Basal conditions at the grounding zone of Whillans Ice Stream, West Antarctica, from ice‐penetrating radar

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.

Actively evolving subglacial conduits and eskers initiate ice shelf channels at an Antarctic grounding line

“…3) gives some evidence that ocean water may penetrate upstream of the tidal flexure through tidal pressure variations20, which has been observed in some locations of the Whillans Ice Stream grounding zone2122. In our case, ocean water may intrude into the conduit causing stratification of the subglacial water on top of the heavier, saline ocean water (Fig.…”

Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

“…Given the observed overpressure, we estimate its contribution to crevasse propagation using a simple model based on Linear Elastic Fracture Mechanics approach of van der Veen (). This model is applicable for stress regimes characterized by uniaxial extension and for a single crevasse propagating up to half the ice thickness (Jimenez & Duddu, ); at this site crevasses visible in ice‐penetrating radar data are relatively sparse and <50 m high (Christianson et al, ; Jezek & Bentley, ). We assume that the stress field in basal ice is well approximated by uniaxial extension in the x direction and confinement in the y direction.…”

“…Basal crevasses increase the basal ice area available for melting and modify the local englacial stress field (Khazendar & Jenkins, ; Luckman et al, ; Sassolas et al, ). Basal crevasses are abundant in grounding zones, where flexural stresses and a contrast in basal shear stress across the grounding line are conducive to their formation (Christianson et al, ; Jezek & Bentley, ). The height of basal crevasses is set by the force balance between ocean pressure in the crevasse and the stress field in ice (Jimenez & Duddu, ; van der Veen, ).…”

Biogeochemical Connectivity Between Freshwater Ecosystems beneath the West Antarctic Ice Sheet and the Sub‐Ice Marine Environment

“…The GZ site was 4.8 km downstream from the physical grounding line of the WIS (Figure 1). The ice cover at the GZ was~760 m thick, and the underlying marine water column was~10 m deep (Begeman et al, 2018;Christianson et al, 2016).…”