Meltwater Penetration Through Temperate Ice Layers in the Percolation Zone of the Greenland Ice Sheet

Supraglacial lakes over the Greenland Ice Sheet can demonstrate multi-model drainage states. Lakes can demonstrate incomplete drainage, where residual melt can become buried under ice and snow and survive throughout the winter. We evaluate atmospheric factors that influence the propensity for the formation of buried lakes over the ice sheet. We examine the spatial and temporal occurrence and behavior of buried lakes over the Jakobshavn Isbrae and Zachariae Isstrøm outlet basins and assess the magnitude of insolation necessary to preserve melt water using a numerical lake model from 2009 to 2012. Buried lakes tend to occur at higher elevations within the ablation zone and those present at elevations > 1000 m tend to reoccur over several seasons. Lakes without buried water are relatively small (∼1 km2), whereas lakes with buried water are larger (∼6–10 km2). Lake area is correlated with the number of seasons sub-surface water persists. Buried lakes are relatively deep and associated with complex supraglacial channel networks. Winter stored water could be a precursor to the formation of supraglacial channels. Simulations of the insulation potential of accumulated snow and ice on the surface of lakes indicate substantial regional differences and inter-annual variability. With the possibility of inland migration of supraglacial lakes, buried lakes could be important in the evolution of ablation/percolation zone hydrology.

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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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Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling

10.5194/tc-2017-277 ◽

2018 ◽

Author(s):

Achim Heilig ◽

Olaf Eisen ◽

Michael MacFerrin ◽

Marco Tedesco ◽

Xavier Fettweis

Keyword(s):

Water Content ◽

Liquid Water ◽

Pore Space ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Liquid Water Content ◽

Water Infiltration ◽

Near Surface ◽

Percolation Zone

Abstract. Increasing melt over the Greenland ice sheet (GrIS) recorded over the past years has resulted in significant changes of the percolation regime of the ice sheet. It remains unclear whether Greenland's percolation zone will act as meltwater buffer in the near future through gradually filling all pore space or if near-surface refreezing causes the formation of impermeable layers, which provoke lateral runoff. Homogeneous ice layers within perennial firn, as well as near-surface ice layers of several meter thickness are observable in firn cores. Because firn coring is a destructive method, deriving stratigraphic changes in firn and allocation of summer melt events is challenging. To overcome this deficit and provide continuous data for model evaluations on snow and firn density, temporal changes in liquid water content and depths of water infiltration, we installed an upward-looking radar system (upGPR) 3.4 m below the snow surface in May 2016 close to Camp Raven (66.4779° N/46.2856° W) at 2120 m a.s.l. The radar is capable to monitor quasi-continuously changes in snow and firn stratigraphy, which occur above the antennas. For summer 2016, we observed four major melt events, which routed liquid water into various depths beneath the surface. The last event in mid-August resulted in the deepest percolation down to about 2.3 m beneath the surface. Comparisons with simulations from the regional climate model MAR are in very good agreement in terms of seasonal changes in accumulation and timing of onset of melt. However, neither bulk density of near-surface layers nor the amounts of liquid water and percolation depths predicted by MAR correspond with upGPR data. Radar data and records of a nearby thermistor string, in contrast, matched very well, for both, timing and depth of temperature changes and observed water percolations. All four melt events transferred a cumulative mass of 56 kg/m2 into firn beneath the summer surface of 2015. We find that continuous observations of liquid water content, percolation depths and rates for the seasonal mass fluxes are sufficiently accurate to provide valuable information for validation of model approaches and help to develop a better understanding of liquid water retention and percolation in perennial firn.

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Modeling Multifrequency Pol-InSAR Data From the Percolation Zone of the Greenland Ice Sheet

IEEE Transactions on Geoscience and Remote Sensing ◽

10.1109/tgrs.2018.2870301 ◽

2019 ◽

Vol 57 (4) ◽

pp. 1963-1976 ◽

Cited By ~ 3

Author(s):

Georg Fischer ◽

Konstantinos P. Papathanassiou ◽

Irena Hajnsek

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Percolation Zone

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Formation and development of supraglacial lakes in the percolation zone of the Greenland ice sheet

Journal of Glaciology ◽

10.1017/jog.2017.50 ◽

2017 ◽

Vol 63 (241) ◽

pp. 847-853 ◽

Cited By ~ 2

Author(s):

CHRISTINE CHEN ◽

IAN M. HOWAT ◽

SANTIAGO DE LA PEÑA

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Low Permeability ◽

Near Surface ◽

Observable Change ◽

Supraglacial Lakes ◽

Run Off ◽

Lake Formation ◽

And Storage ◽

Percolation Zone

AbstractWe examine repeat surface altimetry and radio echo observations of two supraglacial lakes in the percolation zone of the Greenland ice sheet to investigate the changes in firn conditions leading to lake formation and implications for meltwater storage within firn. Both lakes formed in 2011, when an anomalously high melt season was followed by low winter accumulation, resulting in reduced infiltration and storage in the near surface. The lakes expanded during the 2012 record melt season and retained liquid meltwater through the following winter. The lakes then contracted, with one lake slowly draining and refreezing and another rapidly draining to the subsurface. The lack of observable change in firn conditions surrounding the lakes indicates increased run-off in the near surface firn, likely along low-permeability ice layers formed during the previous melt seasons. This implies a reduced ability of the firn to absorb increased meltwater.

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Recent Precipitation Decrease Across the Western Greenland Ice Sheet Percolation Zone

10.5194/tc-2019-103 ◽

2019 ◽

Author(s):

Gabriel Lewis ◽

Erich Osterberg ◽

Robert Hawley ◽

Hans Peter Marshall ◽

Tate Meehan ◽

...

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Climate Models ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Regional Climate Models ◽

The Past ◽

Precipitation Decrease ◽

Percolation Zone

Abstract. The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is of critical interest to scientists and the general public in the context of future sea-level rise. Increased melting in the GrIS percolation zone due to atmospheric warming over the past several decades has led to increased mass loss at lower elevations. Previous studies have hypothesized that this warming is accompanied by a precipitation increase, as would be expected from the Clausius-Clapeyron relationship, negating some of the melt-induced mass loss throughout the Western GrIS. This study tests that hypothesis by calculating snow accumulation rates and trends across the Western GrIS percolation zone, providing new critical accumulation estimates in regions with sparse and/or dated in situ data for calibration of future regional climate models. We present accumulation records from sixteen 22–32 m long firn cores and 4436 km of ground penetrating-radar, covering the past 20–60 years of accumulation, collected across the Western GrIS percolation zone as part of the Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) project. Trends from both radar and firn cores, as well as commonly used regional climate models, show decreasing accumulation and precipitation over the 1996–2016 period, which we attribute to shifting storm-tracks related to stronger atmospheric summer blocking over Greenland. Changes in atmospheric circulation over the past 20 years, specifically anomalously high summertime blocking, have reduced GrIS surface mass balance through both an increase in surface melting and a decrease in accumulation.

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Changes in the firn structure of the Greenland Ice Sheet caused by recent warming

The Cryosphere Discussions ◽

10.5194/tcd-9-541-2015 ◽

2015 ◽

Vol 9 (1) ◽

pp. 541-565 ◽

Cited By ~ 1

Author(s):

S. de la Peña ◽

I. M. Howat ◽

P. W. Nienow ◽

M. R. van den Broeke ◽

E. Mosley-Thompson ◽

...

Keyword(s):

Mass Balance ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Mass Gain ◽

High Elevation ◽

Near Surface ◽

Surface Mass ◽

Ice Sheet Mass Balance ◽

Ice Content ◽

Percolation Zone

Abstract. Atmospheric warming over the Greenland Ice Sheet during the last two decades has increased the amount of surface meltwater production, resulting in the migration of melt and percolation regimes to higher altitudes and an increase in the amount of solid ice from refrozen meltwater found in the firn above the equilibrium line. Here we present observations of near-surface (0–20 m) firn conditions in western Greenland obtained from campaigns between 1998 and 2014. We find a sharp increase in firn ice content in the form of thick widespread layers in the percolation zone, which decreases the capacity of the firn to store meltwater. The estimated total annual ice content retained in the firn in areas with positive surface mass balance west of the ice divide in Greenland reached a maximum of 74 ± 25 Gt in 2012, compared to the 1958–1999 average of 13 ± 2 Gt, while the percolation zone area more than doubled between 2003 and 2012. Increased melt and column densification resulted in surface lowering averaging −0.80 ± 0.39 m yr−1 between 1800 and 2800 m in the accumulation zone of western Greenland. Since 2007, annual melt and refreezing rates in the percolation zone at elevations below 2100 m surpass the annual snowfall from the previous year, implying that mass gain in the region is now in the form of refrozen meltwater. If current melt trends over high elevation regions continue, subsequent changes in firn structure will have implications for the hydrology of the ice sheet and related abrupt seasonal densification could become increasingly significant for altimetry-derived ice sheet mass balance estimates.

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Atmospheric Blocking Drives Recent Albedo Change Across the Western Greenland Ice Sheet Percolation Zone

Geophysical Research Letters ◽

10.1029/2021gl092814 ◽

2021 ◽

Vol 48 (10) ◽

Author(s):

Gabriel Lewis ◽

Erich Osterberg ◽

Robert Hawley ◽

Hans Peter Marshall ◽

Tate Meehan ◽

...

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Atmospheric Blocking ◽

Albedo Change ◽

Percolation Zone

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Georadar-derived estimates of firn density in the percolation zone, western Greenland ice sheet

Journal of Geophysical Research Atmospheres ◽

10.1029/2011jf002089 ◽

2012 ◽

Vol 117 (F1) ◽

pp. n/a-n/a ◽

Cited By ~ 17

Author(s):

Joel Brown ◽

John Bradford ◽

Joel Harper ◽

W. Tad Pfeffer ◽

Neil Humphrey ◽

...

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Percolation Zone

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Recent precipitation decrease across the western Greenland ice sheet percolation zone

The Cryosphere ◽

10.5194/tc-13-2797-2019 ◽

2019 ◽

Vol 13 (11) ◽

pp. 2797-2815 ◽

Cited By ~ 4

Author(s):

Gabriel Lewis ◽

Erich Osterberg ◽

Robert Hawley ◽

Hans Peter Marshall ◽

Tate Meehan ◽

...

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Accumulation Rate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Snow Accumulation ◽

Accumulation Rates ◽

The Past ◽

Precipitation Decrease ◽

Percolation Zone

Abstract. The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is of critical interest in the context of future sea level rise. Increased melting in the GrIS percolation zone due to atmospheric warming over the past several decades has led to increased mass loss at lower elevations. Previous studies have hypothesized that this warming is accompanied by a precipitation increase, as would be expected from the Clausius–Clapeyron relationship, compensating for some of the melt-induced mass loss throughout the western GrIS. This study tests that hypothesis by calculating snow accumulation rates and trends across the western GrIS percolation zone, providing new accumulation rate estimates in regions with sparse in situ data or data that do not span the recent accelerating surface melt. We present accumulation records from sixteen 22–32 m long firn cores and 4436 km of ground-penetrating radar, covering the past 20–60 years of accumulation, collected across the western GrIS percolation zone as part of the Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) project. Trends from both radar and firn cores, as well as commonly used regional climate models, show decreasing accumulation rates of 2.4±1.5 % a−1 over the 1996–2016 period, which we attribute to shifting storm tracks related to stronger atmospheric summer blocking over Greenland. Changes in atmospheric circulation over the past 20 years, specifically anomalously strong summertime blocking, have reduced GrIS surface mass balance through both an increase in surface melting and a decrease in accumulation rates.

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