Adaptively constraining radar attenuation and temperature across the Thwaites Glacier catchment using bed echoes

Dustin M Schroeder,Duncan A Young,Helene Seroussi,Winnie Chu

doi:10.1017/jog.2016.100

Dustin M Schroeder, Duncan A Young + Show 2 more

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https://doi.org/10.1017/jog.2016.100

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Abstract

ABSTRACTEnglacial temperature is a major control on ice rheology and flow. However, it is difficult to measure at the glacier to ice-sheet scale. As a result, ice-sheet models must make assumptions about englacial temperature and rheology, which affect sea level projections. This is problematic if fundamental processes are not captured by models due to a lack of observationally constrained ice temperature values. Although radar sounding data have been exploited to constrain the temperature structure of the Greenland ice sheet using englacial layers, this approach is limited to areas and depths where these layers exist intact. In order to extend empirical radar-based temperature estimation beyond this limitation, we present a new technique for estimating englacial attenuation rates for the entire ice column using adaptive fitting of unfocused radar bed echoes based on the correlation of ice thickness and corrected bed echo power. We apply this technique to an airborne survey of Thwaites Glacier in West Antarctica and compare the results with temperatures and attenuation rates from a numerical ice-sheet model. We find that the estimated attenuation rates reproduce modelled patterns and values across the catchment with the greatest differences near steeply sloping bed topography.

Highlights

The behaviour, evolution and potential instability of the West Antarctic ice sheet is one of the greatest sources of uncertainty in projections of future sea level (Stocker and others, 2013)
This allows us to take advantage of the more accurate estimates of Figure 4a without forfeiting the coverage of Figure 4c. This is especially relevant in the high-attenuation regions near the grounding zone and eastern shear margin where the same fractional variation in 〈N〉 would result in a larger value of 〈Nh〉 relative to low-attenuation regions
The technique we present directly constrains the spatially variable englacial attenuation rate in glaciers and ice sheets using only bed echoes

Summary

Introduction

The behaviour, evolution and potential instability of the West Antarctic ice sheet is one of the greatest sources of uncertainty in projections of future sea level (Stocker and others, 2013). Pine Island Glacier has the larger contemporary negative mass balance, Thwaites Glacier is the only portion of Amundsen Sea sector with a landwardsloping bed that reaches from its current grounding position, on a series of bedrock highs, to the deep interior of the ice sheet (Holt and others, 2006; Tinto and Bell, 2011; Schroeder and others, 2014) This is a potentially unstable configuration (Weertman, 1974; Thomas and Bentley, 1978; Schoof, 2007; Tsai and others, 2015) in which retreat initialized at its grounding zone could spread to the rest of the glacier catchment in a feedback process that may already be under way (Joughin and others, 2014; Rignot and others, 2014). Poor knowledge of the englacial temperature structure of Thwaites Glacier may be a significant source of uncertainty in model-based projections of future sea-level contributions from the Amundsen Sea Embayment and West Antarctic ice sheet

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