Basal conditions at the grounding zone of Whillans Ice Stream, West Antarctica, from ice‐penetrating radar. Issue 11 (4th November 2016)

• Record Type: Journal Article
• Authors: Christianson, Knut; Jacobel, Robert W.; Horgan, Huw J.; Alley, Richard B.; Anandakrishnan, Sridhar; Holland, David M.; DallaSanta, Kevin J.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 11(2016)
• Page Start: 1954
• Page End: 1983
• Publication Date: 2016-11-04
• Subjects: ice stream -- ice shelf -- grounding zone -- ice/ocean interactions -- ice‐penetrating radar; Geomorphology -- Periodicals; 551.3
• DOI: 10.1002/2015JF003806
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract : We present a comprehensive ice‐penetrating radar survey of a subglacial embayment and adjacent peninsula along the grounding zone of Whillans Ice Stream, West Antarctica. Through basal waveform and reflectivity analysis, we identify four distinct basal interfaces: (1) an ice‐water‐saturated till interface inland of grounding; (2) a complex interface in the grounding zone with variations in reflectivity and waveforms caused by reflections from fluting, sediment deposits, and crevasses; (3) an interface of anomalously low‐reflectivity downstream of grounding in unambiguously floating areas of the embayment due to basal roughness and entrained debris; and (4) a high‐reflectivity ice‐seawater interface that occurs immediately seaward of grounding at the subglacial peninsula and several kilometers seaward of grounding in the embayment, occurring after basal debris and grounding zone flutes have melted off the ice bottom. Sediment deposition via basal debris melt‐out occurs in both locations. The higher basal melt rate at the peninsula contributes to greater grounding line stability by enabling faster construction of a stabilizing sediment wedge. In the embayment, the low slopes of the ice bottom and bed prevent development of a strong thermohaline circulation leading to a lower basal melt rate and less rapid sediment deposition. Thus, grounding lines in subglacial embayments are more likely to lack stabilizing sediment deposits and are more prone to external forcing, whether from the ocean, the subglacial water system, or large‐scale ice dynamics. Our conclusions indicate that subglacial peninsulas and embayments should be treated differently in ice sheet‐ocean models if these models are to accurately simulate grounding line response to external forcing. Key Points: Radar basal reflectivity in a grounding zone embayment is lower than that expected from an ice‐seawater interface Radar amplitude and waveform modeling suggests that basal reflectivity is reduced by entrained sediment and basal roughness A reflectivity increase downflow of the grounding line suggests that sediment deposition in grounding zones occurs via basal debris melt‐out