Melt-induced speed-up of Greenland ice sheet offset by efficient 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.

Download Full-text

The effect of the north-east ice stream on the Greenland ice sheet in changing climates

The Cryosphere Discussions ◽

10.5194/tcd-1-41-2007 ◽

2007 ◽

Vol 1 (1) ◽

pp. 41-76 ◽

Cited By ~ 10

Author(s):

R. Greve ◽

S. Otsu

Keyword(s):

Large Scale ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Simulation Code ◽

North East ◽

The North ◽

Ice Stream ◽

Basal Sliding ◽

Speed Up ◽

Fast Flow

Abstract. The north-east Greenland ice stream (NEGIS) was discovered as a large fast-flow feature of the Greenland ice sheet by synthetic aperture radar (SAR) imaginary of the ERS-1 satellite. In this study, the NEGIS is implemented in the dynamic/thermodynamic, large-scale ice-sheet model SICOPOLIS (Simulation Code for POLythermal Ice Sheets). In the first step, we simulate the evolution of the ice sheet on a 10-km grid for the period from 250 ka ago until today, driven by a climatology reconstructed from a combination of present-day observations and GCM results for the past. We assume that the NEGIS area is characterized by enhanced basal sliding compared to the "normal", slowly-flowing areas of the ice sheet, and find that the misfit between simulated and observed ice thicknesses and surface velocities is minimized for a sliding enhancement by the factor three. In the second step, the consequences of the NEGIS, and also of surface-meltwater-induced acceleration of basal sliding, for the possible decay of the Greenland ice sheet in future warming climates are investigated. It is demonstrated that the ice sheet is generally very susceptible to global warming on time-scales of centuries and that surface-meltwater-induced acceleration of basal sliding can speed up the decay significantly, whereas the NEGIS is not likely to dynamically destabilize the ice sheet as a whole.

Download Full-text

Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

The Cryosphere ◽

10.5194/tc-7-1721-2013 ◽

2013 ◽

Vol 7 (6) ◽

pp. 1721-1740 ◽

Cited By ~ 62

Author(s):

S. J. Livingstone ◽

C. D. Clark ◽

J. Woodward ◽

J. Kingslake

Keyword(s):

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Simplified Approach ◽

Subglacial Lake ◽

Ice Stream ◽

Geophysical Surveys ◽

Subglacial Lakes ◽

The Antarctic ◽

Subglacial Drainage

Abstract. We use the Shreve hydraulic potential equation as a simplified approach to investigate potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. We validate the method by demonstrating its ability to recall the locations of >60% of the known subglacial lakes beneath the Antarctic Ice Sheet. This is despite uncertainty in the ice-sheet bed elevation and our simplified modelling approach. However, we predict many more lakes than are observed. Hence we suggest that thousands of subglacial lakes remain to be found. Applying our technique to the Greenland Ice Sheet, where very few subglacial lakes have so far been observed, recalls 1607 potential lake locations, covering 1.2% of the bed. Our results will therefore provide suitable targets for geophysical surveys aimed at identifying lakes beneath Greenland. We also apply the technique to modelled past ice-sheet configurations and find that during deglaciation both ice sheets likely had more subglacial lakes at their beds. These lakes, inherited from past ice-sheet configurations, would not form under current surface conditions, but are able to persist, suggesting a retreating ice-sheet will have many more subglacial lakes than advancing ones. We also investigate subglacial drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are suggested to have been susceptible to subglacial drainage switching. We discuss how our results impact our understanding of meltwater drainage, basal lubrication and ice-stream formation.

Download Full-text

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

Download Full-text

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.

Download Full-text

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.

Download Full-text

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.

Download Full-text

Greenland flow variability from ice-sheet-wide velocity mapping

Journal of Glaciology ◽

10.3189/002214310792447734 ◽

2010 ◽

Vol 56 (197) ◽

pp. 415-430 ◽

Cited By ~ 414

Author(s):

Ian Joughin ◽

Ben E. Smith ◽

Ian M. Howat ◽

Ted Scambos ◽

Twila Moon

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Radar Data ◽

Synthetic Aperture ◽

Velocity Mapping ◽

Outlet Glacier ◽

Synthetic Aperture Radar Data ◽

Bedrock Topography ◽

Speed Up ◽

Glacier Flow

AbstractUsing RADARSAT synthetic aperture radar data, we have mapped the flow velocity over much of the Greenland ice sheet for the winters of 2000/01 and 2005/06. These maps provide a detailed view of the ice-sheet flow, including that of the hundreds of glaciers draining the interior. The focused patterns of flow at the coast suggest a strong influence of bedrock topography. Differences between our two maps confirm numerous early observations of accelerated outlet glacier flow as well as revealing previously unrecognized changes. The overall pattern is one of speed-up accompanied by terminus retreat, but there are also several instances of surge behavior and a few cases of glacier slowdown. Comprehensive mappings such as these, at regular intervals, provide an important new observational capability for understanding ice-sheet variability.

Download Full-text

Correspondence

Journal of Glaciology ◽

10.3189/2015jog14j197 ◽

2015 ◽

Vol 61 (225) ◽

pp. 202-204 ◽

Cited By ~ 1

Author(s):

Christian Helanow ◽

Toby Meierbachtol ◽

Peter Jansson

Keyword(s):

Data Collection ◽

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

Close Correlation ◽

Satisfactory Description ◽

Physical Integrity ◽

Ice Velocity ◽

Process Level ◽

Subglacial Drainage

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.

Download Full-text