Dynamic changes on the Wilkins Ice Shelf during the 2006–2009 retreat derived from satellite observations

Melanie Rankl,Angelika Humbert,Johannes Jakob Fürst,Matthias Holger Braun

doi:10.5194/tc-11-1199-2017

Abstract

Abstract. The vast ice shelves around Antarctica provide significant restraint to the outflow from adjacent tributary glaciers. This important buttressing effect became apparent in the last decades, when outlet glaciers accelerated considerably after several ice shelves were lost around the Antarctic Peninsula (AP). The present study aims to assess dynamic changes on the Wilkins Ice Shelf (WIS) during different stages of ice-front retreat and partial collapse between early 2008 and 2009. The total ice-shelf area lost in these events was 2135 ± 75 km2 ( ∼ 15 % of the ice-shelf area relative to 2007). Here, we use time series of synthetic aperture radar (SAR) satellite observations (1994–1996, 2006–2010) in order to derive variations in surface-flow speed from intensity-offset tracking. Spatial patterns of horizontal strain-rate, stress and stress-flow angle distributions are determined during different ice-front retreat stages. Prior to the final break up of an ice bridge in 2008, a strong speed up is observed, which is also discernible from other derived quantities. We identify areas that are important for buttressing and areas prone to fracturing using in-flow and first principal strain rates as well as principal stress components. Further propagation of fractures can be explained as the first principal components of strain rates and stresses exceed documented threshold values. Positive second principal stresses are another scale-free indicator for ice-shelf areas, where fractures preferentially open. Second principal strain rates are found to be insensitive to ice-front retreat or fracturing. Changes in stress-flow angles highlight similar areas as the in-flow strain rates but are difficult to interpret. Our study reveals the large potential of modern SAR satellite time series to better understand dynamic and structural changes during ice-shelf retreat but also points to uncertainties introduced by the methods applied.

Highlights

During the last few decades several vast floating ice shelves have been lost (Cook and Vaughan, 2010; Doake and Vaughan, 1991; Rott et al, 2002; Scambos et al, 2003, 2000), which entailed significant speed up and thinning of previously restrained outlet glaciers (Berthier et al, 2012; Rignot, 2004; Scambos, 2004)
Surface velocities of the ice shelf and its tributary glaciers were derived from synthetic aperture radar (SAR) intensityoffset tracking (Strozzi et al, 2002) using repeat Advanced Land Observation Satellite (ALOS) Phased Array type Lband Synthetic Aperture Radar (PALSAR), 46 day time interval, single look complex (SLC) image pairs (Table S1 in the Supplement)
March 1996 were taken from InSAR derived surface flow presented in Braun et al (2009) and from applying intensity-offset tracking to image pairs from the European Remote Sensing satellites, ERS-1 and ERS-2 (35 day time interval)

Summary

Introduction

During the last few decades several vast floating ice shelves have been lost (Cook and Vaughan, 2010; Doake and Vaughan, 1991; Rott et al, 2002; Scambos et al, 2003, 2000), which entailed significant speed up and thinning of previously restrained outlet glaciers (Berthier et al, 2012; Rignot, 2004; Scambos, 2004). On the Antarctic Peninsula (AP), 12 major ice shelves have either disintegrated or significantly retreated (Cook and Vaughan, 2010; Doake and Vaughan, 1991; Rott et al, 2002; Scambos et al, 2003, 2000). Over 85 % of the tributary glaciers showed retreating tongues (Cook, 2005) The reasons for this regionally concentrated ice-shelf recession are manifold.

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Conclusion