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.

Public information:
We have decided to organise the chat in two parts:

1. During the first part we will go through the existing displays in order and have 5 minutes for each to answer questions from the participants.
Preliminary schedule below. Since we don't know yet the final number of displays available this timing may still change.

10:45 Intro
10:50 D2558 EGU2020-15058 Did a Beringian ice sheet once exist?
10:55 D2559 EGU2020-5912 Global coupled climate - ice sheet model simulations for the penultimate deglaciation and the last interglacial
11:00 D2561 EGU2020-7844 Impact of mid-glacial ice sheets on the recovery time of the AMOC: Implications on the frequent DO cycles during the mid-glacial period
11:05 D2562 EGU2020-18683 Modelling the surface mass balance of the Greenland Ice Sheet from 6000 BP to the year 2200
11:10 D2563 EGU2020-10601 Greenland ice sheet contribution to 21st century sea level rise as modelled by the coupled CESM2.1-CISM2.1
11:15 D2564 EGU2020-20368 The North Atlantic Oscillation and the Greenland ice sheet in CMIP6
11:20 D2566 EGU2020-5647 A circumpolar coupled ocean – Antarctic ice sheet configuration for investigating recent changes in Southern Ocean heat content
11:25 D2567 EGU2020-2272 Transient Pleistocene simulations with a new coupled climate-ice-sheet model
11:30 D2568 EGU2020-16221 Comparison of peri-Antarctic sub-shelf melt rates in coupled and uncoupled ice-sheet model simulations
11:35 D2570 EGU2020-10255 Coupling the Parallel Ice Sheet Model with the Modular Ocean Model via an Antarctic ice-shelf cavity module
11:40 D2572 EGU2020-11625 AMOC recovery in a multi-centennial scenario using a coupled atmosphere-ocean-ice sheet model
11:45 D2574 EGU2020-21261 The ocean response to changes of the Greenland Ice sheet in a warming climate
11:50 D2577 EGU2020-16815 Dynamic Hydrological Discharge and Lake Modelling for Coupled Climate Model Simulations of the Last Glacial Cycle
11:55 D2578 EGU2020-21686 Greenland ice sheet surface mass balance response to high CO2 forcing: threshold and mechanisms for accelerated surface mass loss
12:00 D2579 EGU2020-17514 A global ensemble-based comparison of the last two glacial inceptions with LCice 2.0

2. Time permitting, we were hoping to discuss a few key questions as an open chat with everybody (authors and participants) around the theme of our session: Ice-sheet and climate interactions. Of course, these discussions are just a starter and we encourage everyone to keep communicating and discussing via other media after the session.

Some examples:

- What is the most important progress in ice sheet-climate model
coupling in the last 5 years? (distinguish paleo and future perspective).

- What model improvement is necessary to address outstanding scientific

- Where do you see important gaps in our knowledge that should be addressed?

- What observational data has had an important impact on our
understanding of ice sheet-climate interactions?

- What paleo archives (kind, location, time frame) would be the most
important to examine/extend to improve our knowledge about ice
sheet-climate interactions?

Please remember that the chat will not be preserved. Comments and questions on individual displays (that have not been answered) are best posted in the online discussion under the display abstracts. Public discussion and feedback of presentation materials is open to 31 May.

Co-organized by CL4
Convener: Heiko Goelzer | Co-conveners: Alexander Robinson, Ricarda Winkelmann, Philippe Huybrechts, Stefanie MackECSECS
| Attendance Wed, 06 May, 10:45–12:30 (CEST)

Files for download

Download all presentations (103MB)

Chat time: Wednesday, 6 May 2020, 10:45–12:30

Chairperson: Heiko Goelzer
D2558 |
Zhongshi Zhang, Qing Yan, Ran Zhang, Florence Colleoni, Gilles Ramstein, Gaowen Dai, Martin Jakobsson, Matt O’Regan, Stefan Liess, Denis-Didier Rousseau, Naiqing Wu, Elizabeth J. Farmer, Camille Contoux, Chuncheng Guo, Ning Tan, and Zhengtang Guo

Did a Beringian ice sheet once exist? This question was hotly debated decades ago until compelling evidence for an ice-free Wrangel Island excluded the possibility of an ice sheet forming over NE Siberia-Beringia during the Last Glacial Maximum (LGM). Today, it is widely believed that during most Northern Hemisphere glaciations only the Laurentide-Eurasian ice sheets across North America and Northwest Eurasia became expansive, while Northeast Siberia-Beringia remained ice-sheet-free. However, recent recognition of glacial landforms and deposits on Northeast Siberia-Beringia and off the Siberian continental shelf has triggered a new round of debate.These local glacial features, though often interpreted as local activities of ice domes on continental shelves and mountain glaciers on continents,   could be explained as an ice sheet over NE Siberia-Beringia. Only based on the direct glacial evidence, the debate can not be resolved. Here, we combine climate and ice sheet modelling with well-dated paleoclimate records from the mid-to-high latitude North Pacific to readdress the debate. Our simulations show that the paleoclimate records are not reconcilable with the established concept of Laurentide-Eurasia-only ice sheets. On the contrary, a Beringian ice sheet over Northeast Siberia-Beringia causes feedbacks between atmosphere and ocean, the result of which well explains the climate records from around the North Pacific during the past four glacial-interglacial cycles. Our ice-climate modelling and synthesis of paleoclimate records from around the North Pacific argue that the Beringian ice sheet waxed and waned rapidly in the past four glacial-interglacial cycles and accounted for ~10-25 m ice-equivalent sea-level change during its peak glacials. The simulated Beringian ice sheet agrees reasonably with the direct glacial and climate evidence from Northeast Siberia-Beringia, and reconciles the paleoclimate records from around the North Pacific. With the Beringian ice sheet involved, the pattern of past NH ice sheet evolution is more complex than previously thought, in particular prior to the LGM.

How to cite: Zhang, Z., Yan, Q., Zhang, R., Colleoni, F., Ramstein, G., Dai, G., Jakobsson, M., O’Regan, M., Liess, S., Rousseau, D.-D., Wu, N., Farmer, E. J., Contoux, C., Guo, C., Tan, N., and Guo, Z.: Did a Beringian ice sheet once exist?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15058, https://doi.org/10.5194/egusphere-egu2020-15058, 2020

D2559 |
Bas de Boer, Aurélien Quiquet, Pepijn Bakker, and Didier Roche

Glacial-interglacial changes of the Earth's climate are largely controlled by internal mechanisms that drive changes in greenhouse gases and ice sheets. In this study, we present model experiments of the penultimate deglaciation into the the last interglacial period, obtained with the Earth system model of intermediate complexity iLOVECLIM (v. 1.1.4). We show experiments with an imposed ice-sheet scenario together with initial results with both North and South interactive ice sheets using the GRISLI (v. 2.0) 3-D ice-sheet model. To this aim, we use a recently developed dynamical downscaling procedure to compute temperature and precipitation fields from the relative low resolution atmospheric model grid (T21, ~5.6º) to the GRISLI spherical grids of both the Northern Hemisphere and Antarctica (both 40 x 40 km). We investigate the separate impact of variations of greenhouse gases (GHG), orbital parameters and ice sheets on glacial-interglacial climate change over the past 240 kyr. Using prescribed greenhouse gases or ice sheets induce comparable changes in global mean temperature. Greenhouse gases, predominantly CO2, mainly have a global impact through radiative forcing on atmospheric temperatures. On the other hand, ice sheets have a more regional impact over the Northern Hemispheric (NH) continents and Antarctica during glacial times. Henceforth, polar amplification is more pronounced during glacial periods following large ice-sheet induced changes. Overall these results are comparable to other studies using a similar experimental design. In order to initiate the coupling between the ice sheets and climate model, we perform a large ensemble of experiments to calibrate ice-sheet model parameters for the present day. We will present how the optimal settings for the two ice-sheet regions are selected, based on a comparison with the present-day ice sheets on Antarctica and Greenland. For the coupling, iLOVECLIM generates downscaled SMB, surface temperatures, ocean temperature and salinity, and GRISLI provides surface elevation and ice extent, the coupling interval is 5 years. These experiments are started during the penultimate glacial maximum. We initialize the coupled iLOVECLIM - GRISLI experiments from a climatic forcing experiment using prescribed greenhouse gases and ice sheets, and generate a spin-up simulation of GRISLI using the optimal settings for three different time points at 136, 135 and 134 kyr ago. Initial experiments show a clear linkage between changes in ice sheets, sea ice and ocean circulation. Following the forced rise in atmospheric GHGs, the magnitude of retreat varries between ice sheets, related to location and insolation change (which increases for the NH but decreased for Antarctica). Moreover, sea ice both decrease following GHGs increase, and vary more in phase with global mean temperature.

How to cite: de Boer, B., Quiquet, A., Bakker, P., and Roche, D.: Global coupled climate - ice sheet model simulations for the penultimate deglaciation and the last interglacial, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5912, https://doi.org/10.5194/egusphere-egu2020-5912, 2020

D2560 |
Nicolas Young, Jason Briner, Gifford Miller, Alia Lesnek, Sarah Crump, Elizabeth Thomas, Simon Pendleton, Joshua Cuzzone, Jennifer Lamp, Susan Zimmerman, Marc Caffee, and Joerg Schaefer

The early Holocene (11.7 ka to 8.2 ka) represents the most recent period when the Laurentide and Greenland ice sheets underwent large-scale recession. Moreover, this ice-sheet recession occurred under the backdrop of regional temperatures that were similar to or warmer than today, and comparable to those projected for the upcoming centuries. Reconstructing Laurentide and Greenland ice sheet behavior during the early Holocene, and elucidating the mechanisms dictating this behavior may serve as a partial analog for future Greenland ice-sheet change in a warming world. Here, we use 123 new 10Be surface exposure ages from two sites on Baffin Island and southwestern Greenland that constrain the behavior of the Laurentide and Greenland ice sheets, and an independent alpine glacier during the early Holocene. On Baffin Island, sixty-one 10Be ages reveal that advances and/or stillstands of the Laurentide Ice Sheet and an alpine glacier occurred in unison around 11.8 ka, 10.3 ka, and 9.2 ka. Sixty-two 10Be ages from southwestern Greenland indicate that the GrIS margin experienced re-advances or stillstands around 11.6 ka, 10.4 ka, 9.1 ka, 8.1 ka, and 7.3 ka. Our results reveal that alpine glaciers and the Laurentide and Greenland ice sheets responded in unison to abrupt early Holocene climate perturbations in the Baffin Bay region. We suggest that during the warming climate of the early Holocene, freshening of the North Atlantic Ocean induced by a melting Laurentide Ice Sheet resulted in regional abrupt cooling and brief periods of ice-sheet stabilization superimposed on net glacier recession. These observations point to a negative feedback mechanism inherent to melting ice sheets in the Baffin Bay region that slows ice-sheet recession during intervals of otherwise rapid deglaciation.

How to cite: Young, N., Briner, J., Miller, G., Lesnek, A., Crump, S., Thomas, E., Pendleton, S., Cuzzone, J., Lamp, J., Zimmerman, S., Caffee, M., and Schaefer, J.: Deglaciation of the Greenland and Laurentide ice sheets interrupted by glacier advance during abrupt coolings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2739, https://doi.org/10.5194/egusphere-egu2020-2739, 2020

D2561 |
Sam Sherriff-Tadano and Ayako Abe-Ouchi

Paleo reconstructions such as ice cores have revealed that the glacial period experienced frequent climate shifts between warm interstadials and cold stadials. The duration of these climate modes varied during glacial periods, and that both the interstadials and stadials were shorter during mid-glacial compared with early glacial period. Recent studies showed that the duration of the interstdials was controlled by the Antarctic temperature through its impact on the Atlantic Meridional Overturning Circulation (AMOC). However, similar relation was not found for the stadials, suggesting that other climate factors (e.g., differences in ice sheet size, greenhouse gases and insolation) might have played a role. In this study, we investigate the role of glacial ice sheets on the duration of stadials. For this purpose, freshwater hosing experiments are conducted with an atmosphere-ocean general circulation model MIROC4m under early-glacial and mid-glacial conditions. Then, a sensitivity experiment is conducted modifying only the configuration of the ice sheets.  The impact of mid-glacial ice sheets on the duration of the stadials is evaluated by comparing the recovery time of the AMOC after the cessation of the freshwater forcing. We find that the expansion of glacial ice sheets during mid-glacial shortens the recovery time of the AMOC. Partially coupled experiments, which switch the surface winds between the two experiments, show that the differences in the surface wind cause the shorter recovery time under mid-glacial ice sheet. The wind shortens the recovery time by increasing the surface salinity and decreasing the sea ice at the deepwater formation region. Thus the results suggest that differences in the surface wind between mid-glacial and early glacial ice sheets play an important role in causing shorter stadials during mid-glacial period.

How to cite: Sherriff-Tadano, S. and Abe-Ouchi, A.: Impact of mid-glacial ice sheets on the recovery time of the AMOC: Implications on the frequent DO cycles during the mid-glacial period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7844, https://doi.org/10.5194/egusphere-egu2020-7844, 2020

D2562 |
Uta Krebs-Kanzow, Shan Xu, Hu Yang, Paul Gierz, and Gerrit Lohmann

The surface mass balance scheme dEBM (diurnal Energy Balance Model) provides a novel interface between atmosphere and land ice for Earth System modelling, which is based on the energy balance of glaciated surfaces. In contrast to empirical schemes, dEBM accounts for changes in the Earth’s orbit and atmospheric composition. The scheme only requires monthly atmospheric forcing (precipitation, temperature, shortwave and longwave radiation and cloud cover) and is computationally inexpensive, which makes it particularly suitable to investigate the response of ice sheets to long term climate change.
Here, we analyze the surface mass balance of the Greenland Ice Sheet (GrIS)  based on a climate simulation which covers the last 6000 years and a climate projection which extends to the year 2200. We validate our results with recent surface mass balance estimates from observations and regional modelling. Our model results allow to compare two distinctly different warm periods: the Mid Holocene (approx. 6000 years before present), which is characterized by intensified summer insolation, and the next centuries,  which will be characterized by reduced outgoing long wave radiation. We also investigate whether the temperature - melt relationship, as used in empirical  schemes, remains stable under changing insolation and atmospheric composition.

Krebs-Kanzow, U., Gierz, P., & Lohmann, G. (2018). Brief communication: An ice surface melt scheme including the diurnal cycle of solar radiation. The Cryosphere, 12(12), 3923-3930.

How to cite: Krebs-Kanzow, U., Xu, S., Yang, H., Gierz, P., and Lohmann, G.: Modelling the surface mass balance of the Greenland Ice Sheet from 6000 BP to the year 2200, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18683, https://doi.org/10.5194/egusphere-egu2020-18683, 2020

D2563 |
Laura Muntjewerf, Michele Petrini, Miren Vizcaino, Carolina Ernani da Silva, Raymond Sellevold, Meike Scherrenberg, Katherine Thayer-Calder, Sarah Bradley, Jan Lenaerts, William Lipscomb, and Marcus Lofverstrom

With the Community Earth System Model version 2.1 (CESM2.1) interactively coupled to the evolving Greenland Ice Sheet as simulated by the Community Ice Sheet Model version 2.1 (CISM2.1), we examine the Greenland Ice Sheet (GrIS) mass balance. The model has been run for the period 1850-2100 with historical and SSP5-8.5 scenario forcing, contributing to the coupled experiments within the framework of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) (Nowicki et al., 2016).

CESM2.1-CISM2.1 simulates a relatively strong global warming signal and strong weakening of meridional overturning circulation by 2100 compared to CMIP5 models. In our projection, the GrIS contributes 23 mm sea-level equivalent by 2050, and 109 mm by 2100, to global mean sea level rise. The southern GrIS drainage basins contribute 73% of the mass loss by mid-century, but the contribution decreases to 55% by 2100, as surface runoff in the northern basins progressively increases.

How to cite: Muntjewerf, L., Petrini, M., Vizcaino, M., Ernani da Silva, C., Sellevold, R., Scherrenberg, M., Thayer-Calder, K., Bradley, S., Lenaerts, J., Lipscomb, W., and Lofverstrom, M.: Greenland ice sheet contribution to 21st century sea level rise as modelled by the coupled CESM2.1-CISM2.1 , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10601, https://doi.org/10.5194/egusphere-egu2020-10601, 2020

D2564 |
Ruth Mottram, Susann Ascheneller, Florian Sauerland, Rasmus Anker Pedersen, Peter Thejll, Peter Lang Langen, Fredrik Boberg, Martin Stendel, Nicolaj Hansen, and Shuting Yang
The North Atlantic Oscillation (NAO) is an important control on both northern European weather and Greenland ice sheet surface mass budget via the path of storm tracks that deliver precipitation, particularly in the winter, and by the strength and persistence of the Greenland blocking high that promotes melt in summer. Within CMIP5 models, atmospheric blocking was generally poorly represented regardless of location, we here examine an ensemble of 10 CMIP6 fully coupled earth system models (ESMs) that were available by Summer 2019 in order to examine if model improvements better represent the NAO in CMIP6.
We examine  temperature over Greenland and the north Atlantic region as well as NAO position, persistence and strength in winter and summer for each model in the historical scenario. No single model performs well on all characteristics but the UKESM and EC-EARTH3 perform the best when compared to the ERA5 climate reanalysis.
We also show how the NAO is expected to change in 8 of these models under different future climate scenarios.  The location of the Icelandic low in particular migrates northwards by varying amounts, likely related to Arctic sea ice changes within the models and with a consequent impact on precipitation.
Downscaling experiments carried out using the HIRHAM5 regional climate model over the Greenland ice sheet show the importance of accurately characterising the NAO in order to correctly  estimate both winter accumulation and summer melt and the combination that gives the ice sheet mass budget. Our study emphasises the importance of assessing a range of different climate and weather variables when selecting models to downscale for obtaining ice sheet mass balance. We also note that while some progress has been made in better representing atmospheric blocking in ESMs, largely down to higher resolution in atmospheric models, there is still a substantial improvement required before ESMs can be said to accurately characterise the climate of the North Atlantic region with consequent impacts on ice sheet surface mass budget projections.

How to cite: Mottram, R., Ascheneller, S., Sauerland, F., Anker Pedersen, R., Thejll, P., Lang Langen, P., Boberg, F., Stendel, M., Hansen, N., and Yang, S.: The North Atlantic Oscillation and the Greenland ice sheet in CMIP6, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20368, https://doi.org/10.5194/egusphere-egu2020-20368, 2020

D2565 |
Sensitivity of the last glacial inception to initial and boundary conditions: lessons from a coupled climate-ice sheet model
not presented
Shan Xu, Uta Krebs-Kanzow, Paul Gierz, and Gerrit Lohmann
D2566 |
Charles Pelletier, Lars Zipf, Konstanze Haubner, Hugues Goosse, Frank Pattyn, and Pierre Mathiot

From 2016 on, observed tendencies of Southern Ocean sea surface temperatures and Antarctic sea ice extent (SIE) have shifted from cooling down (with SIE increase) to warming up (SIE decrease). This change of Southern Ocean surface thermal properties has been sustained since, which indicates that it is not solely due to the interannual variability of the atmosphere, but also to modifications in the ocean itself. Among other physical phenomena, the acceleration of continental ice shelf melt, through its subsequent impact on the Southern Ocean stratification, has been proposed as one of the potential meaningful drivers of the sea ice changes. Reciprocally, recent studies suggest that besides atmosphere forcings, the upper ocean thermal content bears significant impact on ice shelf melt rates and dynamics. Here we present a new circumpolar coupled Southern Ocean – Antarctic ice sheet configuration aiming at investigating the impact of this ocean – continental ice feedback, developed within the framework of the PARAMOUR project. Our setting relies on the ocean and sea ice model NEMO3.6-LIM3 sending ice shelf melt rates to the Antarctic ice sheet model f.ETISh v1.5, who in turn responds to it and provides updated ice shelf cavity geometry. Both technical aspects and first coupled results are presented.

How to cite: Pelletier, C., Zipf, L., Haubner, K., Goosse, H., Pattyn, F., and Mathiot, P.: A circumpolar coupled ocean – Antarctic ice sheet configuration for investigating recent changes in Southern Ocean heat content, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5647, https://doi.org/10.5194/egusphere-egu2020-5647, 2020

D2567 |
Dipayan Choudhury, Axel Timmermann, Fabian Schloesser, and David Pollard

Orbital and COvariations over glacial timescales are widely held responsible as drivers of the ice-age cycles of the Pleistocene. Alongside these glacial cycles, our paleoclimate history is marked with abrupt changes and millennium scale variabilities. However, the relative contributions of these forcings over glacial transitions and mechanisms of abrupt changes are not very well understood. Here, using the recently developed three-dimensional coupled climate – ice-sheet model (LOVECLIM – Penn State University ice-sheet model), we simulate the glacial inception over the period of MIS7 to MIS6 (240-170ka). This period is the coldest interglacial post the Mid-Brunhes Event and includes one of the fastest glaciation/deglaciation events of the Late Pleistocene, over MIS7e-7d-7c (236-218ka); which we use here to benchmark our transient coupled model runs. Our results suggest that glacial inceptions are more sensitive to orbital variations, whereas terminations need both forcings to work in tandem over a tiny ablation zone at the southern margins of ice sheets. And abrupt changes may result from a critical interplay between the climate and the cryosphere systems. Using multiple ensembles in combination with conceptual dynamical systems’ models, we test the sensitivity of ice-sheets to various physical factors and discuss the presence of multiple equilibrium states and runaway effects. Additionally, our simulations show that regional scale variations at the southern end of Laurentide can lead to a bifurcation of the system and play a role even in orbital-scale ice-sheet growth/decay.

How to cite: Choudhury, D., Timmermann, A., Schloesser, F., and Pollard, D.: Transient Pleistocene simulations with a new coupled climate-ice-sheet model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2272, https://doi.org/10.5194/egusphere-egu2020-2272, 2020

D2568 |
Lars Zipf, Charles Pelletier, Konstanze Haubner, Sainan Sun, Hugues Goosse, and Frank Pattyn

Sub-shelf melting is the main driver of the mass loss of the Antarctic ice sheet. Various parametrizations exist to estimate basal melt rates within standalone ice sheet models, but they are not able to capture complex ocean circulation. Therefore, high resolution coupled ice sheet-ocean models are the ultimate approach to simulate observed sub-shelf melt rates on short time scales and thereby improve projections of future Antarctic sea level contribution.

Here, we present first results of a hindcast (last 30 years) of the new circumpolar coupled Southern Ocean – Antarctic ice sheet configuration, developed within the framework of the PARAMOUR project. The configuration, which captures whole Antarctica, is based on the ocean and sea ice model NEMO3.6-LIM3, providing the ice sheet model with monthly sub-shelf melt rates, and the Antarctic ice sheet model f.ETISh v1.5, providing the updated ice shelf cavity geometry to the ocean model. Different difficulties are tackled for the coupling: The initialisation of the ice sheet model is optimised for the chosen resolution of 8km, which is a tradeoff between capturing the main features for the peri-Antarctic setup and respecting the model purpose as fast ice sheet model. Framework conditions for the coupling, e.g. a constant ice-ocean mask, are tested and implemented. The optimal solution to estimate sub-shelf melt for small ice shelves that are not resolved in the ocean model due to the different resolution of the ice sheet and the ocean model, is investigated.
Sub-shelf melt rates of the coupled setup are compared to those modeled by the standalone ocean model and those of the standalone ice sheet model with different sub-shelf melt rate parametrizations (ISMIP6, plume, PICO, PICOP) and the sensitivity of the response of the ice sheet for the different basal melt rate patterns are investigated.

How to cite: Zipf, L., Pelletier, C., Haubner, K., Sun, S., Goosse, H., and Pattyn, F.: Comparison of peri-Antarctic sub-shelf melt rates in coupled and uncoupled ice-sheet model simulations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16221, https://doi.org/10.5194/egusphere-egu2020-16221, 2020

D2569 |
Kenji Izumi, Paul Paul Valdes, Ruza Ivanovic, and Lauren Gregoire

The Last Glacial Maximum (LGM; 21,000 yr before present) is a target period of the paleoclimate simulations in the Coupled Model Intercomparison Project Phase 6 – the Paleoclimate Modeling Intercomparison Project Phase 4 (CMIP6-PMIP4) because of abundant paleoenvironmental data in continental, ice, and marine indicators. The LGM was a period of low atmospheric trace gases when large ice sheets covered over North America and Scandinavia. Paleoclimate reconstructions and modeling studies suggest that the Northern Hemisphere climate differed from today.

In this study, we used the coupled atmosphere and ocean model HadCM3B-M1 in order to investigate the impacts of the main LGM boundary condition changes, in particular, the ICE-6G_C, GLAC-1D, and PMIP3 ice-sheet reconstructions following the PMIP4 protocol, on the mean state of the climate over the Northern Hemisphere. First, we check the surface albedo forcing and feedback with a simplified partial derivative method and assess the surface temperature changes and their composition using a simple surface energy balance equation. Then, we investigate how patterns of stationary waves, westerly jet precipitation over the Northern Hemisphere change in response to the LGM ice-sheet configuration. Finally, we implement a paleo data-model comparison for validation of the large-scale climate changes over the Northern Hemisphere at the LGM. The wintertime stationary waves have the largest amplitude and different responses among the experiments, while stationary waves in summer are weak and similar responses. The LGM simulation with the ICE-6G_C better captures features of the LGM climate, but compared to the reconstructions, the climate model tends to overestimate cooling in summer and underestimate cooling in winter and simulate wetter conditions over the Northern Hemisphere.  

How to cite: Izumi, K., Paul Valdes, P., Ivanovic, R., and Gregoire, L.: Impacts of the PMIP4 ice-sheets on Northern Hemisphere climate during the last glacial period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5346, https://doi.org/10.5194/egusphere-egu2020-5346, 2020

D2570 |
Moritz Kreuzer, Ronja Reese, Willem Huiskamp, Stefan Petri, and Ricarda Winkelmann

Ocean-ice shelf interactions are the main drivers for the current mass loss from the Antarctic Ice Sheet. Recent studies have shown that increased continental meltwater input can enhance discharge through ice-ocean feedbacks. This raises the need for interactive modelling between ocean and ice-sheet systems to assess the consequences of additional freshwater input on the Antarctic region and beyond. While high-resolution simulations (1/4 degree or greater) can resolve detailed interactions between the ocean and ice shelf, the computational costs make them applicable only for regional studies or decadal to centennial time scales. In this study we present a framework for coupling a coarse resolution ocean model (MOM) to the Parallel Ice Sheet Model (PISM) via the Potsdam Ice-shelf Cavity mOdel (PICO). The intermediate model PICO approximates the overturning circulation in ice shelf cavities and includes ice-ocean boundary layer physics. We present this offline coupling approach and discuss the fluxes exchanged between the distinct model runs as well as energy and mass conservation. Using this flexible and computationally efficient framework, feedbacks between the ice and ocean can be analysed on a global spatial scale and paleoclimate time-scales.


How to cite: Kreuzer, M., Reese, R., Huiskamp, W., Petri, S., and Winkelmann, R.: Coupling the Parallel Ice Sheet Model with the Modular Ocean Model via an Antarctic ice-shelf cavity module, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10255, https://doi.org/10.5194/egusphere-egu2020-10255, 2020

D2571 |
Paul Gierz, Lars Ackermann, Christian Rodehacke, Uta Krebs-Kanzow, Christian Stepanek, Dirk Barbi, and Gerrit Lohmann

Interglacials during the Quaternary represent the youngest climate states in the paleoclimate record that are similar to potential warmer-than-present states during the Anthropocene. In particular, those periods with warmer reconstructed temperatures and/or higher sea levels provide insights into the mechanisms that may be at work now and in the future. To date, climate model simulations of Quaternary Interglacials have been restricted to Atmosphere-Biosphere-Ocean simulations, with static ice sheet geometries from glaciological, geological, and geophysical reconstructions. Simulations including fully interactive ice sheets have not been widely available. Here, we present the first simulations of the PMIP4 timeslices for the Holocene and the Last Interglacial (LIG) with a fully coupled multi-resolution climate/cryosphere model, the AWI-ESM. We compare the simulated snapshots for the Holocene and LIG to simulations to proxy reconstructions, and to runs without dynamic ice sheets to highlight the processes now represented by the improved model. Furthermore, we show various schemes implemented in our model system to represent the ice sheet mass balance, both from surface ablation as well as ocean interaction. We find that both the Holocene and Last Interglacial ice sheets contain a smaller volume of ice compared to present day, with relative sea level equivalent changes of -3% and -7%, respectively.

How to cite: Gierz, P., Ackermann, L., Rodehacke, C., Krebs-Kanzow, U., Stepanek, C., Barbi, D., and Lohmann, G.: Warm Climate States during Last Glacial Cycle with a Multi-Resolution Climate/Ice Sheet Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8205, https://doi.org/10.5194/egusphere-egu2020-8205, 2020

D2572 |
Lars Ackermann, Paul Gierz, and Gerrit Lohmann

Future global warming will affect ocean conditions by different mechanisms. One mechanism is the melting of the Greenland Ice Sheet (GIS), which may lead to a freshening of regions of deep water formation and eventually contribute to a possible slowdown of the Atlantic Meridional Overturning Circulation (AMOC). We simulate the two Coupled Model Intercomparison Project (CMIP) scenarios RCP4.5 and RCP8.5, to assess the effects of melt-induced fresh water on the AMOC. We use a newly developed coupled multi-resolution atmosphere-ocean-ice sheet model with high resolution at the coasts resolving the complex ocean dynamics. Our results show an AMOC recovery for both scenarios in simulations run with and without an included ice sheet model. We find that the ice sheet is not only acting as a source of freshwater to the ocean but also as a sink. This leads to local storage and redistribution of freshwater and largely compensates for the meltwater release. This physical consistency is missing in climate models without dynamic ice sheets. Therefore, we argue that freshwater hosing experiments should be assessed critically, as they might overestimate the North Atlantic freshening, induced by ice sheet melting. Because of the compensating effect, we find little effect of the included ice sheet model on the AMOC. Our results show a main freshwater release in West Greenland. There, the freshwater might be trapped in the Labrador Current and transported away from regions of deep water formation. Our results show an AMOC recovery, starting within the first half of the 22nd century. We assume the increase in net evaporation over the Atlantic and the resulting increase in ocean salinity, to be the main driver of this recovery.

How to cite: Ackermann, L., Gierz, P., and Lohmann, G.: AMOC recovery in a multi-centennial scenario using a coupled atmosphere-ocean-ice sheet model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11625, https://doi.org/10.5194/egusphere-egu2020-11625, 2020

D2573 |
Jonas Van Breedam, Philippe Huybrechts, and Michel Crucifix

Fully coupled state-of-the-art Atmosphere-Ocean General Circulation Models are the best tool to investigate feedbacks between the different components of the climate system on a decadal to centennial timescale. On millennial to multi-millennial timescales, Earth System Models of Intermediate Complexity are used to explore the feedbacks in the climate system between the ice sheets, the atmosphere and the ocean. Those fully coupled models, even at coarser resolution, are computationally very expensive and other techniques have been proposed to simulate ice sheet-climate interactions on a million-year timescale. The asynchronous coupling technique proposes to run a climate model for a few decades and subsequently an ice sheet model for a few millennia. Another, more efficient method is the use of a matrix look-up table where climate model runs are performed for end-members and intermediate climatic states are linearly interpolated.

In this study, a novel coupling approach is presented where a Gaussian Process emulator applied to the climate model HadSM3 is coupled to the ice sheet model AISMPALEO. We have tested the sensitivity of the formulation of the ice sheet parameter and of the coupling time to the evolution of the ice sheet over time. Additionally, we used different lapse rate adjustments between the relatively coarse climate model and the much finer ice sheet model topography. It is shown that the ice sheet evolution over a million year timescale is strongly sensitive to the choice of the coupling time and to the implementation of the lapse rate adjustment. With the new coupling procedure, we provide a more realistic and computationally efficient framework for ice sheet-climate interactions on a multi-million year timescale.


How to cite: Van Breedam, J., Huybrechts, P., and Crucifix, M.: A Gaussian process emulator for simulating ice sheet-climate interactions on a multi-million year timescale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11471, https://doi.org/10.5194/egusphere-egu2020-11471, 2020

D2574 |
Marianne S. Madsen, Shuting Yang, Christian Rodehacke, Guðfinna Aðalgeirsdóttir, Synne H. Svendsen, and Ida Margrethe Ringgaard

During recent decades, increased and highly variable mass loss from the Greenland ice sheet has been observed, implying that the ice sheet can respond to changes in ocean and atmospheric conditions on annual to decadal time scales. Changes in ice sheet topography and increased mass loss into the ocean may impact large scale atmosphere and ocean circulation. Therefore, coupling of ice sheet and climate models, to explicitly include the processes and feedbacks of ice sheet changes, is needed to improve the understanding of ice sheet-climate interactions.

Here, we present results from the coupled ice sheet-climate model system, EC-Earth-PISM. The model consists of the atmosphere, ocean and sea-ice model system EC-Earth, two-way coupled to the Parallel Ice Sheet Model, PISM. The surface mass balance (SMB) is calculated within EC-Earth, from the precipitation, evaporation and surface melt of snow and ice, to ensure conservation of mass and energy. The ice sheet model, PISM, calculates ice dynamical changes in ice discharge and basal melt as well as changes in ice extent and thickness. Idealized climate change experiments have been performed starting from pre-industrial conditions for a) constant forcing (pre-industrial control); b) abruptly quadrupling the CO2 concentration; and c) gradually increasing the CO2 concentration by 1% per year until 4xCO2 is reached.  All three experiments are run for 350 years.

Our results show a significant impact of the interactive ice sheet component on heat and fresh water fluxes into the Arctic and North Atlantic Oceans. The interactive ice sheet causes freshening of the Arctic Ocean and affects deep water formation, resulting in a significant delay of the recovery of the Atlantic Meridional Overturning Circulation (AMOC) in the coupled 4xCO2 experiments, when compared with uncoupled experiments.

How to cite: Madsen, M. S., Yang, S., Rodehacke, C., Aðalgeirsdóttir, G., Svendsen, S. H., and Ringgaard, I. M.: The ocean response to changes of the Greenland Ice sheet in a warming climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21261, https://doi.org/10.5194/egusphere-egu2020-21261, 2020

D2575 |
Alexander Robinson, Emilie Capron, Jorge Alvarez-Solas, Michael Bender, Heiko Goelzer, and Marisa Montoya

There is still no consensus concerning the evolution of the Greenland ice sheet during the Last Interglacial period (LIG, 130-115 kyr ago). Ice cores indicate that the ice sheet survived over most of the continent. Proxy data indicate temperature anomalies of up to 6-8°C. However, under these conditions, models predict almost complete deglaciation. This paradox must be resolved to be able to quantify Greenland’s sea-level contribution during the LIG as well as to understand its sensitivity to future climate change. Here we analyze the available evidence and outline strategies to reconcile modeling and data efforts for Greenland during the LIG.

How to cite: Robinson, A., Capron, E., Alvarez-Solas, J., Bender, M., Goelzer, H., and Montoya, M.: Reconciling reconstructions and simulations of the Greenland ice sheet and its climate during the Last Interglacial period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19016, https://doi.org/10.5194/egusphere-egu2020-19016, 2020

D2576 |
Miren Vizcaino, Laura Muntjewerf, Raymond Sellevold, Carolina Ernani da Silva, Michele Petrini, Katherine Thayer-Calder, Meike Scherrenberg, Sarah Bradley, Jeremy Fyke, William Lipscomb, Marcus Lofverstrom, and William Sacks

The Greenland ice sheet (GrIS) has been losing mass in the last several decades, with a current contributing of around 0.7 mm per year to global mean sea level rise (SLR). Projections of future melt rates are often derived from standalone ice sheet models, forced by data from global or regional climate models. In many cases, the surface mass balance parameterization relies on simplified schemes that relate melt with surface temperature.

In this study, we present a mass and energy conserving, 350-year simulation with the Community Earth System Model version 2.1 (CESM2.1) bidirectionally coupled to the Community Ice Sheet Model version 2.1 (CISM2.1). In this simulation, the carbon dioxide concentration is initially increasing by 1% per year  from pre-industrial levels (287 ppmv), to a quadrupling (1140 ppmv) and stabilization after year 140. The model simulates a global warming of 5.3 K and 8.5 K with respect to preindustrial by years 131-150 and 331-150, respectively, and a strong decline in the North Atlantic Meridional Overturning Circulation that is initiated before GrIS runoff substantially increases. 91% of the total GrIS contribution to global mean sea level rise (SLR, 1140 mm) is simulated in the two centuries following CO2 stabilization, as the mass loss increases from 2.2 mm SLR per year in 131-150 to 6.6 mm SLR per year in 331-351. This increase is caused by melt acceleration as the ablation areas expand, and Greenland summer surface temperatures predominantly approach melt conditions when the global warming exceeds a certain threshold (around 4.2 K).  This enhances the albedo and turbulent heat fluxes contribution to total melt energy.  

How to cite: Vizcaino, M., Muntjewerf, L., Sellevold, R., Ernani da Silva, C., Petrini, M., Thayer-Calder, K., Scherrenberg, M., Bradley, S., Fyke, J., Lipscomb, W., Lofverstrom, M., and Sacks, W.: Coupled ice-climate simulation of future Greenland ice sheet evolution: mechanisms, thresholds and feedbacks for accelerated mass loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19692, https://doi.org/10.5194/egusphere-egu2020-19692, 2020

D2577 |
Thomas Riddick, Victor Brovkin, Stefan Hagemann, and Uwe Mikolajewicz

The continually evolving large ice sheets present in the Northern Hemisphere during the last glacial cycle caused significant changes to river pathways both through directly blocking rivers and through glacial isostatic adjustment. Associated with these changing river pathways was the formation and evolution of large glacial lakes such as Lake Agassiz. Studies have shown this changing hydrology had a significant impact on the ocean circulation through changing the pattern of freshwater discharge into the oceans. A coupled Earth system model (ESM) simulation of the last glacial cycle thus requires a hydrological discharge and lake model that uses a set of river pathways and lakes that evolve with Earth's changing orography while being able to reproduce the known present-day river network given the present-day orography. Here, we present a method for dynamically modelling rivers and lakes by applying predefined corrections to an evolving fine-scale orography (accounting for the changing ice sheets and isostatic rebound) each time the river directions and lakes basins are recalculated. The corrected orography thus produced is then used to create a set of fine-scale river pathways and these are then upscaled to a coarser scale on which an existing present-day hydrological discharge model within the JSBACH land surface model simulates the river flow. The associated glacial lakes are delineated from the same corrected fine scale orography; lake inflow and outflow being linked to the river flow model.

How to cite: Riddick, T., Brovkin, V., Hagemann, S., and Mikolajewicz, U.: Dynamic Hydrological Discharge and Lake Modelling for Coupled Climate Model Simulations of the Last Glacial Cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16815, https://doi.org/10.5194/egusphere-egu2020-16815, 2020

D2578 |
Raymond Sellevold and Miren Vizcaino

We use the Community Earth System model 2.1 to investigate the response of the Greenland Ice sheet (GrIS) surface mass balance (SMB) to an idealized high CO2 forcing scenario (1% per year increase to four-times-preindustrial). The SMB calculation is coupled with the atmospheric model, using a physically-based surface energy balance scheme for melt, explicit calculation of snow albedo, and a realistic treatment of polar snow and firn compaction. The SMB becomes negative for a global mean temperature increase of 2.7 K compared to pre-industrial temperature, and the surface mass loss accelerates. Longwave radiation is the primary contributor to melt energy before acceleration. A decrease of the albedo due to ablation area expansion together with turbulent heat flux increase due to the surface of the ice sheet nearing melting point, are the main contributors at/after acceleration. Further, trends towards more positive North Atlantic Oscillation and more negative Greenland Blocking Index partially reduces future melt increase.

How to cite: Sellevold, R. and Vizcaino, M.: Greenland ice sheet surface mass balance response to high CO2 forcing: threshold and mechanisms for accelerated surface mass loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21686, https://doi.org/10.5194/egusphere-egu2020-21686, 2020

D2579 |
Marilena Geng, Lev Tarasov, and Taimaz Bahadory

What determines the character of glacial inceptions? Does the spatio-temporal pattern of ice nucleation and expansion vary much between Late Pleistocene glacial inceptions? According to various benthic del18O stacks, the MIS 7 interglacial was the most anomalous in character of the last 4 interglacials. Key differences include a weaker interglacial state and an initial fast inception interrupted by a return to a similar and extended interglacial state. These anomalies of MIS 7 along with temporal proximity arguably make the last two glacial inceptions the best test case for addressing our opening questions. As part of a larger project to generate and analyze a data-constrained ensemble of fully coupled ice/climate transient simulations for the last two complete glacial cycles, herein we present initial results comparing the last two glacial inceptions (MIS 7 and 5d). We are using a new version of the fully coupled ice/climate model LCice. LCice now simulates all 4 paleo ice sheet complexes with hybrid shallow-shelf and shallow-ice physics. It has already been shown to capture northern hemispheric ice sheet growth and subsequent retreat consistent with inferences from global mean sea level proxies (Bahadory et al, 2019). Orbital and greenhouse gas changes are the only external forcings applied to the model. A 300 member ensemble probes parametric uncertainties in both the 3D Glacial Systems Model and LoveClim (Atmosphere/Ocean/Vegetation) components of LCice. Our presentation will compare the evolution and relative phasing of all 4 paleo ice sheets, and associated changes in the rest of the modelled climate system.

How to cite: Geng, M., Tarasov, L., and Bahadory, T.: A global ensemble-based comparison of the last two glacial inceptions with LCice 2.0, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17514, https://doi.org/10.5194/egusphere-egu2020-17514, 2020

D2580 |
Tobias Zolles and Andreas Born

Surface mass balance models that are run over longer timescales are commonly forced with climatological forcing, disregarding natural climate variability. Here we investigate the impact of inter-annual variability of the present day climate using the energy balance model BESSI. The model is forced with daily data of precipitation, temperature, long and short wave radiation and humidity. We create synthetic time series of realistic climate forcing with different time scales of variability by re-ordering the years of present day reanalysis as well as using the climatology.

We find that the model significantly overestimates the Greenland SMB in case of climatological forcing when compared to the original daily reanalysis (40%). The effect of changing inter-annual variability by the re-ordering of forcing years has a relatively minor effect on the Greenland-wide mass balance (<5%), but is more important around the equilibrium line where positive feedback increase its impact over time. The averaging of precipitation is the key factor. It leads to a surface albedo increase as the nature of snowfall changes from event-based to continuous. To reduce this effect we use monthly climatologies in combination with a sub-monthly variability instead of daily climatologies, to retain the event (storm) based nature of precipitation.

Finally, we characterize the errors in cases of using climatology where interannual variability is unknown, such as simulations of the deep past and future and propose a solution.

How to cite: Zolles, T. and Born, A.: The impact of inter-annual variability on the surface mass balance of Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10978, https://doi.org/10.5194/egusphere-egu2020-10978, 2020