CR3.1

EDI
Ice-sheet and climate interactions

Ice sheets play an active role in the climate system by amplifying, pacing, and potentially driving global climate change over a wide range of time scales. The impact of interactions between ice sheets and climate include changes in atmospheric and ocean temperatures and circulation, global biogeochemical cycles, the global hydrological cycle, vegetation, sea level, and land-surface albedo, which in turn cause additional feedbacks in the climate system. This session will present data and modelling results that examine ice sheet interactions with other components of the climate system over several time scales. Among other topics, issues to be addressed in this session include ice sheet-climate interactions from glacial-interglacial to millennial and centennial time scales, the role of ice sheets in Cenozoic global cooling and the mid-Pleistocene transition, reconstructions of past ice sheets and sea level, the current and future evolution of the ice sheets, and the role of ice sheets in abrupt climate change.

Co-organized by CL4
Convener: Heiko Goelzer | Co-conveners: Emily HillECSECS, Philippe Huybrechts, Alexander Robinson, Ricarda Winkelmann
vPICO presentations
| Fri, 30 Apr, 09:00–10:30 (CEST)

vPICO presentations: Fri, 30 Apr

Chairpersons: Emily Hill, Heiko Goelzer
09:00–09:05
09:05–09:07
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EGU21-8134
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ECS
April S Dalton and Martin Margold

The response of continental ice sheets to late glacial climate fluctuations (Bølling warming, Younger Dryas cooling) offers key insight into the interconnectedness between ice sheets and climate. The Younger Dryas was an abrupt climate cooling event that occurred between 12.9 ka and 11.7 ka, as the Northern Hemisphere was undergoing progressive deglaciation from the last glacial maximum (~25 ka). Ice sheets in Northern Europe (Fennoscandian Ice Sheet) underwent a significant re-advance at that time. However, the reaction of North American ice sheets (Laurentide, Cordilleran, Innuitian; which comprise the largest ice mass in the Northern Hemisphere at the time) to Younger Dryas cooling is not well understood. Some localized studies have shown evidence of ice re-advance or stagnation corresponding to the Younger Dryas; however, no large-scale, unifying study of the impact of Younger Dryas cooling on North American ice sheets has been attempted. Here, we present preliminary maps showing the response of North American ice sheets to the Younger Dryas climate event in key regions. To delineate changes in the ice margin, we integrate a geochronological dataset consisting of calibrated radiocarbon ages and cosmogenic nuclide ages, with mapping of glacial features (ie. moraines) and an extensive literature review. Results suggest a highly variable response of North American ice sheets to Younger Dryas cooling, notably a re-advance of remnant ice lobes in eastern Canada, and stagnation of the ice margin at more western sites.

How to cite: Dalton, A. S. and Margold, M.: The response of North American ice sheets to the Younger Dryas (12.9 ka to 11.7 ka) climate event, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8134, https://doi.org/10.5194/egusphere-egu21-8134, 2021.

09:07–09:09
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EGU21-7211
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ECS
Victor van Aalderen, Sylvie Charbit, Christophe Dumas, and Masa Kageyama

Recent observations show an acceleration of the glacier outflow in the West Antarctic ice sheet (WAIS) since the mid-1990s and an increase in calving events. Compared to the 1979-1990 period, mass loss from WAIS has been increased by a factor six between 2009 and 2017. The reduced buttressing effect from ice-shelf breakup may favour the ice flow from outlet glaciers and in turn the sea-level rise with potential noticeable consequences on human societies. However, despite continuous model improvements, large uncertainties are still present on the representation future evolution of the WAIS. The large panel of different results in the projections of the future sea-level rise stands, in part, to our misunderstanding of the process responsible for the marine ice sheet evolution. A possible approach to better constrain these processes, is to investigate past marine ice sheets, such as the Barents-Kara ice sheet (BKIS) at the Last Glacial Maximum (LGM), which can be considered, to a certain extent, as an analogue of the WAIS. Our objective is to study the processes responsible for the collapse of the BKIS during the last deglaciation. To simulate the evolution of the BKIS, we use the GRISLI ice-sheet model (20 km x 20 km) forced by different CMIP5/PMIP3 and CMIP6/PMIP4 models. We will present the response of the ice sheet to different types of atmospheric and oceanic forcing at the LGM coming from the PMIP models. This study represents a first step before studying more in depth the respective role of each climatic field but also the role of sea level rise coming from other LGM ice sheets in triggering the retreat of the BKIS at the beginning of the last deglaciation and the impacts of the dynamical processes.

How to cite: van Aalderen, V., Charbit, S., Dumas, C., and Kageyama, M.: The Barents-Kara Ice Sheet response to the CMIP6-PMIP4 simulations for the LGM climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7211, https://doi.org/10.5194/egusphere-egu21-7211, 2021.

09:09–09:11
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EGU21-10208
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ECS
Daniel Moreno, Jorge Alvarez-Solas, Alexander Robinson, Javier Blasco, Ilaria Tabone, and Marisa Montoya

The climate during the last glacial period was far from stable. Evidence has shown the presence of layers of ice-rafted debris (IRD) in deep-sea sediments, which have been interpreted to reflect quasi-periodic episodes of massive iceberg calving from the Laurentide Ice Sheet (LIS). Several mechanisms have been proposed, yet the ultimate cause of these events is still under debate. From the point of view of ice dynamics, one of the main sources of uncertainty and diversity in model response is the choice of basal friction law. Therefore, it is essential to determine the impact of basal friction in glacial transport and erosion, deposition of sediments and ice streams. Here we study the effect of a wide range of basal friction parameters and laws under glacial conditions over the LIS by running ensembles of simulations using a higher-order ice-sheet model. Importantly, the potential feedbacks between basal hydrology and thermodynamics are also considered to shed light on the behaviour of the ice flow. Our aim is to determine under what conditions, if any, physically-based oscillations are possible in the LIS with constant boundary conditions. Increasing our understanding of both basal friction laws and basal hydrology will improve not only reconstructions of paleo ice dynamics but also help to constrain the potential future evolution of current ice sheets.

How to cite: Moreno, D., Alvarez-Solas, J., Robinson, A., Blasco, J., Tabone, I., and Montoya, M.: Physically-based oscillations of the Laurentide Ice Sheet under glacial conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10208, https://doi.org/10.5194/egusphere-egu21-10208, 2021.

09:11–09:13
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EGU21-13538
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ECS
Sam Sherriff-Tadano, Ayako Abe-Ouchi, and Akira Oka

This study explores the effect of southward expansion of Northern Hemisphere (American) mid-glacial ice sheets on the global climate and the Atlantic Meridional Overturning Circulation (AMOC), as well as the processes by which the ice sheets modify the AMOC. For this purpose, simulations of Marine Isotope Stage (MIS) 3 (36ka) and 5a (80ka) are performed with an atmosphere-ocean general circulation model. In the MIS3 and MIS5a simulations, the global average temperature decreases by 5.0 °C and 2.2 °C, respectively, compared with the preindustrial climate simulation. The AMOC weakens by 3% in MIS3, whereas it strengthens by 16% in MIS5a, both of which are consistent with an estimate based on 231Pa/230Th. Sensitivity experiments extracting the effect of the southward expansion of glacial ice sheets from MIS5a to MIS3 show a global cooling of 1.1 °C, contributing to about 40% of the total surface cooling from MIS5a to MIS3. These experiments also demonstrate that the ice sheet expansion leads to a surface cooling of 2 °C over the Southern Ocean as a result of colder North Atlantic deep water. We find that the southward expansion of the mid-glacial ice sheet exerts a small impact on the AMOC. Partially coupled experiments reveal that the global surface cooling by the glacial ice sheet tends to reduce the AMOC by increasing the sea ice at both poles, and hence compensates for the strengthening effect of the enhanced surface wind over the North Atlantic. Our results show that the total effect of glacial ice sheets on the AMOC is determined by the two competing effects, surface wind and surface cooling. The relative strength of surface wind and surface cooling effects depends on the ice sheet configuration, and the strength of the surface cooling can be comparable to that of surface wind when changes in the extent of ice sheet are prominent.

How to cite: Sherriff-Tadano, S., Abe-Ouchi, A., and Oka, A.: Impact of mid-glacial ice sheets on deep ocean circulation and global climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13538, https://doi.org/10.5194/egusphere-egu21-13538, 2021.

09:13–09:15
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EGU21-4051
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ECS
Clemens Schannwell, Marie-Luise Kapsch, Uwe Mikolajewicz, and Florian Ziemen

Heinrich-type ice sheet surge events are among the most prominent signals in the paleoclimate data records. Even though these events have previously been intensely studied, it still remains an open question whether the cyclic ice sheet surges are triggered by internal ice dynamics, climate forcing, or a combination of the two. In simulations of the last deglaciation using the fully-coupled Max Planck Institute Earth System Model, surges from the European and North American ice sheets often occur in synchronicity. This model behaviour is in agreement with observations from sediment cores that find a similar pattern in the isotopic fingerprint of the deposited ice-rafted detritus. The synchronicity indicates that climate forcing is playing an important role in initiating ice sheet surges. In this study, we use the coupled ice-sheet-solid earth model PISM-VILMA in a northern hemispheric setup to investigate the modelled synchronicity of the surge events. More specifically, we perform an ensemble of simulations to study if the modelled synchronicity is a direct result of one of the surge locations causing other surge locations to be a activated as well. Moreover, we aim to investigate whether previously suggested trigger mechanisms such as regional changes in sea level or ocean temperatures are indeed key processes in controlling the synchronicity of these surge events.

How to cite: Schannwell, C., Kapsch, M.-L., Mikolajewicz, U., and Ziemen, F.: Identifying drivers controlling the synchronicity of Heinrich-type ice sheet surges from the European and North American ice sheets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4051, https://doi.org/10.5194/egusphere-egu21-4051, 2021.

09:15–09:17
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EGU21-12910
Walter Geibert, Jens Matthiessen, Ingrid Stimac, Jutta Wollenburg, and Ruediger Stein

Numerous studies have addressed the possible existence of large floating ice sheets in the glacial Arctic Ocean from theoretical, modelling, or seafloor morphology perspectives. Here, we add evidence from the sediment record that support the existence of such freshwater ice caps in certain intervals, and we discuss their implications for possible non-linear and rapid behaviour of such a system in the high latitudes.

We present sedimentary activities of 230Th together with 234U/238U ratios, the concentrations of manganese, sulphur and calcium in the context of lithological information and records of microfossils and their isotope composition. New analyses (PS51/038, PS72/396) and a re-analysis of existing marine sediment records (PS1533, PS1235, PS2185, PS2200, amongst others) in view of the naturally occurring radionuclide 230Thex and, where available, 10Be from the Arctic Ocean and the Nordic Seas reveal the widespread occurrence of intervals with a specific geochemical signature. The pattern of these parameters in a pan-Arctic view can best be explained when assuming the repeated presence of freshwater in frozen and liquid form across large parts of the Arctic Ocean and the Nordic Seas.

Based on the sedimentary evidence and known environmental constraints at the time, we develop a glacial scenario that explains how these ice sheets, together with eustatic sea-level changes, may have affected the past oceanography of the Arctic Ocean in a fundamental way that must have led to a drastic and non-linear response to external forcing.

This concept offers a possibility to explain and to some extent reconcile contrasting age models for the Late Pleistocene in the Arctic Ocean. Our view, if adopted, offers a coherent dating approach across the Arctic Ocean and the Nordic Seas, linked to events outside the Arctic.

How to cite: Geibert, W., Matthiessen, J., Stimac, I., Wollenburg, J., and Stein, R.: Geochemical evidence of a floating Arctic ice sheet and underlying freshwater in the Arctic Mediterranean in glacial periods, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12910, https://doi.org/10.5194/egusphere-egu21-12910, 2021.

09:17–09:19
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EGU21-8237
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ECS
Dakota Holmes, David De Vleeschouwer, and Audrey Morley

Abrupt climate events are important features of glacial climate scales on centennial and millennial timescales. These events' mechanistic trigger is often ascribed to either ice sheet-related feedback mechanisms or large freshwater pulses. In both cases, 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. Using sediment core DSDP U610B (53°13.297N, 18°53.213W) located in the Rockall Trough, we present a high-resolution analysis of surface and deep water components of the AMOC spanning the transition from Marine Isotope Stage (MIS) 19.3 to 19.1 to test if orbital boundary conditions similar to our current Holocene can accommodate abrupt climate events. Above the core site, the dominant oceanographic feature is the North Atlantic Current and at 2417-m water depth, U610 is influenced by Wyville Thomson Overflow Water flowing southwards. We utilise a multiproxy approach including paired grain size analysis, planktic foraminifera assemblage counts, and ice-rafted debris counts within the same samples allowing 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. We also present for the first time a new splice and composite depth scale for Site U610. Based on preliminary results, rapid shifts in both deep overflow and surface climate characterise this period.

How to cite: Holmes, D., De Vleeschouwer, D., and Morley, A.: Are Cryosphere-Driven Feedbacks a Requisite for Abrupt Climate Events? (Site U610, DSDP Leg. 94), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8237, https://doi.org/10.5194/egusphere-egu21-8237, 2021.

09:19–09:21
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EGU21-9846
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ECS
Ilaria Tabone, Alexander Robinson, Jorge Alvarez-Solas, Javier Blasco, Daniel Moreno, and Marisa Montoya

Reconstructions of Greenland Summit elevation changes indicate at least 150 m of surface thinning since the onset of the Holocene. Even higher thinning values are found at locations closer to the ice-sheet margin, where the influence of higher ablation rates and ocean-induced retreat is greater. Interestingly, the performance of 3D ice-sheet models in representing such elevation changes is generally poor, even though they can reasonably reproduce the state of the ice sheet at different times, such as the last glacial maximum (LGM) or the present day. The reasons behind this data-model mismatch are still unclear. Here we use a recently developed 3D ice-sheet-shelf model to test the impact of different model parameters and of boundary conditions on simulating the Greenland ice sheet evolution through the last deglaciation to today. Specifically, we investigate the role of past climatologies in reproducing the elevation changes at ice core sites when used to force the ice-sheet model. By applying recently developed transient deglacial climatologies we can investigate the ice-sheet deglaciation with exceptional detail. Results support the need of additional transient climatologies to be released to ensure a robust description of the Greenland retreat history throughout the Holocene. 

How to cite: Tabone, I., Robinson, A., Alvarez-Solas, J., Blasco, J., Moreno, D., and Montoya, M.: Modelled Holocene thinning in Greenland improved by new developed transient past climatologies., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9846, https://doi.org/10.5194/egusphere-egu21-9846, 2021.

09:21–09:23
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EGU21-1367
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ECS
Clara Burgard and Nicolas Jourdain

Ocean-induced melting at the base of ice shelves is one of the main drivers of the currently observed mass loss of the Antarctic Ice Sheet. A good understanding of the interaction between ice and ocean at the base of the ice shelves is therefore crucial to understand and project the Antarctic contribution to global sea-level rise. 

Due to the high difficulty to monitor these regions, our understanding of the processes at work beneath ice shelves is limited. Still, several parameterisations of varying complexity have been developed in past decades to describe the ocean-induced sub-shelf melting. These parameterisations can be implemented into standalone ice-sheet models, for example when conducting long-term projections forced with climate model output.

An assessment of the performance of these parameterisations was conducted in an idealised setup (Favier et al, 2019). However, the application of the better-performing parameterisations in a more realistic setup (e.g. Jourdain et al., 2020) has shown that individual adjustments and corrections are needed for each ice shelf.

In this study, we revisit the assessment of the parameterisations, this time in a more realistic setup than previous studies. To do so, we apply the different parameterisations on several ice shelves around Antarctica and compare the resulting melt rates to satellite and oceanographic estimates. Based on this comparison, we will refine the parameters and propose an approach to reduce uncertainties in long-term sub-shelf melting projections.

References
- Favier, L., Jourdain, N. C., Jenkins, A., Merino, N., Durand, G., Gagliardini, O., Gillet-Chaulet, F., and Mathiot, P.: Assessment of sub-shelf melting parameterisations using the ocean–ice-sheet coupled model NEMO(v3.6)–Elmer/Ice(v8.3) , Geosci. Model Dev., 12, 2255–2283, https://doi.org/10.5194/gmd-12-2255-2019, 2019. 
- Jourdain, N. C., Asay-Davis, X., Hattermann, T., Straneo, F., Seroussi, H., Little, C. M., and Nowicki, S.: A protocol for calculating basal melt rates in the ISMIP6 Antarctic ice sheet projections, The Cryosphere, 14, 3111–3134, https://doi.org/10.5194/tc-14-3111-2020, 2020. 

How to cite: Burgard, C. and Jourdain, N.: An assessment of basal melting parameterisations for Antarctic ice shelves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1367, https://doi.org/10.5194/egusphere-egu21-1367, 2021.

09:23–09:25
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EGU21-2084
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ECS
Paul Halas, Jeremie Mouginot, Basile de Fleurian, and Petra Langebroek

Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise. Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding. The sliding component of glaciers has been observed to be strongly related to surface melting, as water can eventually reach the bed and impact the subglacial water pressure, affecting the basal sliding.  

The link between ice velocities and surface melt on multi-annual time scale is still not totally understood even though it is of major importance with expected increasing surface melting. Several studies showed some correlation between an increase in surface melt and a slowdown in velocities, but there is no consensus on those trends. Moreover those investigations only presented results in a limited area over Southwest Greenland.  

Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.  

Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration. This trend however does not seem to be observed on the whole ice sheet and is probably specific to this region’s climate forcing. 

Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics.

How to cite: Halas, P., Mouginot, J., de Fleurian, B., and Langebroek, P.: Greenland land-terminating glaciers velocity trends during the last two decades, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2084, https://doi.org/10.5194/egusphere-egu21-2084, 2021.

09:25–09:27
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EGU21-9686
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ECS
Benoît Urruty, Olivier Gagliardini, and Fabien Gillet-Chaulet

Global warming has a huge impact on the different climatic components. In Antarctica, small changes on the ice-sheet or the ocean may drive the continent to some large instabilities. At a certain threshold, a tipping point might be crossed and the ice-sheet might retreat faster and irreversibly. The TiPACCs (Tipping Points in Antarctic Climate Components) project aims to a better understanding of the tipping points of Antarctica, both in the ocean and in the glaciers.  3 different ice-flow models (Elmer/Ice, PISM, and Ua) are used in the project.  This study is focusing on the Elmer/Ice model to determine and characterize tipping points for its grounding lines. In this presentation, the most famous instability of Antarctica, the Marine Ice-Sheet Instability (MISI), will be investigated. The goal is to define the stability regime of the current Antarctic ice-sheet. For this purpose, multiple initial states have been created.  The Elmer/Ice model uses the inverse method as it has been done in InitMIP-Antarctica (Seroussi et al. 2019) to define initial states. A common initial state for the three TiPACCs models has been defined by the use of common datasets and parameters. The melt at the base of the ice-shelf is defined by the PICO parametrization (Reese, 2016) which permits to define the melting per basins with a box model. Then, perturbations of basalt melt are be applied by modifying the ocean far-field temperature and salinity. The stability of the current grounding line is evaluated by calculating the grounding line migration for the different ice-shelf. The experiments are driven by a small but numerically significant perturbation to observe a retreat of the grounding line. If the grounding line is moving backward when removing the perturbation, then we can conclude that it is stable. Otherwise, if the grounding line is continuing its retreat then it is unstable.

 

How to cite: Urruty, B., Gagliardini, O., and Gillet-Chaulet, F.: Stability of current Antarctica grounding lines, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9686, https://doi.org/10.5194/egusphere-egu21-9686, 2021.

09:27–09:29
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EGU21-12958
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ECS
Michele Petrini, Miren Vizcaino, Raymond Sellevold, Laura Muntjewerf, Sotiria Georgiou, Meike D.W. Scherrenberg, William Lipscomb, and Gunter Leguy

Previous coupled climate-ice sheet modeling studies indicate that the warming threshold leading to multi-millennial, large-scale deglaciation of the Greenland Ice Sheet (GrIS) is in the range of 1.6-3.0 K above the pre-industrial climate. These studies either used an intermediate complexity RCM (Robinson et al. 2012) or a low resolution GCM (Gregory et al., 2020) coupled to a zero-order ISM. Here, we investigate the warming threshold and long-term response time of the GrIS using the higher-order Community Ice Sheet Model version 2 (CISM2, Lipscomb et al. 2019), forced with surface mass balance (SMB) calculated with the Community Earth System Model version 2 (CESM2, Danabasoglu et al. 2020). We use different forcing climatologies from a coupled CESM2/CISM2 simulation under high greenhouse gas forcing (Muntjewerf et al. 2020), where each climatology corresponds to a different global warming level in the range of 1-8.5 K above the pre-industrial climate. The SMB, which is calculated in CESM2 using an advanced energy balance scheme at multiple elevation classes (Muntjewerf et al. 2020), is downscaled during runtime to CISM2, thus allowing to account for the surface elevation feedback. In all the simulations the forcing is cycled until the ice sheet is fully deglaciated or has reached a new equilibrium. In a first set of simulations, we find that for a warming level higher than 5.2 K above pre-industrial the ice sheet will disappear, with the timing ranging between 2000 (+8.5 K) and 6000 years (+5.2 K). At a warming level of 2.8 K above pre-industrial, the ice loss does not exceed 2 m SLE, and most of the retreat occurs in the first 10,000 years in the south-west and central-west basins. In contrast, with a higher warming level of 3.6 K above pre-industrial as much as 7 m SLE of ice are loss in 20,000 years, with primary contributions from the western, northern and north-eastern basins. We will conclude by showing preliminary results from a second set of simulations focusing on the 2.8-3.6 K warming above pre-industrial interval.

How to cite: Petrini, M., Vizcaino, M., Sellevold, R., Muntjewerf, L., Georgiou, S., Scherrenberg, M. D. W., Lipscomb, W., and Leguy, G.: Multi-millennial response of the Greenland Ice Sheet to anthropogenic warming , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12958, https://doi.org/10.5194/egusphere-egu21-12958, 2021.

09:29–09:31
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EGU21-12603
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ECS
Alison Delhasse, Johanna Beckmann, and Xavier Fettweis

The Greenland ice sheet (GrIS) is a key contributor to see level rise. By melting in surface, ice sheet is thinning and reaches higher temperature which accelerate the melting processes coming from Global Warming. The main goal of our research is to improve the representation of melt-elevation feedback, which is crucial to determine how and when GrIS will melt and will involve in a near future, by coupling two kind of numerical models. The difficulty to model this feedback relies on the fact that ice-sheet models (ISMs) can reproduce the dynamic of the ice sheet and thus provide an evolution of the surface elevation, whereas (regional) climate models (RCMs) can represent the ice/snow and atmosphere interactions trough the surface mass balance (SMB). A coupling between these models appears as a solution and has already been accomplished. However, ISMs responses to a same forcing field may be quite different, while SMB from different RCMs are relatively more similar with the same forcing. Coupling could therefore be dependent of which ISMs are used. To avoid a coupling, costly in computing time, SMB vertical gradient as a function of local elevation variations could be used by ISMs to correct SMB. Nonetheless, these SMB gradients are computed with a RCM using a fixed topography, which could introduce biases if the surface elevation vary significantly. Here we decide to full couple the RCM MAR, specifically developed for polar climate and forced at his lateral boundaries by CESM2 (a CMIP6 model, scenario ssp585), with the ISM PISM. The coupling means that, each year, we exchange ice thickness from PISM to update the topography and ice mask of MAR, and SMB from MAR to update forcing fields of PISM. First of all the aim is to analyze what became the GrIS in 2100 with this extreme scenario. Then we want to define a coupling time threshold to determine after how much years an update of the topography in MAR is needed by varying the time step (from 1 to 5, 10, 20, 30 and 50 years) of the coupling. The final aim is to determine until when the MAR based SMB gradients are valid for a same topography in MAR.

How to cite: Delhasse, A., Beckmann, J., and Fettweis, X.: Greenland mass balance by 2100 using a coupled atmospheric (MAR) and ice sheet (PISM) models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12603, https://doi.org/10.5194/egusphere-egu21-12603, 2021.

09:31–09:33
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EGU21-10213
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ECS
Katharina Meike Holube, Tobias Zolles, and Andreas Born

The surface mass balance (SMB) of the Greenland Ice Sheet is subject to considerable uncertainties that complicate predictions of sea-level rise caused by climate change.
We examine the SMB of the Greenland Ice Sheet and its uncertainty in the 21st century using a wide ensemble of simulations with the surface energy and mass balance model "BErgen Snow SImulator" (BESSI). We conduct simulations for four greenhouse gas emission scenarios using the output of 26 climate models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) to force BESSI. In addition, the uncertainty of the SMB simulation is estimated by using 16 different parameter sets in our SMB model. The median SMB across climate models, integrated over the ice sheet, decreases for every emission scenario and every parameter set. As expected, the decrease in SMB is stronger for higher greenhouse gas emissions. The uncertainty range in SMB is considerably greater in our ensemble than in other studies that used fewer climate models as forcing. An analysis of the different sources of uncertainty shows that the differences between climate models are the main reason for SMB uncertainty, exceeding even the uncertainty due to the choice of climate scenario. In comparison, the uncertainty caused by the snow model parameters is negligible. The differences between the climate models are most pronounced in the north of Greenland and in the area around the equilibrium line, whereas the ensemble of simulations agrees that the SMB decrease is greatest in the west of Greenland. 

How to cite: Holube, K. M., Zolles, T., and Born, A.: Sources of Uncertainty in Greenland Surface Mass Balance in the 21st century., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10213, https://doi.org/10.5194/egusphere-egu21-10213, 2021.

09:33–09:35
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EGU21-12822
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ECS
Emily Hill, Sebastian Rosier, Hilmar Gudmundsson, and Matthew Collins

The future of the Antarctic Ice Sheet under climate warming is one of the largest sources of uncertainty for changes in global mean sea level (GMSL). Accelerated ice loss in recent decades has been concentrated in regions where warm circumpolar deep water forces high rates of sub-shelf melt. It is unclear how ice shelves currently surrounded by cold ocean waters with low melt rates will respond to changes in ocean conditions in future. For example, previous studies have shown that if warm water were to infiltrate beneath the Filchner-Ronne ice shelf, it could drastically increase sub-shelf melt rates. However, the inland ice-sheet response to climate-ocean changes remains uncertain. Here, we set out to quantify uncertainties in projections of GMSL from the Filchner-Ronne region of Antarctica over the next two centuries. To do this we take a large random sample from a probabilistic input parameter space and evaluate these parameter sets in the ice-sheet model Úa under four RCP forcing scenarios. We then use this training sample to generate a statistical surrogate model to capture the parameter to projection relationship from our ice-sheet model. Finally, we use sensitivity analysis to identify which parameters drive the majority of uncertainty in our projections.

Our results suggest that accumulation expected with warming is capable of suppressing increases in ice discharge associated with increased ocean-driven sub-shelf melt rates. This could allow the Filcher-Ronne basin to have a negative contribution to GMSL. However, parameters controlling mass accumulation and sub-shelf melting are highly uncertain. Crucially, there is potential within our input parameter space for major collapse and retreat of ice streams feeding the Filchner-Ronne ice shelf and a positive contribution to sea level rise. Further improvements in the representation of accumulation and sub-shelf melt under climate warming in ice-sheet models will help determine the sign of GMSL projections from this region of the ice sheet.

How to cite: Hill, E., Rosier, S., Gudmundsson, H., and Collins, M.: Quantifying uncertainty in future projections of ice loss from the Filchner-Ronne basin, Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12822, https://doi.org/10.5194/egusphere-egu21-12822, 2021.

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