Sea-level response to melting of Antarctic ice shelves on multi-centennial time scales with the fast Elementary Thermomechanical Ice Sheet model (f.ETISh v1.0)

Sea-level response to melting of Antarctic ice shelves on multi-centennial timescales with the fast Elementary Thermomechanical Ice Sheet model (f.ETISh v1.0)

The Cryosphere ◽

10.5194/tc-11-1851-2017 ◽

2017 ◽

Vol 11 (4) ◽

pp. 1851-1878 ◽

Cited By ~ 32

Author(s):

Frank Pattyn

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Power Law ◽

Coulomb Friction ◽

Ice Sheet ◽

East Antarctica ◽

Ice Shelf ◽

Ice Shelves ◽

Grounding Line ◽

Basal Sliding

Abstract. The magnitude of the Antarctic ice sheet's contribution to global sea-level rise is dominated by the potential of its marine sectors to become unstable and collapse as a response to ocean (and atmospheric) forcing. This paper presents Antarctic sea-level response to sudden atmospheric and oceanic forcings on multi-centennial timescales with the newly developed fast Elementary Thermomechanical Ice Sheet (f.ETISh) model. The f.ETISh model is a vertically integrated hybrid ice sheet–ice shelf model with vertically integrated thermomechanical coupling, making the model two-dimensional. Its marine boundary is represented by two different flux conditions, coherent with power-law basal sliding and Coulomb basal friction. The model has been compared to existing benchmarks. Modelled Antarctic ice sheet response to forcing is dominated by sub-ice shelf melt and the sensitivity is highly dependent on basal conditions at the grounding line. Coulomb friction in the grounding-line transition zone leads to significantly higher mass loss in both West and East Antarctica on centennial timescales, leading to 1.5 m sea-level rise after 500 years for a limited melt scenario of 10 m a−1 under freely floating ice shelves, up to 6 m for a 50 m a−1 scenario. The higher sensitivity is attributed to higher ice fluxes at the grounding line due to vanishing effective pressure. Removing the ice shelves altogether results in a disintegration of the West Antarctic ice sheet and (partially) marine basins in East Antarctica. After 500 years, this leads to a 5 m and a 16 m sea-level rise for the power-law basal sliding and Coulomb friction conditions at the grounding line, respectively. The latter value agrees with simulations by DeConto and Pollard (2016) over a similar period (but with different forcing and including processes of hydrofracturing and cliff failure). The chosen parametrizations make model results largely independent of spatial resolution so that f.ETISh can potentially be integrated in large-scale Earth system models.

Download Full-text

Antarctic ice sheet response to upper-bound scenarios

10.5194/egusphere-egu21-11823 ◽

2021 ◽

Author(s):

Sainan Sun ◽

Frank Pattyn

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Upper Bound ◽

Ice Sheet ◽

Climate Forcing ◽

Ice Shelf ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

Basal Sliding ◽

The Antarctic

Mass loss of the Antarctic ice sheet contributes the largest uncertainty of future sea-level rise projections. Ice-sheet model predictions are limited by uncertainties in climate forcing and poor understanding of processes such as ice viscosity. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) has investigated the 'end-member' scenario, i.e., a total and sustained removal of buttressing from all Antarctic ice shelves, which can be regarded as the upper-bound physical possible, but implausible contribution of sea-level rise due to ice-shelf loss. In this study, we add successive layers of &#8216;realism&#8217; to the ABUMIP scenario by considering sustained regional ice-shelf collapse and by introducing ice-shelf regrowth after collapse with the inclusion of ice-sheet and ice-shelf damage (Sun et al., 2017). Ice shelf regrowth has the ability to stabilize grounding lines, while ice shelf damage may reinforce ice loss. In combination with uncertainties from basal sliding and ice rheology, a more realistic physical upperbound to ice loss is sought. Results are compared in the light of other proposed mechanisms, such as MICI due to ice cliff collapse.

Download Full-text

Stopping the Flood: Could We Use Targeted Geoengineering to Mitigate Sea Level Rise?

10.5194/tc-2018-95 ◽

2018 ◽

Cited By ~ 1

Author(s):

Michael J. Wolovick ◽

John C. Moore

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Dynamic Feedback ◽

West Antarctica ◽

Ice Shelf ◽

Long Run ◽

Grounding Line ◽

Individual Source ◽

Engineering Projects

Abstract. The Marine Ice Sheet Instability (MISI) is a dynamic feedback that can cause an ice sheet to enter a runaway collapse. Thwaites Glacier, West Antarctica, is the largest individual source of future sea level rise and may have already entered the MISI. Here, we use a suite of coupled ice–ocean flowband simulations to explore whether targeted geoengineering using an artificial sill or artificial ice rises could counter a collapse. Successful interventions occur when the floating ice shelf regrounds on the pinning points, increasing buttressing and reducing ice flux across the grounding line. Regrounding is more likely with a continuous sill that is able to block warm water transport to the grounding line. The smallest design we consider is comparable in scale to existing civil engineering projects but has only a 30 % success rate, while larger designs are more effective. There are multiple possible routes forward to improve upon the designs that we considered, and with decades or more to research designs it is plausible that the scientific community could come up with a plan that was both effective and achievable. While reducing emissions remains the short-term priority for minimizing the effects of climate change, in the long run humanity may need to develop contingency plans to deal with an ice sheet collapse.

Download Full-text

The Dynamics of Marine Ice Sheets

Journal of Glaciology ◽

10.3189/s0022143000014726 ◽

1979 ◽

Vol 24 (90) ◽

pp. 167-177 ◽

Cited By ~ 13

Author(s):

Robert H. Thomas

Keyword(s):

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

The North ◽

West Antarctic ◽

Grounding Line ◽

Ice Sheet Dynamics

AbstractMarine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.

Download Full-text

Antarctic ice sheet response to sudden and sustained ice-shelf collapse (ABUMIP)

Journal of Glaciology ◽

10.1017/jog.2020.67 ◽

2020 ◽

Vol 66 (260) ◽

pp. 891-904 ◽

Cited By ~ 1

Author(s):

Sainan Sun ◽

Frank Pattyn ◽

Erika G. Simon ◽

Torsten Albrecht ◽

Stephen Cornford ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Sliding Friction ◽

Ice Sheet ◽

Full Potential ◽

Ice Shelf ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

Ice Shelves ◽

West Antarctic

AbstractAntarctica's ice shelves modulate the grounded ice flow, and weakening of ice shelves due to climate forcing will decrease their ‘buttressing’ effect, causing a response in the grounded ice. While the processes governing ice-shelf weakening are complex, uncertainties in the response of the grounded ice sheet are also difficult to assess. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) compares ice-sheet model responses to decrease in buttressing by investigating the ‘end-member’ scenario of total and sustained loss of ice shelves. Although unrealistic, this scenario enables gauging the sensitivity of an ensemble of 15 ice-sheet models to a total loss of buttressing, hence exhibiting the full potential of marine ice-sheet instability. All models predict that this scenario leads to multi-metre (1–12 m) sea-level rise over 500 years from present day. West Antarctic ice sheet collapse alone leads to a 1.91–5.08 m sea-level rise due to the marine ice-sheet instability. Mass loss rates are a strong function of the sliding/friction law, with plastic laws cause a further destabilization of the Aurora and Wilkes Subglacial Basins, East Antarctica. Improvements to marine ice-sheet models have greatly reduced variability between modelled ice-sheet responses to extreme ice-shelf loss, e.g. compared to the SeaRISE assessments.

Download Full-text

The Dynamics of Marine Ice Sheets

Journal of Glaciology ◽

10.1017/s0022143000014726 ◽

1979 ◽

Vol 24 (90) ◽

pp. 167-177 ◽

Cited By ~ 145

Author(s):

Robert H. Thomas

Keyword(s):

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

The North ◽

West Antarctic ◽

Grounding Line ◽

Ice Sheet Dynamics

AbstractMarine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.

Download Full-text

Decreasing Antarctic surface mass balance due to runoff-dominated ablation by 2100

10.5194/egusphere-egu2020-17355 ◽

2020 ◽

Author(s):

Christoph Kittel ◽

Charles Amory ◽

Cécile Agosta ◽

Nicolas Jourdain ◽

Stefan Hofer ◽

...

Keyword(s):

Mass Balance ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Surface Mass Balance ◽

Ice Shelf ◽

Antarctic Ice Sheet ◽

Surface Mass ◽

Ice Shelves ◽

The Antarctic

The surface mass balance (SMB) of the Antarctic ice sheet is often considered as a negative contributor to the sea level rise as present snowfall accumulation largely compensates for ablation through wind erosion, sublimation and runoff. The latter is even almost negligible since current Antarctic surface melting is limited to relatively scarce events over generally peripheral areas and refreezes almost entirely into the snowpack. However, melting can significantly affect the stability of ice shelves through hydrofracturing, potentially leading to their disintegration, acceleration of grounded ice and increased sea level rise. Although a large increase in snowfall is expected in a warmer climate, more numerous and stronger melting events could conversely lead to a larger risk of ice shelf collapse. In this study, we provide an estimation of the SMB of the Antarctic ice sheet for the end of the 21st&#160;century by forcing the state-of-the-art regional climate model MAR with three different global climate models. We chose the models (from both the Coupled Model Intercomparison Project Phase 5 and 6 - CMIP5 and CMIP6) providing the best metrics for representing the current Antarctic climate. While the increase in snowfall largely compensates snow ablation through runoff in CMIP5-forced projections, CMIP6-forced simulations reveal that runoff cannot be neglected in the future as it accounts for a maximum of 50% of snowfall and becomes the main ablation component over the ice sheet. Furthermore, we identify a tipping point (ie., a warming of 4&#176;C) at which the Antarctic SMB starts to decrease as a result of enhanced runoff particularly over ice shelves. Our results highlight the importance of taking into account meltwater production and runoff and indicate that previous model studies neglecting these processes yield overestimated SMB estimates, ultimately leading to underestimated Antarctic contribution to sea level rise. Finally, melt rates over each ice shelf are higher than those that led to the collapse of the Larsen A and B ice shelves, suggesting a high probability of ice shelf collapses all over peripheral Antarctica by 2100.

Download Full-text

Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

10.5194/tc-2016-144 ◽

2016 ◽

Author(s):

Lionel Favier ◽

Frank Pattyn ◽

Sophie Berger ◽

Reinhard Drews

Keyword(s):

Data Assimilation ◽

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

East Antarctica ◽

Ice Shelf ◽

Ice Dynamics ◽

Ice Shelves ◽

Grounding Line ◽

Dronning Maud Land

Abstract. The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart, because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by (more stable) grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouin ice shelves over the next millennia. Overall, the sub-ice shelf melting substantially impacts the sea level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the collapse of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrates that the onset of the marine ice-sheet retreat and subsequent promontory collapse is controlled by small pinning points within the ice shelves, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning has a small effect on the total amount of sea level rise but locally affects the timing of grounding-line migration, advancing the collapse of a promontory by hundreds of years. On the other hand, omitting the same pinning point in data assimilation decreases the sea level contribution by 10 % and delays the promontory collapse by almost a millennium. This very subtle influence of pinning points on ice dynamics acts on kilometre scale and calls for a better knowledge of the Antarctic margins that will improve sea-level predictions.

Download Full-text

The Antarctic contribution to 21st century sea-level rise predicted by the UK Earth System Model with an interactive ice sheet

10.5194/tc-2021-371 ◽

2021 ◽

Author(s):

Antony Siahaan ◽

Robin Smith ◽

Paul Holland ◽

Adrian Jenkins ◽

Jonathan M. Gregory ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

System Model ◽

Ice Shelf ◽

Ice Shelves ◽

Global Mean Sea Level ◽

Basal Melting ◽

The Antarctic ◽

Global Mean

Abstract. The Antarctic Ice Sheet will play a crucial role in the evolution of global mean sea-level as the climate warms. An interactively coupled climate and ice sheet model is needed to understand the impacts of ice—climate feedbacks during this evolution. Here we use a two-way coupling between the U.K. Earth System Model and the BISICLES dynamic ice sheet model to investigate Antarctic ice—climate interactions under two climate change scenarios. We perform ensembles of SSP1-1.9 and SSP5-8.5 scenario simulations to 2100, which we believe are the first such simulations with a climate model with two-way coupling between both atmosphere and ocean models to dynamic models of the Greenland and Antarctic ice sheets. In SSP1-1.9 simulations, ice shelf basal melting and grounded ice mass loss are generally lower than present rates during the entire simulation period. In contrast, the responses to SSP5-8.5 forcing are strong. By the end of 21st century, these simulations feature order-of-magnitude increases in basal melting of the Ross and Filchner-Ronne ice shelves, caused by intrusions of warm ocean water masses. Due to the slow response of ice sheet drawdown, this strong melting does not cause a substantial increase in ice discharge during the simulations. The surface mass balance in SSP5-8.5 simulations shows a pattern of strong decrease on ice shelves, caused by increased melting, and strong increase on grounded ice, caused by increased snowfall. Despite strong surface and basal melting of the ice shelves, increased snowfall dominates the mass budget of the grounded ice, leading to an ensemble-mean Antarctic contribution to global mean sea level of a fall of 22 mm by 2100 in the SSP5-8.5 scenario. We hypothesise that this signal would revert to sea-level rise on longer timescales, caused by the ice sheet dynamic response to ice shelf thinning. These results demonstrate the need for fully coupled ice—climate models in reducing the substantial uncertainty in sea-level rise from the Antarctic Ice Sheet.

Download Full-text

Simulating Antarctic subglacial hydrology processes underneath Pine Island Glacier, West Antarctica, using GlaDS model in Elmer/Ice

10.5194/egusphere-egu2020-8344 ◽

2020 ◽

Author(s):

yufang zhang ◽

John Moore ◽

Michael Wolovick ◽

Rupert Gladstone ◽

Thomas Zwinger ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Drainage System ◽

The State ◽

Effective Pressure ◽

West Antarctica ◽

Ice Dynamics ◽

Grounding Line ◽

Basal Sliding

Abstract: Very little is known about the subglacial hydrologic system under the Antarctic Ice Sheet due to the difficulty of directly observing the bottom of the ice sheet. Hydrology modeling is a powerful tool to simulate the spatial distribution of crucial hydrologic properties under the ice sheet. Here, we use the state-of-art two-dimensional Glacier Drainage System model (GlaDS) to simulate both distributed sheet flow and continuous channels under Pine Island Glacier (PIG), West Antarctica, one of the largest contributors to sea level rise in Antarctica.We adopt an unstructured triangular mesh which enables channels to form along element edges. We drive the model with meltwater computed from an inversion and steady temperature simulation of PIG using a Stokes flow ice dynamic model. Our domain comprises the full PIG catchment. We aim to study the pattern and development of water pressure, hydraulic potential, water sheet thickness and discharge, as well as channel area and flux, which together describe the state of the basal system.Our results for hydraulic potential correctly route water towards the grounding line, while we find near-zero effective pressure underneath the main trunk of PIG, consistent with the low basal drag and low driving stress there. This has implications for the representation of sliding in ice dynamic models: typical assumptions about hydrology connectivity to the ocean will overestimate effective pressure. When run forward in time, efficient channels evolve near the grounding line indicating an efficient drainage system where water fluxes are high in the downstream part of the PIG.By applying GlaDS to a real marine ice sheet catchment we can better understand how basal hydrology modulates ice dynamics through basal sliding. We plan to compare our model predictions of effective pressure and drainage system with driving stress and inversions of basal drag. This will allow us to see the relationship between basal hydrology and basal sliding under PIG, and provide us better tools to predict the evolution of the region in view of future climate scenarios. Moving forward, we plan to couple the hydrology model with the ice dynamics model to make more accurate projections of sea level rise from PIG.Key Words: West Antarctica, subglacial hydrology, drainage system, GlaDS, Elmer/Ice, Pine Island Glacier

Download Full-text