In-situ observations of ice dynamics on the pinning point of Thwaites Eastern Ice Shelf, Antarctica

Abstract:

The ice rumple and ice rise—termed as a pinning point—play an important role in stabilizing ice shelf or developing a local flow regime. The Eastern Ice shelf downstream of Thwaites Glacier (TG) is presently buttressed by a pinning point near its ice front, whereas the TG Tongue, the western extension of the TG, has recently collapsed. Yet the way in which the Eastern ice shelf’s stability has changed under the recent rapid thinning of TG remains uncertain mostly due to the lack of in-situ observations. In the 2019/2020 austral summer season, we deployed a geophysical monitoring array, consisting of ApRES (Autonomous phase-sensitive Radio Echo Sounder) and RTK (Real-Time Kinematic) GPS stations, on the margin of the pinning point, in order to investigate the ice dynamics associated with a pinning point. In addition, the helicopter-based radar survey acquired dense profiles of ice thickness around the pinning point. Using the combination of ApRES and RTK GPS systems, we can measure the ice velocity, basal melt rate, vertical and horizontal strain rate, surface elevation change, and tidal flexure of ice shelf margin. According to our preliminary results, the ice flow velocity is significantly changing (~30%) in the observation period. The basal melt exceeds the ice thickening due to vertical compression that results from basal traction, resulting in the ice thinning on the pinning point. The tidal motions near the margin of the pinning point indicates the temporal changes in tidal flexure that are not fully explained by a simple elastic response of the ice shelf. The temporal changes in tidal flexure is correlated with the ice flow velocity change. However, more sophisticated flexure models are necessary to understand the relationship between the tidal flexure and the ice dynamics on the pinning point. The long-term observations by remote sensing around the pinning point show significant changes in ice flow velocity and ice thickness. The in-situ observations could more clarify the mechanism of dynamic pinning point.