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CR4.1

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 CL1.1/OS1
Convener: Heiko Goelzer | Co-conveners: Emily HillECSECS, Alexander Robinson, Ricarda Winkelmann, Philippe Huybrechts
Presentations
| Mon, 23 May, 08:30–11:50 (CEST), 13:20–14:46 (CEST)
 
Room L3

Mon, 23 May, 08:30–10:00

Chairpersons: Heiko Goelzer, Emily Hill

08:30–08:33
Introduction

08:33–08:40
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EGU22-1501
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ECS
Jonas Van Breedam et al.

The early Cenozoic Antarctic ice sheet has grown non-linearly to a continental-scale ice sheet close to the Eocene-Oligocene boundary when environmental conditions were favourable. These favourable conditions included the movement of the continent towards the South Pole, the thermal isolation of the Antarctic continent and declining atmospheric CO2 concentrations.  Once the threshold for ice sheet growth was reached, a series of positive feedbacks led to the formation of a continental-scale ice sheet.

The thresholds for growth and decline of a continental scale ice sheet are different. The ice sheet state is dependent on the initial conditions, an effect called hysteresis. Here we present the hysteresis behaviour of the early Cenozoic Antarctic ice sheet for different bedrock elevation reconstructions. The ice sheet-climate coupler CLISEMv1.0 is used and captures both the height-mass balance and the ice-albedo feedback accurately. Additionally, the influence of the different orbital parameters on the threshold to glaciation and deglaciation is investigated in detail. It appears that the long-term eccentricity cycle has a significant influence on the ice sheet growth and decline and is able to pace the ice sheet evolution for constant CO2 concentration close to the glaciation threshold.

How to cite: Van Breedam, J., Huybrechts, P., and Crucifix, M.: Hysteresis and orbital pacing of the early Cenozoic Antarctic ice sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1501, https://doi.org/10.5194/egusphere-egu22-1501, 2022.

08:40–08:47
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EGU22-2829
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ECS
Lennert B. Stap et al.

Benthic δ18O levels vary strongly during the warmer-than-modern early- and mid-Miocene (23 to 14 Myr ago), suggesting a dynamic Antarctic ice sheet (AIS). So far, however, realistic simulations of the Miocene AIS have been limited to equilibrium states under different CO2 levels and orbital settings. Earlier transient simulations lacked ice-sheet-atmosphere interactions, and used a present-day rather than Miocene Antarctic bedrock topography. Here, we quantify the effect of ice-sheet-atmosphere interactions, running IMAU-ICE using climate forcing from Miocene simulations by the general circulation model GENESIS. Utilising a recently developed matrix interpolation method enables us to interpolate the climate forcing based on CO2 levels (between 280 and 840 ppm) as well as varying ice sheet configurations (between no ice and a large East Antarctic ice sheet). We furthermore implement recent reconstructions of Miocene Antarctic bedrock topography. We find that the positive albedo-temperature feedback, partly compensated by a negative feedback between ice volume and precipitation, increases hysteresis in the relation between CO2 and ice volume. Together, these ice-sheet-atmosphere interactions decrease the amplitude of Miocene AIS variability in idealised transient simulations. Forced by quasi-orbital 40-kyr forcing CO2 cycles, the ice volume variability reduces by 21% when ice-sheet-atmosphere interactions are included, compared to when forcing variability is only based on CO2 changes. Thereby, these interactions also diminish the contribution of AIS variability to benthic δ18O fluctuations. Evolving bedrock topography during the early- and mid-Miocene reduces ice volume variability by 10%, under equal 40-kyr cycles of atmosphere and ocean forcing. 

How to cite: Stap, L. B., Berends, C. J., Scherrenberg, M. D. W., van de Wal, R. S. W., and Gasson, E. G. W.: Net effect of ice-sheet-atmosphere interactions reduces simulated transient Miocene Antarctic ice sheet variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2829, https://doi.org/10.5194/egusphere-egu22-2829, 2022.

08:47–08:54
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EGU22-7293
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ECS
Diane Segalla et al.

The mid-Miocene Climatic Optimum (MMCO, ~17-15 Ma) and the mid-Miocene Climatic Transition (MCT, ~15-13.5 Ma),  represents a period of high policy relevance because of the high atmospheric pCO2 concentrations. Exploring this period offers the opportunity to investigate the Antarctic Ice Sheet (AIS) response to CO2 forcings that are close to those projected in the medium to worse case emission scenarios. A set of equilibrium simulations with the 3D ice sheet model Yelmo allows us to study the envelope of the AIS volume and extent during the MMCO (17 Ma) and MCT (14 Ma). These simulations are forced off-line with equilibrium climatic conditions  obtained with the Atmosphere-Ocean General Circulation Model (AOGCM) IPSL CM5A2.  Two values of the reconstructed atmospheric pCO2, i.e. 420 ppm and 700 ppm, are prescribed, for an orbital configuration corresponding to minimum and maximum insolation values at 75°S each (9 climate simulations in total). Thanks to these different configurations we simulated the AIS dynamics. Results show that at 17 Ma, warmer conditions produce an AIS that is drastically reduced with respect to today’s configuration. At 14 Ma, cooler climatic conditions allow the AIS to expand again. This is in agreement with the geological records of the AIS dynamics that reveal a substantial expansion of the ice sheet at the end of the MCT. Since Antarctica is the only ice sheet at this time, our set of climate and ice-sheet simulations capture the envelope of ice volume and extent of the AIS. Moreover, such studies contribute to a better understanding of the 𝛿18O records and of the evolution of deep ocean temperature versus ice volume and global mean sea level change.

How to cite: Segalla, D., Blasco Navarro, J., Ramstein, G., Fluteau, F., Robinson, A. J., Alvarez-Solas, J., Montoya Redondo, M. L., and Colleoni, F.: Antarctic Ice Sheet  simulations using Yelmo ice sheet model and a series of IPSL CM5A2 climate simulations between 17 Ma and 14 Ma, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7293, https://doi.org/10.5194/egusphere-egu22-7293, 2022.

08:54–09:01
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EGU22-10821
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ECS
Matthew Drew and Lev Tarasov

A leading contender for explaining the mid-Pleistocene transition (MPT) from small 40 kyr glaciations to large, abruptly terminating 100 kyr ones is a shift to high friction bed under the Northern hemisphere ice sheets – the North American ice sheet in particular. The regolith hypothesis posits that this occurred with the removal of deformable regolith – laying bare higher-friction bedrock under ice sheet core domains. Is the regolith hypothesis consistent with the physics of glacial removal of mechanically weak surface material?                

                                                                        

Self-consistency of the regolith hypothesis has not been tested for a realistic, 3D North American ice sheet, capturing the transition from soft to hard bedded and 40 to 100 kyr cycles, fully considering basal processes and sediment production. To test self-consistency, we simulate the pace and distribution of regolith removal in a numerical ice sheet model incorporating the relevant glacial processes and their uncertainties. Specifically, the Glacial Systems Model includes: fully coupled sediment production and transport, subglacial hydrology, glacial isostatic adjustment, 3D thermomechanically coupled hybrid ice physics, and internal climate solution from a 2D non-linear energy balance model. The sediment model produces sediment via quarrying and abrasion while transporting material englacially and subglacially. The subglacial hydrology model employs a linked-cavity system with a flux based switch to tunnel drainage, giving dynamic effective pressure needed for realistic sediment and sliding processes. Deflection and rebound of the Earth's surface are calculated for a range of solid Earth visco-elastic rheologies.  The coupled system is driven only by prescribed atmospheric CO2 and orbitally derived insolation.

                                                                         

Starting from a range of initial sediment distributions and simulating an ensemble of model parameter values, we model the rate and spatial distribution of regolith dispersal and compare this against the inferred range of Pliocene regolith thickness, the present day sediment distribution, and the timing of the MPT. A first order fully coupled representation of ice, climate and sediment interactions captures the transition within parametric and observational uncertainty. The system gives the shift from 40 to 100 kyr glacial cycles while broadly reproducing the present day sediment distribution, inferred early Pleistocene extent, LGM ice volume and deglacial margin locations.

How to cite: Drew, M. and Tarasov, L.: A test of the Regolith Hypothesis with fully coupled glacial sediment and ice sheet modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10821, https://doi.org/10.5194/egusphere-egu22-10821, 2022.

09:01–09:06
Short break

09:06–09:13
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EGU22-1635
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ECS
Patricio Velasquez et al.

In this study, we investigate the sensitivity of the glacial Alpine hydro-climate to changes of the Laurentide ice sheet (LIS). Bridging the scale gap by using a chain of global and regional climate models, we perform sensitivity simulations of up to 2 km horizontal resolution over the Alps for the Last Glacial Maximum and the Marine Isotope Stage 4. In winter, we find wetter conditions in the southern part of the Alps during glacial conditions compared to present day, to which dynamical processes, i.e.  changes in the wind speed and direction, substantially contribute. During summer, we find the expected drier conditions in most of the Alpine region during glacial conditions, as thermodynamics suggests drier conditions under lower temperatures. The sensitivity simulations of the LIS changes show that an increase of the ice-sheet thickness leads to a significant intensification of glacial Alpine hydro-climate conditions, which is mainly explained by dynamical processes. The findings demonstrate that the Laurentide ice-sheet topography plays an important role in regulating the Alpine hydro-climate and thus permits a better understanding of the precipitation patterns in the complex Alpine terrain at glacial times.

How to cite: Velasquez, P., Messmer, M., and Raible, C. C.: The role of the Laurentide ice-sheet topography in the Alpine hydro-climate at glacial times, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1635, https://doi.org/10.5194/egusphere-egu22-1635, 2022.

09:13–09:20
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EGU22-3080
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ECS
Daniel Moreno et al.

It is well known that the climate during the last glacial period was far from stable. The presence of layers of ice-rafted debris (IRD) in deep-sea sediments has 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 the basal friction law. Therefore, it is essential to determine the impact of basal friction on ice-stream surges. Here we study the effect of a wide range of basal friction parameters and laws for the LIS under constant LGM boundary conditions by running ensembles of simulations using a higher-order ice-sheet model. The potential feedbacks among till mechanics, 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 internal oscillations are possible in the LIS. 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., Montoya, M., Blasco, J., and Robinson, A.: Could the Laurentide Ice Sheet have exhibited internal oscillations?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3080, https://doi.org/10.5194/egusphere-egu22-3080, 2022.

09:20–09:27
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EGU22-6242
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ECS
Clemens Schannwell et al.

Transitions from a stable, periodically oscillating ice-sheet system to a perpetual ice stream has potentially far-reaching implications for the timing of the onset of the last deglaciation as well as for climate transitions such as the Younger Dryas. These periodical ice-sheet oscillations known as Heinrich-type ice sheet surges are among the most dominant signals of glacial climate variability. They are quasi-periodic events during which large amounts of ice are discharged from ice sheets into the ocean. The addition of freshwater strongly affects the ocean circulation, resulting in a pronounced cooling in the North Atlantic region. In addition, changes in the ice sheet geometry also have significant effects on the climate. Here, we use a coupled ice sheet-solid earth model that is driven with forcing from a comprehensive Earth System Model that includes interactive ice sheets to identify key drivers controlling the surge cycle length of Heinrich-type ice-sheet surges from two main outlet glaciers of the Laurentide ice sheet. Our simulations show different surge initiation behaviour for the land-terminating Mackenzie ice stream and marine-terminating Hudson ice stream. For both ice streams, the surface mass balance has the largest effect on the surge cycle length. Ice surface temperature and geothermal heat flux also influence the surge cycle length, but to a lesser degree. Ocean forcing and different frequencies of the same forcing have a negligible effect on the surge cycle length. The simulations also highlight that a certain parameter space exists under which stable surge oscillations can be maintained. This parameter range is much narrower for the Mackenzie ice stream than for the Hudson ice stream. Leaving the stable regime results in a dynamical switch that turns the system from periodically oscillating system into a perpetual ice stream system. This transition can lead to a volume loss of up to 36% for the respective ice stream drainage basin under otherwise glacial climate conditions.

How to cite: Schannwell, C., Mikolajewicz, U., Ziemen, F., and Kapsch, M.-L.: Sensitivity of Heinrich-type ice sheet surges and their implications for the last deglaciation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6242, https://doi.org/10.5194/egusphere-egu22-6242, 2022.

09:27–09:34
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EGU22-7563
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ECS
Henrieka Detlef et al.

The most prominent events of ice-sheet collapse in the recent geological past are so-called Heinrich events observed during millennial-scale climate oscillations of the last glacial period. They are characterized by the dispersal of ice(berg) rafted debris and freshwater across the North Atlantic, with the Hudson Strait suggested as the predominant source region. One potential mechanism triggering iceberg release invokes cryosphere-ocean interactions, where subsurface warming destabilizes the Laurentide ice sheet. In this scenario, the build-up of a subsurface heat reservoir is caused by an extensive sea ice cover in the Labrador Sea in combination with a reduced overturning circulation in the North Atlantic, preventing the release and downward mixing of heat in the water column.

Here we present high-resolution reconstructions of sea ice dynamics in the outer Labrador Sea between 30 ka and 60 ka at IODP Site U1302/03, located on Orphan Knoll. Sea ice reconstructions are based on a suite of sympagic and pelagic biomarkers, including highly branched isoprenoids and sterols. These results suggest a transition from reduced/seasonal to extended/perennial sea ice conditions preceding the onset of iceberg rafting associated with Heinrich event 3, 4, 5, and 5a by a couple of hundred to a thousand years. Our preliminary results thus support the importance of sea ice in the Labrador Sea for triggering Heinrich events. Future results from the same core will have to confirm the timing and extent of subsurface warming and ocean circulation dynamics.  

How to cite: Detlef, H., Mørk Jensen, M., Glasius, M., and Pearce, C.: Sea ice dynamics in the Labrador Sea across Heinrich events during MIS 3, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7563, https://doi.org/10.5194/egusphere-egu22-7563, 2022.

09:34–09:39
Short break

09:39–09:46
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EGU22-11503
Lauren Gregoire et al.

Coupled climate-ice sheet models are crucial to evaluating climate-ice feedbacks' role in future ice sheet evolution. Such models are calibrated to reproduce modern-day ice sheets, but current observations alone are insufficient to constrain the strength of climate-ice feedbacks. The extent of the Northern Hemisphere ice sheets during the last glacial maximum, ~20,000 years ago, is well known and could provide a benchmark for calibrating coupled climate-ice sheet models. We test this with the FAMOUS-ice coupled Climate-Ice Sheet model (Smith et al., 2020), a fast GCM coupled to the Glimmer ice sheet model. We ran Last Glacial Maximum simulations using FAMOUS-ice with interactive North American Ice Sheet, following the PMIP4 protocol (Kageyama et al., 2018). We find that the standard model setup, calibrated to produce a good present-day Greenland (Smith et al., 2020), produced a collapsed North American ice sheet at the Last Glacial Maximum. We ran ensembles of hundreds of simulations to explore the influence of uncertain ice sheet, albedo, atmospheric, and oceanic parameters on the ice sheet extent. The North American continent deglaciated rapidly in most of our simulations, leaving only a handful of useful simulations out of 280. We thus developed a method to efficiently identify regions of the parameter space that can produce a reasonable ice-sheet extent. This involved emulating the equilibrium ice volume and area as a function of the surface mass balance at the start of our simulations. We then ran three waves of short simulations for 20-50 years to identify parameter values and surface mass balance conditions potentially suitable to grow a realistic ice sheet. This enabled us to find ~160 simulations with good ice extent.

Through analysis of these simulations, we find that albedo parameters determine the majority of uncertainty when simulating the Last Glacial Maximum North American Ice Sheets. The differences in cloud cover over the ablation zones of the North American and Greenland ice sheet explains why the ice sheets have different sensitivities to surface mass balance parameters. Based on our work, we propose that the Last Glacial Maximum can provide an “out-of-sample” target to avoid over calibrating coupled climate-ice sheet models to the present day.

References:

Kageyama, M. et al. The PMIP4 contribution to CMIP6 – Part 4: Scientific objectives and experimental design of the PMIP4-CMIP6 Last Glacial Maximum experiments and PMIP4 sensitivity experiments. Geosci. Model Dev. 10, 4035–4055 (2017).

Smith, R. S., George, S., and Gregory, J. M.: FAMOUS version xotzt (FAMOUS-ice): a general circulation model (GCM) capable of energy- and water-conserving coupling to an ice sheet model, Geosci. Model Dev., 14, 5769–5787, https://doi.org/10.5194/gmd-14-5769-2021, 2021.

 

How to cite: Gregoire, L., Gandy, N., Astfalck, L., Ivanovic, R., Sherriff-Tadano, S., Smith, R., and Williamson, D.: De-tuning a coupled Climate Ice Sheet Model to simulate the North American Ice Sheet at the Last Glacial Maximum , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11503, https://doi.org/10.5194/egusphere-egu22-11503, 2022.

09:46–09:53
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EGU22-2831
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ECS
Christopher Darvill et al.

The Cordilleran Ice Sheet in western North America was of comparable size and topographic setting to the modern Greenland Ice Sheet and exhibited similar dynamics. Ice streams channelled rapid flow and the western ice margin terminated in both marine and terrestrial environments. Reconstructing Cordilleran Ice Sheet retreat can therefore provide a helpful analogue for how the Greenland Ice Sheet may respond to changing climate and underlying topography in the future. Moreover, deglaciation in this region controlled routes available for early human migration into the Americas. Here, we present cosmogenic 10Be nuclide exposure ages from glacial erratics and bedrock on the west coast of British Columbia (53.4°N, 129.8°W) that add to existing chronologies along ~600 km of coastal North America. Collectively, these data show deglaciation back to the present coastline by ca. 18–16 ka. Retreat then slowed and ice seemingly stabilised close to the present coastline for several thousand years until ca. 14–13 ka. Ice may still have been lost during this period of relative stability, but through vertical thinning rather than lateral retreat. We attribute initial retreat to destabilisation and grounding line retreat resulting from rising sea level and/or ocean warming in the northern Pacific. Subsequent stability at the present coast was likely due to the transition from marine to terrestrial margins despite increasing temperatures that may have driven ice sheet thinning. Hence, we show the importance of understanding both climatic and non-climatic drivers of ice sheet change through time. We also show that hundreds of kilometres of coastline were free of ice prior to an important period of early human migration into the Americas.

How to cite: Darvill, C., Menounos, B., Goehring, B., and Lesnek, A.: Reconstructing Cordilleran Ice Sheet stability in western Canada during the Last Deglaciation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2831, https://doi.org/10.5194/egusphere-egu22-2831, 2022.

09:53–10:00
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EGU22-3293
Sam Sherriff-Tadano et al.

Understanding the response of ice sheets to global temperature changes is a critical issue for the climate community. To accurately simulate future ice sheet evolution, we need to know the strength of feedbacks between the climate and ice sheets. Testing the ability of coupled climate-ice sheet models to simulate past ice sheet extent can provide a way to evaluate the models and ground truth projections. One example is the Last Glacial Maximum (LGM), when huge ice sheets covered the Northern Hemisphere, especially over the North America. Here, we performed simulations of the North American ice sheet and climate of the LGM with a recently updated ice sheet-atmosphere coupled model Famous-Ice (Smith et al. 2021, Gregory et al. 2020). The model consists of a low-resolution atmospheric general circulation model Famous (Smith et al. 2008) and an ice sheet model BISICLES (Cornford et al. 2013). It calculates the surface mass balance over ice sheets based on an energy budget scheme and incorporates an updated albedo scheme, which accounts for albedo changes associated with modifications in surface air temperature, grain size and density of the snow. The atmospheric model reproduces the surface mass balance of the modern Greenland ice sheet reasonably well (Smith et al. 2021). Simulations of projections of future sea-level rise (Gregory et al. 2020) and the LGM (Gandy et al. in prep) have also been performed with Famous-Ice using a different ice sheet model GLIMMER.

We present simulations of the LGM with interactive ice sheets in North America and Greenland using FAMOUS-BISICLES. Uncertain input parameters controlling the surface temperatures and ice albedo are varied in our simulations. The global temperature is specified by applying fixed sea surface temperature in the atmospheric model producing a global cooling that ranges from -3K to -6.5K in the simulations. The bare ice minimum albedo is varied from 0.2 to 0.7, which corresponds to the range in PMIP3 models. Our results show a better representation of North American ice sheet when forced with a colder LGM (-6.5K) and high bare ice albedo. We will further discuss potential roles of model biases and compare our results with simulations performed with FAMOUS-GLIMMER (Gandy et al. in prep).

How to cite: Sherriff-Tadano, S., Gandy, N., Ivanovic, R., Gregoire, L., Lang, C., Gregory, J., and Smith, R.: Simulations of North American ice sheet at the LGM with FAMOUS-BISICLES and its sensitivity to global temperatures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3293, https://doi.org/10.5194/egusphere-egu22-3293, 2022.

Mon, 23 May, 10:20–11:50

Chairpersons: Heiko Goelzer, Emily Hill

10:20–10:22
Introduction

10:22–10:29
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EGU22-6624
Kyung-Sook Yun and Axel Timmermann

Here we present first results from a series of transient glacial cycle simulations which were conducted with the Community Earth System model (CESM, version 1.2) coupled to the Penn State University ice sheet-ice-shelf Model (PSUIM). The coupling is achieved by applying CESM-simulated surface air temperature, precipitation, surface shortwave radiation and subsurface-ocean temperatures to the PSUIM. CESM is forced in return by PSUIM-simulated ice sheet cover, topography, and freshwater fluxes. The coupled model, which uses a ~ 4 degree horizontal resolution in the atmosphere and ocean and ~ 40 km for the ice-sheets in both hemispheres, includes representations of the lapse-rate, desert-elevation and albedo-dust feedbacks. The coupled model, which uses moderate bias corrections for temperature and precipitation, reproduces the ice sheet evolution over the last glacial cycle in reasonable agreement with paleo-climate data. In this presentation we will further highlight the sensitivity of simulated glacial variability to changes in key surface parameters as well to the individual orbital and greenhouse gas forcings. Our results reveal that only the combination of orbital and CO2 forcings can generate the full glacial/interglacial amplitude. Single forcings are insufficient to generate glacial variability, which emphasizes the need to understand the mechanisms that led to the orbital pace-making of CO2 during the Pleistocene.

How to cite: Yun, K.-S. and Timmermann, A.: A transient glacial cycle simulation with the coupled CESM1.2-PSUIM climate-ice-sheet model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6624, https://doi.org/10.5194/egusphere-egu22-6624, 2022.

10:29–10:36
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EGU22-5261
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ECS
Meike D.W. Scherrenberg et al.

For simulating ice sheet – climate interactions on multi-millennial time-scales, a set-up that uses a two-way coupled Earth System Model would be ideal. However, running these simulations over multi-millennium time-scales while including ice sheets, is not feasible. Alternatively, ice sheet models can be forced by interpolating climate time-slices, allowing for a transient forcing to an ice sheet model at limited computational costs.

Here, we compare two methods that interpolate between climate time-slices to create a transient forcing for ice sheet simulations. Firstly, we use a glacial index method, in which the climate is linearly interpolated between time-slices based only on prescribed atmospheric CO2 concentrations. Secondly, we use a climate matrix method in which the interpolation is not only dependent on the prescribed CO2 concentration, but also on internally generated thickness, volume and albedo. As a result, the climate matrix method captures ice-sheet atmosphere feedbacks.

Here we present ice sheet simulations of the Last Glacial Cycle using IMAU-ICE forced with Last Glacial Maximum (LGM) and Pre-Industrial time-slices. For the time-slices we use the output from nine Paleoclimate Modelling Intercomparison Project Phase III (PMIP3) GCMs. Our aim is to compare and to evaluate the differences in ice sheet evolution and LGM volume and extent resulting from the different PMIP3 models and the interpolation method used for transient simulations.

For most PMIP3 forcings, both the North-American and Eurasian ice sheets build up quicker in the climate matrix method compared to the glacial index method, which is in better agreement with paleo-observations. This is mostly a result from precipitation differences between the two interpolation methods: In the climate matrix method the interpolation of precipitation is dependent on internally generated ice thickness instead of only CO2. Therefore, when ice thickness is smaller than LGM, the interpolation tends to shift more towards pre-industrial in the climate matrix method compared to the glacial index method. As precipitation is larger during pre-industrial compared to LGM in most Eurasian and North-American regions, this leads to a larger precipitation in the climate matrix method, increasing ice sheet volume. Similarly, the climate matrix method results into warmer temperatures in ice-free areas as the interpolation is dependent on both CO2, albedo and insolation. However, for most PMIP3 models, this ice sheet-temperature feedback does not cancel-out the increased precipitation in the climate matrix method.

How to cite: Scherrenberg, M. D. W., van de Wal, R. S. W., Berends, C. J., and Stap, L. B.: Simulating the Last Glacial Cycle using a Glacial Index and Climate Matrix Method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5261, https://doi.org/10.5194/egusphere-egu22-5261, 2022.

10:36–10:43
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EGU22-6247
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ECS
Lianne Sijbrandij et al.

This study investigates how large proglacial lakes affected regional climate and surface mass balance (SMB) of retreating ice sheets during the last deglaciation. For this purpose we have modified the atmosphere model ECHAM6. The approach is here to limit the surface temperature of proglacial lakes to values below 4°C, while other lakes in ECHAM6 can freely evolve according to a mixed layer scheme.

As a first application we investigate the impact of proglacial lakes during the Allerød interstadial at 13 ka (ka is thousand years before present) with three atmosphere stand-alone experiments:

(i) with 13ka land surface boundary conditions (GLAC1d, Ivanovic et al., 2016) and a modern lake configuration

(ii) same as (i) but with additional lakes around the North American and Fennoscandian Ice Sheets

(iii) same as (ii) but the additional lakes are treated according to our proglacial lake approach.

Over the ocean we use boundary conditions taken from a 15ka coupled climate simulation. These three simulations were evaluated with respect to the regional climate response and the SMB was calculated using the diurnal Energy Balance Model (dEBM, Krebs-Kanzow et al., 2021). Preliminary results are indicating an overall positive effect of regular lakes, and in particular proglacial lakes, on the SMB of the great ice sheets over Northern America and Scandinavia during the Allerød interstadial.

 

References:

Ivanovic, R. F., Gregoire, L. J., Kageyama, M., Roche, D. M., Valdes, P. J., Burke, A., Drummond, R., Peltier, W. R., and Tarasov, L.: Transient climate simulations of the deglaciation 21–9 thousand years before present (version 1) – PMIP4 Core experiment design and boundary conditions, Geosci. Model Dev., 9, 2563–2587, https://doi.org/10.5194/gmd-9-2563-2016, 2016.

Krebs-Kanzow, U., Gierz, P., Rodehacke, C. B., Xu, S., Yang, H., and Lohmann, G., 2021: The diurnal Energy Balance Model (dEBM): a convenient surface mass balance solution for ice sheets in Earth system modeling, The Cryosphere, 15, 2295–2313, https://doi.org/10.5194/tc-15-2295-2021.

How to cite: Sijbrandij, L., Gierz, P., Hinck, S., Krebs-Kanzow, U., Lohmann, G., and Niu, L.: The influence of proglacial lakes on climate and surface mass balance of retreating ice sheets – An Investigation of the Laurentide and Fennoscandian ice sheets,13 ka BP, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6247, https://doi.org/10.5194/egusphere-egu22-6247, 2022.

10:43–10:50
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EGU22-11345
Martin Margold et al.

The North American Ice Sheet Complex (comprising the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass in the Northern Hemisphere that grew towards and waned after the Last Glacial Maximum. The existing ice margin chronology available for the North American Ice Sheet Complex is based on radiocarbon data only and does not reflect other geochronometric information constraining the last deglaciation, such as cosmogenic exposure- or optically stimulated luminescence ages. Here we present a series of newly produced ice margin isochrones from 25 ka to present, in a time step of 500 years. For each isochron, we draw maximum, best estimate, and minimum ice margin position in an attempt to capture the existing uncertainty. The ice margin isochrones are based on (i) an up-to-date dataset of radiocarbon ages (~5000), (ii) 10Be and 26Al cosmogenic nuclide data that directly date ~80 ice-marginal features over North America, (iii) ~350 optically stimulated luminescence ages dating the deposition of an aeolian cover immediately post-deglaciation, (iv) the ice-sheet scale glacial geomorphology record. Our effort brings the information on the last North American Ice Sheet Complex deglaciation on par with that for the Eurasian Ice Sheets and should serve the broad community of Quaternary research from archaeology to numerical ice sheet modelling.

How to cite: Margold, M., Dalton, A. S., Heyman, J., Dulfer, H. E., and Norris, S. L.: New ice margin chronology for the last deglaciation of the North American Ice Sheet Complex, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11345, https://doi.org/10.5194/egusphere-egu22-11345, 2022.

10:50–10:55
Short break

10:55–11:02
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EGU22-530
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ECS
Victor van Aalderen et al.

Rapid sea-level rise, due to melting and destabilization of present-day ice sheets will likely have important consequences on human societies. Observations provide evidences of increased mass loss in the West Antarctic Ice Sheet (WAIS) over the recent decades, partly due to ocean warming. Despite improvements in both climate and ice-sheet models, there are still significant uncertainties about the future of West Antarctica, due, in part, to our misunderstanding of the process responsible for the marine ice sheet evolution. Paleoclimate studies provide important information on ice-sheet collapse in a warming world.

Our study is based on the Eurasian Ice Sheet (EIS) complex, including the British Island Ice Sheet (BIIS), the Fennoscandian Ice Sheet (FIS) and the Barents Kara Ice Sheet (BKIS). Because large parts of both the BKIS and the WAIS are marine-based, the BKIS at the LGM can be considered as a potential analogue to the WAIS.

To improve our understanding of the mechanisms responsible for the EIS retreat, we performed transient simulations of the last EIS deglaciation (21 000 – 8 000 yr BP) with the GRISLI ice sheet model forced by 5 PMIP3/PMIP4 models, and two transients GCM models, TRACE21K and iLOVECLIM. Our main goal is to investigate the sensitivity of the EIS grounding line retreat to climate forcing, sea-level rise and glaciological processes with a focus on the BKIS evolution during the deglaciation and the behaviour of the large Bjornoyrenna ice stream.  

How to cite: van Aalderen, V., Charbit, S., Dumas, C., and Quiquet, A.: The last deglaciation of the Eurasian ice sheet (21,000 - 8,000 yr BP): a sensitivity study to PMIP3/PMIP4 coupled atmosphere-ocean models outputs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-530, https://doi.org/10.5194/egusphere-egu22-530, 2022.

11:02–11:09
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EGU22-7694
|
ECS
Rosie Archer et al.

At the Last Glacial Maximum, the Eurasian Ice Sheet (EIS) was one of the largest ice masses, reaching an area of 5.5 Mkm2 at its maximum. Recent advances in numerical ice sheet modelling hold significant promise for improving our understanding of ice sheet dynamics, but remain limited by the significant uncertainty as to the appropriate values for the various model input parameters. The EIS left behind a rich library of observational evidence, in the form of glacial landforms and sediments. Integrating this evidence with numerical ice sheet models allows inference on these key model parameters, leading to a better understanding of the behaviour of the EIS and a framework for advancing numerical ice sheet models. To quantify how successfully a particular model run matches the available data, model-data comparison tools are required. Here, we model the EIS using the Parallel Ice Sheet Model (PISM), a hybrid shallow-ice shallow shelf ice sheet model. We perform sensitivity analyses to reveal the most important parameters controlling the evolution of our modelled EIS. Results from this analysis allow us to reduce the parameter space required for a future ensemble experiment. This ensemble experiment will utilise novel model-data comparison tools which compare ice-free timings to geochronological evidence and modelled flow directions with drumlins. Unlike previous model-data comparison routines, our tools provide a more nuanced, and probabilistic, assessment of fit than a simple pass-fail. This offers significant benefits for future parameter selection.

How to cite: Archer, R., Ely, J., Heaton, T., and Clark, C.: Sensitivity of the Eurasian Ice Sheet: Improved model-data comparison routines, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7694, https://doi.org/10.5194/egusphere-egu22-7694, 2022.

11:09–11:16
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EGU22-1774
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ECS
Franco Retamal-Ramírez et al.

During the Last Glacial Maximum (LGM, 23,000 to 19,000 years ago), the Patagonian Ice Sheet (PIS) covered the central chain of the Andes between ~ 38 °S to 55 °S. From limited paleoclimatic evidence, especially that derived from glacial landforms, it becomes clear that maximum ice sheet expansions in the Southern and Northern Hemispheres were not synchronized. However, large uncertainties still exist in the timing of the onset of regional deglaciation as well as its major drivers. Ice sheet modelling combined with glacial geochronology and paleoclimate reconstructions can provide important information on the PIS geometry, ice volume and its contribution to the sea level low during the LGM. It can also help to test different paleoclimate scenarios and identify climate models that capture regional climate responses to the global change in a realistic manner.

Here we present an ensemble of numerical simulations of the PIS during the LGM with an aim to constrain the most likely LGM climate conditions that can explain the reconstructed geometry of the PIS in a satisfactory manner. The PIS model is driven by the climate forcing that fuse near-surface air temperatures and precipitation rates from the ERA5 reanalysis with the paleoclimate model outputs from the Paleoclimate Modelling Intercomparison Project (PMIP2 and PMIP3) and the in-house Community Earth System Model (CESM) experiments. Our analysis suggests a strong dependence of the PIS geometry on the near-surface air temperature forcing. All the ensemble experiments designed with PMIP and in-house CESM experiments fail to reproduce the ice sheet extent between 38 and 42 °S. The most realistic performance for the LGM ice sheet extents south of 38 °S has been derived using those climate models that have a higher spatial resolution. The latter helps these models to capture regional climate conditions in a more physically consistent manner. It should be kept in mind that this analysis is based on the evaluation of the modelled ice sheet extents only, as geological evidence on the former ice sheet thickness is still scarce. Nevertheless, it can be shown that a realistic ice sheet geometry during the LGM is consistent with a regional decrease in air temperature of 7 to 12 °C and an increase in precipitation of 400 to 1500 mm/year along the western sectors of the PIS.

How to cite: Retamal-Ramírez, F., Castillo, A., Bernales, J., and Rogozhina, I.: Reconstruction of the Patagonian Ice Sheet during the Last Glacial Maximum using numerical modelling and geological constraints, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1774, https://doi.org/10.5194/egusphere-egu22-1774, 2022.

11:16–11:23
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EGU22-12930
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ECS
Qiang Wei et al.

Glaciers on Tibetan Plateau and its surrounding areas were much more extensive during Last Glacial Maximum (LGM) when global mean temperature was 5-8 K lower than today. Accurately reconstructing glaciers on and around Tibetan Plateau remains vital towards understanding glaciers’ sensitivity against climate change, and vice versa.

Previous simulations on glaciers in High Mountain Asia during LGM are usually forced with prescribed climatology without considering the bi-directional feedbacks. We instead coupled a climate model (CESM) to an ice-sheet model (ISSM). Our results show that the interactions between HMA glaciers and climate was significant. Uncoupled runs that ignore such interaction yielded glacial coverage roughly 10% more than coupled runs. Regional glacial features change considerably in coupled simulation. Glaciers on the mid-west Tibetan Plateau decreased while those in Qilian Mountains, Tianshan Mountains and Pamir Plateau saw pronounced increase. Compared with uncoupled simulations, our coupled results is in better agreement with reconstructions of LGM glaciers.

 

 

 

 

 

 

KEY WORDS: Glacier; Ice-sheet; Tibetan Plateau; High Mountain Asia; Numerical simulation; Climate modelling

 

How to cite: Wei, Q., Liu, Y., and Hu, Y.: Dynamic glaciers improve LGM simulation in High Mountain Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12930, https://doi.org/10.5194/egusphere-egu22-12930, 2022.

11:23–11:29
Short break

11:29–11:36
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EGU22-10758
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ECS
Dulcinea Groff et al.

Glaciers retreating along the western Antarctic Peninsula (AP) reveal previously entombed soils and plants. We collected black (dead) mosses to constrain the timing of late Holocene glacier advances at four sites along the AP from ice-free terrain and from rapidly retreating ice margins. The results of radiocarbon measurements from 39 black mosses were used to infer glacier activity over the past 1500 years along with established criteria for sample collection. The criteria ensure robust estimates of when plant growth ended, referred to hereafter as “kill date”. From these kill dates we report distinct periods of ice advance during ca. 1300, 800, and 200 calibrated calendar years before 1950 (cal yr BP) and the first estimates of glacier rate of advance around 800 cal yr BP of 2.0 and 0.3 meters per year from Gamage and Bonaparte Points (southern Anvers Island), respectively. Kill dates reveal a narrow range of ages within a region, suggesting that multiple glacier termini advanced together, and that the rate of local advances may have varied by an order of magnitude. Other evidence for glacier advances in the northern AP ca. 200 cal yr BP and ages of penguin remains (a proxy for penguin colony abandonment) centered ca. 800 cal yr BP from several sites across the AP coincide with our kill dates. Combining several lines of terrestrial evidence for past glacier activity is critical to improving our understanding of the regional synchroneity of glacial dynamics and cryosphere-biosphere connections.

How to cite: Groff, D., Beilman, D., Yu, Z., and Ford, D.: Kill dates from re-exposed black mosses constrain past glacier advances along the western Antarctic Peninsula, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10758, https://doi.org/10.5194/egusphere-egu22-10758, 2022.

11:36–11:43
|
EGU22-2516
Heiko Goelzer et al.

Long-term simulations of ice sheets and their interaction with the climate system require the application of Earth system models with interactive ice sheet components. To this end we present the first experiments performed with the CMIP6-type Norwegian Earth System Model (NorESM2) including a Greenland ice sheet model component. We present our coupling and modelling strategy, which builds on earlier work with the Community Earth System Model and show first results for two NorESM2 version with different resolution of the atmospheric component. We have performed and analyzed pre-industrial spinup and control experiments, historical runs and future projections under scenario ssp585, following the ISMIP6 protocol.

How to cite: Goelzer, H., Langebroek, P., and Born, A.: Coupled Greenland ice sheet-climate simulations with the Norwegian Earth System Model (NorESM2), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2516, https://doi.org/10.5194/egusphere-egu22-2516, 2022.

11:43–11:50
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EGU22-11275
Marianne S. Madsen et al.

Mon, 23 May, 13:20–14:50

Chairpersons: Emily Hill, Heiko Goelzer

13:20–13:22
Introduction

13:22–13:29
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EGU22-13289
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ECS
André Jüling et al.

The Greenland and Antarctic ice sheets are losing mass to the ocean. This additional freshwater flux to the ocean is only expected to increase in the future, but it is usually not included in current climate model simulations as ice sheets are not modelled interactively. However, this freshwater flux will influence multiple aspects of the climate response. We develop a plausible, future freshwater forcing scenarios for both ice sheets and use a high-resolution, eddy-permitting version of EC-Earth3 to simulate the response to a high emission scenario. We investigate the effect of this additional freshwater on sea ice, ocean circulation, surface temperatures, and sea level by comparing the simulations to the HighResMIP EC-Earth3 simulations without ice sheet mass loss.

How to cite: Jüling, A., Le Bars, D., Lambert, E., Devilliers, M., and Drijfhout, S.: Effects of future freshwater forcing from ice sheet mass loss in a high-resolution climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13289, https://doi.org/10.5194/egusphere-egu22-13289, 2022.

13:29–13:36
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EGU22-11929
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ECS
Charlotte Lang et al.

As part of a project working to improve coupled climate-ice sheet modelling of the response of ice sheets to changes in climate across different periods since the Last Glacial Maximum, we present simulations of the modern Greenland climate and ice sheet using the FAMOUS-BISICLES model.

FAMOUS-BISICLES, a variant of FAMOUS-ice (Smith et al., 2021a), is a low resolution (7.5°X5°) global climate model that is two-way coupled to a higher resolution (minimum grid spacing of 1.2 km) adaptive mesh ice sheet model, BISICLES. It uses a system of elevation classes to downscale the lower resolution atmospheric variables onto the ice sheet grid and calculates surface mass balance using a multilayer snow model. FAMOUS-ice is computationally affordable enough to simulate the millennial evolution of the coupled climate-ice sheet system, and has been shown to simulate Greenland well in previous work using the Glimmer shallow ice model (Gregory et al., 2020).

The ice sheet volume and area are sensitive to a number of parametrisations related to atmospheric and snow surface processes and ice sheet dynamics. Based on that, we designed a perturbed parameters ensemble using a Latin Hypercube sampling technique and ran simulations with climate forcings appropriate for the late 20th century. The ice sheet area and volume are most correlated to parameters that set the snow/firn albedo while the relationship is less simple for parameters related to clouds and precipitation.

We compare FAMOUS-ice SMB and coupled behaviour against the more sophisticated, higher resolution, CMIP6-class UKESM-ice coupled climate ice sheet model for a late 20th century simulation as well as an abrupt 4XCO2 experiment.

Our simulations produce a large range of climate and ice sheet behaviours, including a stable control state for the modern Greenland, and we have been able to highlight the sensitivity of the system to other sets of parameters and future changes in climate.

How to cite: Lang, C., Lee, V., Sherriff-Tadano, S., Gandy, N., Gregory, J., Ivanovic, R., Gregoire, L., and Smith, R. S.: Evaluation of a coupled climate ice sheet model over the Greenland ice sheet and sensitivity to atmospheric, snow and ice sheet parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11929, https://doi.org/10.5194/egusphere-egu22-11929, 2022.

13:36–13:43
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EGU22-12018
|
ECS
Rebekka Neugebauer et al.

The temporal evolution of Greenland’s surface mass balance (SMB) exerts an essential control on its volume, geometry, and sea-level contribution. Surface mass balance simulations based on future climate projections reveal considerable uncertainties. Here, we investigate Greenland’s SMB during past climate periods and assess the uncertainties due to model dependent climate forcing. Specifically we analyse the SMB of the pre-industrial climate and the mid-Holocene warm period.

 

We study the surface mass balance of the Greenland ice sheet with respect to uncertainties due to model dependent climate forcing. For this purpose, we create an ensemble based on the output of climate models of the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the Paleomodel Intercomparison Project (PMIP4) (Brierley et al., 2020). This ensemble is used to simulate the SMB with the diurnal energy balance model (dEBM) (Krebs-Kanzow et al, 2021). As part of the analysis, we inspect anomalies and inter-model deviations of the mid-Holocene climate forcing, and evaluate the spread of spatial patterns of SMB anomalies in CMIP6/PMIP4. Our results indicate that the model-dependent climate forcing adds considerable uncertainty to SMB estimates over Greenland during the Holocene.

 

References

Brierley, C. M., Zhao, A., Harrison, S. P., Braconnot, P., Williams, C. J. R., Thornalley, D. J. R., Shi, X., Peterschmitt, J.-Y., Ohgaito, R., Kaufman, D. S., Kageyama, M., Hargreaves, J. C., Erb, M. P., Emile-Geay, J., D'Agostino, R., Chandan, D., Carré, M., Bartlein, P. J., Zheng, W., Zhang, Z., Zhang, Q., Yang, H., Volodin, E. M., Tomas, R. A., Routson, C., Peltier, W. R., Otto-Bliesner, B., Morozova, P. A., McKay, N. P., Lohmann, G., Legrande, A. N., Guo, C., Cao, J., Brady, E., Annan, J. D., and Abe-Ouchi, A., 2020: Large-scale features and evaluation of the PMIP4-CMIP6 midHolocene simulations, Clim. Past, 16, 1847–1872, doi:10.5194/cp-16-1847-2020, 2020. 

Krebs-Kanzow, U., Gierz, P., Rodehacke, C. B., Xu, S., Yang, H., and Lohmann, G., 2021: The diurnal Energy Balance Model (dEBM): a convenient surface mass balance solution for ice sheets in Earth system modeling, The Cryosphere, 15, 2295–2313, https://doi.org/10.5194/tc-15-2295-2021.

How to cite: Neugebauer, R., Rodehacke, C. B., Lohmann, G., and Krebs-Kanzow, U.: Uncertainties of Surface Mass Balance in Greenland for the mid-Holocene as derived from CMIP6/PMIP4 simulations., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12018, https://doi.org/10.5194/egusphere-egu22-12018, 2022.

13:43–13:50
Short break

13:50–13:57
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EGU22-5599
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ECS
Dennis Höning et al.

Budgets of remaining anthropogenic carbon emissions have been estimated to keep global warming below a limit (IPCC report 2021). A main impact of global warming is the rise of the sea level caused by melting of the Greenland ice sheet. However, the response of the Greenland ice sheet to temperature rise is strongly nonlinear. Melting depends on the time interval at which the ice sheet is exposed to high temperatures and on its rate of change, and a short time interval of high emission would therefore not necessarily result in the same sea level rise as long intervals of low emission. In order to make adequate predictions about sea level rise associated with melting of the Greenland ice sheet at specific times in the future, it is therefore crucial to explore the impact of cumulative emissions in combination with the emission duration.

We simulate Earth’s evolution for the next 20,000 years using CLIMBER-X, a fully coupled Earth System model of intermediate complexity, including modules for atmosphere, ocean, land surface, sea ice and the interactive 3-D polythermal ice sheet model SICOPOLIS, which is applied to the Greenland ice sheet at a spatial resolution of 16 km. In a first step, we explore equilibrium states of the volume of the Greenland ice sheet using constant partial pressures of atmospheric CO2. We also explore tipping points related to these states, i.e. unstable states of the ice volume where smaller values would lead to further melting until the associated stable state is reached. Next, we investigate the critical cumulative carbon emission to cross these tipping points. Finally, we assess the influence of the emission duration on crossing the tipping points and on the convergence rate towards the associated equilibrium states. We also investigate to what extent future negative emissions could limit sea level rise.

Our results show how high carbon emission rates, even throughout a short time interval, cause the Greenland ice sheet system to rapidly approach equilibrium states of smaller ice volume. This convergence cannot completely be offset by future negative emissions. In contrast, a quick decrease of global emissions, even if in combination with an extended time period of small net emissions in the future, would substantially delay sea level rise and could even prevent the system from crossing the tipping points.

How to cite: Höning, D., Calov, R., Talento, S., Willeit, M., and Ganopolski, A.: Impact of cumulative anthropogenic carbon emissions, emission duration, and negative emission scenarios on melting of the Greenland ice sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5599, https://doi.org/10.5194/egusphere-egu22-5599, 2022.

13:57–14:04
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EGU22-11407
Johanna Beckmann and Ricarda Winkelmann

Over the past decade, Greenland has experienced several extreme melt events, the most pronounced ones in the years 2010, 2012 and 2019. With progressing climate change, such extreme melt events can be expected to occur more frequently and potentially become more severe. So far, however, projections of ice loss and sea-level change from Greenland typically rely on scenarios that only take gradual changes in the climate into account. 
Here we investigate the effect of extreme melt events on the ice dynamics and overall mass balance of the Greenland Ice Sheet in simulations using the Parallel Ice Sheet Model (PISM). While the extremes generally lead to thinning of the ice sheet by enhanced melting, they partly also decrease the overall ice surface velocities due to a reduced driving gradient. In our simulations, we find that taking extreme events into account leads to additional ice loss compared to the baseline scenario without extremes. We find that the sea-level contribution from Greenland could increase by up to 45 cm by the year 2300 if severe extreme events are considered in future projections. We conclude that both changes in the frequency and intensity of extreme events need to be taken into account when projecting the future sea-level contribution from the Greenland Ice Sheet.

How to cite: Beckmann, J. and Winkelmann, R.: Effects of extreme melt events on the Greenland ice sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11407, https://doi.org/10.5194/egusphere-egu22-11407, 2022.

14:04–14:11
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EGU22-5016
|
ECS
Maxence Menthon et al.

The response of ice sheets to climate changes can be diverse and complex. The amplitude, speed and irreversibility of the melting of the ice sheets due to current anthropogenic emissions remain largely uncertain after 2100. Being able to reconstruct the evolution of the ice sheets during the past climate changes is a possible approach to constrain their future evolution in time scales further than the end of the century.

Here we aim to reconstruct the evolution of the Antarctic ice sheet during the Last Interglacial (LIG, ~ 130 to 115 kyr BP). The LIG was 0.5 to 1˚C warmer than the pre-industrial era with a sea-level between 6 to 9 m above present level. In other words, the Antarctic ice sheet during the LIG can be considered as an analogue to its future evolution. Moreover, it is the interglacial on which we have the most geological records to compare with simulation results.

Knowing that the oceanic forcing is the main driver of the Antarctic ice sheet retreat, we introduced the sub-shelf melt module PICO (Reese et al. 2018) in the ice sheet model (GRISLI, Quiquet et al. 2018) in order to physically compute the melt. We use outputs from the Earth Sytem Model (iLOVECLIM, Roche et al. 2014) to force idealized experiments. Several time periods will be covered: present-day, last glacial maximum and LIG. This work is a first step towards a fully coupled iLOVECLIM-GRISLI-PICO simulation to explicitly take into account the ice sheet climate - interactions in a physical way in simulations of the Antarctic ice sheet during the LIG and future centuries.

How to cite: Menthon, M., Bakker, P., Quiquet, A., and Roche, D.: Antarctic sub-shelf melt during the present and the last interglacial and its impact on ice sheet dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5016, https://doi.org/10.5194/egusphere-egu22-5016, 2022.

14:11–14:18
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EGU22-4740
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ECS
Gaelle Leloup et al.

Ice sheets and the rest of the climate system interact in various ways, notably via the atmosphere, ocean and solid earth. Atmospheric and oceanic temperatures and circulations affect the evolution of ice-sheets, and conversely ice-sheet evolution impacts the rest of the climate system via various processes, including albedo modification, topographic changes and freshwater flux release into the ocean. To correctly model the evolution of the climate system and sea level rise, these feedbacks therefore need to be considered.

Under the highest emission scenario, temperature is expected to reach levels comparable to the Eocene epoch in a few centuries [1]. At this time, there was no widespread glaciation in Antarctica.

The work of Garbe et al [2] has shown that the Antarctic ice sheet has a hysteresis behavior and gave different temperature thresholds leading to committed Antarctic mass loss. For example, between 6 and 9 degrees of warming (a global temperature increase comparable to the one expected in 2300 for the most emissive scenario), the loss of 70% of the present-day ice volume is triggered. However, the modelling study used idealized perturbations of the climate fields based solely on global mean temperature. More specifically, global mean temperature is translated into local changes of ocean and surface air temperature and increased until a complete deglaciation of the Antarctic ice-sheet is reached. In addition the study did not take into account the ice sheet change feedback on the climate system.

In our work we intend to go a step further by taking into account both the influence of atmosphere and oceanic temperature and circulations on the ice sheet in a physical way, as well as the influence of the ice sheet on the rest of the climate system.

To do so, we use the coupled ocean-atmosphere-vegetation intermediate complexity model iLOVECLIM [3], fully coupled to the GRISLI ice-sheet model for Antarctica [4, 5].

We perform several multi-millenia equilibria simulations for different pCO2 levels, thanks to the relative rapidity of both the iLOVECLIM and GRISLI models. These simulations lead to different atmospheric and oceanic temperatures and Antarctic mass loss. 

These coupled simulations allow us to explore the impact of the ice sheet feedback on the climate and to investigate the differences compared to cases where these feedbacks are not included. The influence of the model parameters linked to the ice sheet coupling is also studied.

 

References :

[1] Westerhold et al 2020, “An astronomically dated record of Earth’s climate and its predictability over the last 66 million years”

[2] Garbe et al 2020 “The hysteresis of the Antarctic Ice Sheet”

[3] Quiquet et al 2018, “Online dynamical downscaling of temperature and precipitation within the iLOVECLIM model (version 1.1)”

[4] Quiquet et al 2018, “The GRISLI ice sheet model (version 2.0): calibration and validation for multi-millennial changes of the Antarctic ice sheet”

[5] Quiquet et al 2021 “Climate and ice sheet evolutions from the last glacial maximum to the pre-industrial period with an ice-sheet–climate coupled model”

How to cite: Leloup, G., Quiquet, A., Dumas, C., Roche, D., and Paillard, D.: Antarctic-climate multi-millenia coupled simulations under different pCO2 levels with the iLOVECLIM-GRISLI model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4740, https://doi.org/10.5194/egusphere-egu22-4740, 2022.

14:18–14:25
Short break

14:25–14:32
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EGU22-9983
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ECS
Lena Nicola et al.

Snowfall is by far the most important positive contributor to the overall mass balance of the Antarctic Ice Sheet, potentially buffering temperature-induced dynamical ice loss in a warming climate. Previous studies have proposed that Antarctic snowfall will increase along the Clausius-Clapeyron relationship, describing the saturation water vapour pressure as a function of temperature (7% change for 1°C of warming). Due to cold temperatures and continentality in the interior, this general, first-order explanation may not hold true for snowfall changes across the ice sheet. In this study, we investigate how this first-order approximation can be modified to more reliably represent snowfall changes in a warming climate for simulations of the Antarctic Ice Sheet.

To characterise the present-day precipitation pattern, we use reanalysis data and make use of state-of-the-art model data from the CMIP6 modelling project as well as regional model data. We analyse how the sensitivity of Antarctic precipitation to temperature changes is represented in models and how it potentially changes in the future. We use least-squares linear regression to determine the sensitivity factor, Antarctica’s x-factor, that is used in ice-sheet models to scale precipitation. 

With our statistical analyses, we show that sensitivities of column-integrated water vapour, precipitation, snowfall, net precipitation, and surface mass balance to temperature changes are fairly similar under present-day conditions; implying that the exponential relationship of saturation water vapour pressure to temperature could generally lead to additional mass gains of the Antarctic Ice Sheet with warming. However, we find that the relationship of Antarctic precipitation to temperatures across the ice sheet is not constant, but decreases with ongoing warming. Taking these changes into account could give a more reliable estimate of future precipitation changes than existing approaches. We demonstrate that a linear approximation of the exponential relationship between Antarctic precipitation and temperature becomes more and more imprecise in a warming climate, both for computing the sensitivity factor and to scale Antarctic precipitation in models.

We propose a new way to extract the sensitivity factor of Antarctic precipitation to temperature which takes regional variations and the temperature dependence into account. The temperature dependence becomes more important the higher the warming becomes. Considering local warming rates, we show the necessity of introducing a temperature-dependent scaling factor in ice-sheet models, especially for high-end or long-term sea-level projections.

How to cite: Nicola, L., Notz, P. D., and Winkelmann, P. R.: Antarctica’s x-factor: How does Antarctic precipitation change with temperature?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9983, https://doi.org/10.5194/egusphere-egu22-9983, 2022.

14:32–14:39
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EGU22-10008
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ECS
Julius Garbe et al.

With a volume of 58 m sea-level equivalent, the Antarctic Ice Sheet represents the largest potential source of future sea-level rise under global warming. While the ice sheet gains mass through snowfall at the surface, it loses mass through dynamic discharge and iceberg calving into the ocean, as well as by melting at the surface and underneath its floating ice shelves.

Already today, Antarctica is contributing to sea-level rise. So far, this contribution has been comparatively modest, but is expected to increase in the future. Most of the current mass losses are concentrated in the West Antarctic Ice Sheet, mainly caused by sub-shelf melting and ice discharge. Because air temperatures are low and thus surface melt rates are small, any significant melting at the surface is restricted to the low-elevation coastal zones. At the same time, most of the mass loss is offset by snowfall, which is projected to further increase in a warming atmosphere.

As warming progresses over the coming centuries, the question arises as to how long the mass losses on the one side will be compensated by the gains on the other. In 21st-century projections, increasing surface mass balance is outweighing increased discharge even under strong warming scenarios. However, in long-term (multi-century to millennium scale) warming simulations the positive surface mass balance trend shows a peak and subsequent reversal. Owing to positive feedbacks, like the surface-elevation or the ice-albedo feedback, this effect can be enhanced once a surface lowering is triggered or the surface reflectivity is lowered by initial melt.

Here, we implement a simplified version of the diurnal Energy Balance Model (dEBM-simple) as a surface module in the Parallel Ice Sheet Model (PISM), which extends the conventional positive-degree-day (PDD) approach to include the influence of solar radiation and parameterizes the ice albedo as a function of melting, implicitly accounting for the ice-albedo feedback.

Using a model sensitivity ensemble, we analyze the range of possible surface mass balance evolutions over the 21st century as well as in long-term simulations based on extended end-of-century climatological conditions with the coupled model. The comparison with the PDD approach hints to a strong overestimation of surface melt rates of the latter, even under present day conditions. The dEBM-simple further allows us to disentangle the respective contributions of temperature- and insolation-driven surface melt to future sea level rise.

How to cite: Garbe, J., Zeitz, M., Krebs-Kanzow, U., and Winkelmann, R.: The evolution of future Antarctic surface melt using PISM-dEBM-simple, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10008, https://doi.org/10.5194/egusphere-egu22-10008, 2022.

14:39–14:46
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EGU22-9235
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ECS
Cyrille Mosbeux et al.

Ice mass loss from Antarctic Ice Sheet is increasing, accelerating its contribution to global sea level rise. Interactions between the ice shelves (the floating portions of the ice sheet that buttress the grounded ice) and the ocean are key processes in this mass loss. The most rapid recent observed mass loss from the Antarctic Ice Sheet is in the Amundsen Sea, where buttressing is declining as small ice shelves are being thinned rapidly by melting driven by inflows of warm Circumpolar Deep Water, leading to important grounding line retreats. Recent research indicates that ice sheets, especially the parts that rest on a bed below sea level such as most of the Amundsen sector, are particularly prone to an unstable and irreversible retreat that might lead to an important and fast global sea level rise.

As part of the European Horizon 2020 research project TiPACCs that assesses the possibility of near-future irreversible changes, so-called tipping points, in the Southern Ocean and the Antarctic Ice Sheet, we conduct numerical simulations perturbating the current conditions of the ice-ocean system in the Amundsen Sea Sector. More particularly, we use the Stokes flow formulation of the open-source ice flow model Elmer/Ice, forced with melt parametrization under the ice shelves to determine the effect of ocean warming on the ice-sheet evolution –eventually looking for the existence of future tipping points in the region. Since 3D-Stokes models can be numerically expensive, using the same Elmer/Ice framework (datasets, ocean and climate forcing), we compare our results to the more efficient but sometimes less accurate 2D-shallow–shelf(y)-Approximation (SSA). This methodology allows us to entangle the differences between the two models and better constrain the uncertainty linked to TiPACCs pan-Antarctic simulations based on the SSA.

How to cite: Mosbeux, C., Gagliardini, O., Jourdain, N., Urruty, B., Chekki, M., Gillet-Chaulet, F., and Durand, G.: Tipping Points in the Amundsen Sea Sector, a comparison between 2D and 3D ice-sheet models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9235, https://doi.org/10.5194/egusphere-egu22-9235, 2022.