Abstract
AbstractIsolated areas of high basal drag, or ‘sticky spots’, are important and poorly understood features in the force balance and dynamics of West Antarctic ice streams. Characterizing sticky spots formed by thin or drying subglacial till using ice-penetrating radar is theoretically possible, as high radar bed-returned power (BRP) is commonly related to an abundance of free water at the ice/bed interface, provided losses from englacial attenuation can be estimated. In this study we use airborne radar data collected over Evans Ice Stream to extract BRP profiles and test the sensitivity of BRP to the adopted englacial attenuation correction. We analyse 11 ~ 2 0 km profiles in four fast-flow areas where sticky spots have been inferred to exist on the basis of model and surface data inversions. In the majority of profiles we note that the increase in basal drag is accompanied by a decrease in BRP and suggest that this is evidence both for the presence of a sticky spot in those locations and that local variations in subglacial hydrology are responsible for their existence. A comparison is made between empirical and numerical modelling approaches for deriving englacial attenuation, and our findings generally support previous studies that advocate a modelling approach.
Highlights
The discharge of ice from Antarctica is dominated by flow along arterial ice streams that drain >90% of its mass (e.g. Rignot and others, 2011a)
Because our primary interest here lies in identifying sticky spots with radar data, we begin by targeting areas for detailed analysis on the basis of the distribution of basal drag inferred by Joughin and others (2006)
In most of the profiles the increase in basal drag associated with the sticky spot is accompanied by a local drop in bed-returned power (BRP)
Summary
The discharge of ice from Antarctica is dominated by flow along arterial ice streams that drain >90% of its mass (e.g. Rignot and others, 2011a). More extreme dynamic variability has been exemplified by ice streams migrating laterally or even shutting down (Retzlaff and Bentley, 1993; Vaughan and others, 2008; Catania and others, 2012) Such observations motivate research into understanding the controls on ice-stream flow. Sediment-rich basal environments, such as those in the lower reaches of ice streams, the latter two styles are the most likely These areas are characterized by having less free water than the surrounding subglacial environment; identifying such regions is theoretically within the capabilities of ice-penetrating radar, as the reflectivity of the ice/bed interface is dominated by the presence of liquid water (Peters and others, 2005). Our principal motivation is to use radar data to ‘ground-truth’ the distribution of sticky spots that can be inferred from satellite and modelling methods, and to better understand what controls the flow of this relatively unstudied Antarctic ice-stream catchment.
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