Oscillatory subglacial drainage in the absence of surface melt

Schoof, Christian; Rada, Camilo; Wilson, Nat; Flowers, G. E.; Haseloff, Marianne

doi:10.5194/tc-8-959-2014

Cited by 46 publications

(105 citation statements)

References 58 publications

(77 reference statements)

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“…Borehole data from Schoof et al (2014) demonstrate that transient pressure oscillations occurred during the winter in a glacier in the Yukon Territory of Canada. These were driven by low water flux rates in a constricted system.…”

Section: Pressure Wavesmentioning

confidence: 99%

“…The oscillations lasted over a period of days, as opposed to years as seen in our model of Antarctic ice streams. Schoof et al (2014) modeled this system on an idealized flowline and demonstrated that storage of water is an important control on the timing of internally driven oscillations. Given the significant differences between a mountain glacier and an Antarctic ice stream it is not surprising that system oscillations would occur at different periodicities.…”

Section: Pressure Wavesmentioning

confidence: 99%

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Modeling Antarctic subglacial lake filling and drainage cycles

et al. 2016

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Abstract. The growth and drainage of active subglacial lakes in Antarctica has previously been inferred from analysis of ice surface altimetry data. We use a subglacial hydrology model applied to a synthetic Antarctic ice stream to examine internal controls on the filling and drainage of subglacial lakes. Our model outputs suggest that the highly constricted subglacial environment of our idealized ice stream, combined with relatively high rates of water flow funneled from a large catchment, can combine to create a system exhibiting slow-moving pressure waves. Over a period of years, the accumulation of water in the ice stream onset region results in a buildup of pressure creating temporary channels, which then evacuate the excess water. This increased flux of water beneath the ice stream drives lake growth. As the water body builds up, it steepens the hydraulic gradient out of the overdeepened lake basin and allows greater flux. Eventually this flux is large enough to melt channels that cause the lake to drain. Lake drainage also depends on the internal hydrological development in the wider system and therefore does not directly correspond to a particular water volume or depth. This creates a highly temporally and spatially variable system, which is of interest for assessing the importance of subglacial lakes in ice stream hydrology and dynamics.

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Section: Pressure Wavesmentioning

confidence: 99%

Section: Pressure Wavesmentioning

confidence: 99%

Modeling Antarctic subglacial lake filling and drainage cycles

et al. 2016

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“…Similar to the study by Bougamont et al (2014), modelled velocities do not capture this behaviour. These velocity events may be the result of internal dynamics of water stored over winter (Schoof et al, 2014), such as flooding events, that the subglacial hydrology model does not capture or early season melt which RACMO2.3 does not predict.…”

Section: Model Fitmentioning

confidence: 99%

Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet

Koziol

Arnold²

2018

The Cryosphere

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Abstract. Surface runoff at the margin of the Greenland Ice Sheet (GrIS) drains to the ice-sheet bed, leading to enhanced summer ice flow. Ice velocities show a pattern of early summer acceleration followed by mid-summer deceleration due to evolution of the subglacial hydrology system in response to meltwater forcing. Modelling the integrated hydrologicalice dynamics system to reproduce measured velocities at the ice margin remains a key challenge for validating the present understanding of the system and constraining the impact of increasing surface runoff rates on dynamic ice mass loss from the GrIS. Here we show that a multi-component model incorporating supraglacial, subglacial, and ice dynamic components applied to a land-terminating catchment in western Greenland produces modelled velocities which are in reasonable agreement with those observed in GPS records for three melt seasons of varying melt intensities. This provides numerical support for the hypothesis that the subglacial system develops analogously to alpine glaciers and supports recent model formulations capturing the transition between distributed and channelized states. The model shows the growth of efficient conduit-based drainage up-glacier from the ice sheet margin, which develops more extensively, and further inland, as melt intensity increases. This suggests current trends of decadal-timescale slowdown of ice velocities in the ablation zone may continue in the near future. The model results also show a strong scaling between average summer velocities and melt season intensity, particularly in the upper ablation area. Assuming winter velocities are not impacted by channelization, our model suggests an upper bound of a 25 % increase in annual surface velocities as surface melt increases to 4× present levels.

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“…Dampening by one order of magnitude of the anti-correlated response is observed from water pressure in boreholes in the Greenland ice sheet (Meierbachtol et al, 2013;Andrews et al, 2014) and alpine glaciers (Gordon et al, 1998;Schoof et al, 2014), although the difference in amplitude is sometimes small (Murray and Clarke, 1995;Dow et al, 2011). Capturing the spatial variation of this dampening can help to identify the origin of the anti-correlation and whether it is a response caused by ice dynamics or, as observed here, by the hydrological system.…”

Section: Discussionmentioning

confidence: 91%

Stress Redistribution Explains Anti-correlated Subglacial Pressure Variations

et al. 2018

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We used a finite element model to interpret anti-correlated pressure variations at the base of a glacier to demonstrate the importance of stress redistribution in the basal ice. We first investigated two pairs of load cells installed 20 m apart at the base of the 210 m thick Engabreen glacier in Northern Norway. The load cell data for July 2003 showed that pressurisation of a subglacial channel located over one load cell pair led to anti-correlation in pressure between the two pairs. To investigate the cause of this anti-correlation, we used a full Stokes 3D model of a 210 m thick and 25-200 m wide glacier with a pressurised subglacial channel represented as a pressure boundary condition. The model reproduced the anti-correlated pressure response at the glacier bed and variations in pressure of the same order of magnitude as the load cell observations. The anti-correlation pattern was shown to depend on the bed/surface slope. On a flat bed with laterally constrained cross-section, the resulting bridging effect diverted some of the normal forces acting on the bed to the sides. The anti-correlated pressure variations were then reproduced at a distance >10-20 m from the channel. In contrast, when the bed was inclined, the channel support of the overlying ice was vertical only, causing a reduction of the normal stress on the bed. With a bed slope of 5 degrees, the anti-correlation occurred within 10 m of the channel. The model thus showed that the effect of stress redistribution can lead to an opposite response in pressure at the same distance from the channel and that anti-correlation in pressure is reproduced without invoking cavity expansion caused by sliding.

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Oscillatory subglacial drainage in the absence of surface melt

Cited by 46 publications

References 58 publications

Modeling Antarctic subglacial lake filling and drainage cycles

Modeling Antarctic subglacial lake filling and drainage cycles

Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet

Stress Redistribution Explains Anti-correlated Subglacial Pressure Variations

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