initMIP-Antarctica: an ice sheet model initialization experiment of ISMIP6

Abstract. Ice sheet numerical modeling is an important tool to estimate the dynamic contribution of the Antarctic ice sheet to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMIP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic ice sheets. Following initMIP-Greenland, initMIP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMIP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the surface mass balance anomaly but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, and the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue.

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initMIP-Antarctica: An ice sheet model initialization experiment of ISMIP6

10.5194/tc-2018-271 ◽

2019 ◽

Author(s):

Hélène Seroussi ◽

Sophie Nowicki ◽

Erika Simon ◽

Ayako Abe Ouchi ◽

Torsten Albrecht ◽

...

Keyword(s):

Initial Conditions ◽

Ice Sheet ◽

Model Parameters ◽

Model Intercomparison ◽

Ice Shelves ◽

External Forcings ◽

Intercomparison Project ◽

Model Initialization ◽

Basal Melting ◽

The Impact

Abstract. Ice sheet numerical modeling is the best approach to estimate the dynamic contribution of Antarctica to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMIP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic Ice Sheets. Following initMIP-Greenland, initMIP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance (SMB) anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMIP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the SMB anomaly, but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, as well as the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue.

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Melting and freezing under Antarctic ice shelves from a combination of ice-sheet modelling and observations

Journal of Glaciology ◽

10.1017/jog.2017.42 ◽

2017 ◽

Vol 63 (240) ◽

pp. 731-744 ◽

Cited By ~ 3

Author(s):

JORGE BERNALES ◽

IRINA ROGOZHINA ◽

MAIK THOMAS

Keyword(s):

Mass Balance ◽

Ice Sheet ◽

Model Parameters ◽

Ice Shelf ◽

Ice Shelves ◽

Continental Scale ◽

Model Set ◽

Set Up ◽

Basal Melting ◽

The Antarctic

ABSTRACTIce-shelf basal melting is the largest contributor to the negative mass balance of the Antarctic ice sheet. However, current implementations of ice/ocean interactions in ice-sheet models disagree with the distribution of sub-shelf melt and freezing rates revealed by recent observational studies. Here we present a novel combination of a continental-scale ice flow model and a calibration technique to derive the spatial distribution of basal melting and freezing rates for the whole Antarctic ice-shelf system. The modelled ice-sheet equilibrium state is evaluated against topographic and velocity observations. Our high-resolution (10-km spacing) simulation predicts an equilibrium ice-shelf basal mass balance of −1648.7 Gt a−1 that increases to −1917.0 Gt a−1 when the observed ice-shelf thinning rates are taken into account. Our estimates reproduce the complexity of the basal mass balance of Antarctic ice shelves, providing a reference for parameterisations of sub-shelf ocean/ice interactions in continental ice-sheet models. We perform a sensitivity analysis to assess the effects of variations in the model set-up, showing that the retrieved estimates of basal melting and freezing rates are largely insensitive to changes in the internal model parameters, but respond strongly to a reduction of model resolution and the uncertainty in the input datasets.

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Some future projections from coupling the U.K. Earth System Model to the Antarctic ice sheets

10.5194/egusphere-egu21-13754 ◽

2021 ◽

Author(s):

Anthony Siahaan

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Ice Sheet ◽

Mass Gain ◽

Ice Shelves ◽

Positive Effects ◽

Basal Melting ◽

The Antarctic ◽

The Impact ◽

Increasing Precipitation

A UKESM climate model which is coupled annually to the BISICLES ice sheet model to enable a two way interactions in Antarctica has been developed&#160; and run through a small ensemble of four SSP1-1.9 & SSP5-8.5 scenario members. Under the extreme anthropogenic forcing, all the initial condition&#160; ensemble members develop strong melting under the cold & large Ross and Filchner-Ronne ice-shelves, where it starts after the first half of simulation&#160; period for the former and in the last decade of the run for the latter. Despite that, during the 85 years timescale of these scenario runs, the stronger radiative forcing has positive effects on the ice-sheet mass gain through increasing precipitation on grounded ice regions which offsets the impact of basal melting in ice discharge across the grounding lines.

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Modelling the long-term response of the Antarctic ice sheet to global warming

Annals of Glaciology ◽

10.3189/1998aog27-1-161-168 ◽

1998 ◽

Vol 27 ◽

pp. 161-168 ◽

Cited By ~ 29

Author(s):

Roland C. Warner ◽

W.Κ. Budd

Keyword(s):

Global Warming ◽

Mass Loss ◽

Ice Sheet ◽

Ice Shelf ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

Basal Melting ◽

The Antarctic ◽

Term Response

The primary effects of global warming on the Antarctic ice sheet can involve increases in surface melt for limited areas at lower elevations, increases in net accumulation, and increased basal melting under floating ice. For moderate global wanning, resulting in ocean temperature increases of a few °C, the large- increase in basal melting can become the dominant factor in the long-term response of the ice sheet. The results from ice-sheet modelling show that the increased basal melt rates lead to a reduction of the ice shelves, increased strain rates and flow at the grounding lines, then thinning and floating of the marine ice sheets, with consequential further basal melting. The mass loss from basal melting is counteracted to some extent by the increased accumulation, but in the long term the area of ice cover decreases, particularly in West Antarctica, and the mass loss can dominate. The ice-sheet ice-shelf model of Budd and others (1994) with 20 km resolution has been modified and used to carry out a number of sensitivity studies of the long-term response of the ice sheet to prescribed amounts of global warming. The changes in the ice sheet are computed out to near-equilibrium, but most of the changes take place with in the first lew thousand years. For a global mean temperature increase of 3°C with an ice-shelf basal melt rate of 5 m a−1 the ice shelves disappear with in the first few hundred years, and the marine-based parts of the ice sheet thin and retreat. By 2000 years the West Antarctic region is reduced to a number of small, isolated ice caps based on the bedrock regions which are near or above sea level. This allows the warmer surface ocean water to circulate through the archipelago in summer, causing a large change to the local climate of the region.

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Viscous and elastic buoyancy stresses as drivers of ice-shelf calving

Journal of Glaciology ◽

10.1017/jog.2020.35 ◽

2020 ◽

Vol 66 (258) ◽

pp. 643-657 ◽

Cited By ~ 1

Author(s):

Cyrille Mosbeux ◽

Till J. W. Wagner ◽

Maya K. Becker ◽

Helen A. Fricker

Keyword(s):

Ice Sheet ◽

Elastic Model ◽

Ice Shelf ◽

Ice Shelves ◽

Bending Stresses ◽

Iceberg Calving ◽

Basal Melting ◽

The Antarctic ◽

The Impact ◽

Maximum Stresses

AbstractThe Antarctic Ice Sheet loses mass via its ice shelves predominantly through two processes: basal melting and iceberg calving. Iceberg calving is episodic and infrequent, and not well parameterized in ice-sheet models. Here, we investigate the impact of hydrostatic forces on calving. We develop two-dimensional elastic and viscous numerical frameworks to model the ‘footloose’ calving mechanism. This mechanism is triggered by submerged ice protrusions at the ice front, which induce unbalanced buoyancy forces that can lead to fracturing. We compare the results to identify the different roles that viscous and elastic deformations play in setting the rate and magnitude of calving events. Our results show that, although the bending stresses in both frameworks share some characteristics, their differences have important implications for modeling the calving process. In particular, the elastic model predicts that maximum stresses arise farther from the ice front than in the viscous model, leading to larger calving events. We also find that the elastic model would likely lead to more frequent events than the viscous one. Our work provides a theoretical framework for the development of a better understanding of the physical processes that govern glacier and ice-shelf calving cycles.

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Impact of transient increases in atmospheric CO2 on the accumulation and mass balance of the Antarctic ice sheet

Annals of Glaciology ◽

10.1017/s0260305500013938 ◽

1997 ◽

Vol 25 ◽

pp. 137-144 ◽

Cited By ~ 6

Author(s):

Siobhan P. O’Farrell ◽

John L. McGregor ◽

Leon D. Rotstayn ◽

William F. Budd ◽

Christopher Zweck ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Coupled Model ◽

Negative Contribution ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

Basal Melting ◽

Main Effects ◽

The Antarctic

The response of the Antarctic ice sheet to climate change over the next 500 years is calculated using the output of a transient-coupled ocean-atmosphere simulation assuming the atmospheric CO2value increases up to three times present levels. The main effects on the ice sheet on this time-scale include increasing rates of accumulation, minimal surface melting, and basal melting of ice shelves. A semi-Lagrangian transport scheme for moisture was used to improve the model’s ability to represent realistic rates of accumulation under present-day conditions, and thereby increase confidence in the anomalies calculated under a warmer climate. The response of the Antarctic ice sheet to the warming is increased accumulation inland, offset by loss from basal melting from the floating ice, and increased ice flow near the grounding line. The preliminary results of this study show that the change to the ice-sheet balance for the transient-coupled model forcing amounted to a minimal sea-level contribution in the next century, but a net positive sea-level rise of 0.21 m by 500 years. This new result supercedes earlier results that showed the Antarctic ice sheet made a net negative contribution to sea-level rise over the next century. However, the amplitude of the sea-level rise is still dominated In the much larger contributions expected from thermal expansion of the ocean of 0.25 m for 100 years and 1.00 m for 500 years.

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Diverging future surface mass balance between the Antarctic ice shelves and grounded ice sheet

The Cryosphere ◽

10.5194/tc-15-1215-2021 ◽

2021 ◽

Vol 15 (3) ◽

pp. 1215-1236

Author(s):

Christoph Kittel ◽

Charles Amory ◽

Cécile Agosta ◽

Nicolas C. Jourdain ◽

Stefan Hofer ◽

...

Keyword(s):

Mass Balance ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Surface Mass Balance ◽

Near Surface ◽

Surface Mass ◽

Ice Shelves ◽

Run Off ◽

The Antarctic

Abstract. The future surface mass balance (SMB) will influence the ice dynamics and the contribution of the Antarctic ice sheet (AIS) to the sea level rise. Most of recent Antarctic SMB projections were based on the fifth phase of the Coupled Model Intercomparison Project (CMIP5). However, new CMIP6 results have revealed a +1.3 ∘C higher mean Antarctic near-surface temperature than in CMIP5 at the end of the 21st century, enabling estimations of future SMB in warmer climates. Here, we investigate the AIS sensitivity to different warmings with an ensemble of four simulations performed with the polar regional climate model Modèle Atmosphérique Régional (MAR) forced by two CMIP5 and two CMIP6 models over 1981–2100. Statistical extrapolation enables us to expand our results to the whole CMIP5 and CMIP6 ensembles. Our results highlight a contrasting effect on the future grounded ice sheet and the ice shelves. The SMB over grounded ice is projected to increase as a response to stronger snowfall, only partly offset by enhanced meltwater run-off. This leads to a cumulated sea-level-rise mitigation (i.e. an increase in surface mass) of the grounded Antarctic surface by 5.1 ± 1.9 cm sea level equivalent (SLE) in CMIP5-RCP8.5 (Relative Concentration Pathway 8.5) and 6.3 ± 2.0 cm SLE in CMIP6-ssp585 (Shared Socioeconomic Pathways 585). Additionally, the CMIP6 low-emission ssp126 and intermediate-emission ssp245 scenarios project a stabilized surface mass gain, resulting in a lower mitigation to sea level rise than in ssp585. Over the ice shelves, the strong run-off increase associated with higher temperature is projected to decrease the SMB (more strongly in CMIP6-ssp585 compared to CMIP5-RCP8.5). Ice shelves are however predicted to have a close-to-present-equilibrium stable SMB under CMIP6 ssp126 and ssp245 scenarios. Future uncertainties are mainly due to the sensitivity to anthropogenic forcing and the timing of the projected warming. While ice shelves should remain at a close-to-equilibrium stable SMB under the Paris Agreement, MAR projects strong SMB decrease for an Antarctic near-surface warming above +2.5 ∘C compared to 1981–2010 mean temperature, limiting the warming range before potential irreversible damages on the ice shelves. Finally, our results reveal the existence of a potential threshold (+7.5 ∘C) that leads to a lower grounded-SMB increase. This however has to be confirmed in following studies using more extreme or longer future scenarios.

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Supplementary material to "Diverging future surface mass balance between the Antarctic ice shelves and grounded ice sheet"

10.5194/tc-2020-291-supplement ◽

2020 ◽

Author(s):

Christoph Kittel ◽

Charles Amory ◽

Cécile Agosta ◽

Nicolas C. Jourdain ◽

Stefan Hofer ◽

...

Keyword(s):

Mass Balance ◽

Ice Sheet ◽

Surface Mass Balance ◽

Surface Mass ◽

Ice Shelves ◽

Supplementary Material ◽

The Antarctic

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Uncertainties in projected surface mass balance over the polar ice sheets from downscaled EC-Earth models

10.5194/tc-2021-140 ◽

2021 ◽

Author(s):

Fredrik Boberg ◽

Ruth Mottram ◽

Nicolaj Hansen ◽

Shuting Yang ◽

Peter L. Langen

Keyword(s):

Mass Balance ◽

Climate Model ◽

Global Climate ◽

Ice Sheet ◽

Coupled Model ◽

Surface Mass Balance ◽

Model Intercomparison ◽

Surface Mass ◽

Intercomparison Project ◽

The Mean

Abstract. The future rates of ice sheet melt in Greenland and Antarctica are an important factor when making estimates of the likely rate of sea level rise. Global climate models that took part in the fifth Coupled Model Intercomparison Project (CMIP5) have generally been unable to replicate observed rates of ice sheet melt. With the advent of the sixth Coupled Model Intercomparison Project (CMIP6), with a general increase in the equilibrium climate sensitivity, we here compare two versions of the global climate model EC-Earth using the regional climate model HIRHAM5 downscaling EC-Earth for Greenland and Antarctica. One version (v2) of EC-Earth is taken from CMIP5 for the high-emissions Representative Concentration Pathways (RCP8.5) scenario and the other (v3) from CMIP6 for the comparable high-emissions Shared Socioeconomic Pathways (SSP5-8.5) scenario). For Greenland, we downscale the two versions of EC-Earth for the historical period 1991–2010 and for the scenario period 2081–2100. For Antarctica, the periods are 1971–2000 and 2071–2100, respectively. For the Greenland Ice Sheet, we find that the mean change in temperature is 5.9 °C when downscaling EC-Earth v2 and 6.8 °C when downscaling EC-Earth v3. Corresponding values for Antarctica are 4.1 °C for v2 and 4.8 °C for v3. The mean change in surface mass balance at the end of the century under these high emissions scenarios is found to be −210 Gt yr−1 (v2) and −1150 Gt yr−1 (v3) for Greenland and 420 Gt yr−1 (v2) and 80 Gt yr−1 (v3) for Antarctica. These distinct differences in temperature change and particularly surface mass balance change are a result of the higher equilibrium climate sensitivity in EC-Earth v3 (4.3 K) compared with 3.3 K in EC-Earth v2 and the differences in greenhouse gas concentrations between the RCP8.5 and the SSP5-8.5 scenarios.

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An assessment of basal melting parameterisations for Antarctic ice shelves

10.5194/egusphere-egu21-1367 ◽

2021 ◽

Author(s):

Clara Burgard ◽

Nicolas Jourdain

Keyword(s):

Climate Model ◽

Ice Sheet ◽

Coupled Model ◽

Ice Shelf ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

Global Sea Level ◽

Basal Melting ◽

The Antarctic

Ocean-induced melting at the base of ice shelves is one of the main drivers of the currently observed mass loss of the Antarctic Ice Sheet. A good understanding of the interaction between ice and ocean at the base of the ice shelves is therefore crucial to understand and project the Antarctic contribution to global sea-level rise.&#160;Due to the high difficulty to monitor these regions, our understanding of the processes at work beneath ice shelves is limited. Still, several parameterisations of varying complexity have been developed in past decades to describe the ocean-induced sub-shelf melting. These parameterisations can be implemented into standalone ice-sheet models, for example when conducting long-term projections forced with climate model output.An assessment of the performance of these parameterisations was conducted in an idealised setup (Favier et al, 2019). However, the application of the better-performing parameterisations in a more realistic setup (e.g. Jourdain et al., 2020) has shown that individual adjustments and corrections are needed for each ice shelf.In this study, we revisit the assessment of the parameterisations, this time in a more realistic setup than previous studies. To do so, we apply the different parameterisations on several ice shelves around Antarctica and compare the resulting melt rates to satellite and oceanographic estimates. Based on this comparison, we will refine the parameters and propose an approach to reduce uncertainties in long-term sub-shelf melting projections.References - Favier, L., Jourdain, N. C., Jenkins, A., Merino, N., Durand, G., Gagliardini, O., Gillet-Chaulet, F., and Mathiot, P.: Assessment of sub-shelf melting parameterisations using the ocean&#8211;ice-sheet coupled model NEMO(v3.6)&#8211;Elmer/Ice(v8.3) , Geosci. Model Dev., 12, 2255&#8211;2283, https://doi.org/10.5194/gmd-12-2255-2019, 2019.&#160; - Jourdain, N. C., Asay-Davis, X., Hattermann, T., Straneo, F., Seroussi, H., Little, C. M., and Nowicki, S.: A protocol for calculating basal melt rates in the ISMIP6 Antarctic ice sheet projections, The Cryosphere, 14, 3111&#8211;3134, https://doi.org/10.5194/tc-14-3111-2020, 2020.&#160;

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