Basal sliding of Ice Stream B, West Antarctica

Krogmeier

et al. 2017

Sci Rep

Marine geological data show that the West Antarctic Ice Sheet (WAIS) advanced to the eastern Ross Sea shelf edge during the Last Glacial Maximum (LGM) and eventually retreated ~1000 km to the current grounding-line position on the inner shelf. During the early deglacial, the WAIS deposited a voluminous stack of overlapping grounding zone wedges (GZWs) on the outer shelf of the Whales Deep Basin. The large sediment volume of the GZW cluster suggests that the grounding-line position of the paleo-Bindschadler Ice Stream was relatively stationary for a significant time interval. We used an upper bound estimate of paleo-sediment flux to investigate the lower bound duration over which the ice stream would have deposited sediment to account for the GZW volume. Our calculations show that the cluster represents more than three millennia of ice-stream sedimentation. This long duration grounding was probably facilitated by rapid GZW growth. The subsequent punctuated large-distance (~200 km) grounding-line retreat may have been a highly non-linear ice sheet response to relatively continuous external forcing such as gradual climate warming or sea-level rise. These findings indicate that reliable predictions of future WAIS retreat may require incorporation of realistic calculations of sediment erosion, transport and deposition.

Section: Discussionmentioning

confidence: 99%

The paradox of a long grounding during West Antarctic Ice Sheet retreat in Ross Sea

Krogmeier

et al. 2017

Sci Rep

“…Ice streams flow fast despite their relatively flat surface slopes due to slip at the ice–bed interface, which occurs by regelation or enhanced plastic creep (Cuffey and Paterson, 2010), or through pervasive deformation of the underlying till (Engelhardt and others, 1990; Kamb, 1991; Hermann and Barclay, 1998; Tulaczyk and others, 2000, 2001; Bindschadler and others, 2001; Cuffey and Paterson, 2010; Zoet and Iverson, 2018). The processes by which ice stream slip occurs are influenced by a complex interaction of factors including basal topography, subglacial drainage networks, water pressure, debris entrained in basal ice, substrate material properties, overburden pressure, driving stress and heat flow.…”

Section: Introductionmentioning

confidence: 99%

Basal seismicity of the Northeast Greenland Ice Stream

2020

Seismic studies of glaciers yield insights into spatio-temporal processes within and beneath glaciers on scales relevant to flow and deformation of the ice. These methods enable direct monitoring of the bed in ways that complement other geophysical techniques, such as geodetic or ground penetrating radar observations. In this work, we report on the analysis of passive seismic data collected from the interior of the North East Greenland Ice Stream, the Greenland ice sheet's largest outlet glacier. We record thousands of basal earthquakes, many of which repeat with nearly identical waveforms. We also record many long-duration glacial tremor episodes that migrate across the seismic network with slow velocities (e.g. ~4–12 m s−1). Analysis of the basal earthquakes indicates a transition between times of individual event activity and times of tremor activity. We suggest that both processes are produced by shear slip at localized asperities along the bed. The transition between discrete and quasi-continuous slipping modes may be driven by pore-water pressure transients or heterogeneous strain accumulation in the ice due to strength contrasts of the underlying till.

“…Since the flow of many ice streams in Antarctica is known to be associated with rapid sliding [31,32], with faster shearing due to lower ice viscosity a minor contributor to ice discharge, a legitimate question is whether the dissipation of heat can cause patterning even if we treat ice viscosity as temperature-independent. The thermomechanical feedback in that case is purely between sliding and dissipation.…”

Section: Introductionmentioning

confidence: 99%

Ice sheet flow with thermally activated sliding. Part 1: the role of advection

2019

Flow organization into systems of fast-moving ice streams is a well-known feature of ice sheets. Fast motion is frequently the result of sliding at the base of the ice sheet. Here, we consider how this basal sliding is first initiated as the result of changes in bed temperature. We show that an abrupt sliding onset at the melting point, with no sliding possible below that temperature, leads to rapid drawdown of cold ice and refreezing as the result of the increased temperature gradient within the ice, and demonstrate that this result holds regardless of the mechanical model used to describe the flow of ice. Using this as a motivation, we then consider the possibility of a region of 'subtemperate sliding' in which sliding at reduced velocities occurs in a narrow range of temperatures just below the melting point. We confirm that this prevents the rapid drawdown of ice and refreezing of the bed, and construct a simple numerical method for computing steady-state ice sheet profiles that include a subtemperate region. The stability of such an ice sheet is analysed in a companion paper.