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 Extraordinary runoff from the Greenland Ice Sheet in 2012 amplified by hypsometry and depleted firn-retention

2015 ◽  
Vol 9 (5) ◽  
pp. 4625-4660 ◽  
Author(s):  
A. B. Mikkelsen ◽  
A. Hubbard ◽  
M. MacFerrin ◽  
J. Box ◽  
S. Doyle ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Strong Support ◽  
Greenland Ice Sheet ◽  
Equilibrium Line ◽  
Aerial Photographs ◽  
Discharge Data ◽  
Unit Energy ◽  
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 runoff across the Kangerlussuaq catchment of the Greenland ice sheet, which drains into Watson River. The bulk discharge in 2012 of 6.8 km3 exceeded that of 2010 of 5.3 km3 by 28 %, despite only a 3 % difference in net energy available for melt between the two summers. This large disparity in discharge response can be explained by a 24 % contribution of runoff originating from above the long-term equilibrium line in 2012, triggered by diminished firn retention that culminated in three days of record discharge from 11 July of 3100 m3 s−1 (0.27 km3 d−1) that washed-out the Kangerlussuaq bridge. Throughout the 2010 melt-season, there was a steady increase in the residual difference between integrated melt over the catchment and cumulative proglacial discharge that by mid-September equated to 21 % (~1.1 km3) of the total melt generated being retained within the catchment. In 2012 a similar pattern is observed until 11 July, after which the residual fell by 50 % and further diminished so that less than 0.4 km3 (~5 %) of the total melt was retained by the end of the summer. Cumulative energy receipts versus bulk discharge further indicate a marked contrast between the two melt-seasons, such that in 2012 there was a noteably higher discharge response per unit energy forcing after the 11 July. Density profiles from cores and pits within the accumulation area acquired in April 2012 reveal an extensive, dense, ice-layer between 0.9 to 1.4 m snow depth that extended from the equilibrium line to at least 1840 m elevation. This perched superimposed ice layer can be attributed to melt refreezing during previous summers and we hypothesise that in July 2012, it provided a barrier to further infiltration rendering the underlying pore space inaccessible thereby forcing extensive runoff from the accumulation zone. Discharge was further amplified by catchment hypsometry, leading to a disproportionate increase in the area contributing to runoff as the melt-level rose above the ice sheet plateau in July 2012. Satellite imagery and oblique aerial photographs confirm an active network of supraglacial rivers extending 140 km from the ice margin providing strong support for the hypothesis. Our findings substantiate active infiltration processes across the percolation zone of the Greenland ice sheet though the resulting patterns of refreezing are complex and can lead to spatially extensive, perched superimposed layers within the firn. In 2012, such layers extended to 1840 m providing a low-permeable obstruction to further meltwater storage, thereby promoting runoff into the hydrological system that contributed directly to sea-level rise.

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.

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

<p>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’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. <strong>Since the early 1990’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.  </strong>Cumulative ice losses from both ice sheets have been close to the IPCC’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.</p>

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

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.

scholarly journals 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

2021 ◽  
Vol 15 (2) ◽  
pp. 1015-1030 ◽  
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.

Greenland ice sheet contribution to future global sea level rise based on CMIP5 models

2013 ◽  
Vol 31 (1) ◽  
pp. 8-16 ◽  
Author(s):  
Qing Yan ◽  
Huijun Wang ◽  
Ola M. Johannessen ◽  
Zhongshi Zhang
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Cmip5 Models ◽  
Global Sea Level

scholarly journals Modeling the response of Greenland outlet glaciers to global warming using a coupled flowline-plume model

2018 ◽  
Author(s):  
Johanna Beckmann ◽  
Mahé Perrette ◽  
Sebastian Beyer ◽  
Reinhard Calov ◽  
Matteo Willeit ◽  
...  
Keyword(s):  
Global Warming ◽  
Mass Loss ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Ocean Temperature ◽  
Surface Mass ◽  
Global Sea Level

Abstract. In recent decades, the Greenland Ice Sheet has experienced an accelerated mass loss, contributing to approximately 25 % of contemporary sea level rise. This mass loss is caused by increased surface melt over a large area of the ice sheet and by the thinning, retreat and acceleration of numerous Greenland outlet glaciers. The latter is likely connected to enhanced submarine melting that, in turn, can be explained by ocean warming and enhanced subglacial discharge. The mechanisms involved in submarine melting are not yet fully understood and are only crudely incorporated in some models of the Greenland Ice Sheet. Here, we investigate the response of twelve representative Greenland outlet glaciers to atmospheric and oceanic warming using a coupled 1D line-plume glacier-flowline model. The model parameters have been tuned for individual outlet glaciers using present-day observational constraints. We then run the model from present to the year 2100, forcing the model with changes in surface mass balance and surface runoff from simulations with a regional climate model for the RCP 8.5 scenario, and applying a linear ocean temperature warming with different rates of changes representing uncertainties in the CMIP 5 model experiments for the same climate change scenario. We also used different initial temperature-salinity profiles obtained from direct measurements and from ocean reanalysis data. Using different combinations of submarine melting and calving parameters that reproduce the present-day state of the glaciers, we estimated uncertainties in the contribution to global sea level rise for individual glaciers. We also performed a factor analysis, which shows that the role of different forcing (change in surface mass balance, ocean temperature and subglacial discharge) are diverse for individual glaciers. We found that changes in, ocean temperature and subglacial discharge are of comparable importance for the cumulative contribution of all twelve glaciers to global sea level rise in the 21st century. The median range of the cumulative contribution to the global sea level rise for all twelve glaciers is about 14 mm from which roughly 85 % are associated with the response to increased submarine melting and the remaining part to surface mass loss. We also found a weak correlation (correlation coefficient 0.35) between present-day grounding line discharge and their future contribution to sea level rise in 2100. If the contribution of the twelve glaciers is scaled up to the total present-day discharge of Greenland, we estimate the contribution of all Greenland glaciers to 21st-century sea level rise to be approximately 50 mm. This result confirms earlier studies that the response of the outlet glaciers to global warming has to be taken into account to correctly assess the total contribution of Greenland to sea level change.

scholarly journals The GRISLI-LSCE contribution to ISMIP6, Part 1: projections of the Greenland ice sheet evolution by the end of the 21<sup>st</sup> century

2020 ◽  
Author(s):  
Aurélien Quiquet ◽  
Christophe Dumas
Keyword(s):  
Mass Loss ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Companion Paper ◽  
The Arctic ◽  
The Future ◽  
Common Framework ◽  
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 increase 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 behind 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 CMIP6. While in a companion paper we present the GRISLI-LSCE 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 be thus as low as 20 mmSLE to as high as 160 mmSLE. The CMIP6 models produce much larger ice sheet retreat than their CMIP5 counterparts. Low emission scenarios in the future drastically reduce the ice mass loss. The mass loss is mostly driven by atmospheric warming and associated ablation at the ice sheet margin while oceanic forcing contributes to about 10 mmSLE in 2100 in our simulations.

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