Sensitivity of a calving glacier to ice–ocean interactions under climate change: new insights from a 3-D full-Stokes model

Abstract. Iceberg calving accounts for between 30 % and 60 % of net mass loss from the Greenland Ice Sheet, which has intensified and is now the single largest contributor to global sea level rise in the cryosphere. Changes to calving rates and the dynamics of calving glaciers represent a significant uncertainty in projections of future sea level rise. A growing body of observational evidence suggests that calving glaciers respond rapidly to regional environmental change, but predictive capacity is limited by the lack of suitable models capable of simulating calving mechanisms realistically. Here, we use a 3-D full-Stokes calving model to investigate the environmental sensitivity of Store Glacier, a large outlet glacier in West Greenland. We focus on two environmental processes: undercutting by submarine melting and buttressing by ice mélange, and our results indicate that Store Glacier is likely to be able to withstand moderate warming perturbations in which the former is increased by 50 % and the latter reduced by 50 %. However, severe perturbation with a doubling of submarine melt rates or a complete loss of ice mélange destabilises the calving front in our model runs. Furthermore, our analysis reveals that stress and fracture patterns at Store's terminus are complex and varied, primarily due to the influence of basal topography. Calving style and environmental sensitivity vary greatly, with propagation of surface crevasses significantly influencing iceberg production in the northern side, whereas basal crevasses dominate in the south. Any future retreat is likely to be initiated in the southern side by a combination of increased submarine melt rates in summer and reduced mélange strength in winter. The lateral variability, as well as the importance of rotational and bending forces at the terminus, underlines the importance of using the 3-D full-Stokes stress solution when modelling Greenland's calving glaciers.

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Sensitivity of calving glaciers to ice-ocean interactions under climate change: New insights from a 3D full-Stokes model

10.5194/tc-2019-20 ◽

2019 ◽

Author(s):

Joe Todd ◽

Poul Christoffersen ◽

Thomas Zwinger ◽

Peter Råback ◽

Douglas I. Benn

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Greenland Ice Sheet ◽

Environmental Sensitivity ◽

Predictive Capacity ◽

Outlet Glacier ◽

Iceberg Calving ◽

Southern Side ◽

Northern Side ◽

Global Sea Level

Abstract. Iceberg calving accounts for between 30–60 % of net mass loss from the Greenland Ice Sheet, which has intensified and is now the single largest contributor to global sea level rise in the cryosphere. Changes to calving rates and the dynamics of calving glaciers represent one of the largest uncertainties in projections of future sea level rise. A growing body of observational evidence suggests that calving glaciers respond rapidly to regional environmental change, but predictive capacity is limited by the lack of suitable models capable of simulating the calving mechanism realistically. Here, we use a 3D full-Stokes calving model to investigate the environmental sensitivity of Store Glacier, a large outlet glacier in West Greenland. We focus on two environmental processes: undercutting by submarine melting and buttressing by ice mélange, and our results indicate that Store Glacier is likely to be able to withstand moderate warming perturbations in which the former is increased by 50 % and the latter reduced equivalently. However, severe perturbation with a doubling of submarine melt rates or a complete loss of ice mélange destabilizes the calving front in our model runs. Furthermore, our analysis reveals that stress and fracture patterns at Store’s terminus are complex and varied, primarily due to the influence of basal topography. Calving style and environmental sensitivity varies greatly, with propagation of surface crevasses significantly influencing iceberg production in the northern side, whereas basal crevasses dominate in the south. Any future retreat is likely to be initiated in the southern side by a combination of increased melt rate in summer and reduced mélange strength in winter. The lateral variability, as well as the importance of rotational and bending forces at the terminus, underlines the importance of using the 3D full-Stokes stress solution when modelling Greenland’s calving glaciers.

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

Climate of the Past ◽

10.5194/cp-9-353-2013 ◽

2013 ◽

Vol 9 (1) ◽

pp. 353-366 ◽

Cited By ~ 42

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.

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Greenland ice sheet hydrology

Progress in Physical Geography Earth and Environment ◽

10.1177/0309133313507075 ◽

2013 ◽

Vol 38 (1) ◽

pp. 19-54 ◽

Cited By ~ 85

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.

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

The Cryosphere ◽

10.5194/tc-10-1147-2016 ◽

2016 ◽

Vol 10 (3) ◽

pp. 1147-1159 ◽

Cited By ~ 23

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.

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Viscoelastic modeling results of the 79°N Glacier, Greenland

10.5194/egusphere-egu2020-16736 ◽

2020 ◽

Author(s):

Julia Christmann ◽

Martin Rückamp ◽

Ole Zeising ◽

Daniel Steinhage ◽

Niklas Neckel ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Greenland Ice Sheet ◽

Material Model ◽

Outlet Glacier ◽

Tidal Forcing ◽

North East ◽

Periodic Movement ◽

Grounding Line ◽

Horizontal Displacements

Grounding line/zone dynamics of floating-tongue glaciers is of major importance for changes in their contribution to sea-level rise. For floating-tongue glaciers, thermal forcing of oceanic heat and tidal forcing are the major processes acting in that zone. Here we deal with the response to tidal forcing. The 79&#176;N Glacier, an outlet glacier of the North East Greenland Ice Stream, is the focus of the Greenland Ice Sheet Ocean Interaction project (GROCE) funded by the German Ministry of Education and Research. We present a study of this region considering the deformation of the glacier in response to ocean tidal forcing by means of observations and modeling. GPS measurements realized in 2017-2018 are analyzed for vertical and horizontal displacements of the glacier and its floating tongue. Observations on fully-grounded ice reveal a periodic horizontal displacement in response to ocean tidal forcing in a distance of more than 35 km upstream from the grounding line. In the hinge zone, i.e. the transition between grounded and floating ice, the tidal forcing leads to a measurable vertical bending of the ice and a periodic movement of the grounding line. Understanding the mechanisms of grounding line migration is important to better evaluate the contribution of grounded ice discharge to sea-level rise.In order to model the measured displacements, a viscoelastic material model is required using the observed vertical displacements at the floating ice tongue as external forcing. Geometries obtained from AWI&#8217;s new ultrawideband radar form the basis for finite-element simulations in COMSOL. With the viscoelastic Maxwell material model, the response of the ice to ocean tidal forcing can successfully be modeled. Results obtained with a nonlinear Glen-type viscosity agree very well with the observed bending near the grounding line. The expected phase shift of the horizontal displacements upstream from the grounding line is well reproduced in the model.

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Trends and projections in ice sheet mass balance

10.5194/egusphere-egu2020-20660 ◽

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

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&#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. Since the early 1990&#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. &#160;Cumulative ice losses from both ice sheets have been close to the IPCC&#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.

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Glacier dynamics over the last quarter of a century at Jakobshavn Isbræ

The Cryosphere Discussions ◽

10.5194/tcd-9-4865-2015 ◽

2015 ◽

Vol 9 (5) ◽

pp. 4865-4892

Author(s):

I. S. Muresan ◽

S. A. Khan ◽

A. Aschwanden ◽

C. Khroulev ◽

T. Van Dam ◽

...

Keyword(s):

Mass Loss ◽

Sea Level Rise ◽

Sea Level ◽

21St Century ◽

Greenland Ice Sheet ◽

Outlet Glacier ◽

The Past ◽

Glacier Dynamics ◽

The Future ◽

Oceanic Forcing

Abstract. Observations over the past two decades show substantial ice loss associated with the speedup of marine terminating glaciers in Greenland. Here we use a regional 3-D outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in west Greenland. Using atmospheric and oceanic forcing we tune our model to reproduce the observed frontal changes of JI during 1990–2014. We identify two major accelerations. The first occurs in 1998, and is triggered by moderate thinning prior to 1998. The second acceleration, which starts in 2003 and peaks in summer 2004, is triggered by the final breakup of the floating tongue, which generates a reduction in buttressing at the JI terminus. This results in further thinning, and as the slope steepens inland, sustained high velocities have been observed at JI over the last decade. As opposed to other regions on the Greenland Ice Sheet (GrIS), where dynamically induced mass loss has slowed down over recent years, both modelled and observed results for JI suggest a continuation of the acceleration in mass loss. Further, we find that our model is not able to capture the 2012 peak in the observed velocities. Our analysis suggests that the 2012 acceleration of JI is likely the result of an exceptionally long melt season dominated by extreme melt events. Considering that such extreme surface melt events are expected to intensify in the future, our findings suggest that the 21st century projections of the GrIS mass loss and the future sea level rise may be larger than predicted by existing modelling results.

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Semi-equilibrated global sea-level change projections for the next 10 000 years

Earth System Dynamics ◽

10.5194/esd-11-953-2020 ◽

2020 ◽

Vol 11 (4) ◽

pp. 953-976

Author(s):

Jonas Van Breedam ◽

Heiko Goelzer ◽

Philippe Huybrechts

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Sea Level Change ◽

Strong Increase ◽

Antarctic Ice Sheet ◽

Level Change ◽

Global Sea Level ◽

The Antarctic

Abstract. The emphasis for informing policy makers on future sea-level rise has been on projections by the end of the 21st century. However, due to the long lifetime of atmospheric CO2, the thermal inertia of the climate system and the slow equilibration of the ice sheets, global sea level will continue to rise on a multi-millennial timescale even when anthropogenic CO2 emissions cease completely during the coming decades to centuries. Here we present global sea-level change projections due to the melting of land ice combined with steric sea effects during the next 10 000 years calculated in a fully interactive way with the Earth system model of intermediate complexity LOVECLIMv1.3. The greenhouse forcing is based on the Extended Concentration Pathways defined until 2300 CE with no carbon dioxide emissions thereafter, equivalent to a cumulative CO2 release of between 460 and 5300 GtC. We performed one additional experiment for the highest-forcing scenario with the inclusion of a methane emission feedback where methane is slowly released due to a strong increase in surface and oceanic temperatures. After 10 000 years, the sea-level change rate drops below 0.05 m per century and a semi-equilibrated state is reached. The Greenland ice sheet is found to nearly disappear for all forcing scenarios. The Antarctic ice sheet contributes only about 1.6 m to sea level for the lowest forcing scenario with a limited retreat of the grounding line in West Antarctica. For the higher-forcing scenarios, the marine basins of the East Antarctic Ice Sheet also become ice free, resulting in a sea-level rise of up to 27 m. The global mean sea-level change after 10 000 years ranges from 9.2 to more than 37 m. For the highest-forcing scenario, the model uncertainty does not exclude the complete melting of the Antarctic ice sheet during the next 10 000 years.

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The GRISLI-LSCE contribution to the Ice Sheet Model Intercomparison Project for phase 6 of the Coupled Model Intercomparison Project (ISMIP6) – Part 1: Projections of the Greenland ice sheet evolution by the end of the 21st century

The Cryosphere ◽

10.5194/tc-15-1015-2021 ◽

2021 ◽

Vol 15 (2) ◽

pp. 1015-1030 ◽

Cited By ~ 1

Author(s):

Aurélien Quiquet ◽

Christophe Dumas

Keyword(s):

Mass Loss ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Coupled Model ◽

Greenland Ice Sheet ◽

Model Intercomparison ◽

The Future ◽

Intercomparison Project ◽

Global Sea Level

Abstract. Polar amplification will result in amplified temperature changes in the Arctic with respect to the rest of the globe, making the Greenland ice sheet particularly vulnerable to global warming. While the ice sheet has been showing an increased mass loss in the past decades, its contribution to global sea level rise in the future is of primary importance since it is at present the largest single-source contribution after the thermosteric contribution. The question of the fate of the Greenland and Antarctic ice sheets for the next century has recently gathered various ice sheet models in a common framework within the Ice Sheet Model Intercomparison Project for the Coupled Model Intercomparison Project – phase 6 (ISMIP6). While in a companion paper 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 present here the GRISLI-LSCE contribution to ISMIP6-Greenland. We show an important spread in the simulated Greenland ice loss in the future depending on the climate forcing used. The contribution of the ice sheet to global sea level rise in 2100 can thus be from as low as 20 mm sea level equivalent (SLE) to as high as 160 mm SLE. Amongst the models tested in ISMIP6, the Coupled Model Intercomparison Project – phase 6 (CMIP6) models produce larger ice sheet retreat than their CMIP5 counterparts. Low-emission scenarios in the future drastically reduce the ice mass loss. The oceanic forcing contributes to about 10 mm SLE in 2100 in our simulations. In addition, the dynamical contribution to ice thickness change is small compared to the impact of surface mass balance. This suggests that mass loss is mostly driven by atmospheric warming and associated ablation at the ice sheet margin. With additional sensitivity experiments we also show that the spread in mass loss is only weakly affected by the choice of the ice sheet model mechanical parameters.

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The role of an interactive Greenland Ice Sheet in abrupt 4xCO2 forcing experiments.

10.5194/egusphere-egu21-13327 ◽

2021 ◽

Author(s):

Victoria Lee ◽

Robin S. Smith ◽

Antony J. Payne

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ocean Model ◽

Surface Melting ◽

Surface Mass ◽

Meltwater Runoff ◽

Iceberg Calving

We compare the response of a coupled atmosphere-ocean-Greenland Ice Sheet (GrIS) model forced with an abrupt quadrupling of CO2 from greenhouse gas concentrations in 1970 with the response of the atmosphere-ocean model with a static GrIS . The model, UKESM1.ice.N96.ORCA1, consists of HadGEM GC3.1 coupled to the BISICLES ice sheet model with mean annual surface mass balance (SMB) passed to BISICLES and orography and cumulated iceberg flux passed back to the atmosphere and ocean, respectively, at the end of each year. The differences in the surface temperature and atmospheric fields between the two experiments are confined to Greenland, with no discernible global effects from the evolving orography. The volume of the GrIS decreases by 15 % in 330 years. The surface height decreases the most (over 800m in 330 years) in southwest&#160;GrIS due to surface melting enhanced by feedbacks between elevation, air temperature and albedo. The input of freshwater to the ocean from Greenland is enhanced due to increased meltwater runoff, but the flux from melting icebergs decays to zero as calving from glaciers declines. The resulting sea level rise is dominated by SMB, where the equivalent sea level rise is 1179 mm (5.0 mm/yr) for the static GrIS and 1120 mm (4.4 mm/yr) for the interactive ice sheet at 2300.&#160; There is less sea level rise in the interactive GrIS experiment, even though more mass is lost through surface melting, because the amount lost through iceberg calving decreases as the grounding line of marine-terminating glaciers retreat inland whereas calving in the static experiment is constant.&#160;&#160;&#160;&#160;

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