scholarly journals Impact of ocean forcing on the Aurora Basin in the 21st and 22nd centuries

2016 ◽  
Vol 57 (73) ◽  
pp. 79-86 ◽  
Author(s):  
S. Sun ◽  
S. L. Cornford ◽  
D. E. Gwyther ◽  
R. M. Gladstone ◽  
B. K. Galton-Fenzi ◽  
...  
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Ice Sheet ◽  
Adaptive Mesh ◽  
Global Climate Models ◽  
Ice Shelf ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Future Warming ◽  
East West

ABSTRACTThe grounded ice in the Totten and Dalton glaciers is an essential component of the buttressing for the marine-based Aurora basin, and hence their stability is important to the future rate of mass loss from East Antarctica. Totten and Vanderford glaciers are joined by a deep east-west running subglacial trench between the continental ice sheet and Law Dome, while a shallower trench links the Totten and Dalton glaciers. All three glaciers flow into the ocean close to the Antarctic circle and experience ocean-driven ice shelf melt rates comparable with the Amundsen Sea Embayment. We investigate this combination of trenches and ice shelves with the BISICLES adaptive mesh ice-sheet model and ocean-forcing melt rates derived from two global climate models. We find that ice shelf ablation at a rate comparable with the present day is sufficient to cause widespread grounding line retreat in an east-west direction across Totten and Dalton glaciers, with projected future warming causing faster retreat. Meanwhile, southward retreat is limited by the shallower ocean facing slopes between the coast and the bulk of the Aurora sub-glacial trench. However the two climate models produce completely different future ice shelf basal melt rates in this region: HadCM3 drives increasing sub-ice shelf melting to ~2150, while ECHAM5 shows little or no increase in sub-ice shelf melting under the two greenhouse gas forcing scenarios.

scholarly journals Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat

2020 ◽  
Author(s):  
Kate E. Ashley ◽  
James A. Bendle ◽  
Robert McKay ◽  
Johan Etourneau ◽  
Francis J. Jimenez-Espejo ◽  
...  
Keyword(s):  
Sea Ice ◽  
Climate Models ◽  
Global Climate ◽  
Feedback Mechanism ◽  
Global Climate Models ◽  
Ice Shelf ◽  
Sea Ice Extent ◽  
Glacial Meltwater ◽  
Ice Shelves ◽  
Antarctic Sea Ice

Abstract. Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large cavity ice shelves is not included in current models and may be a driver of this phenomena. We examine a Holocene sediment core off East Antarctica that records the Neoglacial transition, the last major baseline shift of Antarctic sea-ice, and part of a late-Holocene global cooling trend. We provide a multi-proxy record of Holocene glacial meltwater input, sediment transport and sea-ice variability which includes. Our record, supported by high-resolution ocean modelling, shows that a rapid Antarctic sea-ice increase occurred against a backdrop of increasing glacial meltwater input and gradual climate warming. We suggest that mid-Holocene ice shelf cavity expansion led to supercooling of surface waters and sea-ice growth which slowed basal ice shelf melting. Incorporating this feedback mechanism into global climate models will be important for future projections of Antarctic changes.

scholarly journals Regions of intensification of extreme snowfall under future warming

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Lennart Quante ◽  
Sven N. Willner ◽  
Robin Middelanis ◽  
Anders Levermann
Keyword(s):  
Climate Change ◽  
Global Warming ◽  
Observational Data ◽  
Climate Models ◽  
Hydrological Cycle ◽  
Global Climate ◽  
Global Climate Models ◽  
Average Intensity ◽  
High Latitudes ◽  
Future Warming

AbstractDue to climate change the frequency and character of precipitation are changing as the hydrological cycle intensifies. With regards to snowfall, global warming has two opposing influences; increasing humidity enables intense snowfall, whereas higher temperatures decrease the likelihood of snowfall. Here we show an intensification of extreme snowfall across large areas of the Northern Hemisphere under future warming. This is robust across an ensemble of global climate models when they are bias-corrected with observational data. While mean daily snowfall decreases, both the 99th and the 99.9th percentiles of daily snowfall increase in many regions in the next decades, especially for Northern America and Asia. Additionally, the average intensity of snowfall events exceeding these percentiles as experienced historically increases in many regions. This is likely to pose a challenge to municipalities in mid to high latitudes. Overall, extreme snowfall events are likely to become an increasingly important impact of climate change in the next decades, even if they will become rarer, but not necessarily less intense, in the second half of the century.

Simulating detailed spatial patterns of ice shelf basal melt

2021 ◽  
Author(s):  
Erwin Lambert ◽  
André Jüling ◽  
Paul Holland ◽  
Roderik van de Wal
Keyword(s):  
Flow Direction ◽  
Ice Sheet ◽  
Realistic Model ◽  
Western Boundary ◽  
Layer Model ◽  
Ice Shelf ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Grounding Line ◽  
Ocean Properties

<p>The contact between ice shelves and relatively warm ocean waters causes basal melt, ice shelf thinning, and ultimately ice sheet mass loss. This basal melt, and its dependence on ocean properties, is poorly understood due to an overall lack of direct observations and a difficulty in explicit simulation of the circulation in sub-shelf cavities. In this study, we compare a number of parameterisations and models of increasing complexity, up to a 2D ‘Layer’ model. Each model is aimed at quantifying basal melt rates as a function of offshore temperature and salinity. We test these models in an idealised setting (ISOMIP+) and in a realistic setting for the Amundsen Sea Embayment. All models show a comparable non-linear sensitivity of ice-shelf average basal melt to ocean warming, indicating a positive feedback between melt and circulation. However, the Layer model is the only one which explicitly resolves the flow direction of the buoyant melt plumes, which is primarily governed by rotation and by the basal topography of the ice shelves. At 500m resolution, this model simulates locally enhanced basal melt near the grounding line, in topographical channels, and near the western boundary. The simulated melt patterns for the Amundsen Sea ice shelves are compared to satellite observations of ice shelf thinning and to 3D numerical simulations of the sub-shelf cavity circulation. As detailed melt rates near the grounding line are essential for the stability of ice sheets, spatially realistic melt rates are crucial for future projections of ice sheet dynamics. We conclude that the Layer model can function as a relatively cheap yet realistic model to downscale 3D ocean simulations of ocean properties to sub-kilometer scale basal melt fields to provide detailed forcing fields to ice sheet models.</p>

scholarly journals CMIP5 model selection for ISMIP6 ice sheet model forcing: Greenland and Antarctica

2020 ◽  
Vol 14 (3) ◽  
pp. 855-879 ◽  
Author(s):  
Alice Barthel ◽  
Cécile Agosta ◽  
Christopher M. Little ◽  
Tore Hattermann ◽  
Nicolas C. Jourdain ◽  
...  
Keyword(s):  
Model Selection ◽  
Climate Models ◽  
Climate Modeling ◽  
Global Climate ◽  
Ice Sheet ◽  
Global Climate Models ◽  
Historical Period ◽  
Climate Projections ◽  
Subsurface Ocean ◽  
Spatial Domains

Abstract. The ice sheet model intercomparison project for CMIP6 (ISMIP6) effort brings together the ice sheet and climate modeling communities to gain understanding of the ice sheet contribution to sea level rise. ISMIP6 conducts stand-alone ice sheet experiments that use space- and time-varying forcing derived from atmosphere–ocean coupled global climate models (AOGCMs) to reflect plausible trajectories for climate projections. The goal of this study is to recommend a subset of CMIP5 AOGCMs (three core and three targeted) to produce forcing for ISMIP6 stand-alone ice sheet simulations, based on (i) their representation of current climate near Antarctica and Greenland relative to observations and (ii) their ability to sample a diversity of projected atmosphere and ocean changes over the 21st century. The selection is performed separately for Greenland and Antarctica. Model evaluation over the historical period focuses on variables used to generate ice sheet forcing. For stage (i), we combine metrics of atmosphere and surface ocean state (annual- and seasonal-mean variables over large spatial domains) with metrics of time-mean subsurface ocean temperature biases averaged over sectors of the continental shelf. For stage (ii), we maximize the diversity of climate projections among the best-performing models. Model selection is also constrained by technical limitations, such as availability of required data from RCP2.6 and RCP8.5 projections. The selected top three CMIP5 climate models are CCSM4, MIROC-ESM-CHEM, and NorESM1-M for Antarctica and HadGEM2-ES, MIROC5, and NorESM1-M for Greenland. This model selection was designed specifically for ISMIP6 but can be adapted for other applications.

scholarly journals Climate, the Antarctic ice sheet and ground heat flux

1995 ◽  
Vol 21 ◽  
pp. 144-148
Author(s):  
Garth W. Paltridge ◽  
Christopher M. Zweck
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Climate Models ◽  
Global Climate ◽  
Ice Sheet ◽  
Global Climate Models ◽  
Balance Model ◽  
Antarctic Ice Sheet ◽  
Ground Heat Flux ◽  
The Antarctic

A simple steady-state energy and mass-balance model of the Antarctic ice sheet is developed. Basically it is a set of two equations with two unknowns of steady-state height h and potential basal temperature Tb. Tb determines whether, and to what extent, there is liquid water at the base of the ice which in turn affects the values of h and Tb. Simultaneous changes of sea-level temperature and precipitation (changes related to each other as might be expected from global climate models) indicate a maximum in the field of possible steady-state ice volumes which may not be far from the presently observed conditions. The possibility of cyclical variation in ground heat flux associated with convection of water and heat in the continental crust is discussed. The mechanism might be capable of generating cycles of ice-sheet volume with relatively short periods similar to those of Milankovitch forcing.

ISMIP6-based projections of ocean-forced Antarctic ice loss using the Community Ice Sheet Model 

2021 ◽  
Author(s):  
William Lipscomb ◽  
Gunter Leguy ◽  
Nicolas Jourdain ◽  
Xylar Asay-Davis ◽  
Hélène Seroussi ◽  
...  
Keyword(s):  
Sea Level ◽  
Climate Models ◽  
Global Climate ◽  
Ice Sheet ◽  
High Sensitivity ◽  
Global Climate Models ◽  
Thermal Forcing ◽  
Antarctic Ice Sheet ◽  
Basal Friction ◽  
West Antarctic

<p>The future retreat rate for marine-based regions of the Antarctic Ice Sheet is one of the largest uncertainties in sea-level projections. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) aims to improve projections and quantify uncertainties by running an ensemble of ice sheet models with forcing derived from global climate models. Here, the Community Ice Sheet Model (CISM) is used to run ISMIP6-based projections of ocean-forced Antarctic Ice Sheet evolution. Using several combinations of sub-ice-shelf melt schemes, CISM is spun up to steady state over many millennia. During the spin-up, basal-friction and thermal-forcing parameters are adjusted to optimize agreement with the observed ice thickness. The model is then run forward to year 2500, applying ocean thermal forcing anomalies from six climate models. In all simulations, ocean warming triggers long-term retreat of the West Antarctic Ice Sheet, especially in the Filchner-Ronne and Ross sectors. The ocean-forced sea-level rise in 2500 varies from about 150 mm to 1300 mm, depending on the melt scheme and ocean forcing applied. Further experiments show relatively high sensitivity to the basal friction law, and moderate sensitivity to grid resolution and the prescribed collapse of small ice shelves. The Amundsen sector exhibits threshold behavior, with modest retreat under many parameter settings, but complete collapse under some combinations of low basal friction and high thermal-forcing anomalies. Large uncertainties remain, as a result of parameterized sub-shelf melt rates, simplified treatments of calving and basal friction, and the lack of ice–ocean coupling.</p>

Impacts of initialisation of coupled ice sheet-ocean models forecasting.

2020 ◽  
Author(s):  
Daniel Goldberg ◽  
Paul Holland ◽  
Mathieu Morlighem
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Ice Sheet ◽  
Ocean Model ◽  
Global Climate Models ◽  
Surface Velocity ◽  
Long Time ◽  
Ocean Models ◽  
Transient Calibration ◽  
Calibrated Simulation

<p>In recent years, there have been great advances in coupled ice sheet-ocean modelling, to the point where ice-ocean interactions can be represented in global climate models — with potential to greatly improve forecasting of marine ice-sheet loss and sea level rise in the coming century and beyond. However, initialisation of coupled ice sheet-ocean models has not yet been properly examined; and initialisation approaches applied to ocean and coupled atmosphere-ocean models may not be appropriate due to the long time scales inherent in dynamic ice sheets. Moreover, as ocean melt rates and ice-shelf geometry strongly influence each other, nonphysical transients in incorrectly initialised coupled ice-ocean models may persist for longer than in ice-sheet models alone.</p><p>In this work, two approaches to coupled initialisation are considered using a synchronously coupled ice-ocean model. The two approaches are based on two commonly used approaches to ice sheet model initialisation: “snapshot” calibration, where ice-sheet basal and internal parameters are configured to optimise fit with observed surface velocity; and “transient” calibration, where these parameters are configured to jointly optimise fit with velocity and geometry change; however, the transient calibration makes use of the ocean component to ensure the ice model is not subject to “initialisation shock” from ocean melting. The approaches are applied to Smith Glacier, a small but fast-thinning glacier in West Antarctica, and the model is forced under ocean warming scenarios in multidecadal runs. Initially there is much faster retreat seen in the Snapshot-calibrated simulation, but this difference decays over several decades, and ultimately the Transiently-calibrated model sees more retreat.</p><p>The experiments further suggest that Smith Glacier is not likely to exhibit Marine Ice Sheet instability in the next century. But the methods discrepancy has strong implications for glaciers which are susceptible to this instability.</p>

scholarly journals ISMIP6 projections of ocean-forced Antarctic Ice Sheet evolution using the Community Ice Sheet Model

2020 ◽  
Author(s):  
William H. Lipscomb ◽  
Gunter R. Leguy ◽  
Nicolas C. Jourdain ◽  
Xylar S. Asay-Davis ◽  
Hélène Seroussi ◽  
...  
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Ice Sheet ◽  
Global Climate Models ◽  
Thermal Forcing ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Basin Scale ◽  
Friction Parameters

Abstract. The future retreat rate for marine-based regions of the Antarctic Ice Sheet is one of the largest uncertainties in sea-level projections. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) aims to improve projections and quantify uncertainties by running an ensemble of ice sheet models with atmosphere and ocean forcing derived from global climate models. Here, ISMIP6 projections of ocean-forced Antarctic Ice Sheet evolution are illustrated using the Community Ice Sheet Model (CISM). Using multiple combinations of sub-ice-shelf melt parameterizations and calibrations, CISM is spun up to steady state over many millennia. During the spin-up, basal friction parameters and basin-scale thermal forcing corrections are adjusted to nudge the ice thickness toward observed values. The model is then run forward for 500 years, applying ocean thermal forcing anomalies from six climate models. In all simulations, the ocean forcing triggers long-term retreat of the West Antarctic Ice Sheet, including the Amundsen, Filchner-Ronne, and Ross Basins. Mass loss accelerates late in the 21st century and rises steadily over the next several centuries without leveling off. The resulting ocean-forced SLR at year 2500 varies from about 10 cm to nearly 2 m, depending on the melt scheme and model forcing. Relatively little ice loss is simulated in East Antarctica. Large uncertainties remain, as a result of parameterized basal melt rates, missing ocean and ice sheet physics, and the lack of ice–ocean coupling.

scholarly journals AMOC-emulator M-AMOC1.0 for uncertainty assessment of future projections

2016 ◽  
Author(s):  
Pepijn Bakker ◽  
Andreas Schmittner
Keyword(s):  
Global Warming ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Uncertainty Assessment ◽  
Global Climate Models ◽  
Meridional Overturning Circulation

Abstract. State-of-the-science global climate models show that global warming is likely to weaken the Atlantic Meridional Overturning Circulation (AMOC). While such models are arguably the best tools to perform AMOC projections, they do not allow a comprehensive uncertainty assessment because of limited computational resources. Here we present an AMOC-emulator, a box model with a number of free parameters that can be tuned to mimic the sensitivity of the AMOC to climate change of a specific global climate model. The AMOC-emulator (M-AMOC1.0) is applied to simulations of global warming and melting of the Greenland Ice Sheet, performed with an intermediate complexity model. Predictive power of the AMOC-emulator is shown by comparison with a number of additional warming and Greenland Ice Sheet melt scenario that have not been used in the tuning of the AMOC-emulator, highlighting the potential of the AMOC-emulator to assess the uncertainty in AMOC projections.

scholarly journals Climate, the Antarctic ice sheet and ground heat flux

1995 ◽  
Vol 21 ◽  
pp. 144-148 ◽  
Author(s):  
Garth W. Paltridge ◽  
Christopher M. Zweck
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Climate Models ◽  
Global Climate ◽  
Ice Sheet ◽  
Global Climate Models ◽  
Balance Model ◽  
Antarctic Ice Sheet ◽  
Ground Heat Flux ◽  
The Antarctic

A simple steady-state energy and mass-balance model of the Antarctic ice sheet is developed. Basically it is a set of two equations with two unknowns of steady-state heighthand potential basal temperatureTb.Tbdetermines whether, and to what extent, there is liquid water at the base of the ice which in turn affects the values ofhandTb. Simultaneous changes of sea-level temperature and precipitation (changes related to each other as might be expected from global climate models) indicate a maximum in the field of possible steady-state ice volumes which may not be far from the presently observed conditions. The possibility of cyclical variation in ground heat flux associated with convection of water and heat in the continental crust is discussed. The mechanism might be capable of generating cycles of ice-sheet volume with relatively short periods similar to those of Milankovitch forcing.

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