Two decades of dynamic change and progressive destabilization on the Thwaites Eastern Ice Shelf

Karen E Alley,Jan T M Lenaerts,Eric Keenan,Michelle Maclennan,Cyrus Hulen,Tyler Sutterley,Martin Truffer,Devon Dunmire,Christian T Wild,Adrian Luckman,Ted A Scambos,Marin Klinger,Bruce Wallin,Sarah F Child,Atsuhiro Muto,Erin C Pettit

doi:10.5194/tc-15-5187-2021

Abstract

Abstract. The Thwaites Eastern Ice Shelf (TEIS) buttresses the eastern grounded portion of Thwaites Glacier through contact with a pinning point at its seaward limit. Loss of this ice shelf will promote further acceleration of Thwaites Glacier. Understanding the dynamic controls and structural integrity of the TEIS is therefore important to estimating Thwaites' future sea-level contribution. We present a ∼ 20-year record of change on the TEIS that reveals the dynamic controls governing the ice shelf's past behaviour and ongoing evolution. We derived ice velocities from MODIS and Sentinel-1 image data using feature tracking and speckle tracking, respectively, and we combined these records with ITS_LIVE and GOLIVE velocity products from Landsat-7 and Landsat-8. In addition, we estimated surface lowering and basal melt rates using the Reference Elevation Model of Antarctica (REMA) DEM in comparison to ICESat and ICESat-2 altimetry. Early in the record, TEIS flow dynamics were strongly controlled by the neighbouring Thwaites Western Ice Tongue (TWIT). Flow patterns on the TEIS changed following the disintegration of the TWIT around 2008, with a new divergence in ice flow developing around the pinning point at its seaward limit. Simultaneously, the TEIS developed new rifting that extends from the shear zone upstream of the ice rise and increased strain concentration within this shear zone. As these horizontal changes occurred, sustained thinning driven by basal melt reduced ice thickness, particularly near the grounding line and in the shear zone area upstream of the pinning point. This evidence of weakening at a rapid pace suggests that the TEIS is likely to fully destabilize in the next few decades, leading to further acceleration of Thwaites Glacier.

Highlights

Thwaites Glacier in West Antarctica holds the most important control on global sea-level rise over the few centuries (Scambos et al, 2017)
For our small areas of interest, we chose three square sites covering 25 km2 in regions of the Thwaites Eastern Ice Shelf (TEIS) that behave in different ways (Fig. 1): site 1 crosses the 2011 grounding zone (Rignot et al, 2016), site 2 represents midshelf patterns, and site 3 is just upstream of the pinning point that constrains the ice shelf
By 2007, large rifts developed across the shear margin, and by the 2008–2009 season a full separation between the TEIS and Thwaites Western Ice Tongue (TWIT) had developed in the shear margin

Summary

Introduction

Thwaites Glacier in West Antarctica holds the most important control on global sea-level rise over the few centuries (Scambos et al, 2017). The broad causes and implications of the destabilization of Thwaites have been understood for decades: increased delivery of warm modified Circumpo-. Alley et al.: Dynamic change and destabilization on the Thwaites Eastern Ice Shelf lar Deep Water (mCDW) to grounding zones triggers retreat of an ice sheet grounded well below sea level Recent evidence suggests that the predicted irreversible retreat of Thwaites Glacier is already underway (Joughin et al, 2014; Rignot et al, 2014). Knowing the details of the timing, magnitude, and pace of the collapse of Thwaites are essential for more detailed forecasting of its sea-level contribution

Results

Discussion

Conclusion