Abstract
AbstractFast ice flow on the Antarctic continent constitutes much of the mass loss from the ice sheet. However, geophysical methods struggle to constrain ice flow history at depth, or separate the signatures of topography, ice dynamics and basal conditions on layer structure. We develop and demonstrate a methodology to compare layer signatures in multiple airborne radar transects in order to characterize ice flow at depth, or improve coverage of existing radar surveys. We apply this technique to generate synthetic, along-flow radargrams and compare different deformation regimes to observed radargram structure. Specifically, we investigate flow around the central sticky spot of Whillans Ice Stream, West Antarctica. Our study suggests that present-day velocity flowlines are insufficient to characterize flow at depth as expressed in layer geometry, and streaklines provide a better characterization of flow around a basal sticky spot. For Whillans Ice Stream, this suggests that ice flow wraps around the central sticky spot, supported by idealized flow simulations. While tracking isochrone translation and rotation across survey lines is complex, we demonstrate that our approach to combine radargram interpretation and modeling can reveal critical details of past ice flow.
Highlights
Ice streams and outlet glaciers account for the majority of ice loss from the Antarcticice sheet (e.g. Bamber and others, 2000; Rignot and others, 2019), but observational data are limited by a short observational period and inherent difficulty in viewing the subsurface
We apply the Synthetic Advected Radargram Algorithm to sample the advection of Profile A along Profile B, across the central sticky spot of Whillans Ice Stream
Comparing the synthetic radargram to the actual radargram across Profile B, we find that the synthetic radargram does not reproduce many of the complex isochrone structural features
Summary
Ice streams and outlet glaciers account for the majority of ice loss from the Antarcticice sheet (e.g. Bamber and others, 2000; Rignot and others, 2019), but observational data are limited by a short observational period and inherent difficulty in viewing the subsurface. Since the 1960s (Evans and Smith, 1970), airborne radar has been used to image large swaths of the Greenland and Antarctic ice sheets. These airborne surveys record the depth-varying return of electromagnetic waves reflected by englacial reflective layers, interpreted as isochrones (i.e. layers of snow deposited at the same time; e.g. Eisen and others, 2008; Grima and others, 2014; Cavitte and others, 2018). Hudleston, 2015; Macgregor and others, 2016) These layers are passively advected with flow, recording cumulative deformation of the ice mass Large deformations in the ice column make it challenging to reliably infer the past flow history from radar sounding interpretations
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