Deriving a Physically-Based Calving Rate Law for Marine Ice-Cliff Instability

2020 ◽  
Author(s):  
Anna Crawford ◽  
Joe Todd ◽  
Doug Benn ◽  
Jan Åström ◽  
Thomas Zwinger
Keyword(s):  
Viscous Flow ◽  
Sea Level Rise ◽  
Sea Level ◽  
Large Scale ◽  
Ice Sheet ◽  
Rate Law ◽  
Grounding Line ◽  
Physically Based ◽  
Calving Rate ◽  
Global Sea Level

<p><span>Rapid grounding line retreat at marine-terminating glaciers could expose ice cliffs with heights greater than those on observational record. However, the finite strength of ice places a limit on the height of subareal cliffs. It is proposed that marine ice-cliff instability (MICI) will begin once a stable height threshold is exceeded. If a glacier is situated over a retrograde slope, as is the case for Thwaites Glacier and much of the West Antarctic Ice Sheet, MICI can be expected to accelerate </span><span>as retreat progresses</span><span> and increasingly tall and unstable ice cliffs are </span><span>formed. This is consequential for global sea level rise, yet large uncertainties remain in the prediction of MICI retreat rates. </span></p><p><span>We investigate MICI by pairing the full Stokes continuum model Elmer/Ice and the Helsinki Discrete Element Model (HiDEM)</span><span>. Viscous flow, simulated in Elmer/Ice, is found to be a necessary pre-condition for MICI collapse. Forward advance and bulging lead to ice-front instability and pervasive crevassing in HiDEM. This culminates in full-thickness calving events. We do not observe calving at ice faces prior to viscous deformation. </span><span>HiDEM simulations that implement viscous flow (HiDEM-ve) also show forward advance and waterline bulging, similar to the Elmer/Ice simulations. However, the importance of granular shear is highlighted by pronounced shear bands and patterns of surface lowering in HiDEM-ve output. These results emphasize the importance and complexity of viscous and brittle process interaction during MICI.</span></p><p><span>A simulation matrix of grounded termini shows that calving frequency and magnitude increase with the thickness of the calving front. The time required for viscous flow to recreate unstable conditions is influenced by thickness as well as ice temperature and basal friction. Simulations of buoyant termini are seen to calve through basal-crevassing and block-rotation, as opposed to incising surface-crevasses. Lastly, we observe that b</span><span>uttressing </span><span>mélange can</span><span> suppress retreat rate</span><span> if a sufficient resistive force is delivered to the calving front. A </span><span>physically-based law for MICI retreat rate is derived from our simulation matrix; this calving rate law can be incorporated into large-scale ice sheet models to constrain projections of Antarctic retreat and associated global sea level rise. Our results will also be used to investigate the future retreat of Thwaites Glacier, which is vulnerable to MICI due to a retreating grounding line, fragile floating ice shelf, and precarious positioning above an overdeepening basin</span><span>. </span></p>

scholarly journals Aurora Basin, the weak underbelly of East Antarctica

2020 ◽  
Author(s):  
Tyler Pelle ◽  
Mathieu Morlighem ◽  
Felicity S. McCormack
Keyword(s):  
Mass Balance ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Emission Scenarios ◽  
Thermal Forcing ◽  
Surface Mass ◽  
Grounding Line ◽  
Glacial Discharge ◽  
Global Sea Level

<p>Containing ~52 m sea level rise equivalent ice mass (SLRe), the East Antarctic Ice Sheet (EAIS) is a major component of the global sea level budget; yet, uncertainty remains in how this ice sheet will respond to enhanced atmospheric and oceanic thermal forcing through the turn of the century. To address this uncertainty, we model the most dynamic catchments of EAIS out to 2100 using the Ice Sheet System Model. We employ three basal melt rate parameterizations to resolve ice-ocean interactions and force our model with anomalies in both surface mass balance and ocean thermal forcing from both CMIP5 and CMIP6 model output. We find that this sector of EAIS gains approximately 10 mm SLRe by 2100 under high emission scenarios (RCP8.5 and SSP585), and loses mass under low emission scenarios (RCP2.6). All basins within the domain either gain mass or are in near mass balance through the 86-year experimental period, except the Aurora Subglacial Basin. The primary region of mass loss in this basin is located within 50 km upstream of Totten Glacier’s grounding line, which loses up to 6 mm SLRe by 2100. Glacial discharge from Totten is modulated by buttress supplied by a 10 km ice plain, located along the southern-most end of Totten’s grounding line. This ice plain is sensitive to brief changes in ocean temperature and once ungrounded, glacial discharge from Totten accelerates by up to 70% of it present day configuration. In all, we present plausible bounds on the contribution of a large sector of EAIS to global sea level rise out to the end of the century and target Totten as the most vulnerable glacier in this region. In doing so, we reduce uncertainty in century-scale global sea level projections and help steer scientific focus to the most dynamic regions of EAIS.</p>

scholarly journals The GRISLI-LSCE contribution to ISMIP6, Part 2: projections of the Antarctic ice sheet evolution by the end of the 21<sup>st</sup> century

2020 ◽  
Author(s):  
Aurélien Quiquet ◽  
Christophe Dumas
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Greenhouse Gas Emission ◽  
Ice Sheet ◽  
Companion Paper ◽  
Antarctic Ice Sheet ◽  
Grounding Line ◽  
Common Framework ◽  
Global Sea Level ◽  
The Antarctic

Abstract. Of primary societal importance, the ice sheet contribution to global sea level rise over the 21st century remains largely uncertain. In particular, the contribution of the Antarctic ice sheet by 2100 ranges from a few millimetres to more than one metre in the recent literature. The Ice Sheet Model Intercomparison Project for CMIP6 aimed at reducing the uncertainties on the fate of the ice sheets in the future by gathering various ice sheet models in a common framework. While in a companion paper we present the GRISLI-LSCE contribution to ISMIP6-Greenland, we present here the GRISLI-LSCE contribution to ISMIP6-Antarctica. We show that our model is strongly sensitive to the climate forcing used, with a contribution of the Antarctic ice sheet to global sea level rise by 2100 that ranges from −50 mm to +150 mm of sea level equivalent. Future oceanic warming leads to a decrease in thickness of the ice shelves and implies grounding line retreats while increased precipitation partially mitigates the ice sheet contribution to global sea level rise. Most of ice sheet changes over the next century are dampened under low greenhouse gas emission scenarios. Uncertainties related to sub-shelf basal melt induce large differences in simulated grounding line retreats, confirming the importance of this process and its representation in ice sheet models for the projections of the Antarctic ice sheet.

scholarly journals The GRISLI-LSCE contribution to the Ice Sheet Model Intercomparison Project for phase 6 of the Coupled Model Intercomparison Project (ISMIP6) – Part 2: Projections of the Antarctic ice sheet evolution by the end of the 21st century

2021 ◽  
Vol 15 (2) ◽  
pp. 1031-1052
Author(s):  
Aurélien Quiquet ◽  
Christophe Dumas
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Coupled Model ◽  
Model Intercomparison ◽  
Antarctic Ice Sheet ◽  
Grounding Line ◽  
Intercomparison Project ◽  
Global Sea Level ◽  
The Antarctic

Abstract. The Antarctic ice sheet's contribution to global sea level rise over the 21st century is of primary societal importance and remains largely uncertain as of yet. In particular, in the recent literature, the contribution of the Antarctic ice sheet by 2100 can be negative (sea level fall) by a few centimetres or positive (sea level rise), with some estimates above 1 m. The Ice Sheet Model Intercomparison Project for the Coupled Model Intercomparison Project – phase 6 (ISMIP6) aimed at reducing the uncertainties in the fate of the ice sheets in the future by gathering various ice sheet models in a common framework. Here, we present the GRISLI-LSCE (Grenoble Ice Sheet and Land Ice model of the Laboratoire des Sciences du Climat et de l'Environnement) contribution to ISMIP6-Antarctica. We show that our model is strongly sensitive to the climate forcing used, with a contribution of the Antarctic ice sheet to global sea level rise by 2100 that ranges from −50 to +150 mm sea level equivalent (SLE). Future oceanic warming leads to a decrease in thickness of the ice shelves, resulting in grounding-line retreat, while increased surface mass balance partially mitigates or even overcompensates the dynamic ice sheet contribution to global sea level rise. Most of the ice sheet changes over the next century are dampened under low-greenhouse-gas-emission scenarios. Uncertainties related to sub-ice-shelf melt rates induce large differences in simulated grounding-line retreat, confirming the importance of this process and its representation in ice sheet models for projections of the Antarctic ice sheet's evolution.

scholarly journals Greenland ice sheet contribution to sea level rise during the last interglacial period: a modelling study driven and constrained by ice core data

2013 ◽  
Vol 9 (1) ◽  
pp. 353-366 ◽  
Author(s):  
A. Quiquet ◽  
C. Ritz ◽  
H. J. Punge ◽  
D. Salas y Mélia
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Interglacial Period ◽  
Last Interglacial ◽  
Intergovernmental Panel ◽  
Orbital Configuration ◽  
Global Sea Level

Abstract. As pointed out by the forth assessment report of the Intergovernmental Panel on Climate Change, IPCC-AR4 (Meehl et al., 2007), the contribution of the two major ice sheets, Antarctica and Greenland, to global sea level rise, is a subject of key importance for the scientific community. By the end of the next century, a 3–5 °C warming is expected in Greenland. Similar temperatures in this region were reached during the last interglacial (LIG) period, 130–115 ka BP, due to a change in orbital configuration rather than to an anthropogenic forcing. Ice core evidence suggests that the Greenland ice sheet (GIS) survived this warm period, but great uncertainties remain about the total Greenland ice reduction during the LIG. Here we perform long-term simulations of the GIS using an improved ice sheet model. Both the methodologies chosen to reconstruct palaeoclimate and to calibrate the model are strongly based on proxy data. We suggest a relatively low contribution to LIG sea level rise from Greenland melting, ranging from 0.7 to 1.5 m of sea level equivalent, contrasting with previous studies. Our results suggest an important contribution of the Antarctic ice sheet to the LIG highstand.

Greenland ice sheet hydrology

2013 ◽  
Vol 38 (1) ◽  
pp. 19-54 ◽  
Author(s):  
Vena W. Chu
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Field Studies ◽  
Ice Dynamics ◽  
Surface Water Hydrology ◽  
Basal Sliding ◽  
Hydrologic System ◽  
Global Sea Level

Understanding Greenland ice sheet (GrIS) hydrology is essential for evaluating response of ice dynamics to a warming climate and future contributions to global sea level rise. Recently observed increases in temperature and melt extent over the GrIS have prompted numerous remote sensing, modeling, and field studies gauging the response of the ice sheet and outlet glaciers to increasing meltwater input, providing a quickly growing body of literature describing seasonal and annual development of the GrIS hydrologic system. This system is characterized by supraglacial streams and lakes that drain through moulins, providing an influx of meltwater into englacial and subglacial environments that increases basal sliding speeds of outlet glaciers in the short term. However, englacial and subglacial drainage systems may adjust to efficiently drain increased meltwater without significant changes to ice dynamics over seasonal and annual scales. Both proglacial rivers originating from land-terminating glaciers and subglacial conduits under marine-terminating glaciers represent direct meltwater outputs in the form of fjord sediment plumes, visible in remotely sensed imagery. This review provides the current state of knowledge on GrIS surface water hydrology, following ice sheet surface meltwater production and transport via supra-, en-, sub-, and proglacial processes to final meltwater export to the ocean. With continued efforts targeting both process-level and systems analysis of the hydrologic system, the larger picture of how future changes in Greenland hydrology will affect ice sheet glacier dynamics and ultimately global sea level rise can be advanced.

scholarly journals Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models

2014 ◽  
Vol 5 (2) ◽  
pp. 271-293 ◽  
Author(s):  
A. Levermann ◽  
R. Winkelmann ◽  
S. Nowicki ◽  
J. L. Fastook ◽  
K. Frieler ◽  
...  
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Response Functions ◽  
Ice Shelf ◽  
Uncertainty Range ◽  
Basal Ice ◽  
Grounding Line ◽  
Rcp 8.5 ◽  
Intercomparison Project ◽  
Global Sea Level

Abstract. The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02–0.14 m; 90% range: 0.0–0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04–0.21 m; 90% range: 0.01–0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these values increase to 0.09 m (66% range: 0.04–0.17 m; 90% range: 0.02–0.25 m) for RCP-2.6 and 0.15 m (66% range: 0.07–0.28 m; 90% range: 0.04–0.43 m) for RCP-8.5. All probability distributions are highly skewed towards high values. The applied ice-sheet models are coarse resolution with limitations in the representation of grounding-line motion. Within the constraints of the applied methods, the uncertainty induced from different ice-sheet models is smaller than that induced by the external forcing to the ice sheets.

scholarly journals Decadal-scale onset and termination of Antarctic ice-mass loss during the last deglaciation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Michael E. Weber ◽  
Nicholas R. Golledge ◽  
Chris J. Fogwill ◽  
Chris S. M. Turney ◽  
Zoë A. Thomas
Keyword(s):  
Mass Loss ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ross Sea ◽  
Ice Sheet ◽  
Rate Of Change ◽  
Last Deglaciation ◽  
Decadal Scale ◽  
Ice Sheet Modeling ◽  
Global Sea Level

AbstractEmerging ice-sheet modeling suggests once initiated, retreat of the Antarctic Ice Sheet (AIS) can continue for centuries. Unfortunately, the short observational record cannot resolve the tipping points, rate of change, and timescale of responses. Iceberg-rafted debris data from Iceberg Alley identify eight retreat phases after the Last Glacial Maximum that each destabilized the AIS within a decade, contributing to global sea-level rise for centuries to a millennium, which subsequently re-stabilized equally rapidly. This dynamic response of the AIS is supported by (i) a West Antarctic blue ice record of ice-elevation drawdown >600 m during three such retreat events related to globally recognized deglacial meltwater pulses, (ii) step-wise retreat up to 400 km across the Ross Sea shelf, (iii) independent ice sheet modeling, and (iv) tipping point analysis. Our findings are consistent with a growing body of evidence suggesting the recent acceleration of AIS mass loss may mark the beginning of a prolonged period of ice sheet retreat and substantial global sea level rise.

scholarly journals Extraordinary runoff from the Greenland ice sheet in 2012 amplified by hypsometry and depleted firn retention

2016 ◽  
Vol 10 (3) ◽  
pp. 1147-1159 ◽  
Author(s):  
Andreas Bech Mikkelsen ◽  
Alun Hubbard ◽  
Mike MacFerrin ◽  
Jason Eric Box ◽  
Sam H. Doyle ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Equilibrium Line ◽  
Aerial Photographs ◽  
Discharge Data ◽  
Impermeable Barrier ◽  
Global Sea Level ◽  
Percolation Zone

Abstract. It has been argued that the infiltration and retention of meltwater within firn across the percolation zone of the Greenland ice sheet has the potential to buffer up to  ∼  3.6 mm of global sea-level rise (Harper et al., 2012). Despite evidence confirming active refreezing processes above the equilibrium line, their impact on runoff and proglacial discharge has yet to be assessed. Here, we compare meteorological, melt, firn stratigraphy and discharge data from the extreme 2010 and 2012 summers to determine the relationship between atmospheric forcing and melt runoff at the land-terminating Kangerlussuaq sector of the Greenland ice sheet, which drains into the Watson River. The 6.8 km3 bulk discharge in 2012 exceeded that in 2010 by 28 %, despite only a 3 % difference in net incoming melt energy between the two years. This large disparity can be explained by a 10 % contribution of runoff originating from above the long-term equilibrium line in 2012 caused by diminished firn retention. The amplified 2012 response was compounded by catchment hypsometry; the disproportionate increase in area contributing to runoff as the melt-level rose high into the accumulation area.Satellite imagery and aerial photographs reveal an extensive supraglacial network extending 140 km from the ice margin that confirms active meltwater runoff originating well above the equilibrium line. This runoff culminated in three days with record discharge of 3100 m3 s−1 (0.27 Gt d−1) that peaked on 11 July and washed out the Watson River Bridge. Our findings corroborate melt infiltration processes in the percolation zone, though the resulting patterns of refreezing are complex and can lead to spatially extensive, perched superimposed ice layers within the firn. In 2012, such layers extended to an elevation of at least 1840 m and provided a semi-impermeable barrier to further meltwater storage, thereby promoting widespread runoff from the accumulation area of the Greenland ice sheet that contributed directly to proglacial discharge and global sea-level rise.

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.

Trends and projections in ice sheet mass balance

2020 ◽  
Author(s):  
Andrew Shepherd ◽  
Keyword(s):  
Mass Balance ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Sea Levels ◽  
Global Sea Level

&lt;p&gt;In recent decades, the Antarctic and Greenland Ice Sheets have been major contributors to global sea-level rise and are expected to be so in the future. Although increases in glacier flow and surface melting have been driven by oceanic and atmospheric warming, the degree and trajectory of today&amp;#8217;s imbalance remain uncertain. Here we compare and combine 26 individual satellite records of changes in polar ice sheet volume, flow and gravitational potential to produce a reconciled estimate of their mass balance. &lt;strong&gt;Since the early 1990&amp;#8217;s, ice losses from Antarctica and Greenland have caused global sea-levels to rise by 18.4 millimetres, on average, and there has been a sixfold increase in the volume of ice loss over time. Of this total, 41 % (7.6 millimetres) originates from Antarctica and 59 % (10.8 millimetres) is from Greenland. In this presentation, we compare our reconciled estimates of Antarctic and Greenland ice sheet mass change to IPCC projection of sea level rise to assess the model skill in predicting changes in ice dynamics and surface mass balance. &amp;#160;&lt;/strong&gt;Cumulative ice losses from both ice sheets have been close to the IPCC&amp;#8217;s predicted rates for their high-end climate warming scenario, which forecast an additional 170 millimetres of global sea-level rise by 2100 when compared to their central estimate.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document