The 32-year record-high surface melt in 2019/2020 on the northern George VI Ice Shelf, Antarctic Peninsula

Alison F Banwell,Laura A Stevens,Rebecca L Dell,Ghislain Picard,Mahsa Moussavi,Rajashree Tri Datta,Ludovic Brucker,Christopher A Shuman

doi:10.5194/tc-15-909-2021

Abstract

Abstract. In the 2019/2020 austral summer, the surface melt duration and extent on the northern George VI Ice Shelf (GVIIS) was exceptional compared to the 31 previous summers of distinctly lower melt. This finding is based on analysis of near-continuous 41-year satellite microwave radiometer and scatterometer data, which are sensitive to meltwater on the ice shelf surface and in the near-surface snow. Using optical satellite imagery from Landsat 8 (2013 to 2020) and Sentinel-2 (2017 to 2020), record volumes of surface meltwater ponding were also observed on the northern GVIIS in 2019/2020, with 23 % of the surface area covered by 0.62 km3 of ponded meltwater on 19 January. These exceptional melt and surface ponding conditions in 2019/2020 were driven by sustained air temperatures ≥0 ∘C for anomalously long periods (55 to 90 h) from late November onwards, which limited meltwater refreezing. The sustained warm periods were likely driven by warm, low-speed (≤7.5 m s−1) northwesterly and northeasterly winds and not by foehn wind conditions, which were only present for 9 h total in the 2019/2020 melt season. Increased surface ponding on ice shelves may threaten their stability through increased potential for hydrofracture initiation; a risk that may increase due to firn air content depletion in response to near-surface melting.

Highlights

Since the 1950s, the Antarctic Peninsula (AP) (Fig. 1a) has experienced faster increases in ocean and atmospheric warming than the rest of the Antarctic Ice Sheet (Siegert et al, 2019; Smith et al, 2020; Trusel et al, 2015)
In this study we focus on the northern area of the George VI Ice Shelf (GVIIS) only; defined as our area of interest (AOI) with a total area of 7850 km2
As the penetration depth at 5 GHz in dry snow and firn is larger than at 19 GHz, Advanced SCATterometer (ASCAT) C-band radar is likely to be more sensitive to melt at depth than microwave radiometers at 19 GHz

Summary

Introduction

Since the 1950s, the Antarctic Peninsula (AP) (Fig. 1a) has experienced faster increases in ocean and atmospheric warming than the rest of the Antarctic Ice Sheet (Siegert et al, 2019; Smith et al, 2020; Trusel et al, 2015). Mass loss is currently focused at marine margins, where the mass balance is controlled by complex interactions between the ice, ocean, atmosphere, and inland bed conditions (Scambos et al, 2000; Bell et al, 2018; Shepherd et al, 2018; Tuckett et al, 2019; Smith et al, 2020). Banwell et al.: 32-year record-high melt on the northern George VI Ice Shelf, Antarctica grounded ice flowing into the ocean (Scambos et al, 2004; De Rydt et al, 2015; Fürst et al, 2016; Gudmundsson et al, 2019)

Results

Discussion

Conclusion