Abstract
Abstract. Repeat-pass ICESat altimetry has revealed 124 discrete surface height changes across the Antarctic Ice Sheet, interpreted to be caused by subglacial lake discharges (surface lowering) and inputs (surface uplift). Few of these active lakes have been confirmed by radio-echo sounding (RES) despite several attempts (notable exceptions are Lake Whillans and three in the Adventure Subglacial Trench). Here we present targeted RES and radar altimeter data from an "active lake" location within the upstream Institute Ice Stream, into which at least 0.12 km3 of water was previously calculated to have flowed between October 2003 and February 2008. We use a series of transects to establish an accurate depiction of the influences of bed topography and ice surface elevation on water storage potential. The location of surface height change is downstream of a subglacial hill on the flank of a distinct topographic hollow, where RES reveals no obvious evidence for deep (> 10 m) water. The regional hydropotential reveals a sink coincident with the surface change, however. Governed by the location of the hydrological sink, basal water will likely "drape" over topography in a manner dissimilar to subglacial lakes where flat strong specular RES reflections are measured. The inability of RES to detect the active lake means that more of the Antarctic ice sheet bed may contain stored water than is currently appreciated. Variation in ice surface elevation data sets leads to significant alteration in calculations of the local flow of basal water indicating the value of, and need for, high-resolution altimetry data in both space and time to establish and characterise subglacial hydrological processes.
Highlights
Over the last ten years, our appreciation of basal hydrology in Antarctica has changed significantly
Between October 2003 and November 2008, ICESat surface altimetry revealed a discrete zone of ice sheet uplift within the Institute Ice Stream, interpreted by Smith et al (2009) to be due to the filling of a subglacial lake by at least 0.12 km3 of water
In the austral summer of 2010–2011, an airborne geophysical survey of the Weddell Sea sector of West Antarctica targeted Institute E2 by flying a series of transects centred on the middle of the uplifted region
Summary
Over the last ten years, our appreciation of basal hydrology in Antarctica has changed significantly. Around half of the “active lake” inventory (Smith et al, 2009) is comprised of evidence for losses/gains of subglacial water from fewer than five transects, often just two and occasionally only one In such cases, interpretation of discrete ice surface height changes as “active lakes” beneath the ice is plausible yet, given the paucity of data, inconclusive. “active lakes” were found to coincide with radio reflections showing one or two of these traits (e.g. Lake Mercer in the Siple Coast of West Antarctica; Fricker et al, 2007; Carter et al, 2007) Explanations for this mismatch include both the inability of radar to detect subglacial lakes under certain glaciological conditions (e.g. surface crevasses, or warm, > −10 ◦C, ice), and a lack of water during the time of RES data acquisition. We reveal how the subglacial system can store and route basal water without the build-up of deep-water lakes, and demonstrate the ability of (and necessity for) high-resolution surface altimetry and RES to detect and understand such a system
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