Short-term variability in Greenland Ice Sheet motion forced by time-varying meltwater drainage: Implications for the relationship between subglacial drainage system behavior and ice velocity

Recent efforts have been made to increase our understanding of the dynamics of ice-sheet hydrology. Notably, much work has focused on the southwest sector of the Greenland ice sheet (GrIS), with intense data collection on diurnal to interannual timescales (e.g. Bartholomew and others, 2012; Cowton and others, 2013; Doyle and others, 2013). Observations show a close correlation between surface meltwater production and the seasonal ice-sheet acceleration, and it is a well-accepted hypothesis that an increase in the former drives the latter via meltwater transfer through the subglacial drainage system (e.g. Zwally and others, 2002). However, due to the remote nature and complexity of the subglacial domain, a satisfactory description at the process level has remained elusive. Better understanding of the coupling of meltwater forcing on ice velocity through the subglacial component is therefore necessary to improve the physical integrity of ice-sheet models.

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Evolution of the subglacial drainage system beneath the Greenland Ice Sheet revealed by tracers

Nature Geoscience ◽

10.1038/ngeo1737 ◽

2013 ◽

Vol 6 (3) ◽

pp. 195-198 ◽

Cited By ~ 145

Author(s):

D. M. Chandler ◽

J. L. Wadham ◽

G. P. Lis ◽

T. Cowton ◽

A. Sole ◽

...

Keyword(s):

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

Subglacial Drainage

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High-resolution modelling of the seasonal evolution of surface water storage on the Greenland Ice Sheet

The Cryosphere Discussions ◽

10.5194/tcd-7-6143-2013 ◽

2013 ◽

Vol 7 (6) ◽

pp. 6143-6170 ◽

Cited By ~ 1

Author(s):

N. S. Arnold ◽

A. F. Banwell ◽

I. C. Willis

Keyword(s):

Surface Water ◽

High Resolution ◽

Water Storage ◽

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

Water Volume ◽

Seasonal Evolution ◽

Surface Water Storage ◽

Subglacial Drainage

Abstract. Seasonal meltwater lakes on the Greenland Ice Sheet form when surface runoff is temporarily trapped in surface topographic depressions. The development of such lakes affects both the surface energy balance and dynamics of the ice sheet. Although areal extents, depths, and lifespans of lakes can be inferred from satellite imagery, such observational studies have a limited temporal resolution. Here, we adopt a modelling-based strategy to estimate the seasonal evolution of surface water storage for the ~ 3600 km2 Paakitsoq region of W. Greenland. We use a high-resolution time dependent surface mass balance model to calculate surface melt, a supraglacial water routing model to calculate lake filling and a prescribed water-volume based threshold to predict lake drainage events. The model shows good agreement between modelled lake locations and volumes and those observed in 9 Landsat 7 ETM+ images from 2001, 2002 and 2005. We use the model to investigate the lake water volume required to trigger drainage, and the impact that this threshold volume has on the proportion of meltwater that runs off the ice supraglacially, is stored in surface lakes, or enters the subglacial drainage system. Model performance is maximised with prescribed lake volume thresholds between 4000 and 7500 times the local ice thickness. For these thresholds, lakes transiently store < 40% of meltwater at the beginning of the melt season, decreasing to ~ 5 to 10% by the middle of the melt season. 40 to 50% of meltwater runs off the ice surface directly, and the remainder enters the subglacial drainage system through moulins at the bottom of drained lakes.

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The meltwater feedbacks on ice dynamics, influence of melt amplitude, duration and extent.

10.5194/egusphere-egu21-1099 ◽

2021 ◽

Author(s):

Basile de Fleurian ◽

Petra M. Langebroeke ◽

Richard Davy

Keyword(s):

Water Pressure ◽

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

System Model ◽

Ice Dynamics ◽

Mountain Glaciers ◽

Different Characteristics ◽

Crucial Parameter ◽

Subglacial Drainage

In recent years, temperatures over the Greenland ice sheet have been rising, leading to an increase in surface melt. This increase however can not be reduced to a simple number. Throughout the recent years we have seen some extreme melt seasons with melt extending over the whole surface of the ice sheet (2012) or melt seasons of lower amplitudes but with a longer duration (2010). The effect of those variations on the subglacial system and hence on ice dynamic are poorly understood and are still mainly deduced from studies based on mountain glaciers.Here we apply the Ice-sheet and Sea-level System Model (ISSM) to a synthetic glacier with a geometry similar to a Greenland ice sheet land terminating glacier. The forcing is designed such that it allows to investigate different characteristics of the melt season: its length, intensity or the spatial extension of the melt. Subglacial hydrology and ice dynamics are coupled within ISSM is coupled to a subglacial hydrology model, allowing to study the response of the system in terms of subglacial water pressure and the final impact on ice dynamics. Of particular interest is the evolution of the distribution of the efficient and inefficient component of the subglacial drainage system which directly impacts the water pressure evolution at the base of the glacier.We note that the initiation of the melt season and the intensity of the melt at this period is a crucial parameter when studying the dynamic response of the glacier to different melt season characteristics. From those results, we can infer a more precise evolution of the dynamics of land terminating glaciers that are heavily driven by their subglacial drainage system. We also highlight which changes in the melt season pattern would be the most damageable for glacier stability in the future.

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Seasonal Variations in the Flow of Land-Terminating Glaciers in Central-West Greenland Using Sentinel-1 Imagery

Remote Sensing ◽

10.3390/rs10121878 ◽

2018 ◽

Vol 10 (12) ◽

pp. 1878 ◽

Cited By ~ 2

Author(s):

Adriano Lemos ◽

Andrew Shepherd ◽

Malcolm McMillan ◽

Anna Hogg

Keyword(s):

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

Sheet Flow ◽

Altitudinal Variation ◽

Weekly Basis ◽

Ice Flow ◽

Temporal Sampling ◽

First Time ◽

Subglacial Drainage

Land-terminating sectors of the Greenland ice sheet flow faster in summer after surface meltwater reaches the subglacial drainage system. Speedup occurs when the subglacial drainage system becomes saturated, leading to a reduction in the effective pressure which promotes sliding of the overlying ice. Here, we use observations acquired by the Sentinel-1a and b synthetic aperture radar to track changes in the speed of land-terminating glaciers across a 14,000 km2 sector of west-central Greenland on a weekly basis in 2016 and 2017. The fine spatial and temporal sampling of the satellite data allows us to map the speed of summer and winter across the entire sector and to resolve the weekly evolution of ice flow across the downstream portions of five glaciers. Near to the ice sheet margin (at 650 m.a.s.l.), glacier speedup begins around day 130, persisting for around 90 days, and then peaks around day 150. At four of the five glaciers included in our survey the peak speedup is similar in both years, in Russell Glacier there is marked interannual variability of 32% between 2016 and 2017. We present, for the first time, seasonal and altitudinal variation in speedup persistence. Our study demonstrates the value of Sentinel-1’s systematic and frequent acquisition plan for studying seasonal changes in ice sheet flow.

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The annual glaciohydrology cycle in the ablation zone of the Greenland ice sheet: Part 1. Hydrology model

Journal of Glaciology ◽

10.3189/002214311797409668 ◽

2011 ◽

Vol 57 (204) ◽

pp. 697-709 ◽

Cited By ~ 38

Author(s):

William Colgan ◽

Harihar Rajaram ◽

Robert Anderson ◽

Konrad Steffen ◽

Thomas Phillips ◽

...

Keyword(s):

Residence Time ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Hydraulic Head ◽

Ablation Zone ◽

Hydrology Model ◽

Hydrologic System ◽

Speed Up ◽

Ice Velocity ◽

Subglacial Drainage

AbstractWe apply a novel one-dimensional glacier hydrology model that calculates hydraulic head to the tidewater-terminating Sermeq Avannarleq flowline of the Greenland ice sheet. Within a plausible parameter space, the model achieves a quasi-steady-state annual cycle in which hydraulic head oscillates close to flotation throughout the ablation zone. Flotation is briefly achieved during the summer melt season along a ∼17 km stretch of the ∼50 km of flowline within the ablation zone. Beneath the majority of the flowline, subglacial conduit storage ‘closes’ (i.e. obtains minimum radius) during the winter and ‘opens’ (i.e. obtains maximum radius) during the summer. Along certain stretches of the flowline, the model predicts that subglacial conduit storage remains open throughout the year. A calculated mean glacier water residence time of ∼2.2 years implies that significant amounts of water are stored in the glacier throughout the year. We interpret this residence time as being indicative of the timescale over which the glacier hydrologic system is capable of adjusting to external surface meltwater forcings. Based on in situ ice velocity observations, we suggest that the summer speed-up event generally corresponds to conditions of increasing hydraulic head during inefficient subglacial drainage. Conversely, the slowdown during fall generally corresponds to conditions of decreasing hydraulic head during efficient subglacial drainage.

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High-resolution modelling of the seasonal evolution of surface water storage on the Greenland Ice Sheet

The Cryosphere ◽

10.5194/tc-8-1149-2014 ◽

2014 ◽

Vol 8 (4) ◽

pp. 1149-1160 ◽

Cited By ~ 32

Author(s):

N. S. Arnold ◽

A. F. Banwell ◽

I. C. Willis

Keyword(s):

Surface Water ◽

High Resolution ◽

Water Storage ◽

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

Water Volume ◽

Seasonal Evolution ◽

Surface Water Storage ◽

Subglacial Drainage

Abstract. Seasonal meltwater lakes on the Greenland Ice Sheet form when surface runoff is temporarily trapped in surface topographic depressions. The development of such lakes affects both the surface energy balance and dynamics of the ice sheet. Although areal extents, depths and lifespan of lakes can be inferred from satellite imagery, such observational studies have a limited temporal resolution. Here, we adopt a modelling-based strategy to estimate the seasonal evolution of surface water storage for the ~ 3600 km2 Paakitsoq region of W. Greenland. We use a high-resolution time-dependent surface mass balance model to calculate surface melt, a supraglacial water routing model to calculate lake filling and a prescribed water-volume-based threshold to predict rapid lake drainage events. This threshold assumes that drainage will occur through a fracture if V = Fa ⋅ H, where V is lake volume, H is the local ice thickness and Fa is the potential fracture area. The model shows good agreement between modelled lake locations and volumes and those observed in nine Landsat 7 ETM images from 2001, 2002 and 2005. We use the model to investigate the lake water volume required to trigger drainage, and the impact that varying this threshold volume has on the proportion of meltwater that is stored in surface lakes and enters the subglacial drainage system. Model performance is maximised with values of Fa between 4000 and 7500 m2. For these thresholds, lakes transiently store < 40% of available meltwater at the beginning of the melt season, decreasing to ~ 5 to 10% by the middle of the melt season; over the course of a melt season, 40 to 50% of total meltwater production enters the subglacial drainage system through moulins at the bottom of drained lakes.

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The Short-term Mass Change of Greenland Ice Sheet and the Atmospheric Forcing

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/660/1/012091 ◽

2021 ◽

Vol 660 (1) ◽

pp. 012091

Author(s):

Zhenran Peng ◽

Linsong Wang ◽

Chao Chen

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Mass Change ◽

Atmospheric Forcing ◽

Short Term

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Hydraulic transmissivity inferred from ice-sheet relaxation following Greenland supraglacial lake drainages

Nature Communications ◽

10.1038/s41467-021-24186-6 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Ching-Yao Lai ◽

Laura A. Stevens ◽

Danielle L. Chase ◽

Timothy T. Creyts ◽

Mark D. Behn ◽

...

Keyword(s):

Laboratory Experiments ◽

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

Field Observations ◽

Surface Uplift ◽

Drainage Networks ◽

Order Of Magnitude ◽

Lake Drainage ◽

Magnitude Increase

AbstractSurface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye and gas-tracing studies conducted in the western margin sector of the ice sheet have directly observed drainage efficiency to evolve seasonally along the drainage pathway. However, the local evolution of drainage systems further inland, where ice thicknesses exceed 1000 m, remains largely unknown. Here, we infer drainage system transmissivity based on surface uplift relaxation following rapid lake drainage events. Combining field observations of five lake drainage events with a mathematical model and laboratory experiments, we show that the surface uplift decreases exponentially with time, as the water in the blister formed beneath the drained lake permeates through the subglacial drainage system. This deflation obeys a universal relaxation law with a timescale that reveals hydraulic transmissivity and indicates a two-order-of-magnitude increase in subglacial transmissivity (from 0.8 ± 0.3 $${\rm{m}}{{\rm{m}}}^{3}$$ m m 3 to 215 ± 90.2 $${\rm{m}}{{\rm{m}}}^{3}$$ m m 3 ) as the melt season progresses, suggesting significant changes in basal hydrology beneath the lakes driven by seasonal meltwater input.

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Seasonal variability in the dynamics of marine-terminating outlet glaciers in Greenland

Journal of Glaciology ◽

10.3189/002214310793146232 ◽

2010 ◽

Vol 56 (198) ◽

pp. 601-613 ◽

Cited By ~ 148

Author(s):

Ian M. Howat ◽

Jason E. Box ◽

Yushin Ahn ◽

Adam Herrington ◽

Ellyn M. McFadden

Keyword(s):

Ice Sheet ◽

Drainage System ◽

Surface Air Temperature ◽

Greenland Ice Sheet ◽

Flow Speed ◽

High Temporal Resolution ◽

Sea Ice Concentration ◽

Seasonal Behavior ◽

Near Surface ◽

Front Position

AbstractRecent studies indicate that the dynamics of fast-flowing, marine-terminating outlet glaciers of the Greenland ice sheet may be sensitive to climate and ocean forcing on sub-annual timescales. Observations of seasonal behavior of these glaciers at such high temporal resolution, however, are currently few. Here we present observations of front position, flow speed, near-surface air temperature and ocean conditions for six large marine-terminating glaciers in the Uummannaq region of West Greenland, to investigate controls on short-term glacier dynamics. As proposed by other studies, we find that seasonal front advance and retreat correlates with the formation and disappearance of an ice melange. Our data suggest that high sea-surface temperature, anomalously low sea-ice concentration and reduced melange formation in early 2003 have triggered multi-year retreat of several glaciers in the study area, which is consistent with other regions in Greenland. Of the stable glaciers, only Rink Isbræ exhibits a seasonal speed variation that correlates with variations in front position, with the others undergoing mid-summer deceleration that indicates the effects of subglacial meltwater discharge and drainage system evolution. Drainage of supraglacial lakes and water-filled crevasses results in substantial decreases in speed (40–60%) on fast-flowing glaciers. Our results demonstrate that attempts to model ice-sheet evolution must take into account short-timescale flow dynamics resulting from drainage events and oceanographic conditions.

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