Greenland ice sheet annual motion insensitive to spatial variations in subglacial hydraulic structure

Tedstone, Andrew; Nienow, Peter; Gourmelen, Noël; Sole, Andrew

doi:10.1002/2014gl062386

Cited by 26 publications

(37 citation statements)

References 35 publications

(53 reference statements)

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“…There is observational and modelling evidence to suggest that, at least in the ablation area of western Greenland, this is indeed the case. Firstly, GPS observations along transects parallel and transverse to ice flow show that the patterns of short-term speedup in response to runoff variations were strikingly similar up to at least ∼75 km from the margin (∼1,500 m a.s.l, ∼1,200 m ice thickness; Bartholomew et al, 2011a) and extend at least 2.8 km transverse to an inferred subglacial channel (Tedstone et al, 2014). Secondly, Hewitt (2011) suggested a theoretical subglacial channel spacing of ∼2-15 km depending on the permeability of the substrate-similar to the spacing of Canadian eskers, which are interpreted as relict subglacial drainage pathways (Storrar et al, 2014).…”

Section: Ice Flow Modulation By the Connected Drainage Systemmentioning

confidence: 97%

“…In addition, across-flow transects of ice velocity (Bingham et al, 2006;Tedstone et al, 2014) and borehole water pressure (Hubbard et al, 1995;Fudge et al, 2008), and modelling (e.g., Schoof, 2010;McGrath et al, 2011), suggest that sufficiently large or rapid pulses of runoff can cause transient spikes in channel water pressure of sufficient magnitude to reverse the hydraulic gradient between channels and the surrounding inefficient drainage system. The pressure gradient reversal could force water out of the channel into the adjacent inefficient drainage system across a "variable pressure axis" (Hubbard et al, 1995;Nienow et al, 2005;Tedstone et al, 2014). The inefficient system in the variable pressure axis is envisioned to take the form of one or a combination of linked cavities and films, where sediment cover is thin or absent, or Darcian flow and canals, where sediment cover is both thick and pervasive (e.g., Stone and Clarke, 1993;Kyrke-Smith and Fowler, 2014).…”

Section: Spatial Variations In Subglacial Hydrological Structurementioning

confidence: 99%

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The Influence of Hydrology on the Dynamics of Land-Terminating Sectors of the Greenland Ice Sheet

et al. 2019

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Coupling between runoff, hydrology, basal motion, and mass loss ("hydrology-dynamics") is a critical component of the Greenland Ice Sheet system. Despite considerable research effort, the mechanisms by which runoff influences ice dynamics and the net long-term (decadal and longer) dynamical effect of variations in the timing and magnitude of runoff delivery to the bed remain a subject of debate. We synthesise key research into land-terminating ice sheet hydrology-dynamics, in order to reconcile several apparent contradictions that have recently arisen as understanding of the topic has developed. We suggest that meltwater interaction with subglacial channels, cavities, and deforming subglacial sediment modulates ice flow variability. Increasing surface runoff supply to the bed induces cavity expansion and sediment deformation, leading to early-melt season ice flow acceleration. In the ablation area, drainage of water at times of low runoff from high-pressure subglacial environments toward more efficient drainage pathways is thought to result in reductions in water pressure, ice-bed separation and sediment deformation, causing net slowdown on annual to decadal timescales (ice flow self-regulation), despite increasing surface melt. Further inland, thicker ice, small surface gradients and reduced runoff suppress efficient drainage development, and a small net increase in both summer and winter ice flow is observed. Predicting ice motion across land-terminating sectors of the ice sheet over the twenty-first century is confounded by inadequate understanding of the processes and feedbacks between runoff and subglacial motion. However, if runoff supply increases, we suggest that ice flow in marginal regions will continue to decrease on annual and longer timescales, principally due to (i) increasing drainage system efficiency in marginal areas, (ii) progressive depression of basal water pressure, and (iii) thinning-induced lowering of driving stresses. At higher elevations, we suggest that minor year-on-year ice flow acceleration will continue and extend further into the interior where self-regulation mechanisms cannot operate and if surface-to-bed meltwater connections form. Based on current understanding, we expect that ice flow deceleration due to the seasonal development of efficient drainage beneath the land-terminating margins of the Greenland Ice Sheet will continue to regulate its future mass loss.

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Section: Ice Flow Modulation By the Connected Drainage Systemmentioning

confidence: 97%

Section: Spatial Variations In Subglacial Hydrological Structurementioning

confidence: 99%

The Influence of Hydrology on the Dynamics of Land-Terminating Sectors of the Greenland Ice Sheet

et al. 2019

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“…In other words, equation (4) represents situations where the water pressure field mimics the ice thickness field or some spatially invariant fraction thereof. Equation (4) has been applied to Greenland at the basin scale [e.g., Tedstone et al, 2014;Lindbäck et al, 2015] and the ice sheet scale [Lewis and Smith, 2009;Liston and Mernild, 2012;Livingstone et al, 2013] to delineate drainage basins and associated sediment and water fluxes. Adjustment of water pressure has been found to strongly impact the computed potential gradients [Lindbäck et al, 2015].…”

Section: Gradients Of Water Pressure and Hydraulic Potentialmentioning

confidence: 99%

Measured basal water pressure variability of the western Greenland Ice Sheet: Implications for hydraulic potential

et al. 2016

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The gradient of the hydraulic potential field at the ice‐bedrock interface beneath the Greenland Ice Sheet (GrIS) dictates the routing and energetics of subglacial water, thereby influencing drainage system characteristics and sliding dynamics. In the ablation zone of the GrIS, variable water pressure due to an active subglacial drainage system and basal topography with high relief potentially interact to drive unknown spatial patterns and temporal changes in the hydraulic potential field. Here we present a suite of water pressure measurements collected in 13 boreholes along a 46 km transect on the western GrIS to investigate the role of spatial and temporal basal water pressure adjustments in hydraulic potential gradient dynamics. All borehole sites show pressures with similar seasonality, having relatively steady and high values during winter, variable and irregular behavior during spring and fall, and diurnal cycles that can persist for multiple weeks during the peak melt season. Despite much higher variability during the melt season, the median pressure of the summer period is nearly the same as the median pressure of the winter period. However, time variability of water pressure due to basal drainage processes can force changes in the magnitude and orientation of the hydraulic potential field over diurnal periods. We find that the basal water pressure across the transect generally mimics the ice thickness field but with superimposed large pressure gradients that develop at shorter scales within the basal drainage system. This leads to a complex hydraulic potential field across regions of similar ice thickness.

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“…Three 20 m resolution ice tongue velocity maps were created based on conventional feature tracking applied to TerraSAR-X imagery (Tedstone et al, 2014) Figure 1A), the date of our first DEM, was estimated assuming a linear trend in velocity between the velocity maps from 12-23 February to 8-19 April, and ranges from 28.5 to 30.5 m d −1 over the ice tongue. The last available velocity map was from 30 April to 11 May Frontiers in Earth Science | www.frontiersin.org …”

Section: Dem and Ice Velocity Data Generationmentioning

confidence: 99%

Estimating Spring Terminus Submarine Melt Rates at a Greenlandic Tidewater Glacier Using Satellite Imagery

et al. 2017

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Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at tidewater glaciers, with submarine melting proposed as a potential trigger of increased glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia (KNS) at the head of Kangersuneq Fjord (KF), southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models (DEMs), in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d −1 near the glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d −1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates (SMRs) at tidewater glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.

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Greenland ice sheet annual motion insensitive to spatial variations in subglacial hydraulic structure

Cited by 26 publications

References 35 publications

The Influence of Hydrology on the Dynamics of Land-Terminating Sectors of the Greenland Ice Sheet

The Influence of Hydrology on the Dynamics of Land-Terminating Sectors of the Greenland Ice Sheet

Measured basal water pressure variability of the western Greenland Ice Sheet: Implications for hydraulic potential

Estimating Spring Terminus Submarine Melt Rates at a Greenlandic Tidewater Glacier Using Satellite Imagery

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