Simulating Interactive Ice Sheets in the Multi-Resolution AWI-ESM: A case study using the SCOPE Coupler

Abstract. Interactions between the climate and the cryosphere have the potential to induce strong non-linear transitions in the Earth's climate. These interactions influence both the atmospheric circulation, by changing the ice sheet's geometry, as well as the oceanic circulation, by modification of the water mass properties. Furthermore, the waxing and waning of large continental ice sheets influences the global albedo, altering the energy balance of the Earth System and inducing climate-ice sheet feedbacks on a global scale as evident in Pleistocene glacial-interglacial cycles. To date, few fully comprehensive models exist, that do not only contain a coupled atmosphere/land/ocean component, but also consider interactive cryosphere physics. Yet, on glacial-interglacial and tectonic time scales, as well as in the Anthropocene, ice sheets are not in equilibrium with the climate, and prescribed fixed ice sheet representations in the model can principally be only an approximation to reality. Only climate models, that contain interactive ice sheets, can produce simulations of the Earth's climate which include all feedbacks and processes related to atmosphere-land-ocean-ice interactions. Previous fully coupled models were limited either by low spatial resolution or an incomplete representation of ice sheet processes, such as iceberg calving, surface ablation processes, and ocean/ice-shelf interactions. Here, we present the newly developed AWI-Earth System Model (AWI-ESM), which tackles some of these problems. Our modelling toolbox is based on the AWI-climate model, including atmosphere and vegetation components suitable for paleoclimate studies, a multi-resolution global ocean component which can be refined to simulate regions of interest at high resolution, and an ice sheet component suitable for simulating both ice sheet and ice shelf dynamics and thermodynamics. We describe the currently implemented coupling between these components, present first results for the Mid-Holocene and Last Interglacial, and introduce further ideas for scientific applications for both future and past climate states with a focus on the Northern Hemisphere. Finally, we provide an outlook on the potential of such fully coupled Earth System models in improving representation of climate-ice sheet feedbacks in future paleoclimate studies with this model.

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Asynchronous Antarctic and Greenland ice-volume contributions to the last interglacial sea-level highstand

10.5194/egusphere-egu2020-1513 ◽

2020 ◽

Author(s):

Eelco Rohling ◽

Fiona Hibbert

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Global Climate ◽

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Climate Forcing ◽

Potential Contribution ◽

Last Interglacial ◽

Ice Shelf

Sea-level rise is among the greatest risks that arise from anthropogenic global climate change. It is receiving a lot of attention, among others in the IPCC reports, but major questions remain as to the potential contribution from the great continental ice sheets. In recent years, some modelling work has suggested that the ice-component of sea-level rise may be much faster than previously thought, but the rapidity of rise seen in these results depends on inclusion of scientifically debated mechanisms of ice-shelf decay and associated ice-sheet instability. The processes have not been active during historical times, so data are needed from previous warm periods to evaluate whether the suggested rates of sea-level rise are supported by observations or not. Also, we then need to assess which of the ice sheets was most sensitive, and why. The last interglacial (LIG; ~130,000 to ~118,000 years ago, ka) was the last time global sea level rose well above its present level, reaching a highstand of +6 to +9 m or more. Because Greenland Ice Sheet (GrIS) contributions were smaller than that, this implies substantial Antarctic Ice Sheet (AIS) contributions. However, this still leaves the timings, magnitudes, and drivers of GrIS and AIS reductions open to debate. I will discuss recently published sea-level reconstructions for the LIG highstand, which reveal that AIS and GrIS contributions were distinctly asynchronous, and that rates of rise to values above 0 m (present-day sea level) reached up to 3.5 m per century. Such high pre-anthropogenic rates of sea-level rise lend credibility to high rates inferred by ice modelling under certain ice-shelf instability parameterisations, for both the past and future. Climate forcing was distinctly asynchronous between the southern and northern hemispheres as well during the LIG, explaining the asynchronous sea-level contributions from AIS and GrIS. Today, climate forcing is synchronous between the two hemispheres, and also faster and greater than during the LIG. Therefore, LIG rates of sea-level rise should likely be considered minimum estimates for the future.

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A Gaussian process emulator for simulating ice sheet-climate interactions on a multi-million year timescale

10.5194/egusphere-egu2020-11471 ◽

2020 ◽

Author(s):

Jonas Van Breedam ◽

Philippe Huybrechts ◽

Michel Crucifix

Keyword(s):

Gaussian Process ◽

Climate Model ◽

Ice Sheet ◽

Climate System ◽

Lapse Rate ◽

Coupled Models ◽

Climate Interactions ◽

Coupling Time ◽

Fully Coupled ◽

Gaussian Process Emulator

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.&#160;

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Simulation of the Global Coupled Climate/Ice Sheet System over Millennial Timescales

10.26686/wgtn.16992892 ◽

2021 ◽

Author(s):

◽

Jeremy Fyke

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Co2 Emissions ◽

Climate Model ◽

Ice Sheets ◽

Ice Sheet ◽

Earth System ◽

Ice Shelves ◽

Stability Threshold ◽

Ice Caps

Ice sheets are important components of the Earth system that are expected to respond strongly to anthropogenic forcing of climate. The aim of this work is to use numerical climate and ice sheet modelling to identify and understand the millennial-scale interaction between the Antarctic and Greenland Ice Sheets (AIS and GIS) and global climate. An initial modelling effort evaluated the response of ice shelves and ice sheets to future CO2 emission scenarios by quantifying the duration and magnitude of summer melt periods. A temperature threshold based on positive degree days was applied to bias-corrected University of Victoria Earth System Climate Model (UVic ESCM) output spanning 1000 years into the future. The simulations indicated that an increase in summer melting over most of the GIS, the Ross and Ronne-Filchner ice shelves, and large sections of the West Antarctic Ice Sheet (where little present-day ablation occurs) could occur if future emissions are not curtailed. This initial work highlighted the need to assess the dynamic response of ice sheets to climate change. I therefore developed an ice sheet/climate model comprised of the UVic ESCM and the Pennsylvania State University Ice Sheet Model. Coupling these models required development of new techniques, including subgrid-scale energy balance calculations that incorporate a surface air temperature (SAT) model bias correction procedure. In testing the model, I found that climate model SAT bias, meltwater refreezing and albedo variations play an important role in simulated ice sheet evolution, particularly as more of the ice surface experiences melting conditions. The model realistically reproduced the AIS and GIS, and captured the surface mass balance (SMB) distributions for both ice sheets well for the present day, including narrow GIS ablation zones. The newly developed model was used to carry out a suite of experiments designed to assess the behavior of the GIS under elevated-CO2 conditions. A deglacial SMB-based GIS stability threshold was identified between 3-4x preindustrial atmospheric levels (PAL) of CO2. Below the threshold, GIS retreat still occurred but the ice ultimately stabilized in a ‘reduced ice sheet’ configuration, while at CO2 >= 4x PAL CO2, ice retreated to mountain ice caps. Ice sheet inception simulations indicated that above 4x PAL CO2, ice growth was limited, while at 4x PAL CO2 ice was able to reach the eastern Greenland coastline. Between 2-3x PAL CO2, separate ice caps in the southern and eastern mountains coalesced and exported ice onto the lowland plains. Large-scale ice sheet growth was limited until 1-2x PAL CO2. GIS ice loss increased with greater cumulative CO2 emissions in transient simulations. However, the ice sheet was able to briefly overshoot the CO2 stability threshold without experiencing drastic ice retreat due to the long response time of the simulated GIS relative to the rate of deep ocean carbon uptake. Finally, several model experiments were carried out using the coupled model to examine the impact of ocean melt-driven AIS retreat on the oceanic circulation and structure. This retreat produced freshwater fluxes to the Southern Ocean that were of the same magnitude (and initially greater) than the background continental flux, and continued for 3000 years after the initial shift to high-melt conditions. The Ross and Weddell Seas became productive sea ice export regions, which resulted in higher salinities in these seas and very low ocean temperatures. Enhanced sea ice export and melt in the open Southern Ocean contributed to a slight shallowing and weakening of the North Atlantic Deepwater circulation cell, that would reinforce predicted trends expected as a result of future anthropogenic CO2 emissions.

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Modelling the evolution of the Antarctic ice sheet since the last interglacial

The Cryosphere ◽

10.5194/tc-8-1347-2014 ◽

2014 ◽

Vol 8 (4) ◽

pp. 1347-1360 ◽

Cited By ~ 20

Author(s):

M. N. A. Maris ◽

B. de Boer ◽

S. R. M. Ligtenberg ◽

M. Crucifix ◽

W. J. van de Berg ◽

...

Keyword(s):

Climate Model ◽

Ice Sheet ◽

Global Ocean ◽

Last Interglacial ◽

Antarctic Ice Sheet ◽

Velocity Parameter ◽

Ice Volume ◽

Reference Simulation ◽

Parameter Values ◽

The Antarctic

Abstract. We present the effects of changing two sliding parameters, a deformational velocity parameter and two bedrock deflection parameters on the evolution of the Antarctic ice sheet over the period from the last interglacial until the present. These sensitivity experiments have been conducted by running the dynamic ice model ANICE forward in time. The temporal climatological forcing is established by interpolating between two temporal climate states created with a regional climate model. The interpolation is done in such a way that both temperature and surface mass balance follow the European Project for Ice Coring in Antarctica (EPICA) Dome C ice-core proxy record for temperature. We have determined an optimal set of parameter values, for which a realistic grounding-line retreat history and present-day ice sheet can be simulated; the simulation with this set of parameter values is defined as the reference simulation. An increase of sliding with respect to this reference simulation leads to a decrease of the Antarctic ice volume due to enhanced ice velocities on mainly the West Antarctic ice sheet. The effect of changing the deformational velocity parameter mainly yields a change in east Antarctic ice volume. Furthermore, we have found a minimum in the Antarctic ice volume during the mid-Holocene, in accordance with observations. This is a robust feature in our model results, where the strength and the timing of this minimum are both dependent on the investigated parameters. More sliding and a slower responding bedrock lead to a stronger minimum which emerges at an earlier time. From the model results, we conclude that the Antarctic ice sheet has contributed 10.7 ± 1.3 m of eustatic sea level to the global ocean from the last glacial maximum (about 16 ka for the Antarctic ice sheet) until the present.

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Warm Climate States during Last Glacial Cycle with a Multi-Resolution Climate/Ice Sheet Model

10.5194/egusphere-egu2020-8205 ◽

2020 ◽

Author(s):

Paul Gierz ◽

Lars Ackermann ◽

Christian Rodehacke ◽

Uta Krebs-Kanzow ◽

Christian Stepanek ◽

...

Keyword(s):

Climate Model ◽

Ice Sheets ◽

Ice Sheet ◽

Glacial Cycle ◽

Last Interglacial ◽

Sea Levels ◽

The Holocene ◽

Climate Model Simulations ◽

Proxy Reconstructions ◽

Improved Model

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.

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Simulation of the Global Coupled Climate/Ice Sheet System over Millennial Timescales

10.26686/wgtn.16992892.v1 ◽

2021 ◽

Author(s):

◽

Jeremy Fyke

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Co2 Emissions ◽

Climate Model ◽

Ice Sheets ◽

Ice Sheet ◽

Earth System ◽

Ice Shelves ◽

Stability Threshold ◽

Ice Caps

Ice sheets are important components of the Earth system that are expected to respond strongly to anthropogenic forcing of climate. The aim of this work is to use numerical climate and ice sheet modelling to identify and understand the millennial-scale interaction between the Antarctic and Greenland Ice Sheets (AIS and GIS) and global climate. An initial modelling effort evaluated the response of ice shelves and ice sheets to future CO2 emission scenarios by quantifying the duration and magnitude of summer melt periods. A temperature threshold based on positive degree days was applied to bias-corrected University of Victoria Earth System Climate Model (UVic ESCM) output spanning 1000 years into the future. The simulations indicated that an increase in summer melting over most of the GIS, the Ross and Ronne-Filchner ice shelves, and large sections of the West Antarctic Ice Sheet (where little present-day ablation occurs) could occur if future emissions are not curtailed. This initial work highlighted the need to assess the dynamic response of ice sheets to climate change. I therefore developed an ice sheet/climate model comprised of the UVic ESCM and the Pennsylvania State University Ice Sheet Model. Coupling these models required development of new techniques, including subgrid-scale energy balance calculations that incorporate a surface air temperature (SAT) model bias correction procedure. In testing the model, I found that climate model SAT bias, meltwater refreezing and albedo variations play an important role in simulated ice sheet evolution, particularly as more of the ice surface experiences melting conditions. The model realistically reproduced the AIS and GIS, and captured the surface mass balance (SMB) distributions for both ice sheets well for the present day, including narrow GIS ablation zones. The newly developed model was used to carry out a suite of experiments designed to assess the behavior of the GIS under elevated-CO2 conditions. A deglacial SMB-based GIS stability threshold was identified between 3-4x preindustrial atmospheric levels (PAL) of CO2. Below the threshold, GIS retreat still occurred but the ice ultimately stabilized in a ‘reduced ice sheet’ configuration, while at CO2 >= 4x PAL CO2, ice retreated to mountain ice caps. Ice sheet inception simulations indicated that above 4x PAL CO2, ice growth was limited, while at 4x PAL CO2 ice was able to reach the eastern Greenland coastline. Between 2-3x PAL CO2, separate ice caps in the southern and eastern mountains coalesced and exported ice onto the lowland plains. Large-scale ice sheet growth was limited until 1-2x PAL CO2. GIS ice loss increased with greater cumulative CO2 emissions in transient simulations. However, the ice sheet was able to briefly overshoot the CO2 stability threshold without experiencing drastic ice retreat due to the long response time of the simulated GIS relative to the rate of deep ocean carbon uptake. Finally, several model experiments were carried out using the coupled model to examine the impact of ocean melt-driven AIS retreat on the oceanic circulation and structure. This retreat produced freshwater fluxes to the Southern Ocean that were of the same magnitude (and initially greater) than the background continental flux, and continued for 3000 years after the initial shift to high-melt conditions. The Ross and Weddell Seas became productive sea ice export regions, which resulted in higher salinities in these seas and very low ocean temperatures. Enhanced sea ice export and melt in the open Southern Ocean contributed to a slight shallowing and weakening of the North Atlantic Deepwater circulation cell, that would reinforce predicted trends expected as a result of future anthropogenic CO2 emissions.

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The Framework For Ice Sheet–Ocean Coupling (FISOC) V1.1

Geoscientific Model Development ◽

10.5194/gmd-14-889-2021 ◽

2021 ◽

Vol 14 (2) ◽

pp. 889-905

Author(s):

Rupert Gladstone ◽

Benjamin Galton-Fenzi ◽

David Gwyther ◽

Qin Zhou ◽

Tore Hattermann ◽

...

Keyword(s):

Dynamic Model ◽

Ice Sheets ◽

Ice Sheet ◽

Coupled Processes ◽

Earth System ◽

Ice Shelf ◽

Time Step ◽

Ice Dynamics ◽

Ocean Coupling ◽

The Impact

Abstract. A number of important questions concern processes at the margins of ice sheets where multiple components of the Earth system, most crucially ice sheets and oceans, interact. Such processes include thermodynamic interaction at the ice–ocean interface, the impact of meltwater on ice shelf cavity circulation, the impact of basal melting of ice shelves on grounded ice dynamics and ocean controls on iceberg calving. These include fundamentally coupled processes in which feedback mechanisms between ice and ocean play an important role. Some of these mechanisms have major implications for humanity, most notably the impact of retreating marine ice sheets on the global sea level. In order to better quantify these mechanisms using computer models, feedbacks need to be incorporated into the modelling system. To achieve this, ocean and ice dynamic models must be coupled, allowing runtime information sharing between components. We have developed a flexible coupling framework based on existing Earth system coupling technologies. The open-source Framework for Ice Sheet–Ocean Coupling (FISOC) provides a modular approach to coupling, facilitating switching between different ice dynamic and ocean components. FISOC allows fully synchronous coupling, in which both ice and ocean run on the same time step, or semi-synchronous coupling in which the ice dynamic model uses a longer time step. Multiple regridding options are available, and there are multiple methods for coupling the sub-ice-shelf cavity geometry. Thermodynamic coupling may also be activated. We present idealized simulations using FISOC with a Stokes flow ice dynamic model coupled to a regional ocean model. We demonstrate the modularity of FISOC by switching between two different regional ocean models and presenting outputs for both. We demonstrate conservation of mass and other verification steps during evolution of an idealized coupled ice–ocean system, both with and without grounding line movement.

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A Framework for Ice Sheet – Ocean Coupling (FISOC) V1.1

10.5194/gmd-2020-206 ◽

2020 ◽

Author(s):

Rupert Gladstone ◽

Benjamin Galton-Fenzi ◽

David Gwyther ◽

Qin Zhou ◽

Tore Hattermann ◽

...

Keyword(s):

Dynamic Model ◽

Ice Sheets ◽

Ice Sheet ◽

Coupled Processes ◽

Earth System ◽

Ice Shelf ◽

Time Step ◽

Ice Dynamics ◽

Ocean Coupling ◽

The Impact

Abstract. A number of important questions concern processes at the margins of ice sheets where multiple components of the Earth System, most crucially ice sheets and oceans, interact. Such processes include thermodynamic interaction at the ice-ocean interface, the impact of melt water on ice shelf cavity circulation, the impact of basal melting of ice shelves on grounded ice dynamics, and ocean controls on iceberg calving. These include fundamentally coupled processes in which feedback mechanisms between ice and ocean play an important role. Some of these mechanisms have major implications for humanity, most notably the impact of retreating marine ice sheets on global sea level. In order to better quantify these mechanisms using computer models, feedbacks need to be incorporated into the modelling system. To achieve this ocean and ice dynamic models must be coupled, allowing run time information sharing between components. We have developed a flexible coupling framework based on existing Earth System coupling technologies. The open-source Framework for Ice Sheet – Ocean Coupling (FISOC) provides a modular approach to online coupling, facilitating switching between different ice dynamic and ocean components. FISOC allows fully synchronous coupling, in which both ice and ocean run on the same time-step, or semi-synchronous coupling in which the ice dynamic model uses a longer time step. Multiple regridding options are available, and multiple methods for coupling the sub ice shelf cavity geometry. Thermodynamic coupling may also be activated. We present idealised simulations using FISOC with a Stokes flow ice dynamic model coupled to a regional ocean model. We demonstrate the modularity of FISOC by switching between two different regional ocean models and presenting outputs for both. We demonstrate conservation of mass and other verification steps during evolution of an idealised coupled ice – ocean system, both with and without grounding line movement.

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Dynamical processes involved in the retreat of marine ice sheets

Journal of Glaciology ◽

10.3189/172756501781832269 ◽

2001 ◽

Vol 47 (157) ◽

pp. 271-282 ◽

Cited By ~ 95

Author(s):

Richard C.A. Hindmarsh ◽

E. Le Meur

Keyword(s):

Ice Sheets ◽

Ice Sheet ◽

Ice Shelf ◽

Ice Streams ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Grounding Line ◽

Neutral Equilibrium ◽

Generally True

AbstractMarine ice sheets with mechanics described by the shallow-ice approximation by definition do not couple mechanically with the shelf. Such ice sheets are known to have neutral equilibria. We consider the implications of this for their dynamics and in particular for mechanisms which promote marine ice-sheet retreat. The removal of ice-shelf buttressing leading to enhanced flow in grounded ice is discounted as a significant influence on mechanical grounds. Sea-level rise leading to reduced effective pressures under ice streams is shown to be a feasible mechanism for producing postglacial West Antarctic ice-sheet retreat but is inconsistent with borehole evidence. Warming thins the ice sheet by reducing the average viscosity but does not lead to grounding-line retreat. Internal oscillations either specified or generated via a MacAyeal–Payne thermal mechanism promote migration. This is a noise-induced drift phenomenon stemming from the neutral equilibrium property of marine ice sheets. This migration occurs at quite slow rates, but these are sufficiently large to have possibly played a role in the dynamics of the West Antarctic ice sheet after the glacial maximum. Numerical experiments suggest that it is generally true that while significant changes in thickness can be caused by spatially uniform changes, spatial variability coupled with dynamical variability is needed to cause margin movement.

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