Mapping the grounding zone of Larsen C Ice Shelf, Antarctica, from ICESat-2 laser altimetry

Tian Li,Jonathan L Bamber,Geoffrey J Dawson,Stephen J Chuter

doi:10.5194/tc-14-3629-2020

Abstract

Abstract. We present a new, fully automated method of mapping the Antarctic Ice Sheet's grounding zone using a repeat-track analysis and crossover analysis of newly acquired ICESat-2 laser altimeter data. We map the position of the landward limit of tidal flexure and the inshore limit of hydrostatic equilibrium, as demonstrated over the mountainous and hitherto difficult to survey grounding zone of Larsen C Ice Shelf. Since the start of data acquisition in 2018, our method has already achieved a near 9-fold increase in the number of grounding zone observations compared with ICESat, which operated between 2003 and 2009. We have improved coverage in particular over the previously poorly mapped the Bawden and Gipps ice rises and Hearst Island. Acting as a reliable proxy for the grounding line, which cannot be directly imaged by satellites, our ICESat-2-derived landward limit of tidal flexure locations agrees well with independently obtained measurements, with a mean absolute difference and standard deviation of 0.39 and 0.32 km, respectively, compared to interferometric synthetic-aperture-radar-based observations. Our results demonstrate the efficiency, density, and high spatial accuracy with which ICESat-2 can image complex grounding zones and its clear potential for future mapping of the pan-ice sheet grounding zone.

Highlights

Long-term satellite observations have linked the on-going thinning of Antarctic ice shelves (Paolo et al, 2015) with enhanced rates of ice discharge across the grounding line – the point where the grounded ice sheet first detaches from the bedrock and begins to float (Fricker and Padman, 2006)
The GL (Point G in Fig. 1) lies towards the landward edge of a transition zone between the fully grounded ice sheet and the freely floating ice shelf, forming the grounding zone
Using the newly developed ICESat-2-based GZ detection algorithm in this study, we identified 253 Point F and 263 Point H over Larsen C Ice Shelf, which is a near 9-fold increase in the number of GZ features identified by ICESat (30 of each point; Brunt et al, 2010a)

Summary

Introduction

Long-term satellite observations have linked the on-going thinning of Antarctic ice shelves (Paolo et al, 2015) with enhanced rates of ice discharge across the grounding line (hereinafter referred to as the GL) – the point where the grounded ice sheet first detaches from the bedrock and begins to float (Fricker and Padman, 2006). Ice discharge calculations are sensitive to the assumed location of the GL, and accurate GL mapping is required for mass balance estimates of the grounded ice sheet using the input–output method (IOM) (Chuter and Bamber, 2015; Rignot et al, 2019). While Point G cannot be detected directly from satellite-based observations, Point F lies close to this location and is generally considered to be the most robust satellite-observable proxy for Point G (Fricker and Padman, 2006; Fricker et al, 2009; Brunt et al, 2010b, 2011; Rignot et al, 2011)

Methods

Results

Conclusion