess of several petabytes and different data handling practices of the participating communities require dedicated management of the data workflow both in- and outside of the immediate PalMod community.

The PalMod II data management takes place in close collaboration between data management specialists and the scientists. The objectives include the standardisation of each simulation and proxy dataset, the facilitation of data sharing and data reuse between work packages, the access channels for external collaborators, and the long-term preservation of the data. The data management follows the concept of the "Active Data Management Plan", which foresees a continuous development of the data management plan (DMP), starting with an initial basic version. The DMP covers the entire life cycle of the research data generated in the project, from generation and analysis to data publication and archiving. This includes aspects such as data formats, metadata standards and data usage licenses. Ownership and responsibilities for simulation and paleo data sets as well as the input data during and after the end of the project will also be considered.

This contribution will present the initial DMP for PalMod II. It will describe the amount of data produced in the project, highlight how the above mentioned aspects will be dealt with, and present how the project aims to ensure the Findability, Accessibility, Interoperability, and Reusability, i.e. the FAIR data principles, of simulation output, post-processed model data, and paleo-proxy data from PalMod II.

* This contribution presents results of the full PalMod II initiative, the authors present them on behalf of the initiative.

How to cite: Bothe, O. and Peters, K.: The initial Data Management Plan for PalMod II - FAIR simulation and paleo data from the Last Interglacial to the Anthropocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13189, https://doi.org/10.5194/egusphere-egu2020-13189, 2020.

CL1.8 – Orbital forcing and internal climate feedbacks in climate transitions of the last 5 million years

EGU2020-17480 | Displays | CL1.8

Ocean carbon storage and release over a glacial cycle

James Rae, Alan Foreman, Jessica Crumpton-Banks, Andrea Burke, Christopher Charles, and Jess Adkins

Perhaps the most important feedback to orbital climate change is CO2 storage in the deep ocean.  By regulating atmospheric CO2, ocean carbon storage synchronizes glacial climate in both hemispheres, and drives the full magnitude of glacial-interglacial climate change.  However few data exist that directly track the deep ocean’s carbon chemistry over a glacial cycle.  Here, we present geochemical reconstructions of deep ocean circulation, redox, and carbon chemistry from sediment cores making up a detailed depth profile in the South Atlantic, alongside a record of Southern Ocean surface water CO2, spanning the last glacial cycle.  These data indicate that initial glacial CO2 drawdown is associated with a major increase in surface ocean pH in the Antarctic Zone of the Southern Ocean, cooling at depth, enhanced deep ocean stratification, and carbon storage.  Deep ocean carbon storage and deep stratification are further enhanced when CO2 falls at the onset of Marine Isotope Stage 4, and are also pronounced during the LGM, illustrating a link between orbital scale climate stages and deep ocean carbon.  However our data also illustrate non-linear feedbacks to orbital forcing during glacial terminations, which show abrupt decreases in pH in Southern Ocean surface and subsurface waters, as CO2 is rapidly expelled from the deep ocean at the end of the last ice age.

How to cite: Rae, J., Foreman, A., Crumpton-Banks, J., Burke, A., Charles, C., and Adkins, J.: Ocean carbon storage and release over a glacial cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17480, https://doi.org/10.5194/egusphere-egu2020-17480, 2020.

EGU2020-6778 | Displays | CL1.8 | Highlight

Millennial-scale variability in Antarctic Circumpolar Current and its impacts during the last glacial cycle

Shuzhuang Wu, Frank Lamy, Gerhard Kuhn, Lester Lembke-Jene, Xu Zhang, Christian Haas, Nortbert Nowaczyk, Helge W. Arz, and Ralf Tiedemann

The Antarctic Circumpolar Current (ACC) is the largest current system in the world, linking the Pacific, Atlantic and Indian Ocean basins. However, the variability of the ACC, which plays a fundamental role on global ocean circulation and climate variability, is still poorly constrained. This information is crucial for understanding the role of the ACC on global ocean circulation in response to global warming. Here, we reconstruct changes in the ACC over the past 155,000 years based on sediment grain size variations recorded in a highly-resolved marine sedimentary record from the central Drake Passage near the Polar Front. Our results show significant changes in the ACC during the last glacial cycle and a remarkable boundary between the glacial and interglacial periods. Substantial decreases (~33% to ~47%) in the ACC flow speed from interglacial to glacial period, which corroborates and extends results of previous studies along the subantarctic northern limit of the ACC into the central Drake Passage. This strong variation of ACC likely plays a significant role in regulating Pacific-Atlantic water mass exchange via the “cold water route” and could significantly affect the Atlantic Meridional Overturning Circulation. Superimposed on these glacial-interglacial changes, we found strong millennial-scale variations in ACC current speed, increasing in amplitude close to full glacial conditions. We hypothesise that the central ACC increases its sensitivity to Southern Hemisphere millennial-scale climates oscillations, likely associated with westerlies’ wind stress and Antarctic sea ice extent once glacial conditions fully formed.

How to cite: Wu, S., Lamy, F., Kuhn, G., Lembke-Jene, L., Zhang, X., Haas, C., Nowaczyk, N., W. Arz, H., and Tiedemann, R.: Millennial-scale variability in Antarctic Circumpolar Current and its impacts during the last glacial cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6778, https://doi.org/10.5194/egusphere-egu2020-6778, 2020.

EGU2020-9828 | Displays | CL1.8

The Role of Changing Indian Ocean Salinity in shaping Pleistocene Climate

Sophie Nuber, James W. B. Rae, Morten B. Andersen, Bas de Boer, Xu Zhang, Ian R. Hall, and Stephen Barker

Indian Ocean surface salinity dynamics are thought to play an important role in shaping glacial-interglacial climate through controlling Agulhas leakage efficiency. It is proposed that a strong Agulhas leakage supplies warm and salty Indian ocean surface waters to Atlantic surface currents influencing convective potential at North Atlantic deep-water formation sites. Here, we present new planktonic foraminiferal Mg/Ca and stable isotope-derived salinity reconstructions for the last 1.2Ma from the northern Mozambique channel. We find salinity increases well before terminations, followed by early decrease before glacial inception. We present a possible link between the hydrography in the northern Mozambique channel and whole ocean salinity changes due to unique surface circulation in the Indian ocean. Despite being a mostly tropical and subtropical ocean, salinity in the modern tropical Indian Ocean is fresher than at comparable latitudes in the Atlantic or Pacific. This is due to the inflow of freshwater from the Indonesian throughflow and recycling via an active Agulhas leakage. We show that salinity in the glacial western Indian Ocean was significantly higher due to a reduced ITF and a weaker Agulhas leakage. We hypothesise that opening and closing of these two gateways influences the development/diminishment of a strong subtropical Indian Ocean gyre which controls sea surface salinity and temperature of tropical Indian Ocean water masses and subsequently the efficiency of the Agulhas Leakage.

How to cite: Nuber, S., Rae, J. W. B., Andersen, M. B., de Boer, B., Zhang, X., Hall, I. R., and Barker, S.: The Role of Changing Indian Ocean Salinity in shaping Pleistocene Climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9828, https://doi.org/10.5194/egusphere-egu2020-9828, 2020.

EGU2020-10495 | Displays | CL1.8 | Highlight

The Evolution of Subantarctic Fronts, Deep Ocean Ventilation and Flow Vigour at the Agulhas Plateau: Surface-Deep Coupling Across Climate Transitions of the past 3 Ma

Aidan Starr, Ian R. Hall, Stephen Barker, Jeroen van der Lubbe, Sidney R. Hemming, Francisco J. Jimenez-Espejo, and Nambiyathodi Lathika

The geometry of large-scale deep ocean circulation is closely linked to processes occurring in the Southern Ocean (SO). The SO is the ‘window’ through which much of the world’s ocean interior interacts with the atmosphere, and understanding the complex relationships coupling SO dynamics to deep circulation can provide valuable insights into biogeochemical and physical processes important to global climate. Of particular interest is how these processes interacted with, and behaved under different climate states, such as the glacial-interglacial cycles of the Pleistocene (0-2.8 Ma), and the intensification of Northern Hemisphere glaciation during the transition from the warm Mid-Pliocene (3.3-3.1 Ma) to the early Pleistocene. Here, we utilise new composite sediment core records (41oS, 25oE, 2700-2900 m water depth) to reconstruct deep chemical and physical ventilation at the Agulhas Plateau, as well as the competing presence of warm Subtropical waters vs cold Subantarctic waters in the surface, over the past ~3 Ma. We present records of the ‘sortable silt’ flow speed proxy, the stable isotope (δ18O, δ13C) composition of benthic foraminifera, bulk sediment element concentrations, and the accumulation of ice-rafted debris (IRD). The sortable silt proxy demonstrates that deep physical ventilation is largely decoupled from deep chemical ventilation as indicated by benthic δ13C, with higher flow speeds coincident with more depleted δ13C. Furthermore, deep ventilation is related to changes in the terrigenous sediment composition: deep flow speeds and δ13C vary concurrently with bulk sediment geochemistry (K/Al, Ti). At the Agulhas Plateau, we interpret deep chemical ventilation and near-bottom flow speeds to reflect changes in the advection of northern-sourced deep waters (e.g. North Atlantic Deep Water and its glacial equivalent) and meridional variability in the location of the deep-reaching Antarctic Circumpolar Current (ACC) and its associated fronts. The presence of IRD at the Agulhas Plateau is controlled primarily by the equatorward survivability far-travelling Antarctic icebergs, and therefore represents the relative presence of cold, iceberg-bearing Subantarctic Zone (SAZ) surface waters. Generally, at times of high near-bottom flow speed and more ‘southern’ terrigenous sediment composition, IRD is higher, implying a meridional expansion of the SAZ. Together, these proxy records provide a continuous and long-term insight into the evolution of coupled surface-deep conditions at the Agulhas Plateau. We postulate that these conditions may reflect the wider geometry of ocean circulation in the SO, documenting the interactions between the ACC and circum-Antarctic fronts with the upwelling, conversion, and export of deep water masses. Our records represent the first multi-proxy reconstruction of this system across climate transitions of the past ~3 Ma, allowing us to explore its evolution across a range of timescales, from million-year to orbital-scale. Furthermore, by measuring multiple proxies on the same samples, we are able to determine the relative phasing between different processes independent of chronostratigraphic uncertainties, for example the timing of SAZ changes vs perturbations in deep ocean circulation at the site.   

How to cite: Starr, A., Hall, I. R., Barker, S., van der Lubbe, J., Hemming, S. R., Jimenez-Espejo, F. J., and Lathika, N.: The Evolution of Subantarctic Fronts, Deep Ocean Ventilation and Flow Vigour at the Agulhas Plateau: Surface-Deep Coupling Across Climate Transitions of the past 3 Ma, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10495, https://doi.org/10.5194/egusphere-egu2020-10495, 2020.

EGU2020-18340 | Displays | CL1.8

Glacial-to-interglacial variations in the deep water at the Bermuda Rise inferred from a Nd isotope record covering the last million years

Maria Jaume-Seguí, Joohee Kim, Karla P. Knudson, Maayan Yehudai, Steven L. Goldstein, Louise Bolge, Patrizia Ferretti, and Leopoldo D. Pena

The formation of North Atlantic Deep Water (NADW) in the North Atlantic is an important modulator of the climate system, as it drives the global termohaline circulation, responsible for the distribution of heat, salts and nutrients across the oceans. ODP Site 1063 (4584 m), on the deep Bermuda Rise, is located in the mixing zone between NADW and Antarctic Bottom Water (AABW) and appears to be a good location to study how ocean circulation and climate interconnect. Here we present a new record based on Nd isotope ratios that covers ~1 Ma at that Site. Our data shows Nd isotope ratios during parts of interglacials that are much lower than present day NADW. These results are coherent with recent published studies on the last interglacial–glacial cycle that show that the deep North Atlantic Nd isotope ratios are also lower than NADW during the early interglacial. However, Nd isotope values from the shallower DSDP Site 607 (3427 m), within the core of NADW, have remained similar to modern NADW during interglacials over the same time interval. Site 607 is thought to represent the deep North Atlantic, as shown by an Atlantic meriodional transect that displays Nd isotopes ratios for glacial and interglacial maxima over the last ~1 Ma. We suggest that Nd isotope ratios at Site 1063 do not fully represent the North Atlantic endmember of the AMOC during interglacials, but regional or local processes. However, glacial values at Site 1063 fitting those of Site 607 suggest that Nd isotope ratios represent, indeed, water mass mixing during glacial periods. The low Nd-isotope ratios in the deep Bermuda Rise during interglacials would be the result of particle-seawater exchange derived from the arrival of freshly ground, poorly weathered bedrock from the Canadian shield to the North Atlantic during major ice sheet retreats, such as deglaciations as well as stadial-to-interstadial transitions. Consequently, a deep, regionally constrained layer of seawater is tagged with this extreme Nd isotope signature that is not representative of the AMOC. We suggest that a benthic nepheloid layer, whose development is driven by a deep-recirculating gyre system regulated by the interaction between the northward flowing Gulf Stream and the southward flowing deep western boundary current, facilitates the periodical masking of the deep Atlantic Nd isotope signature at Site 1063. The intermittence of the masking allows for a speculation on how the deep-recirculating gyre system might have changed over the last ~1 Ma glacial-to-interglacial cycles.

How to cite: Jaume-Seguí, M., Kim, J., Knudson, K. P., Yehudai, M., Goldstein, S. L., Bolge, L., Ferretti, P., and Pena, L. D.: Glacial-to-interglacial variations in the deep water at the Bermuda Rise inferred from a Nd isotope record covering the last million years , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18340, https://doi.org/10.5194/egusphere-egu2020-18340, 2020.

EGU2020-5427 | Displays | CL1.8 | Highlight

Exploring the nature and timing of glacial climate transitions

Henning Bauch

The causes for major climate transitions in the Upper Pleistocene are based on the assumption that orbital forcing, i.e. the increase in northern hemisphere summer insolation (NHSI), initiates glacial ice sheets to melt away leading to the formation of warm interglacials. Good examples are plentiful available, e.g. major glacial terminations (T) such as T1, 2, or 5. Besides these major climate transitions there are also other glacial terminations across marine substage boundaries that, although seemingly of minor scale, had nevertheless massive climate impacts either globally (MIS4/3, MIS7d/7c) or regionally (MIS5b/5a). While an interglacial decrease in NHSI seems to run in parallel with early glacial inception - as can be noted for the later Holocene and MIS5e - the onset of T2 vs. T1 has long been controversially discussed with respect to its orbitally forced timing. This study therefore explores the involvement of other mechanisms. Primarily, these have to do not so much with internally produced feedback processes but are the consequence of temperature changes to be found in the low-latitudes. Transferred northward through the atmosphere and ocean these changes then feed ice sheet growth and determine its geographical configuration of different magnitudes, also eventually leading to a glacial maximum. During the past, climate transitions from a glacial into an interglacial world therefore did not start with the end of a glacial maximum. It is the time just prior to that particular maximum when the major change occurred.

How to cite: Bauch, H.: Exploring the nature and timing of glacial climate transitions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5427, https://doi.org/10.5194/egusphere-egu2020-5427, 2020.

From the combination of orbital theory with benthic δ18O it has been suggested which obliquity cycles led to interglacials during the Quaternary (e.g. Tzedakis et al., 2017). Here, we define interglacials, as deduced for the last 800 kyr (Past Interglacials Working Group of PAGES, 2016), by the absence of substantial northern hemispheric land ice outside of Greenland. When applied to land-ice distribution derived from a 3D-ice-sheet model-based deconvolution of the LR04-benthic δ18O stack into its temperature and sea-level components (de Boer et al., 2014) we find an irregular pattern of interglacials not only, as suggested so far, in the late Pleistocene but across most of the last 2.6 Myr. In the early Pleistocene eight obliquity cycles miss the onset of new interglacials, therefore increasing the average interglacial periodicity to 60 kyr. Both prolonged glacials (due to skipped terminations) and prolonged interglacials (so-called continued interglacials) are the reasons for these new irregularities. This finding adds new irregularities to the already known glacial/interglacial pattern during the last 1 Myr that include eleven obliquity cycles without new interglacials. Only in the Mid-Pleistocene in-between interglacials reappear regularly once in each obliquity cycle (every 41 kyr) with an exception around 1.1 Myr BP in which the onset of two successing interglacials is more than 100 kyr apart. This finding suggests that the notation of the Quaternary as an obliquity driven period with a growing influence of ice volume on the timing of deglaciations is too simple, or that our definition of interglacials, that seems to be suitable for the last 1.6 Myr, is not applicable to the whole Quaternary.

References:

de Boer, B., Lourens, L. J. & van de Wal, R. S. Persistent 400,000-year variability of Antarctic ice volume and the carbon cycle is revealed throughout the Plio-Pleistocene. Nature Communications 5, 2999 (2014). doi: 10.1038/ncomms3999.

Past Interglacials Working Group of PAGES. Interglacials of the last 800,000 years. Reviews of Geophysics 54, 162–219 (2016). doi: 10.1002/2015RG000482.

Tzedakis, P. C., Crucifix, M., Mitsui, T. & Wolff, E. W. A simple rule to determine which insolation cycles lead to interglacials. Nature 542, 427–432 (2017). doi: 10.1038/nature21364.

How to cite: Köhler, P. and van de Wal, R.: Land ice distribution suggests an irregular pattern of interglacials across most of the Quaternary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1340, https://doi.org/10.5194/egusphere-egu2020-1340, 2020.

EGU2020-9574 | Displays | CL1.8

The role of eccentricity in determining the spacing between interglacials

Eric Wolff, Michel Crucifix, and Chronis Tzedakis

In a recent paper Tzedakis et al (2017) described a simple rule that predicts, using only caloric summer half-year insolation as input, which insolation cycles lead to the onset of an interglacial. The rule is based on an energy threshold, one of whose characteristics is that it reduces with time since the last interglacial onset, reflecting increased fragility of glacial climate as ice sheets get larger. The rule correctly predicts every complete deglaciation of the past million years, a period in which interglacial onset skips both precession and obliquity cycle maxima. This then raises the question to what extent the approximate 100 ka period observed in the last million years is due simply to internal dynamics rather than to the period of eccentricity present in the insolation record. Here we will test this by creating synthetic insolation curves from which eccentricity (or other orbital components) have been removed.  We will then use the proposed rule to test to what extent eccentricity influences the spacing of interglacials. We will also assess the impact of other orbital components and the impact earlier in the Quaternary when the energy threshold was lower.

How to cite: Wolff, E., Crucifix, M., and Tzedakis, C.: The role of eccentricity in determining the spacing between interglacials, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9574, https://doi.org/10.5194/egusphere-egu2020-9574, 2020.

EGU2020-4227 | Displays | CL1.8 | Highlight

Glacial Termination: Going, Going, Gone

Gregor Knorr and Stephen Barker

Within the Late Pleistocene, a ‘termination’ is the name given to the rapid (~10kyr) deglacial transition marking the end of a (~100kyr) glacial cycle. These massive events involve all the critical elements of Earth’s climate system: global temperatures, precipitation patterns, ice sheet extent, ocean and atmospheric circulation systems, atmospheric composition and biological activity. Investigations into the mechanisms of glacial termination have been many and it is now thought that abrupt shifts in the ocean/atmosphere system play a ubiquitous and critical role in deglaciation. However, significant uncertainties remain concerning the timing and magnitude of deglacial changes and the likelihood that they will be interrupted by ‘terminal oscillations’ such as the Bølling-Allerød / Younger Dryas oscillation during Termination 1. In this presentation we will address these uncertainties in the light of recent developments in the understanding of glacial terminations as the ultimate expression of the interaction between millennial and orbital timescale variations in Earth’s climate. Innovations in numerical climate simulation and new geologic records that enable us to test these simulations allow us to highlight new avenues of research as well as to emphasise the importance of lingering uncertainties in key climatic parameters such as sea level variability through time.

How to cite: Knorr, G. and Barker, S.: Glacial Termination: Going, Going, Gone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4227, https://doi.org/10.5194/egusphere-egu2020-4227, 2020.

EGU2020-12928 | Displays | CL1.8 | Highlight

Reconstructions of Global and Regional Temperature Change for the Last 5 Myr

Peter U. Clark, Jeremy Shakun, Yair Rosenthal, Patrick Bartlein, Peter Koehler, and Hari Mix

We use a global array of ~120 sea-surface temperature (SST) records based on Mg/Ca, alkenone, and faunal proxies to reconstruct global and regional temperature change over the last 5 Myr. All records are placed on the LR04 age model. Here we report the reconstructions and discuss their implications for characterizing global climate evolution (frequency, variance, transitions) over this interval and its relationship to changes in CO2, orbital forcing, and mean ocean temperature. Average global temperature has cooled by ~6.5oC since 5 Ma, with significant breakpoints tentatively identified at ~3.38 Ma, 1.34 Ma, and 0.88 Ma. We also invert the global reconstruction to reconstruct global sea level for the last 5 Myr.

How to cite: Clark, P. U., Shakun, J., Rosenthal, Y., Bartlein, P., Koehler, P., and Mix, H.: Reconstructions of Global and Regional Temperature Change for the Last 5 Myr, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12928, https://doi.org/10.5194/egusphere-egu2020-12928, 2020.

EGU2020-8762 | Displays | CL1.8

Reconstructing the evolution of ice sheets, sea level and atmospheric CO2 during the past 3.6 million years

Tijn Berends, Bas de Boer, and Roderik van de Wal

Understanding the evolution of, and the interactions between, ice sheets and the global climate over geological time is important for being able to constrain earth system sensitivity. However, direct observational evidence of past CO2 concentrations only exists for the past 800,000 years. Records of benthic d18O date back millions of years, but contain signals from both land ice volume and ocean temperature. In recent years, inverse forward modelling has been developed as a method to disentangle these two signals, resulting in mutually consistent reconstructions of ice volume, temperature and CO2. We use this approach to force a hybrid ice-sheet – climate model with a benthic d18O stack, reconstructing the evolution of the ice sheets, global mean sea-level and atmospheric CO2 during the late Pliocene and the Pleistocene, from 3.6 Myr ago to the present day. The resulting reconstructions of CO2 and sea level agree well with the ice core record and different sea-level proxies, indicating that this model set-up yields useful information for colder-than-present climates. For the warmer-than-present climates of the Late Pliocene, different proxies for both CO2 and sea level are contradictory, making model validation difficult. During the early Pleistocene, 2.6 – 1.2 Myr ago, we simulate 40 kyr glacial cycles with CO2 ranging between 270 – 280 ppmv during interglacials and 210 – 240 ppmv during glacial maxima. After the Mid-Pleistocene Transition (MPT), when the glacial cycles change from 40 kyr to 80/120 kyr cyclicity, these values change to 260 to 280 ppmv during interglacials, and 180 – 200 ppmv during glacial maxima.

How to cite: Berends, T., de Boer, B., and van de Wal, R.: Reconstructing the evolution of ice sheets, sea level and atmospheric CO2 during the past 3.6 million years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8762, https://doi.org/10.5194/egusphere-egu2020-8762, 2020.

EGU2020-20914 | Displays | CL1.8

Simulations of large climate transition occurring at high and low latitudes during the late Pliocene (3.3 Ma) and the Plio/Pleistocene (3-2.5 Ma) boundary

Ning Tan, Emma Yule, Gilles Ramstein, Doris Barboni, Rani Raj, and Christophe Dumas

The late Pliocene corresponds to a large cooling over Northern Hemisphere associated with sporadic occurrences of glaciations. The most important event occurred during the marine isotope stage M2 (MIS M2, 3.312–3.264 Ma) when a large glaciation took place with a sea level drop from 20 to 60 m, but its duration is short and the summer insolation forcing change at 65°N is weak. De Schepper et al (2013) invoked to explain the onset and termination of this glaciation with the opening and closing of the Central American Seaway (shallow CAS). Based on their hypothesis, we have intensively studied the onset mechanism of  MIS M2 through a series of sensitivity experiments using the IPSL AOGCM and the asynchronous coupling with an Ice sheet model (GRISLI). Our results demonstrate that the shallow CAS helps to precondition the low-latitude oceanic circulation and affects the related northward energy transport, but cannot alone explain the onset of the M2 glaciation, the most important contribution on MIS M2 are from the large change of pCO2 as well as the internal feedbacks of vegetation and ice sheet. Moreover, we have also investigated the period from the late Pliocene to the early Pleistocene (3-2.5 Ma) through a transient-like simulation using the same AOGCM and ISM. This enables to simulate the Greenland Ice Sheet (GRIS) onset and development using the pCO2 reconstructions from different proxies. All these simulations were analyzed with emphasis on cryosphere and focused on the Northern Hemisphere (mid-to-high latitudes). Here we used the same modeling simulations but with a focus over the tropical Africa. We first depict the large changes of temperatures and hydrological cycle produced over this area during these two periods and compare our data to reconstructions. Moreover, by prescribing our climate results as inputs for the vegetation model (Biome4), we compare more directly the simulated plant functional types (PFTs) with that constructed by the pollen data. In addition, we further quantify the respective impact of various driving factors on these PFTs variations.

How to cite: Tan, N., Yule, E., Ramstein, G., Barboni, D., Raj, R., and Dumas, C.: Simulations of large climate transition occurring at high and low latitudes during the late Pliocene (3.3 Ma) and the Plio/Pleistocene (3-2.5 Ma) boundary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20914, https://doi.org/10.5194/egusphere-egu2020-20914, 2020.

EGU2020-10925 | Displays | CL1.8 | Highlight

High resolution CO2 record of the great Plio-Pleistocene glaciations using boron isotopes

Rachel Brown, Thomas Chalk, Paul Wilson, Eelco Rohling, and Gavin Foster

The intensification of Northern Hemisphere glaciation (iNHG) at 3.4-2.5 million years ago (Ma) represents the last great transition in Cenozoic climate state with the development of large scale ice sheets in the Northern Hemisphere that waxed and waned with changes in insolation. Declining atmospheric CO2 levels are widely suggested to have been the main cause of iNHG but the CO2 proxy record is too poorly resolved to provide an adequate test of this hypothesis. The boron isotope-pH proxy, in particular, has shown promise when it comes to accurately estimating past CO2 concentrations and is very good at reconstructing relative changes in CO2 on orbital timescales. Here we present a new orbitally resolved record of atmospheric CO2 (1 sample per 3 kyr) change from Integrated Ocean Drilling Program Site 999 (12.74˚N, -78.74 ˚E) spanning ~2.6–2.4 Ma based on the boron isotope (δ11B) composition of planktic foraminiferal calcite, Globingerinoides ruber (senso stricto, white).  We find that δ11B values of G. ruber show clear glacial-interglacial cycles with a magnitude that is similar to those of the Mid-Pleistocene at the same site and elsewhere.  This new high-resolution view of CO2 during the first large glacial events of the Pleistocene confirms the importance of CO2 in amplifying orbital forcing of climate and offers new insights into the mechanistic drivers of natural CO2 change. 

How to cite: Brown, R., Chalk, T., Wilson, P., Rohling, E., and Foster, G.: High resolution CO2 record of the great Plio-Pleistocene glaciations using boron isotopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10925, https://doi.org/10.5194/egusphere-egu2020-10925, 2020.

EGU2020-14645 | Displays | CL1.8

Reconstruction of environmental and climatic change during the late Pliocene and early Pleistocene in northwestern North America based on a new drill core from paleo-Lake Idaho

Frederik Allstädt, Andreas Koutsodendris, Erwin Appel, Wolfgang Rösler, Alexander Prokopenko, Tammo Reichgelt, and Jörg Pross

The Pliocene to early Pleistocene yields a close analogy to near-future climate, with atmospheric pCO2 between pre-industrial and anthropogenically perturbed levels as they may be reached in few decades. A sedimentary archive that is well suited to study Plio-Pleistocene climate dynamics in the terrestrial realm has recently become available through the ICDP-sponsored HOTSPOT project on the evolution of the Snake River Plain (Idaho, USA). At the Mountain Home site, HOTSPOT drilling has yielded the MHAFB11 core that comprises 635 m of fine-grained lacustrine sediments (Shervais et al. 2013). Based on the yet available paleomagnetic age control, these sediments span from the late Pliocene to the early Pleistocene, which makes them the first archive in continental North America that covers this time interval at one site. Based on their geographic position, the sediments from paleo-Lake Idaho can contribute to a better understanding of climate variability across the Plio-Pleistocene transition in western North America, notably with respect to the hypothesis that enhanced moisture transport into the higher latitudes of North America from ~2.7 Ma onwards allowed the initiation of Northern Hemisphere glaciation (Haug et al., 2005).

To gain insight into the paleoclimatic evolution of northwestern North America during the late Pliocene to early Pleistocene, we have palynologically analyzed 131 samples from the 732–439 m depth interval (corresponding to an age of ~2.8 to ~2 Ma) of the MHAFB11 core. The obtained palynological dataset, which has a mean temporal resolution of ~7 ka, documents that a Pinus-dominated coniferous forest biome prevailed in the catchment area of paleo-Lake Idaho throughout the study interval. However, percentages of pollen from conifer taxa decrease in the latest Pliocene before reaching consistently lower values in the early Pleistocene at ~2.4 Ma. In contrast, pollen taxa representing an open vegetation (e.g., Artemisia, Asteraceae) and deciduous trees (e.g., Quercus, Betula and Alnus) become increasingly abundant in the early Pleistocene (at ~2.4 Ma). We interpret this vegetation shift to an open mixed conifer/deciduous forest to be caused by wetter climate conditions. This interpretation is supported by quantitative climate estimates, which show a gradual increase in mean annual precipitation in the early Pleistocene. This trend towards wetter conditions supports the notion that enhanced moisture transport to northern North America from the subarctic Pacific Ocean contributed to the onset of Northern Hemisphere glaciation at ~2.7 Ma (Haug et al., 2005).

 

References:

Haug, G.H., Ganopolski, A., Sigman, D.M., Rosell-Mele, A., Swann, G.E., Tiedemann, R., Jaccard, S.L., Bollmann, J., Maslin, M.A., Leng, M.J. and Eglinton, G., 2005. North Pacific seasonality and the glaciation of North America 2.7 million years ago. Nature, 433, 821-825.

Shervais, J.W., Schmitt, D.R., Nielson, D., Evans, J.P., Christiansen, E.H., Morgan, L.A., Shanks, P. W.C., Prokopenko, A.A., Lachmar, T., Liberty, L.M., Blackwell, D.D., Glen, J.M., Champion, D., Potter, K.E., Kessler, J., 2013. First Results from HOTSPOT: The Snake River Plain Scientific Drilling Project, Idaho, U.S.A. Scientific Drilling, 3, 36-45.

 

How to cite: Allstädt, F., Koutsodendris, A., Appel, E., Rösler, W., Prokopenko, A., Reichgelt, T., and Pross, J.: Reconstruction of environmental and climatic change during the late Pliocene and early Pleistocene in northwestern North America based on a new drill core from paleo-Lake Idaho , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14645, https://doi.org/10.5194/egusphere-egu2020-14645, 2020.

EGU2020-9940 | Displays | CL1.8

A Simple Model for Glacial Cycles and Impact of fossil fuel CO2 emissions

Stefanie Talento and Andrey Ganopolski

We propose a simple physically-based model of the coupled evolution of Northern Hemisphere (NH) landmass ice-volume, atmospheric CO2 concentration and global mean temperature. The model only external forcings are the orbital forcing (maximum solar insolation at 65°N) and anthropogenic CO2 emissions. The model consist of a system of 3 coupled non-linear differential equations, representing physical mechanisms relevant for the evolution of the climate system in time-scales longer than thousands of years.

 

When forced by the orbital forcing only, the model is successful in reproducing the natural glacial-interglacial cycles of the last 800kyr, in agreement with paleorecords and simulations performed with the CLIMBER-2 Earth System Model of intermediate complexity. The model is successful in reproducing both the timing and amplitude of the glacial-interglacial variations, producing a correlation with paleodata of 0.75 in terms of NH ice-volume.

 

For the next million years, we analyse the model results under different scenarios: the natural scenario (in which only orbital forcing is applied) and scenarios in which various magnitudes of fossil fuel CO2 emissions are considered (in addition to the orbital forcing).

 

When anthropogenic emissions are included the model shows that even fairly low CO2 anthropogenic emissions (100 Pg or larger) are capable of affecting the next glacial inception, expected to occur in 120kyr from now, delaying large NH ice formation by 50kyr. Considering total carbon releases ranging between 1000 and 5000 Pg (a reasonable expectation of fossil fuel CO2 emissions to occur in the next few hundred years) the temporal evolution of the climate system could be significantly different from the natural progression. Emissions larger than 3000 Pg could have long-lasting effects, being natural conditions not resumed even after 1 Million years have passed. In addition, emissions larger than 4000 Pg prevent glacial cycles in the next half million years.

How to cite: Talento, S. and Ganopolski, A.: A Simple Model for Glacial Cycles and Impact of fossil fuel CO2 emissions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9940, https://doi.org/10.5194/egusphere-egu2020-9940, 2020.

EGU2020-11682 | Displays | CL1.8

Orbital CO2 cycles and the Mid-Pleistocene Transition

Thomas Chalk, Mathis Hain, Gavin Foster, Sophie Nuber, Eelco Rohling, Stephen Barker, Soraya Cherry, and Paul Wilson

Over the past 1.5 million years, Earth’s climate has shifted from a predominantly 41 thousand year (kyr) dominated climate cycle to one dominated by longer and larger glacial-interglacial cycles, known as the Mid-Pleistocene Transition (MPT). The MPT occurs over a period of several hundreds of thousands of years, with little change to Earth’s external orbital forcing, thus implicating internal climate feedbacks. Here we interrogate the current capacity, and future potential, of boron isotope records to provide high quality carbon cycle information for the Pleistocene. We also present a compilation of boron isotope-derived pH-CO2 records from low-latitude ocean drill cores which closely follow the evolution of atmospheric CO2 over the ice core interval but extend it to 1.5 million years ago with a resolution of up to ~1 sample per 3 kyr. This new, near continuous δ11B-derived CO2 record is compared against other independent CO2 data from blue-ice cores and records of ocean and climate change., This confirms there is a decline in mean CO2 across the MPT which manifests as a lengthening and deepening of glacial CO2, and highlights the distinct difference in the nature of CO2 cycles in the 41-kyr world.

 

How to cite: Chalk, T., Hain, M., Foster, G., Nuber, S., Rohling, E., Barker, S., Cherry, S., and Wilson, P.: Orbital CO2 cycles and the Mid-Pleistocene Transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11682, https://doi.org/10.5194/egusphere-egu2020-11682, 2020.

The Mid-Pleistocene Transition (MPT, ~1.3-0.7 Ma) is one of the most drastic climatic transition in the recent climatic history of our planet. During this transition, glacial-interglacial variability shifted from 41- to 100-ka cycles, without notable changes in the orbital forcing. Internal forcing mechanisms in Earth’s climate likely shifted the system towards particularly more extreme glacial periods. A decrease in the atmospheric CO₂ contemporary to a severe weakening of the Atlantic deep-ocean circulation around 900 ky suggests that weakened deep-ocean circulation facilitated the capture of CO₂ into the deep ocean and thus contributed to the switch towards more intense and longer glacial periods.

 

ODP Site 668B, in the deep eastern equatorial Atlantic, has been previously used to reconstruct the atmospheric CO₂ evolution across the MPT using boron isotopes in surface dwelling foraminifera. Here we present new high resolution proxies from the same site covering the last 2 Ma. In particular, benthic foraminifera stable isotopes and trace elements (B/Ca, Mg/Ca, Cd/Ca), as well as Nd isotope data (εNd) from Fe-Mn encrusted foraminifera shells. Using the newly improved chronology based on benthic foraminifera stable isotopes we show that our new εNd data covaries substantially with the atmospheric pCO₂ data and shows a glacial-interglacial variability through the entire record, with εNd values matching typical glacial-interglacial range values in the North-Atlantic basin (~-11 to ~-14). Between ~1 to 2 Ma, when the 41-ka-cycles were dominant, εNd data also covaries with carbonate ion saturation index (ΔCO₃²-) as derived from the new B/Ca data, Bottom Water Temperatures (BWT, Mg/Ca) and, with deep ocean nutrient content (phosphate derived from Cd/Ca). Results indicate a higher fraction of warmer, less corrosive and nutrient-poor northern-sourced waters (higher BWT, higher ΔCO32-, lower Cd/Ca, lower εNd) reaching the deep-equatorial Atlantic during interglacial periods compared to glacial periods. Interestingly, this covariation does not stand after ~0.9Ma. Even though εNd and BWT data suggest an increased contribution of southern-sourced waters to the site during glacial periods after 0.9Ma, as shown by a gradual decrease in glacial BWT (>1°C) and increasing glacial εNd values (~1ε units), both B/Ca and Cd/Ca show a distinctive low frequency variability superimposed to the glacial-interglacial variability. These oscillations can be interpreted as infiltrations and/or overflows of southern-sourced waters across the mid-ocean ridge into the SE Atlantic basin that do not completely follow glacial-interglacial periodicity. We propose that bathymetrical constrains exert a control on the chemistry of the deep waters in the deep eastern equatorial Atlantic with potential impacts on global climate. Partially isolated sub-basins such as the SE Atlantic could have effectively acted as carbon reservoirs over longer time scales than glacial-interglacial changes.

How to cite: Pena, L. D. and Jaume-Seguí, M.: Deep water mass geometry in the south east Atlantic across the Mid-Pleistocene Transition: bathimetric vs oceanographic controls , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13196, https://doi.org/10.5194/egusphere-egu2020-13196, 2020.

EGU2020-19225 | Displays | CL1.8

Are Cryosphere-Driven Feedbacks a Requisite for Abrupt Climate Events?

Dakota Holmes and Audrey Morley

Abrupt climate events are generally believed to be characteristic of glacial (intermediate-to-large cryosphere) climate states, requiring either sizeable ice-sheets or large freshwater pulses to act as triggers for abrupt climate changes to occur. Amplification occurs when these triggers bear upon the Atlantic Meridional Overturning Circulation (AMOC). However, the focus on glacial climate states in abrupt climate change research has led to an underrepresentation of research into interglacial periods. It thus remains unclear whether high-magnitude climate variability requires large cryosphere-driven feedbacks or whether it can also occur under low ice conditions. Here we present a high resolution analysis of surface and deep water components of the AMOC spanning the transition from Marine Isotope Stage (MIS) 19c to 19a to test if orbital boundary conditions similar to our current Holocene can accommodate abrupt climate events. Sediment core DSDP 610B (53°13.297N, 18°53.213W), located approximately 700-km west of Ireland, was specifically chosen due to its high sedimentation rate during interglacial periods, excellent core recovery over the Quaternary and its unique geographical location. Above the core site, the dominant oceanographic feature is the North Atlantic Current and at 2417-m water depth, 610B is influenced by Wyville Thomson Overflow Water flowing southwards. A multiproxy approach including paired grain size analysis, planktic foraminifer assemblage counts, and ice-rafted debris counts within the same samples allows us to resolve the timing between both surface and bottom components of the AMOC and their response to abrupt climate events during MIS-19 in the eastern subpolar gyre. This study is societally relevant as future freshwater inputs from a melting Greenland ice sheet may impact ocean circulation, potentially causing shifts in climate for many European countries.

How to cite: Holmes, D. and Morley, A.: Are Cryosphere-Driven Feedbacks a Requisite for Abrupt Climate Events?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19225, https://doi.org/10.5194/egusphere-egu2020-19225, 2020.

EGU2020-19780 | Displays | CL1.8 | Highlight

The role of obliquity forcing on the interglacial climate instabilities in the mid-latitudes of the North Atlantic

Teresa Rodrigues, Xu Zeng, Mária Padilha, Dulce Oliveira, Joan O. Grimalt, and Fátima Abrantes

Anthropogenic CO2 release into the atmosphere leads to temperature projections for 2100 only experienced on Earth since many million years. However, those periods are poorly known due to low temporal and spatial data and ill-defined climate forcings. However past warm periods (interglacials), occurring during the Quaternary, under variable boundary conditions (e.g. greenhouse gases concentration, sea level and ice sheets size, insolation and orbital forcing), can provide invaluable information on the dynamics and processes behind natural warm climates. Here we present records for the sea surface temperature based in Uk’37-SST at orbital and millennial-scale over the last 1.25 Ma, with special focus on the past interglacials of two SW Iberian margin sedimentary sequences recovered during IODP Expedition 339,  Sites U1385 (37°34.285′N, 10°7.562′W;  2589m) and U1391 (37°21.5322′N, 9°24.6558′W; 991m). We also performed a data-model comparison to explore the dynamics related with the role of obliquity on the Atlantic Meridional Overturning Circulation (AMOC) changes. Our data  show that Interglacials are characterized by an interval of maximum warmth followed by a temperature decline punctuated by millennial-scale SST oscillations. In most cases the first stadial marks the beginning of a glacial inception that is characterized by an abrupt SST decrease, followed by high frequency SST oscillations, and large amounts of freshwater input. This suggests a climatic change from interglacial to glacial conditions linked to the start of ice sheets growth (enrichment of d18O) and the AMOC slowdown resulting in an enhanced cooling of the mid-latitudes.

How to cite: Rodrigues, T., Zeng, X., Padilha, M., Oliveira, D., O. Grimalt, J., and Abrantes, F.: The role of obliquity forcing on the interglacial climate instabilities in the mid-latitudes of the North Atlantic , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19780, https://doi.org/10.5194/egusphere-egu2020-19780, 2020.

EGU2020-21063 | Displays | CL1.8

Was the Atlantic a predominantly Polar Ocean during the last glacial?

Marleen Lausecker, Freya Hemsing, Thomas Krengel, Julius Förstel, Andrea Schröder-Ritzrau, Evan Border, Covadonga Orejas, Jürgen Titschack, Claudia Wienberg, Dierk Hebbeln, Anne-Marie Wefing, Paolo Montagna, Eric Douville, Lelia Matos, Jacek Raddatz, and Norbert Frank

The Last Glacial Maximum (LGM) is marked by significant cooling of the global ocean, which was recently estimated to 2.6°C using noble gases trapped in ice cores (1). This cooling is not equally distributed throughout the world oceans, since global ocean circulation models predict regional temperature anomalies during the LGM of up to 7°C (annually and zonally averaged) when compared to modern interior ocean temperature (2). The oceans deep interior thus became haline stratified (3) due to the drop in temperature to near freezing and the global increase in salinity from ice sheet growth. In contrast to a deepening of the modern thermocline as a result of anthropogenic global warming, cooling causes the thermocline to rise in the sub-tropics as more polar waters enter the mid-depth ocean.

Here we present glacial thermocline temperature reconstructions since the LGM based on the Li/Mg ratio in aragonite skeletons of precisely dated cold-water corals. Corals have been collected from 300-1000m water depths from sites in the northern and southern Atlantic (62°N to 25°S) and demonstrate synchronous 5 - 7°C glacial cooling, and a dramatic shoaling of the thermocline. Through the deglaciation the warming of the upper thermocline ocean occurs early in the southern hemisphere followed by fluctuating warming and thermocline deepening in the northern Hemisphere, which supports the oceanic climate seesaw proposed by Stocker and Johnson in 2003 (4). We thus propose dramatic changes in export of polar waters towards the Equator and augmented subsurface ocean stratification leading to a mostly polar Atlantic with a shallow permanent thermocline. This shoaling possibly increased the rate of nutrient recycling causing higher biological surface ocean activity and the cooling promoted carbon storage. During the glacial, we assume an atmospheric forcing, such as equatorward displacement of the Hadley circulation, to steer the glacial polar water advance as mid-depth boundary currents in the northern and southern hemisphere to effectively spread the cold water through the entire mid-depth Atlantic.

References:

  1. Bereiter et al.: Mean global ocean temperatures during the last glacial transition. Nature 553, 39-44 (2018).
  2. Ballarotta et al.: Last Glacial Maximum world ocean simulations at eddy-permitting and coarse resolutions: do eddies contribute to a better consistency between models and palaeoproxies?, Clim. Past 9, 2669-2686 (2013).
  3. Adkins et al.: The Salinity, Temperature, and d18O of the Glacial Deep Ocean. Science 298, 1769-1773 (2002).
  4. Stocker and Johnsen: A minimum thermodynamic model for the bipolar seesaw, Paleoceanography 18, 1087 (2003).

How to cite: Lausecker, M., Hemsing, F., Krengel, T., Förstel, J., Schröder-Ritzrau, A., Border, E., Orejas, C., Titschack, J., Wienberg, C., Hebbeln, D., Wefing, A.-M., Montagna, P., Douville, E., Matos, L., Raddatz, J., and Frank, N.: Was the Atlantic a predominantly Polar Ocean during the last glacial?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21063, https://doi.org/10.5194/egusphere-egu2020-21063, 2020.

EGU2020-2844 | Displays | CL1.8 | Highlight

Centennial-scale evolution of methane during the penultimate deglaciation

Loïc Schmidely, Lucas Silva, Christoph Nehrbass-Ahles, Juhyeong Han, Jinhwa Shin, Jochen Schmitt, Hubertus Fischer, and Thomas Stocker

Small air inclusions in ice cores represent a direct archive of past atmospheric compositions, allowing us to measure the concentration of the three most potent non-condensable Greenhouse Gases (GHG) CO2, CH4 and N2O as far back as 800,000 years before present (kyr BP). These records demonstrate that transitions from glacial to interglacial conditions are accompanied by a substantial net increase of CO2, CH4 and N2O in the atmosphere (Lüthi et al. 2008, Loulergue et al. 2008, Schilt et al. 2010). A sound understanding of the interplay between the reorganization of the climate system and the perturbation of GHG inventories during glacial terminations is partly limited by the temporal resolution of the records derived from ice cores. In fact, with the exception of the last deglaciation (23-9 kyr BP) centennial-scale GHG variability remained uncaptured for precedings glacial terminations.

In this work, we exploit the exceptionally long temporal coverage of the EPICA Dome C (EDC) ice core to reconstruct, for the first time, centennial-scale fluctuations of CH4 mole fractions from 145 to 125 kyr BP, encompassing the entire penultimate deglaciation (138-128 kyr BP). With a temporal resolution of ~100 years, our new record is now unveiling all climate-driven signals enclosed into the EDC ice core, exploiting the maximum resolution possible at Dome C (). This offers us the opportunity to study the timing and rates of change of CH4 in unprecedented details.

Preliminary analysis reveals that the deglacial CH4 rise is a superimposition of gradual millennial-scale increases (~0.01-0.02 ppb/year) and abrupt and partly intermittent centennial-scale events (~80-200 ppb in less than a millennium). We will investigate processes modulating the observed changes in the CH4 cycle, compare the structure of our record with the CH4 profile of the last deglaciation (Marcott, 2014) and contrast it with the EDC CO2 and N2O records over the penultimate glacial termination now available in similar resolution.

How to cite: Schmidely, L., Silva, L., Nehrbass-Ahles, C., Han, J., Shin, J., Schmitt, J., Fischer, H., and Stocker, T.: Centennial-scale evolution of methane during the penultimate deglaciation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2844, https://doi.org/10.5194/egusphere-egu2020-2844, 2020.

EGU2020-10253 | Displays | CL1.8

Primary productivity dynamics in the northeastern Bay of Bengal over the last 26,000 years

Xinquan Zhou, Stéphanie Duchamp-Alphonse, Masa Kageyama, Franck Bassinot, Luc Beaufort, and Christophe Colin

Paleo-records of primary productivity (PP) changes from the Arabian Sea (AS) have revealed the major influence of monsoon-wind intensity in controlling productivity variations at different timescales, through mixed-layer dynamics and upwelling activity. Much less is known, however, about past changes in paleo-PP in the Bay of Bengal (BoB).

       In the present study, we have reconstructed PP over the last 26,000 years from a sediment core located on the northeastern (NE-) BoB. Paleo-PP was estimated by a PP empirical equation using the relative abundance of Florisphaera profunda, a deep dwelling coccolithophore that develops in the lower euphotic zone. Our record does not reveal any obvious difference of PP between the Last Glacial Maximum (LGM) and the late Holocene, but strong oscillations characterize the deglaciation. Our NE-BoB record is anti-phased to PP records in the AS, and positively correlated to surface seawater salinity (SSS) changes reconstructed from the same core since the LGM. We propose that the strong correlation to salinity variations reflects the role of salinity-stratification related to monsoon precipitation on PP at both orbital- and millennial-scales. Outputs of a climatic transient simulation (TraCE-21) and runs obtained with the Earth System Model IPSL-CM5 support the above interpretation of a strong control of past PP variations by local hydrological changes in the NE-BoB. Our data also highlight the potential teleconnection of the Atlantic Meridional Overturning Circulation strength and Indian Monsoon intensity during the deglaciation.

How to cite: Zhou, X., Duchamp-Alphonse, S., Kageyama, M., Bassinot, F., Beaufort, L., and Colin, C.: Primary productivity dynamics in the northeastern Bay of Bengal over the last 26,000 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10253, https://doi.org/10.5194/egusphere-egu2020-10253, 2020.

EGU2020-17440 | Displays | CL1.8

Millennial-scale oceanic CO2 release during marine isotope stage 3

Rachael Shuttleworth, Helen Bostock, and Gavin Foster

During the last glacial period atmospheric CO2 and temperature in Antarctica varied together on millennial timescales, with CO2 abruptly increasing by 10-20 ppm in <1000 years in some cases. The exact causes of these rapid CO2 changes during a cold glacial climate remain unclear. Here we examine the role of ocean carbon storage and atmospheric exchange by applying the boron isotope-pH (CO2) proxy to Globigerina bulloides from core site TAN110628 located in the Pacific Sector of the Southern Ocean.  By reconstructing the surface carbonate system at TAN110628 at high temporal resolution (1 sample every 1 kyr) from 30 to 64 kyr we are able to fully constrain the nature of carbon leakage from the Sub Antarctic Zone of the Southern Pacific Ocean associated with these millennial-scale changes in atmospheric CO2.  This provides unique insights into the causes of abrupt changes in atmospheric CO2 during Marine Isotope Stage 3 and the last termination. 

How to cite: Shuttleworth, R., Bostock, H., and Foster, G.: Millennial-scale oceanic CO2 release during marine isotope stage 3, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17440, https://doi.org/10.5194/egusphere-egu2020-17440, 2020.

EGU2020-20750 | Displays | CL1.8

Deep water circulation patterns in the Atlantic during MISs 12-11

Jasmin M. Link and Norbert Frank

Glacial Termination V is one of the most extreme glacial-interglacial transitions of the past 800 ka [1]. However, the changes in orbital forcing from Marine Isotope Stage (MIS) 12 to 11 are comparatively weak. In addition, MIS 11c is exceptionally distinct compared to other interglacials with for example a longer duration [2] and a higher-than-present sea level [3] despite a relative low incoming insolation. Therefore, the term “MIS 11 paradox” was coined [4]. However, only little is known about the Atlantic overturning circulation during this time interval [e.g. 5,6].

Here, we present Atlantic-wide deep water circulation patterns spanning the glacial maximum of MIS 12, Termination V, and MIS 11. Therefore, sediment cores throughout the Atlantic were analyzed regarding their Nd isotopic composition of authigenic coatings to reconstruct the provenance of the prevailing bottom water masses.

During the glacial maximum of MIS 12, the deep Atlantic Ocean was bathed with a higher amount of southern sourced water compared to the following interglacial. Termination V is represented by a sharp transition in the high-accumulating sites from the North Atlantic with a switch to northern sourced water masses. MIS 11 is characterized through an active deep water formation in the North Atlantic with active overflows from the Nordic Seas, only disrupted by a short deterioration. A strong export of northern sourced water masses to the South Atlantic points to an overall strong overturning circulation.

 

[1] Lang and Wolff 2011, Climate of the Past 7: 361-380.

[2] Candy et al. 2014, Earth-Science Reviews 128: 18-51.

[3] Dutton et al. 2015, Science 349: aaa4019.

[4] Berger and Wefer 2003, Geophysical Monograph 137: 41-60.

[5] Dickson et al. 2009, Nature Geoscience 2: 428-433.

[6] Vázquez Riveiros et al. 2013, EPSL 371-372: 258-268.

How to cite: Link, J. M. and Frank, N.: Deep water circulation patterns in the Atlantic during MISs 12-11, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20750, https://doi.org/10.5194/egusphere-egu2020-20750, 2020.

Antarctic ice core and deep ocean sediment core records imply that the interglacial climate during Marine Isotope Stage 13 (MIS 13) was relatively cold, and ice sheets were likely larger than today. We model the MIS 13 climate with a coupled climate-ice sheet model AWI-ESM1.2-LR under different orbital configurations at 495, 506 and 517 kyr BP. Summer insolation at 65 °N at 495 kyr BP is similar to the preindustrial, but the lower greenhouse gas values lead to an ice sheet buildup relative to today. Boreal summer at perihelion at 506 kyr BP causes a warmer summer over Northern Hemisphere continents, inhibiting the development of Northern Hemisphere ice sheets. Lower obliquity induces cooling over the polar regions and is favorable for the ice sheet buildup. Aside from the polar regions, mountains with high elevation also have favorable conditions for ice sheet buildup. The Cordilleran Ice Sheet is more sensitive and has a faster response to boreal summer insolation change than the other large scale Northern Hemisphere ice sheets. This indicates that different ice sheets might have different development processes. In addition, ice sheets do not build up over northeastern North America and Eurasia in our simulations. In our final set of simulations, we address the multi-stability of the ice sheets which could be a reason for causing this phenomenon.

How to cite: Niu, L., Gierz, P., J. Gowan, E., and Lohmann, G.: The influence of orbital configurations on Northern Hemisphere ice sheet evolution during MIS 13 with a coupled climate-ice sheet model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9156, https://doi.org/10.5194/egusphere-egu2020-9156, 2020.

CL1.9 – Orbital forcing, tectonics and global climate change

EGU2020-158 | Displays | CL1.9 | Highlight

Astronomically paced climate changes during the demise of the penultimate icehouse

Qiang Fang and Huaichun Wu

Late Paleozoic deglaciation is the only deep-time analogue of an icehouse-to-greenhouse transition in a vegetated world, but the detailed processes of this climatic upheaval are still under debate due to the absence of higher precision and accuracy in global correlations. The astronomical calibration of sedimentary cycles (3–4 m) in a carbonate succession from Naqing in South China to the 405 kyr eccentricity cycle reveals short eccentricity (135 kyr and 96.1 kyr), main obliquity (31.6 kyr), and precession (21.5 kyr and 19.3 kyr) for the early Cisuralian (Early Permian). 405-kyr-eccentricity-forced teleconnections are established between Paleo-Tethyan deep-marine carbonate cyclicity and U-Pb zircon ages-calibrated cyclothems from Euramerica in the Pangean paleotropics, providing a refined chronostratigraphy for the Asselian and Sakmarian stages on global scale. Geological record indicates a (s4s3) − (g4g3) resonance likely transited into (s4s3) − 2(g4g3) resonance at ~296.8 Ma, which confirms the chaotic dynamical behaviour of the Solar System during the Cisuralian. The synchronized proxies from marine records (magnetic susceptibility, gamma ray, carbon and oxygen isotope) and terrestrial climate indicators (paleosols, evaporates and tillites) across continents and latitudes demonstrate that long-term glacial, glacioeustatic, and climatic events were in pace with eccentricity and obliquity modulation cycles superimposed on secular global warming, reinforcing solid linkage between climate changes at low and high latitudes regardless of the ice sheet volume. Quasi-periodic alignments of the maxima (minima) of eccentricity and obliquity amplitude decelerated (accelerated) the trajectory of the CO2-forced deglaciation. Intermittent nondeposition of the Cisuralian cyclothems on the North American Midcontinent correspond to the enhanced none-astronomical-related noise in the sedimentary record from South China, both of which were likely attributed to weaker or less apparent influence of astronomical forcing on the climate changes without an ice-sheet amplifier. Our study provides a better temporal resolution and understanding of the late Paleozoic deglaciation.

How to cite: Fang, Q. and Wu, H.: Astronomically paced climate changes during the demise of the penultimate icehouse, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-158, https://doi.org/10.5194/egusphere-egu2020-158, 2020.

EGU2020-5383 | Displays | CL1.9 | Highlight

Orbital pacing of large fluctuations in wildfire activity during the Pliensbachian

Teuntje Hollaar, Sarah Baker, Jean-Francois Deconinck, Luke Mander, Micha Ruhl, Stephen Hesselbo, and Claire Belcher

At present Earth’s climate is warming and the frequency of large wildfires appears to be increasing (Westerling and Bryant, 2008). Long term trends in climate and the effect on wildfire are understudied and examining the geological record can aid current understanding of natural variability of wildfire over longer time scales. The Early Jurassic is a period of overall global warmth, and therefore serves as a suitable modern-day analogue to understand changes in the Earth System. The Early Jurassic was characterized by major climatic and environmental perturbations which can be seen preserved at high resolution on orbital timescales. Recent research has indicated from Quaternary deposits that wildfires respond to orbital forcings (Daniau et al., 2013). This study tests whether wildfire activity corresponds to changes over Milankovitch timescales in the deep past.

        A high-resolution astrochronology exists for the Upper Pliensbachian in the Llanbedr (Mochras Farm) borehole (NW Wales). Ruhl et al. (2016) show that elemental concentration recorded by hand-held X-ray fluorescence (XRF), changes mainly at periodicities of ~21,000 year, ~100,000 year and ~400,000 year, and which can be related to visually described sedimentary bundles.

        We have quantified the abundance of fossil charcoal at a high resolution (10-15 cm) to test the hypothesis that these well-preserved climatic cycles influenced fire activity throughout this globally warm period. Our results suggest that variations in charcoal abundance are coupled to Milankovitch forcings over periods of ~21,000 and ~400,000 years. Supplementary to the charcoal record, a high-resolution clay minerology dataset has been generated, which indicates the presence of the 400ky cycle. Decreased hydrology on land, corresponds to increased charcoal production. We suggest that these changes in fire relate to changes in seasonality and monsoonal activity that drove changes in vegetation that are linked to variations in the orbital forcing.

How to cite: Hollaar, T., Baker, S., Deconinck, J.-F., Mander, L., Ruhl, M., Hesselbo, S., and Belcher, C.: Orbital pacing of large fluctuations in wildfire activity during the Pliensbachian, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5383, https://doi.org/10.5194/egusphere-egu2020-5383, 2020.

EGU2020-2209 | Displays | CL1.9

Pliocene ocean and climate dynamics in the eastern Indian Ocean and their implications for the global climate state.

David De Vleeschouwer, Angelina Füllberg, Rebecca Smith, Gerald Auer, Benjamin Petrick, Isla Castañeda, and Beth Christensen

The Indonesian Throughflow (ITF) operates as an important link in global thermohaline circulation and is often considered a modulator of global past climate changes, with effects as far as Africa or the Atlantic Ocean. Yet, to what extent ITF variability accounted for oceanographic change along the west Australian coast remains controversial. A tectonically reduced ITF has been invoked to explain the short, but intense Pliocene glaciation Marine Isotope Stage (MIS) M2 (3.3 Ma). The hypothesis hinges on a reduced equator-to-pole heat transfer in the Indian Ocean, in response to low connectivity with the Indo-Pacific warm pool. To clarify links between regional oceanographic change and global climate, we present a two-site multiproxy reconstruction from the Perth (U1459) and the Carnarvon (U1463) Basin. These sites provide the opportunity to unravel the Pliocene history of the Leeuwin Current (LC). We use the LC as a proxy for ITF connectivity, as the ITF is the source for the warm, low-salinity, nutrient-deficient LC. A U1459-U1463 comparison thus allows for investigating the possible relationship between mid-Pliocene glaciations and ITF heat flux. We show that the LC was active throughout the Pliocene, albeit with fluctuations in intensity and scope. We identify three main factors that controlled LC strength. First, a tectonic ITF reorganization caused an abrupt and permanent LC reduction at 3.7 Ma, coeval with the remarkably intense Pliocene glacial MIS Gi4. On shorter timescales, eustatic sea level and direct orbital forcing of wind patterns hampered or promoted the LC. At 3.3 Ma, LC intensity plunged in response to a eustatic ITF restriction. MIS M2 caused the latitudinal U1463–U1459 planktonic oxygen isotope gradient to steepen from 1.2 to 2.0‰ and the TEX86 sea surface temperatures gradient to increase from 3 to 6°C. Yet, comparison with Exmouth Plateau Site 763 shows that the LC did not shut down completely during MIS M2: The ITF heat flux dwindled but did not cease. Weakened ITF connectivity led to a significant drop in Indian Ocean poleward heat transport and thus constitutes a positive feedback mechanism that contributed to the relative intensity of MIS M2 and the thermal isolation of Antarctica. This positive feedback mechanism is ultimately driven by orbital-scale changes in relative sea level in the ITF region.

How to cite: De Vleeschouwer, D., Füllberg, A., Smith, R., Auer, G., Petrick, B., Castañeda, I., and Christensen, B.: Pliocene ocean and climate dynamics in the eastern Indian Ocean and their implications for the global climate state., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2209, https://doi.org/10.5194/egusphere-egu2020-2209, 2020.

EGU2020-19313 | Displays | CL1.9

Are models becoming more sensitive to Pliocene boundary conditions?

Alan Haywood and Julia Tindall

The nature and dynamics of Pliocene climate has been a focus of intense study for many years. This is because the Pliocene has a unique potential to inform science/society about how the Earth system responds to forcing of direct relevance to future climate change. We examine large-scale climate features derived from the second phase of the Pliocene Model Intercomparison Project. PlioMIP2 is composed of simulations derived from sixteen coupled atmosphere-ocean and Earth System Models of a variety of vintages (IPCC AR3/4 to 6). This represents one of the largest ensembles of models ever assembled to represent a particular interval in Earth history. Each model has been set up to include the very latest Pliocene boundary conditions provided by the U.S. Geological Survey Pliocene Research Interpretation and Synoptic Mapping Project (PRISM4). As well as examining large-scale features of the PlioMIP2 model ensemble we further examine trends in model sensitivity versus model age in order to ascertain if newer versions of models are becoming more sensitive to Pliocene boundary conditions. We examine this across the PlioMIP2 ensemble as a whole and within individual model families, and examine what this implies in terms of the potential for individual models, or families of models, to represent patterns of surface temperature change reconstructed from geological proxies.

How to cite: Haywood, A. and Tindall, J.: Are models becoming more sensitive to Pliocene boundary conditions?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19313, https://doi.org/10.5194/egusphere-egu2020-19313, 2020.

EGU2020-5897 | Displays | CL1.9

Reconstructing the intensity and location of Northern Hemisphere westerlies during the Plio-Pleistocene using marine sediments

Jordan T. Abell, Gisela Winckler, Robert F. Anderson, and Timothy Herbert

The warm Pliocene serves as an analogue for predicted warming over the next century. However, large uncertainties exist for atmospheric circulation and land surface conditions during the Pliocene. Dust transported by wind to locations of accumulation (terrestrial or marine) can provide a record of wind intensity and/or direction. Few dust flux records spanning the Plio-Pleistocene exist. As such, there is ample opportunity to use marine sediments to reconstruct changes in atmospheric conditions during a warmer-than-present world, as well as across the onset/intensification of Northern Hemisphere Glaciation (NHG). During this time, East Asia’s interior, the second largest source of mineral dust today, experienced aridification, occurring alongside a major reorganization of the subarctic North Pacific circulation which led to stratification of the surface ocean. Here, we present two North Pacific marine sediment records of extraterrestrial (ET) 3He-derived terrigenous dust flux proxies (4HeTerr and Th), along with a record of multiple paleoproductivity proxies (Baxs, Opal, and C37Total) for the period spanning ~2.5-4.5 Ma. Our results show that dust flux to the western North Pacific was relatively low and constant through the Pliocene up until ~2.7 Ma, with minor peaks during cooler phases from ~2.9-3.1 Ma. At ~2.7 Ma, concurrent with the intensification of NHG and formation of a permanent halocline cap in the subarctic North Pacific, dust fluxes increase dramatically. The central North Pacific record shows a less drastic shift in dust, but generally displays higher fluxes after ~3 Ma. Dust fluxes in East Asia and the North Pacific are consistent during this time interval, as are global dust fluxes from the North Atlantic, South Atlantic and North Pacific. Western North Pacific dust, SST, and paleoproductivity records point to northward-shifted and weakened Northern Hemisphere westerlies during the warm Pliocene, with evidence for strengthening and southward movement of the westerlies during glacials after ~2.7 Ma. Changes in both winds and dust production mechanisms are likely working in tandem to produce the coherent global dust signals.

How to cite: Abell, J. T., Winckler, G., Anderson, R. F., and Herbert, T.: Reconstructing the intensity and location of Northern Hemisphere westerlies during the Plio-Pleistocene using marine sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5897, https://doi.org/10.5194/egusphere-egu2020-5897, 2020.

EGU2020-9472 | Displays | CL1.9

Orbitally-paced South American Summer Monsoon variability during the mid- to late-Pleistocene

Alicia Meng Xiao Hou, André Bahr, Jacek Raddatz, Silke Voigt, Ana Luiza Albuquerque, Cristiano M. Chiessi, and Oliver Friedrich

Hydrological extremes related to the South American Summer Monsoon (SASM) are expected to become more frequent in the near future and might have devastating socioeconomic consequences for the densely populated region of eastern Brazil. Given the complexity in SASM behaviour in space and time, a dense coverage of monsoonal precipitation records, particular those spanning multiple glacial-interglacial cycles, are urgently needed to constrain this high spatial-temporal variability. This information is necessary to reduce the uncertainty associated with projections of SASM precipitation in response to rising anthropogenic greenhouse gas (GHG) emissions. Here we use elemental ratios from X-ray fluorescence scanning of two sediment cores retrieved off the eastern Brazil margin to reconstruct long-term rainfall changes in the hinterland. Our findings from core M125-55-7 (offshore the Doce River, 20°S) reveal that during the past ~320 kyr, precession-paced insolation forcing is the primary pacemaker of variations in SASM precipitation over the Doce basin. We also determined an anomalous interval of weak monsoonal response to insolation forcing during Marine Isotope Stage 6, which we attribute to enhanced wintertime precipitation due to exceptionally strong southeast trade winds created by a steep South Atlantic latitudinal temperature gradient. Moreover, our results suggest that albeit predominantly driven by insolation forcing, the intensity of SASM rainfall responds negatively to GHG forcing, most likely through indirect feedbacks. We propose that GHG forcing directly influences the magnitude of both the inter- and intrahemispheric latitudinal temperature gradients, which in turn modify the strength of atmospheric circulation and precipitation in the tropics. Thus, we suggest that SASM rainfall intensity over tropical eastern Brazil will likely be suppressed by rising CO2 emissions in the future. Our preliminary analysis of core M125-73-3 (off the Contas River; 12°S) reveals regional differences in monsoonal precipitation between the more northerly Contas basin and the more southerly Doce basin. Most notably, unlike the insolation-paced continental rainfall variability recorded at site M125-55-7, SASM rainfall intensity over the Contas basin appears to be more sensitive to glacial-interglacial scale pacing over the past ~800 kyr. Taken together, our records reveal both the high spatial variability in SASM precipitation over eastern Brazil and the dominant influence of orbital forcing on monsoonal rainfall intensity.

How to cite: Hou, A. M. X., Bahr, A., Raddatz, J., Voigt, S., Albuquerque, A. L., Chiessi, C. M., and Friedrich, O.: Orbitally-paced South American Summer Monsoon variability during the mid- to late-Pleistocene , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9472, https://doi.org/10.5194/egusphere-egu2020-9472, 2020.

EGU2020-4765 | Displays | CL1.9

Different response of sea surface temperature and sea ice to precession and obliquity between the two hemispheres

Zhipeng Wu, Qiuzhen Yin, Zhengtang Guo, and André Berger

The response of the climate system to astronomical parameters is an important scientific issue, but the internal processes and feedbacks need to be better understood. This study investigates the differences of the climate response to the astronomical forcing between the Northern (NH) and Southern (SH) hemispheres based on a more than 90,000-year long transient simulation using the model LOVECLIM. Our results show that the response of sea ice and sea surface temperature (SST) to precession and obliquity are different between the two hemispheres. Precession plays a dominant role on the NH sea ice. This is mainly due to its response to the local summer insolation and also, to a less degree, the influence of the northward oceanic heat transports. However, obliquity plays a dominant role on the SH sea ice through its influence on insolation and the westerly winds. As far as the SST is concerned, it shows a strong precession signal at low latitudes in both hemispheres. For the SST in the mid and high latitudes, obliquity plays a dominant role in the SH whereas precession is more important in the NH. This is largely due to the different response to insolation and feedbacks related to the different land-ocean distribution in the two hemispheres. Near the Equator, besides the precessional signal, the SST also shows strong half-precessional signal, which can be explained by the unique characteristics of the insolation variations at the Equator.

How to cite: Wu, Z., Yin, Q., Guo, Z., and Berger, A.: Different response of sea surface temperature and sea ice to precession and obliquity between the two hemispheres, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4765, https://doi.org/10.5194/egusphere-egu2020-4765, 2020.

EGU2020-7565 | Displays | CL1.9

Exceptionally preserved Milankovitch cycles in Lower Devonian argillaceous limestone of the Hudson Valley, New York State (USA)

Anne-Christine Da Silva, Alex Bartholomew, Carlton Brett, Frits Hilgen, Charles Ver Straeten, and Mark Dekkers

Uncertainties on the radiometric ages of Devonian stage boundaries are currently on the order of several millions of years. A cyclostratigraphic approach is the foremost way forward to improve the Devonian geological time scale. To do so requires well-preserved continuous records, as well as reliable paleoclimatic proxies.  The NY Route 199 section, from Kingston, in the Hudson Valley of eastern New York, is a road cut outcrop, which exposes most of the Schoharie Formation. It corresponds to the upper portion of the Emsian Stage (upper Lower Devonian, ~400 to ~394 Ma), with essentially continuous deposition. The lithology consists of a mixed siliciclastic-carbonate succession with overall increasing carbonate upsection, showing various degrees of bioturbation (traces includes primarily Zoophycos, Planolites and Chondrites); colors range from white to beige, brown or dark grey. The quality of most of the outcrop is so remarkable that the color variations by themselves permit recognition of Milankovitch cycles, with prominent bundles of light and dark beds. One type of cycle expression is represented by a succession of about six darker beds nested between lighter beds, which is interpreted as six precession cycles within a short eccentricity cycle (precession in the Devonian was ~17 kyr).

Samples were collected every 2 cm through 38 m of the section for magnetic susceptibility measurements. On top of these measurements, we provide elemental geochemistry, carbon isotopes and hysteresis measurements (every 50 cm) to constrain the depositional setting and the diagenesis. Hysteresis measurements show that despite being remagnetized (throughout the Appalachians, these Paleozoic rock sequences are all remagnetized during the Variscan-Alleghenian Orogeny), the magnetic susceptibility reflects depositional information. The geochemistry and carbon isotopes give insight into the occurrence of oxic/reducing conditions and detrital inputs. Milankovitch cycles are visible on the outcrop and in the magnetic susceptibility record, allowing a precise floating timescale framework to be constructed for this interval.

How to cite: Da Silva, A.-C., Bartholomew, A., Brett, C., Hilgen, F., Ver Straeten, C., and Dekkers, M.: Exceptionally preserved Milankovitch cycles in Lower Devonian argillaceous limestone of the Hudson Valley, New York State (USA) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7565, https://doi.org/10.5194/egusphere-egu2020-7565, 2020.

The Late Paleozoic Ice Age (LPIA), one of the best known and prolonged glaciation events in Earth's history, resulted in the widespread deposition of glacial sediments over Gondwana (Crowell, 1999). Some of the most important LPIA deposits of the multiple glacial-deglacial episodes (Isbell et al., 2003) were preserved in the Itararé Group of the Paraná Basin (Brazil). This unit presents continental and marine glacially-influenced deposits formed by advances and retreats of glaciers and consists in an opportunity to better understand the mechanisms forcing climate shifts during the LPIA. In low latitudes, the deposition of the Carboniferous cyclothems was controlled by long- and short-eccentricity (Davydov et al., 2010). In high latitudes, orbital-scale climate cycles may also be preserved in the sedimentary succession. We aim to recognize whether or not orbital and millennial-scale climate cycles are preserved in the sedimentary succession of a core drilled in the southeastern border of the Paraná Basin. Here, we present the first cyclostratigraphic study based on X-ray fluorescence records from a 27 m-long interval of LPIA rhythmites of the Rio do Sul Formation (top of the Itararé Group). The sedimentary succession is composed of lithological couplets of fine-grained siliciclastic sediments, locally displaying subtle plane-bedding. Such rhythmites are characterized by abrupt contacts between couplets and normal grading internally. TiO2 and Fe2O3 vary in phase and display well-defined cyclicities in the stratigraphic domain. The TiO2 series presents millennial and orbital scale periodicities. Variations in the concentrations of the analyzed terrigenous components are likely indicative of glacial-interglacial changes, reflected by advances and retreats of glaciers under drier and wetter climate conditions, respectively. Here we show that these high latitude glacial-interglacial cycles were probably paced by short-eccentricity, as previously suggested for Carboniferous cyclothems in low latitude deposits, and highlight the importance of millennial-scale climate cycles forcing high latitudes glacial-related deposits, similar to patterns seen in Pleistocene records.

 

References:

Crowell, J. C. (1999). Pre-Mesozoic Ice Ages: Their Bearing on Understanding the Climate 375 System. Geologic Society of America Memoir 192, pp. 1–112.

Davydov, V. I., Crowley, J. L., Schmitz, M. D., & Poletaev, V. I. (2010). High-precision U-Pb zircon age calibration of the global Carboniferous time scale and Milankovitch band cyclicity in the Donets Basin, eastern Ukraine. Geochemistry, Geophysics, Geosystems, 11.

Isbell, J. L., Miller, M. F., Wolfe, K. L., & Lenaker, P. A. (2003). Timing of late Paleozoic glaciation in Gondwana: Was glaciation responsible for the development of Northern Hemisphere cyclothems? In Geologic Society of America Special Paper 370, pp. 5–24.

How to cite: Kochhann, M., Cagliari, J., Kochhann, K., and Franco, D.: Climate variability during the Late Paleozoic Ice Age in the southwestern Gondwana: records of orbital and millennial-scale cycles in the Carboniferous rhythmite of the Paraná Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11886, https://doi.org/10.5194/egusphere-egu2020-11886, 2020.

EGU2020-9556 | Displays | CL1.9

Cyclo and chemostratigraphic characteristics of the Middle Silurian in Gotland, Sweden

Michiel Arts, Bradley Cramer, Mikael Calner, Christian Rasmussen, Alyssa Bancroft, Stephan Oborny, Emma Hartke, Ellie Biebesheimer, and Anne-Christine Da Silva

The cumulative work of geoscientists over the past decades has shown that the Silurian Period which was once thought as warm and climatically stable time interval is in fact punctuated by numerous paleoenvironmental perturbations or events. These Silurian events follow a similar pattern where a minor extinction event precedes a substantial carbon isotope excursion. Many theories have been brought forward to explain these events ranging from glaciations, to changes in precipitations patterns, ocean currents and ocean anoxia. Constraints on the duration and timing of these extinction events and subsequent positive carbon isotope excursions are weak, which hampers a full understanding of the processes at play.

The data from the Altajme core from Gotland, Sweden provides us with a unique opportunity to look at two of these climatic perturbations during the Silurian. The Altajme core spans both the Sheinwoodian Ireviken event and the Homerian Mulde event. The Altajme core dataset includes a litholog, high-resolution δ13C data, correlated bentonites with U-Pb dates and a high-resolution XRF core scan: important data required for and integrated stratigraphic study. The U-Pb-dated bentonites give us age constraints. The δ13C data in combination with the high resolution XRF scan gives us insights into the changes in the ocean before during and after the events, while the XRF is also used to build cyclostratigraphic age constraints for the events and for the whole core. This stratigraphic study will provide us with a palaeoclimatological insights to explain these two events and provide us with a cyclostratigraphy based age model for the Middle Silurian.

How to cite: Arts, M., Cramer, B., Calner, M., Rasmussen, C., Bancroft, A., Oborny, S., Hartke, E., Biebesheimer, E., and Da Silva, A.-C.: Cyclo and chemostratigraphic characteristics of the Middle Silurian in Gotland, Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9556, https://doi.org/10.5194/egusphere-egu2020-9556, 2020.

EGU2020-8923 | Displays | CL1.9

Astrochronology of the Barremian Stage: implications for the dynamics of the anoxic events in the Early Cretaceous

Mathieu Martinez, Roque Aguado, Miguel Company, Jose Sandoval, and Luis O'Dogherty

Large uncertainties exist on the numerical ages of the stages in the Early Cretaceous which hamper from an accurate reconstruction of the past climate. Recent radio-astrochronologic data suggest to move the ages of the Tithonian to the Hauterivian stages by 3 to 5 Myr toward younger ages (Lena et al., 2019; Aguirre-Urreta et al., 2019). As the numerical ages in the Cenomanian are constrained with radio-astrochronology, this means that the duration of the Barremian to the Albian stages is overestimated. The duration of the Barremian Stage was estimated by bed counting on the assumption of a control by precession and eccentricity cycles (e.g., Bodin et al., 2006). The alternations and bundling can vanish leading to uncertainties in the duration estimates. Here, we provide an astrochronology from the eccentricity cycles based on spectral analyses performed on both magnetic susceptibility and calcium carbonate content series. Two sections are studied here in the Subbetic Domain (SE Spain). They are composed of marl-limestone alternations which reflect humid-arid cycles orbitally-driven. Detailed ammonite and calcareous nannofossil controls allow correlations with other sections in the basin and in the Tethyan Realm. The short and long-eccentricity cycles are identified throughout the Late Hauterivian to the earliest Aptian. The interval around the Hauterivian-Barremian boundary was recovered in a section previously studied for astrochronology and shows that the eccentricity cycles can be correlated to the sections studied here, validating the interpretations. From the record of the 405-kyr eccentricity cycle, the duration of the Barremian Stage is proposed at 4.25 ± 0.13 Myr. Anchoring this duration on previously obtained radio-astrochronology at the end of the Hauterivian, the Barremian Stage started at 125.91 ± 0.06 Ma and ended at 121.67 ± 0.11 Ma. The age of the latest Barremian agrees well with the age of the base of magnetochron M0r calculated from a synthesis of radiometric ages (Olierook et al., 2019). The Faraoni, Mid-Barremian and Taxy episodes show a pacing of 2.34 Myr, suggesting a strong orbital control on the expansion of oceanic anoxic conditions in the Tethys.

References:

Aguirre-Urreta, B., et al., 2019. Gondwana Res., 70, 104–132. https://doi.org/10.1016/j.gr.2019.01.006.

Bodin, S., et al., 2006. Palaeo-3, 235, 245–264. https://doi.org/10.1016/j.palaeo.2005.09.030.

Lena, L., et al., 2019. Solid Earth, 10, 1–14. https://doi.org/10.5194/se-10-1-2019.

Olierook, H.K.H., et al., 2019. Earth-Sci. Rev., 197, 102906. https://doi.org/10.1016/j.earscirev.2019.102906.

How to cite: Martinez, M., Aguado, R., Company, M., Sandoval, J., and O'Dogherty, L.: Astrochronology of the Barremian Stage: implications for the dynamics of the anoxic events in the Early Cretaceous, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8923, https://doi.org/10.5194/egusphere-egu2020-8923, 2020.

EGU2020-21479 | Displays | CL1.9 | Highlight

Thirty-five million years of changing climate – carbon cycle dynamics

David De Vleeschouwer, Anna Joy Drury, Maximilian Vahlenkamp, Diederik Liebrand, Fiona Rochholz, and Heiko Pälike

Fifty-one years of scientific ocean drilling through the International Ocean Discovery Program (IODP) and its predecessors generated a treasure trove of Cenozoic climate and carbon cycle dynamics. Yet, it remains unclear how climate system and carbon cycle interacted under changing geologic boundary conditions. Here, we present the carbon isotope (d13C) megasplice, documenting deep-ocean d13C evolution since 35 million years ago (Ma). We juxtapose the d13C megasplice with its d18O counterpart and determine their phase-difference on ~100-kyr eccentricity time-scales. This analysis uncovers that 2.4-Myr eccentricity modulates the in-phase relationship between d13C and d18O during the Oligo-Miocene (34-6 Ma), potentially related to changes in continental weathering. At 6 Ma, a striking switch from in-phase to anti-phase behaviour occurs, signalling a threshold in the climate system. We hypothesize that Arctic glaciation and the emergence of bipolar ice sheets enabled eccentricity to exert a major influence on the size of continental carbon reservoirs. Our results suggest that a reverse change in climate - carbon cycle interaction should be anticipated if CO2 levels rise further and we return to a world of unipolar ice sheets.

How to cite: De Vleeschouwer, D., Drury, A. J., Vahlenkamp, M., Liebrand, D., Rochholz, F., and Pälike, H.: Thirty-five million years of changing climate – carbon cycle dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21479, https://doi.org/10.5194/egusphere-egu2020-21479, 2020.

EGU2020-15256 | Displays | CL1.9

Eccentricity-paced ice sheet variability and obliquity-driven bottom-water changes during the Oligocene-Miocene

Tim van Peer, Victoria Taylor, Diederik Liebrand, Swaantje Brzelinski, Iris Möbius, André Bornemann, Oliver Friedrich, Steven Bohaty, Chuang Xuan, Peter Lippert, and Paul Wilson

Variations in solar insolation exert a fundamental control on the high-latitude climate–cryosphere system. Controversy, however, exists about the relative importance of orbital eccentricity versus axial tilt (obliquity) in driving pre-Quaternary Antarctic ice sheet variability. This problem is particularly acute during the late Oligocene-to-early Miocene interval (Oligo-Miocene, ~27-21 Ma), because several benthic foraminiferal oxygen isotopes (δ18O) records show strong pacing by obliquity, while others primarily show eccentricity pacing. The differences in orbital pacing are impossible to reconcile with the globally congruent imprint of ice volume on benthic δ18O on orbital time scales. Here we present a new astronomically tuned δ18O record generated at Integrated Ocean Drilling Program (IODP) Site U1406 (north-western Atlantic Ocean), a key area in modern-day thermohaline circulation. Clear imprints of both obliquity and eccentricity on the δ18O record are observed at Site U1406 throughout the study interval, irrespective of changes in sedimentation rate. The eccentricity variations at Site U1406 are remarkably similar to those seen in all other δ18O records, suggesting that eccentricity exerts a strong control on the high-latitude climate–cryosphere system via the modulation of the precession cycle. In contrast, the δ18O sensitivity to obliquity is globally variable, suggesting the influence of temperature in different bottom-water masses.

How to cite: van Peer, T., Taylor, V., Liebrand, D., Brzelinski, S., Möbius, I., Bornemann, A., Friedrich, O., Bohaty, S., Xuan, C., Lippert, P., and Wilson, P.: Eccentricity-paced ice sheet variability and obliquity-driven bottom-water changes during the Oligocene-Miocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15256, https://doi.org/10.5194/egusphere-egu2020-15256, 2020.

EGU2020-10667 | Displays | CL1.9

Early to Late Pliocene climate change in the mid-latitude North Atlantic

Antje H. L. Voelker, Francisco J. Sierro, B. David A. Naafs, Nils Andersen, and Henning Kuhnert

The early Pliocene, with atmospheric CO2 concentrations at levels similar to today, is seen as a case study for Earth’s future climate evolution. During this period the progressive closing of the Central American Seaway led to increased poleward heat and salt transport within the Atlantic with North Atlantic Deep Water (NADW) becoming warmer and saltier and resulting in an enhanced Atlantic Meridional Overturning Circulation (AMOC). In order to evaluate how stable the Pliocene AMOC really was, we are producing surface and deep-water records for IODP Site U1313 (41°N, 33°W, 3412m) for the interval from 3.3 to 4.1 Ma. This site is ideally located to monitor past AMOC changes with North Atlantic Drift waters at the surface and NADW, exported by the deep western boundary current, in the deep. Surface water conditions are reconstructed based on the stable isotope data of planktonic foraminifer species Globigerinoides ruber (white) or Globigerinoides extremus with centennial-scale resolution and on sea-surface temperatures (Uk37' alkenone thermometer) with an average 4 ky resolution. Stable isotope records of the benthic foraminifer genus Cibicidoides reveal changes in the deep water.

Besides the interglacial/glacial cycles, higher frequency oscillations are recorded in both the planktonic and benthic foraminifer stable isotope records. Varying surface water conditions, especially during Late Pliocene interglacial periods, are reflected in the Globigerinoides isotope data and appear to be linked to salinity changes since they are not recorded in the sea-surface temperature data. The high-frequency oscillations in the planktonic isotope records are related to precession (insolation) forcing, especially its harmonics in the 5.5 ky and 11 ky ranges. The benthic δ13C values indicate nearly continuous NADW presence and confirm a strong AMOC throughout the studied interval, also during most of the glacial periods. Excluding the pronounced M2 glacial, glacial stage Gi 6 had a stronger impact on the AMOC, as revealed by cooler, less ventilated surface waters and a less ventilated NADW, than Gi 2 and Gi 4. Overall, the AMOC was strong throughout, but experienced high frequency oscillations at a level similar to the middle Pleistocene interglacial periods.

How to cite: Voelker, A. H. L., Sierro, F. J., Naafs, B. D. A., Andersen, N., and Kuhnert, H.: Early to Late Pliocene climate change in the mid-latitude North Atlantic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10667, https://doi.org/10.5194/egusphere-egu2020-10667, 2020.

EGU2020-20327 | Displays | CL1.9 | Highlight

Green Sahara Megaperiods during the Pliocene: What was the role of North Atlantic Ocean temperature?

Paul Wilson, Amy Jewell, Anya Crocker, Solana Buchanan, Bryce Mitsunaga, Thomas Westerhold, Ursula Röhl, James Russell, and Timothy Herbert

The Sahel region is one of the most vulnerable regions on Earth to anthropogenically-driven climate change, but also one of the least equipped to deal with the consequences. Predictions of precipitation levels over the forthcoming centuries diverge, not only in magnitude, but also in the sign of change. One key aspect of this uncertainty comes from the role of Atlantic Ocean sea surface temperatures (SST), which are known to exert a strong control over precipitation in the Sahel and are implicated in both the major drought of the late 20th century and extreme droughts associated with the Heinrich events of the last glacial. To better understand how Sahelian hydroclimate may respond to SST variability in a warmer world, we turn to the Pliocene epoch, when atmospheric CO2 levels were comparable to present.

 

We studied sediments from Ocean Drilling Project Site 659, which is situated in the subtropical North Atlantic beneath the major modern summer Saharan dust plume. Our new dust accumulation rates and X-ray fluorescence core scan data indicate that there were major shifts between highly arid conditions and humid intervals with vegetated or “Green Sahara” conditions over much of northern Africa, driven by both solar insolation and glacial-interglacial variability. We also report three unusually long Plio-Pliocene humid intervals (each lasting ca. 100 kyr) characterised by very low dust emissions, that we term “Green Sahara Megaperiods (GSMPs)”. All three of these GSMPs occur at times when insolation variability was weak, resulting in values close to the long-term mean. This observation strongly suggests that factors other than insolation drove the sustained humidity of GSMPs. We present paired alkenone SST estimates and multi-species planktonic foramaniferal isotope records from 3.5–2.3 Myr ago to explore the extent to which the GSMPs were accompanied by intervals of extended warmth in the surface waters of the North Atlantic Ocean.

How to cite: Wilson, P., Jewell, A., Crocker, A., Buchanan, S., Mitsunaga, B., Westerhold, T., Röhl, U., Russell, J., and Herbert, T.: Green Sahara Megaperiods during the Pliocene: What was the role of North Atlantic Ocean temperature?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20327, https://doi.org/10.5194/egusphere-egu2020-20327, 2020.

EGU2020-11480 | Displays | CL1.9 | Highlight

Atmospheric CO2 during the Mid-Piacenzian Warm Period and the M2 glaciation.

Elwyn de la Vega, Thomas B. Chalk, Paul A. Wilson, Ratna Bysani, and Gavin L. Foster

The Piacenzian stage of the Pliocene (2.6 to 3.6 Ma) is the most recent past interval of sustained global warmth with mean global temperatures markedly higher (by ~2-3 oC) than today. Quantifying CO2 levels during the mid-Piacenzian Warm Period (mPWP) provides a means, therefore, to deepen our understanding of Earth System behaviour in a warm climate state. Here we present a new high-resolution record of atmospheric CO2 using the δ11B-pH proxy from 3.35 to 3.15 million years ago (Ma) at a temporal resolution of 1 sample per 3-6 thousand years. Our study interval covers both the coolest marine isotope stage of the mPWP, M2 (~3.3 Ma) and the transition into its warmest phase including interglacial KM5c (centered on ~3.205 Ma) which has a similar orbital configuration to present. We find that CO2 ranged from ca. 390 ppm to ca. 330 ppm, with CO2 during the KM5c interglacial being ca. 370 ppm. Our findings corroborate the idea that changes in atmospheric CO2 levels played a distinct role in climate variability during the mPWP. They also facilitate ongoing data-model comparisons and suggest that, at present rates of human emissions, there will be more CO2 in Earth’s atmosphere by 2025 than at any time for at least the last 3.3 million years.  

How to cite: de la Vega, E., Chalk, T. B., Wilson, P. A., Bysani, R., and Foster, G. L.: Atmospheric CO2 during the Mid-Piacenzian Warm Period and the M2 glaciation., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11480, https://doi.org/10.5194/egusphere-egu2020-11480, 2020.

EGU2020-19088 | Displays | CL1.9

Modelling Tropical Precipitation in the mid-Pliocene Warm Period

Julia Tindall and Alan Haywood

Models from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) show that the mid-Pliocene Warm Period (mPWP) was a warmer and wetter world than today. However, there is not strong model agreement as to how tropical precipitation was different in the mPWP. Although PlioMIP2 models agree that there was more precipitation associated with the African Monsoon and the Asian Monsoon, away from these regions models do not show a consistent and robust change in precipitation between the mPWP and the preindustrial.

Here we use the HadGEM2 model to explore changes in tropical precipitation between the mPWP and the preindustrial, particularly those associated with the position and strength of the Intertropical Convergence Zone (ITCZ). Reasons for these changes within HadGEM2 will be discussed. We will also expand our discussion of the ITCZ to the PlioMIP2 ensemble in order to show the differing factors that could influence ITCZ characteristics in a warmer world.

How to cite: Tindall, J. and Haywood, A.: Modelling Tropical Precipitation in the mid-Pliocene Warm Period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19088, https://doi.org/10.5194/egusphere-egu2020-19088, 2020.

EGU2020-21860 | Displays | CL1.9

Pacific Meridional Overturning Circulation during the Mid-Pliocene Warm Period

Heather L. Ford, Natalie Burls, and David Hodell

Today in the North Pacific only intermediate water forms because of a strong halocline, but Pacific Meridional Overturning Circulation (PMOC) may have existed in the past. The mid-Pliocene warm period (3.264-3.025 Ma) is a time of sustained warmth where atmospheric carbon dioxide concentrations were similar to today and the northern hemisphere was relatively ice free – making it a pseudo-analogue for future climate change. North Pacific sedimentological and climate modeling evidence suggests a PMOC formed during this time.  To determine the spatial extent of a PMOC during the mid-Pliocene warm period, we constructed a depth transect of sites between 2400 to 3400 m water depth on Shatsky Rise by measuring stable isotopes of Cibicidoides wuellerstorfi. We compare these new results with previously published records and calculate anomalies using the OC3 water column and core-top data products. The δ13C spatial pattern is consistent with a modest PMOC of intermediate depth (core ~2000 m) extending to the equator during the mid-Pliocene warm period. Ventilation of the North Pacific by a PMOC has broad implications for deep ocean carbon storage as the North Pacific contains the oldest, carbon-rich waters today. Future work will include minor and trace element analyses to determine the temperature and carbon characteristics of the PMOC water mass and comparisons with PlioMIP modeling outputs.

How to cite: Ford, H. L., Burls, N., and Hodell, D.: Pacific Meridional Overturning Circulation during the Mid-Pliocene Warm Period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21860, https://doi.org/10.5194/egusphere-egu2020-21860, 2020.

EGU2020-399 | Displays | CL1.9

Reconstructing Past Indian Summer Monsoon Productivity and Stratification During the Late Pliocene and Early Pleistocene

Emmeline Gray, Pallavi Anand, Clara Bolton, Masafumi Murayama, and Marcus Badger

The South Asian or Indian Summer Monsoon (ISM) brings seasonal winds and rains to the Indian subcontinent and affects billions of people.  It is likely that the global monsoon will strengthen in a 1.5 °C warming scenario (IPCC special report (2018)), however our ability to predict ISM behaviour in the future is restricted due to lack of understanding of its behaviour under varying climatic conditions before instrumental records began.  Thus, reconstructing the palaeo-monsoon using proxies gives insight into past and potentially future controls on the ISM.  We present new data covering the interval ~5 to ~2 million years ago (Ma), during the Pliocene and early Pleistocene when the long-term Cenozoic cooling trend culminated in intense northern hemisphere glaciations from 2.7 Ma.  At this time, global temperatures are suggested to have been 2-3 °C warmer than today and atmospheric CO2 was over 400 ppm (similar to today). 

This study focuses on sediments from Site U1443 ( 5°N, 90°E), drilled during International Ocean Discovery Program (IODP) Expedition 353 in the Bay of Bengal (BoB) for the Pliocene – early Pleistocene.  We present X-ray fluorescence (XRF)-derived bulk sediment geochemical data and suggest that erosional flux (terrigenous elements/total counts) as well as productivity (Br/Cl) varied in response to runoff strength, precipitation, and wind stress at the study site to reconstruct ISM variability.  Additionally, new nannofossil assemblage and morphometric data, collected using the automated system SYRACO, are used to reconstruct BoB stratification and productivity and thereby assess ISM dynamics.  A new benthic oxygen isotope-based age model will allow us to place the Site U1443 records into the context of existing climate and monsoon records and evaluate ISM response due to external and internal climate forcing factors.

How to cite: Gray, E., Anand, P., Bolton, C., Murayama, M., and Badger, M.: Reconstructing Past Indian Summer Monsoon Productivity and Stratification During the Late Pliocene and Early Pleistocene , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-399, https://doi.org/10.5194/egusphere-egu2020-399, 2020.

EGU2020-2427 | Displays | CL1.9 | Highlight

Lessons from a high CO2 world: an ocean view from ~3 million years ago

Erin McClymont, Heather Ford, Sze Ling Ho, Julia Tindall, Alan Haywood, Montserrat Alonso Garcia, Ian Bailey, Melissa Berke, Kate Littler, Molly Patterson, Benjamin Petrick, Francien Peterse, Christina Ravelo, Bjorg Risebrobakken, Stijn De Schepper, George Swann, Kaustubh Thirumalai, Jessica Tierney, Carolien van der Weijst, and Sarah White

A range of future climate scenarios are projected for high atmospheric CO2 concentrations, given uncertainties over future human actions as well as potential environmental and climatic feedbacks. The geological record offers an opportunity to understand climate system response to a range of forcings and feedbacks which operate over multiple temporal and spatial scales. Here, we examine a single interglacial during the late Pliocene (KM5c, ca. 3.205 +/- 0.01 Ma) when atmospheric CO2 concentrations were higher than pre-industrial, but similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were almost identical to today, we are able to focus on equilibrium climate system response to modern and near-future CO2. Using proxy data from 32 sites, we demonstrate that global mean sea-surface temperatures were warmer than pre-industrial, by ~2.3 ºC for the combined proxy data (foraminifera Mg/Ca and alkenones), or by ~3.2ºC (alkenones only). Compared to the pre-industrial, reduced meridional gradients and enhanced warming in the North Atlantic are consistently reconstructed. There is broad agreement between data and models at the global scale, with regional differences reflecting ocean circulation and/or proxy signals. An uneven distribution of proxy data in time and space does, however, add uncertainty to our anomaly calculations. The reconstructed global mean sea-surface temperature anomaly for KM5c is warmer than all but three of the PlioMIP2 model outputs, and the reconstructed North Atlantic data tend to align with the warmest KM5c model values.  Our results demonstrate that even under low CO2 emission scenarios, surface ocean warming may be expected to exceed model projections, and will be accentuated in the higher latitudes.

How to cite: McClymont, E., Ford, H., Ho, S. L., Tindall, J., Haywood, A., Alonso Garcia, M., Bailey, I., Berke, M., Littler, K., Patterson, M., Petrick, B., Peterse, F., Ravelo, C., Risebrobakken, B., De Schepper, S., Swann, G., Thirumalai, K., Tierney, J., van der Weijst, C., and White, S.: Lessons from a high CO2 world: an ocean view from ~3 million years ago, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2427, https://doi.org/10.5194/egusphere-egu2020-2427, 2020.

It remains unclear how El Niño–Southern Oscillation (ENSO)—the prominent interannual anomalous climate mode—varied during the full glacial cycles. We study the evolution of ENSO of the last 300,000 years using continuous fully-coupled climate model simulations. How the slow time‐varying changes in insolation, greenhouse gases concentration, and continental ice sheets could influence the behaviours of El Niño are taken into account. The simulated ENSO variance and the tropical eastern Pacific annual cycle (AC) amplitude change in phase, and both have pronounced precession-band variance (~21,000 years) rather than the obliquity-band (~40,000 years). The precession‐modulated slow (orbital time scales) ENSO evolution is determined linearly by the change of the coupled ocean‐atmosphere instability, notably the Ekman upwelling feedback and thermocline feedback. In contrast, the greenhouse gases and ice sheet forcings (~100,000‐year cycles with sawtooth shapes) are opposed to each other as they influence ENSO variability through changes in AC amplitude via a common nonlinear frequency entrainment mechanism. The relatively long simulations which involve pronounced glacial‐interglacial forcing effects gives us more confidence in understanding ENSO forcing mechanisms, so they may shed light on ENSO dynamics and how ENSO will change in the future.

How to cite: Lu, Z.: Prominent precession-band variance in El Niño–Southern Oscillation Intensity over the last 300,000 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11315, https://doi.org/10.5194/egusphere-egu2020-11315, 2020.

EGU2020-1092 | Displays | CL1.9

Coral reconstructed Mid-Holocene seasonality in the southwestern Caribbean

Vanessa Skiba, Ulrich Struck, Lars Reuning, Dieter Garbe-Schönberg, Norbert Frank, Reinhold Leinfelder, Aaron O'Dea, and Jens Zinke

Seasonality is a dominant factor in the Earth’s climate system, but proxy reconstructions on this time scale are sparse. Corals provide an excellent archive to reconstruct environmental conditions on seasonal time scale using geochemical proxies. Here, we use subfossil (~6.2-7.1 ka BP) Siderastrea siderea and Pseudodiploria labyrinthiformis corals from a pristine Mid-Holocene reef, located in Panamá, southwestern Caribbean. Mid-Holocene insolation seasonality in the Northern Hemisphere was stronger than at present. We investigate the resulting changes in SST and hydrological seasonality using coral Sr/Ca, δ18O and δ13C. To evaluate, if the coral heads can be utilised for geochemical analyses, they have been screened for diagenetic alteration (2D-XRD, thin section analysis). Obtained modern coral Sr/Ca-SST based annual cycle corresponds well with in situ measured SST. Fossil coral Sr/Ca-SST based cycles exceed the modern one by up to 50%. Fossil coral δ18O seasonal amplitudes are higher than the modern one by up to 30% and show a reduction in the mean gradient between wet and dry period, attributable to the northward shift of the Intertropical Convergence Zone. Increased SST and δ18O seasonality are consistent with model simulated SSTs (Kiel Climate Model) and model-based calculated pseudocoral δ18O, but the model underestimates the seasonality increase in the Mid-Holocene.

How to cite: Skiba, V., Struck, U., Reuning, L., Garbe-Schönberg, D., Frank, N., Leinfelder, R., O'Dea, A., and Zinke, J.: Coral reconstructed Mid-Holocene seasonality in the southwestern Caribbean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1092, https://doi.org/10.5194/egusphere-egu2020-1092, 2020.

EGU2020-2961 | Displays | CL1.9 | Highlight

Identifying sources of changed precipitation in paleoclimate studies through moisture tracking: A case study for orbital extremes over the Mediterranean Sea

Ruud van der Ent, Joyce Bosmans, Rein Haarsma, Sybren Drijfhout, and Frits Hilgen

Enhanced winter precipitation over the Mediterranean Sea at times of minimum precession and maximum obliquity could provide freshwater required to form orbitally-paced sedimentary cycles across the Mediterranean Sea floor, offering an alternative to monsoonal runoff. We investigate the sources of the enhanced winter precipitation by applying a moisture tracking model (WAM-2layers) on the results of idealized orbital extreme experiments with a state-of-the-art climate model (EC-Earth).

Tracking the moisture sources of the enhanced winter precipitation over the Mediterranean Sea shows that the source differs during the winter half year. In fall, the majority of the precession-induced precipitation increase originates from the Mediterranean itself. However, in late winter, the increase can be attributed to enhanced moisture advection from the Atlantic. This agrees with changes in evaporation and air-sea temperature differences over the Mediterranean. The obliquity-induced precipitation increase shows much less differences, with an equal contribution of local and Atlantic sources.

The mechanism behind the Atlantic source of moisture is not related to storm track activity, but to a weakened Azores High and slightly higher surface pressure over North Africa. The resulting anomalous circulation patterns generate enhanced Atlantic moisture transport towards the Mediterranean. Our combined climate and moisture tracking modelling approach thus provides an alternative mechanism for Atlantic sources of orbitally-paced Mediterranean precipitation changes.

The results of this study have been published in:

Bosmans, J. H. C., van der Ent, R. J., Haarsma, R. J., Drijfhout, S. S. and Hilgen, F. J.: Identifying sources of changed precipitation in paleoclimate studies through moisture tracking: A case study for orbital extremes over the Mediterranean Sea, Paleoceanogr. Paleoclimatology, accepted, doi:10.1029/2019PA003655, 2020.

The atmospheric moisture tracking through WAM-2layers revealed concrete information about the evaporative sources of enhanced/reduced precipitation. This method has not been previously applied in paleoclimate studies, but thus proved to be a powerful tool in attributing reasons for precipitation changes in addition to climate model experiments and classical meteorological analyses. New ideas for collaborations to apply this method in other (paleo)climate studies are welcome.

How to cite: van der Ent, R., Bosmans, J., Haarsma, R., Drijfhout, S., and Hilgen, F.: Identifying sources of changed precipitation in paleoclimate studies through moisture tracking: A case study for orbital extremes over the Mediterranean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2961, https://doi.org/10.5194/egusphere-egu2020-2961, 2020.