Impact of glacial isostatic adjustment on the long-term stability of the Antarctic ice sheet

2021 ◽  
Author(s):  
Violaine Coulon ◽  
Kevin Bulthuis ◽  
Pippa Whitehouse ◽  
Sainan Sun ◽  
Frank Pattyn
Keyword(s):  
Sea Level ◽  
Viscoelastic Properties ◽  
Ice Sheet ◽  
West Antarctica ◽  
Antarctic Ice Sheet ◽  
Isostatic Adjustment ◽  
West Antarctic ◽  
Mantle Viscosity ◽  
The Antarctic

<p>Projections of the contribution of the Antarctic ice sheet to future sea-level rise remain highly uncertain, especially on long timescales. One of the reasons for this uncertainty lies in the uncertainty in the intensity of the feedbacks of glacial isostatic adjustment (GIA; i.e. the combination of bedrock adjustment and gravitationally-consistent sea-surface changes due to ice mass changes) on ice-sheet evolution. Indeed, the Antarctic ice sheet lies on a solid Earth that displays large spatial variations in rheological properties, with a thin lithosphere and low-viscosity upper mantle beneath West Antarctica and an opposing structure beneath East Antarctica (Morelli & Danesi, 2004; Lloyd et al., 2020). In addition to this West-East dichotomy, strong viscoelastic heterogeneities (sometimes by several orders of magnitude across relatively short spatial scales) exist within the East and West Antarctic regions (An et al., 2015). These lateral variations are known to have a significant impact on the ice-sheet grounding-line stability (Gomez et al., 2015; Konrad et al., 2015). However, large uncertainties remain in determining these viscoelastic properties with precision.</p><p>Here, we investigate the influence of GIA feedbacks on the uncertainty in assessing the long-term contribution of the Antarctic ice sheet to future sea-level rise (SLR). In this framework, we design an ensemble approach, taking advantage of the computational efficiency of the Elementary GIA model (Coulon et al., under review). The latter consists of a modified Elastic Lithosphere—Relaxing Asthenosphere model able to consider spatially-varying viscoelastic properties supplemented with an approximation of gravitationally-consistent geoid changes, allowing to approximate near-field relative sea-level changes. Using existing upper-mantle viscosity and lithosphere thickness maps, we produce a large range of plausible Antarctic viscoelastic properties by varying the level of lateral variability in the associated relaxation time and flexural rigidity. We thereby take into account (i) the important lateral variations in rheological properties observed beneath the Antarctic ice sheet as well as (ii) the strong uncertainty characterizing the estimation of Antarctic solid Earth properties. We investigate the potential stabilizing role of GIA effects as well as their influence on multi-centennial to multi-millenial SLR. In addition, we investigate whether GIA feedbacks are able to stabilize the Antarctic ice sheet on short or longer timescales for strong and intermediate mitigation climate scenarios. Preliminary results (Coulon et al., under review) show that the weak Earth structure observed beneath West Antarctica plays a significant role in promoting the stability of the West Antarctic ice sheet (WAIS). However, WAIS collapse cannot be prevented under high-emissions climate scenarios. The highest uncertainty arises from the East Antarctic ice sheet (EAIS) where ice retreat in the Aurora Basin is highly dependent on mantle viscosity.</p>

scholarly journals Contrasting response of West and East Antarctic ice sheets to Glacial Isostatic Adjustment

2020 ◽  
Author(s):  
Violaine Coulon ◽  
Kevin Bulthuis ◽  
Sainan Sun ◽  
Konstanze Haubner ◽  
Frank Pattyn
Keyword(s):  
Solid Earth ◽  
Sea Level ◽  
Ice Sheet ◽  
East Antarctica ◽  
Climate Forcing ◽  
West Antarctica ◽  
Antarctic Ice Sheet ◽  
West Antarctic ◽  
Earth Structures ◽  
The Antarctic

<p>The Antarctic ice sheet (AIS) lies on a solid Earth that displays large spatial variations in rheological properties, with a thin lithosphere and low-viscosity upper mantle (weak Earth structure) beneath West Antarctica and an opposing structure beneath East Antarctica. This contrast is known to have a significant impact on ice-sheet grounding-line stability. Here, we embedded a modified glacial-isostatic ELRA model within an Antarctic ice sheet model that considers a weak Earth structure for West Antarctica supplemented with an approximation of gravitationally-consistent local sea-level changes. By taking advantage of the computational efficiency of this elementary GIA model, we assess in a probabilistic way the impact of uncertainties in the Antarctic viscoelastic properties on the response of the Antarctic ice sheet to future warming by using an ensemble of 2000 Monte Carlo simulations that span a range of plausible solid Earth structures for both West and East Antarctica. <br>We show that on multicentennial-to-millennial timescales, model projections that do not consider the dichotomy between East and West Antarctic solid Earth structures systematically overestimate the sea-level contribution from the Antarctic ice sheet because regional solid-Earth deformation plays a significant role in promoting the stability of the West Antarctic ice sheet (WAIS). However, WAIS collapse cannot be prevented under high-emissions climate scenarios. At longer timescales and under unabated climate forcing, future mass loss may be underestimated because in East Antarctica, GIA feedbacks have the potential to re-enforce the influence of the climate forcing as compared with a spatially-uniform GIA model. In this context, the AIS response might be an even larger source of uncertainty in projecting sea-level rise than previously thought, with the highest uncertainty arising from the East Antarctic ice sheet where the Aurora Basin is very GIA-dependent.</p>

scholarly journals Antarctic Ice-Sheet Volume at 18000 Years B.P. and Holocene Sea-Level Changes at the West Antarctic Margin

1979 ◽  
Vol 24 (90) ◽  
pp. 213-230 ◽  
Author(s):  
Craig S. Lingle ◽  
James A. Clark
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Sea Level Changes ◽  
Ice Shelf ◽  
Relative Sea Level ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
The Antarctic

AbstractThe Antarctic ice sheet has been reconstructed at 18000 years b.p. by Hughes and others (in press) using an ice-flow model. The volume of the portion of this reconstruction which contributed to a rise of post-glacial eustatic sea-level has been calculated and found to be (9.8±1.5) × 106 km3. This volume is equivalent to 25±4 m of eustatic sea-level rise, defined as the volume of water added to the ocean divided by ocean area. The total volume of the reconstructed Antarctic ice sheet was found to be (37±6) × 106 km3. If the results of Hughes and others are correct, Antarctica was the second largest contributor to post-glacial eustatic sea-level rise after the Laurentide ice sheet. The Farrell and Clark (1976) model for computation of the relative sea-level changes caused by changes in ice and water loading on a visco-elastic Earth has been applied to the ice-sheet reconstruction, and the results have been combined with the changes in relative sea-level caused by Northern Hemisphere deglaciation as previously calculated by Clark and others (1978). Three families of curves have been compiled, showing calculated relative sea-level change at different times near the margin of the possibly unstable West Antarctic ice sheet in the Ross Sea, Pine Island Bay, and the Weddell Sea. The curves suggest that the West Antarctic ice sheet remained grounded to the edge of the continental shelf until c. 13000 years b.p., when the rate of sea-level rise due to northern ice disintegration became sufficient to dominate emergence near the margin predicted otherwise to have been caused by shrinkage of the Antarctic ice mass. In addition, the curves suggest that falling relative sea-levels played a significant role in slowing and, perhaps, reversing retreat when grounding lines approached their present positions in the Ross and Weddell Seas. A predicted fall of relative sea-level beneath the central Ross Ice Shelf of as much as 23 m during the past 2000 years is found to be compatible with recent field evidence that the ice shelf is thickening in the south-east quadrant.

scholarly journals Antarctic Palaeotopography

2021 ◽  
pp. M56-2020-7
Author(s):  
Guy J. G. Paxman
Keyword(s):  
Ice Sheet ◽  
Future Research ◽  
Dynamic Topography ◽  
Antarctic Ice Sheet ◽  
Isostatic Adjustment ◽  
Subglacial Topography ◽  
Mantle Processes ◽  
Ice Sheet Dynamics ◽  
The Antarctic

AbstractThe development of a robust understanding of the response of the Antarctic Ice Sheet to present and projected future climatic change is a matter of key global societal importance. Numerical ice sheet models that simulate future ice sheet behaviour are typically evaluated with recourse to how well they reproduce past ice sheet behaviour, which is constrained by the geological record. However, subglacial topography, a key boundary condition in ice sheet models, has evolved significantly throughout Antarctica's glacial history. Since mantle processes play a fundamental role in the generation and modification of topography over geological timescales, an understanding of the interactions between the Antarctic mantle and palaeotopography is crucial for developing more accurate simulations of past ice sheet dynamics. This chapter provides a review of the influence of the Antarctic mantle on the long-term evolution of the subglacial landscape, through processes including structural inheritance, flexural isostatic adjustment, lithospheric cooling and thermal subsidence, volcanism and dynamic topography. The uncertainties associated with reconstructing these processes through time are discussed, as are important directions for future research and the implications of the evolving subglacial topography for the response of the Antarctic Ice Sheet to climatic and oceanographic change.

scholarly journals Combustion of available fossil fuel resources sufficient to eliminate the Antarctic Ice Sheet

2015 ◽  
Vol 1 (8) ◽  
pp. e1500589 ◽  
Author(s):  
Ricarda Winkelmann ◽  
Anders Levermann ◽  
Andy Ridgwell ◽  
Ken Caldeira
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Carbon Emissions ◽  
Fossil Fuel ◽  
Ice Sheet ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Global Sea Level ◽  
The Antarctic

The Antarctic Ice Sheet stores water equivalent to 58 m in global sea-level rise. We show in simulations using the Parallel Ice Sheet Model that burning the currently attainable fossil fuel resources is sufficient to eliminate the ice sheet. With cumulative fossil fuel emissions of 10,000 gigatonnes of carbon (GtC), Antarctica is projected to become almost ice-free with an average contribution to sea-level rise exceeding 3 m per century during the first millennium. Consistent with recent observations and simulations, the West Antarctic Ice Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of ice basins in both West and East Antarctica results in a threshold increase in global sea level. Unabated carbon emissions thus threaten the Antarctic Ice Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources.

scholarly journals Changes in ice dynamics and mass balance of the Antarctic ice sheet

2006 ◽  
Vol 364 (1844) ◽  
pp. 1637-1655 ◽  
Author(s):  
Eric Rignot
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
Ice Sheet ◽  
East Antarctica ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
The Antarctic

The concept that the Antarctic ice sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered ice shelf collapse, which led to a 10-fold increase in glacier flow and rapid ice sheet retreat. This chain of events illustrated the vulnerability of ice shelves to climate warming and their buffering role on the mass balance of Antarctica. In West Antarctica, the Pine Island Bay sector is draining far more ice into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1 m and trigger widespread retreat of ice in West Antarctica. Pine Island Glacier accelerated 38% since 1975, and most of the speed up took place over the last decade. Its neighbour Thwaites Glacier is widening up and may double its width when its weakened eastern ice shelf breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from ice shelf melting by an ocean that has recently warmed by 0.3 °C. In contrast, glaciers buffered from oceanic change by large ice shelves have only small contributions to sea level. In East Antarctica, many glaciers are close to a state of mass balance, but sectors grounded well below sea level, such as Cook Ice Shelf, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.

scholarly journals Uncertainty quantification of the multi-centennial response of the Antarctic Ice Sheet to climate change

2018 ◽  
Author(s):  
Kevin Bulthuis ◽  
Maarten Arnst ◽  
Sainan Sun ◽  
Frank Pattyn
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Parametric Uncertainty ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
Sources Of Uncertainty ◽  
West Antarctic ◽  
The Antarctic

Abstract. Ice loss from the Antarctic ice sheet (AIS) is expected to become the major contributor to sea-level rise in the next centuries. Projections of the AIS response to climate change based on numerical ice-sheet models remain challenging to establish due to the complexity of physical processes involved in ice-sheet dynamics, including instability mechanisms that can destabilise marine sectors with retrograde slopes. Moreover, uncertainties in ice-sheet models limit the ability to provide accurate sea-level rise projections. Here, we apply probabilistic methods to a hybrid ice-sheet model to investigate the influence of several sources of uncertainty, namely sources of uncertainty in atmospheric forcing, basal sliding, grounding-line flux parameterisation, calving, sub-shelf melting, ice-shelf rheology and bedrock relaxation, on the continental response of the Antarctic ice sheet to climate change over the next millennium. We provide probabilistic projections of sea-level rise and grounding-line retreat and we carry out stochastic sensitivity analyses to determine the most influential sources of uncertainty. We find that all sources of uncertainty, except perhaps the bedrock relaxation times, contribute to the uncertainty in the projections. We show that the sensitivity of the projections to uncertainties increases and the contribution of the uncertainty in sub-shelf melting to the uncertainty in the projections becomes more and more dominant as the scenario gets warmer. We show that the significance of the AIS contribution to sea-level rise is controlled by marine ice-sheet instability (MISI) in marine basins, with the biggest contribution stemming from the more vulnerable West Antarctic ice sheet. We find that, irrespectively of parametric uncertainty, the strongly mitigated RCP 2.6 scenario prevents the collapse of the West Antarctic ice sheet, that in both RCP 4.5 and RCP 6.0 scenarios the occurrence of MISI in marine basins is more sensitive to parametric uncertainty and that, almost irrespectively of parametric uncertainty, RCP 8.5 triggers the collapse of the West Antarctic ice sheet.

History, mass loss, structure, and dynamic behavior of the Antarctic Ice Sheet

Science ◽  
2020 ◽  
Vol 367 (6484) ◽  
pp. 1321-1325 ◽  
Author(s):  
Robin E. Bell ◽  
Helene Seroussi
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Satellite Measurements ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
Mountain Ranges ◽  
West Antarctic ◽  
The Antarctic

Antarctica contains most of Earth’s fresh water stored in two large ice sheets. The more stable East Antarctic Ice Sheet is larger and older, rests on higher topography, and hides entire mountain ranges and ancient lakes. The less stable West Antarctic Ice Sheet is smaller and younger and was formed on what was once a shallow sea. Recent observations made with several independent satellite measurements demonstrate that several regions of Antarctica are losing mass, flowing faster, and retreating where ice is exposed to warm ocean waters. The Antarctic contribution to sea level rise has reached ~8 millimeters since 1992. In the future, if warming ocean waters and increased surface meltwater trigger faster ice flow, sea level rise will accelerate.

scholarly journals Antarctic Ice-Sheet Volume at 18000 Years B.P. and Holocene Sea-Level Changes at the West Antarctic Margin

1979 ◽  
Vol 24 (90) ◽  
pp. 213-230 ◽  
Author(s):  
Craig S. Lingle ◽  
James A. Clark
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Sea Level Changes ◽  
Ice Shelf ◽  
Relative Sea Level ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
The Antarctic

AbstractThe Antarctic ice sheet has been reconstructed at 18000 years b.p. by Hughes and others (in press) using an ice-flow model. The volume of the portion of this reconstruction which contributed to a rise of post-glacial eustatic sea-level has been calculated and found to be (9.8±1.5) × 106km3. This volume is equivalent to 25±4 m of eustatic sea-level rise, defined as the volume of water added to the ocean divided by ocean area. The total volume of the reconstructed Antarctic ice sheet was found to be (37±6) × 106km3. If the results of Hughes and others are correct, Antarctica was the second largest contributor to post-glacial eustatic sea-level rise after the Laurentide ice sheet. The Farrell and Clark (1976) model for computation of the relative sea-level changes caused by changes in ice and water loading on a visco-elastic Earth has been applied to the ice-sheet reconstruction, and the results have been combined with the changes in relative sea-level caused by Northern Hemisphere deglaciation as previously calculated by Clark and others (1978). Three families of curves have been compiled, showing calculated relative sea-level change at different times near the margin of the possibly unstable West Antarctic ice sheet in the Ross Sea, Pine Island Bay, and the Weddell Sea. The curves suggest that the West Antarctic ice sheet remained grounded to the edge of the continental shelf untilc. 13000 years b.p., when the rate of sea-level rise due to northern ice disintegration became sufficient to dominate emergence near the margin predicted otherwise to have been caused by shrinkage of the Antarctic ice mass. In addition, the curves suggest that falling relative sea-levels played a significant role in slowing and, perhaps, reversing retreat when grounding lines approached their present positions in the Ross and Weddell Seas. A predicted fall of relative sea-level beneath the central Ross Ice Shelf of as much as 23 m during the past 2000 years is found to be compatible with recent field evidence that the ice shelf is thickening in the south-east quadrant.

Upper mantle viscosity structure and lithospheric thickness of Antarctica inferred from recent seismic models

2020 ◽  
Author(s):  
Douglas Wiens ◽  
Andrew Lloyd ◽  
Weisen Shen ◽  
Andrew Nyblade ◽  
Richard Aster ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Upper Mantle ◽  
Ice Sheet ◽  
West Antarctica ◽  
Lithospheric Thickness ◽  
Isostatic Adjustment ◽  
Low Viscosity ◽  
Mantle Viscosity ◽  
Seismic Models ◽  
The Antarctic

<p>Upper mantle viscosity structure and lithospheric thickness control the solid Earth response to variations in ice sheet loading. These parameters vary significantly across Antarctica, leading to strong regional differences in the timescale of glacial isostatic adjustment (GIA), with important implications for ice sheet models.  We estimate upper mantle viscosity structure and lithospheric thickness using two new seismic models for Antarctica, which take advantage of temporary broadband seismic stations deployed across Antarctica over the past 18 years. Shen et al. [2018] use receiver functions and Rayleigh wave velocities from earthquakes and ambient noise to develop a higher resolution model for the upper 200 km beneath Central and West Antarctica, where most of the seismic stations have been deployed. Lloyd et al [2019] use full waveform adjoint tomography to invert three-component earthquake seismograms for a radially anisotropic model covering Antarctica and adjacent oceanic regions to 800 km depth. We estimate the mantle viscosity structure from seismic structure using laboratory-derived relationships between seismic velocity, temperature, and rheology. Choice of parameters for this mapping is guided in part by recent regional estimates of mantle viscosity from geodetic measurements. We also describe and compare several different methods of estimating lithospheric thickness from seismic constraints.</p><p>The mantle viscosity estimates indicate regional variations of several orders of magnitude, with extremely low viscosity (< 10<sup>19</sup> Pa s) beneath the Amundsen Sea Embayment (ASE) and the Antarctic Peninsula, consistent with estimates from GIA models constrained by GPS data.  Lithospheric thickness is also highly variable, ranging from around 60 km in parts of West Antarctica to greater than 200 km beneath central East Antarctica. In East Antarctica, several prominent regions such as Dronning Maude Land and the Lambert Graben show much thinner lithosphere, consistent with Phanerozoic tectonic activity and lithospheric disruption. Thin lithosphere and low viscosity between the ASE and the Antarctic Peninsula likely result from the thermal effects of the slab window as the Phoenix-Antarctic plate boundary migrated northward during the Cenozoic. Low viscosity regions beneath the ASE and Marie Byrd Land coast connect to an offshore anomaly at depths of ~ 250 km, suggesting larger-scale thermal and geodynamic processes that may be linked to the initial Cretaceous rifting of New Zealand and Antarctica. Low mantle viscosity results in a characteristic GIA time scale on the order of several hundred years, such that isostatic adjustment occurs on the same time scale as grounding line retreat.  Thus the associated rebound may lessen the effect of the marine ice sheet instability proposed for the ASE region. </p>

scholarly journals Sensitivity of the Antarctic ice sheets to the warming of marine isotope substage 11c

2021 ◽  
Vol 15 (1) ◽  
pp. 459-478
Author(s):  
Martim Mas e Braga ◽  
Jorge Bernales ◽  
Matthias Prange ◽  
Arjen P. Stroeven ◽  
Irina Rogozhina
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Antarctic Ice Sheet ◽  
Climate Signal ◽  
West Antarctic Ice Sheet ◽  
Climate Conditions ◽  
West Antarctic ◽  
The Antarctic ◽  
Antarctic Ice Sheets

Abstract. Studying the response of the Antarctic ice sheets during periods when climate conditions were similar to the present can provide important insights into current observed changes and help identify natural drivers of ice sheet retreat. In this context, the marine isotope substage 11c (MIS11c) interglacial offers a suitable scenario, given that during its later portion orbital parameters were close to our current interglacial. Ice core data indicate that warmer-than-present temperatures lasted for longer than during other interglacials. However, the response of the Antarctic ice sheets and their contribution to sea level rise remain unclear. We explore the dynamics of the Antarctic ice sheets during this period using a numerical ice sheet model forced by MIS11c climate conditions derived from climate model outputs scaled by three glaciological and one sedimentary proxy records of ice volume. Our results indicate that the East and West Antarctic ice sheets contributed 4.0–8.2 m to the MIS11c sea level rise. In the case of a West Antarctic Ice Sheet collapse, which is the most probable scenario according to far-field sea level reconstructions, the range is reduced to 6.7–8.2 m independently of the choices of external sea level forcing and millennial-scale climate variability. Within this latter range, the main source of uncertainty arises from the sensitivity of the East Antarctic Ice Sheet to a choice of initial ice sheet configuration. We found that the warmer regional climate signal captured by Antarctic ice cores during peak MIS11c is crucial to reproduce the contribution expected from Antarctica during the recorded global sea level highstand. This climate signal translates to a modest threshold of 0.4 ∘C oceanic warming at intermediate depths, which leads to a collapse of the West Antarctic Ice Sheet if sustained for at least 4000 years.

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