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

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.

Changes in Supraglacial Lakes on George VI Ice Shelf, Antarctic Peninsula: 1973–2020

“…The seasonal maximum in lake coverage is consistently observed in January or February, coinciding with the peak of the AP melt season (Smith et al, 2007). We find that in the record melt year of 2020 (Banwell et al, 2021), 11.8% of the study region was covered by lakes, 1.93 standard deviations (SD) higher than the long-term mean of 4.1%, and greater than the ~10% coverage of lakes on LBIS prior to its collapse (Banwell et al, 2013). Of course, this does not necessarily mean north GVIIS is surpassing its limit of vulnerability, due to previously mentioned structural factors in the ice shelf's compressive flow regime.…”

“…The austral summer of 2020 saw extreme melting across this region of Antarctica, including the hottest day ever recorded on the continent (Robinson et al, 2020). This melting led to extensive SGLs on north GVIIS which, at their peak, covered a similar percentage of the ice shelf surface to that observed on LBIS prior to collapse (Banwell et al, 2021). Although melting was at a record high and lakes were widespread, it remains unclear whether lake coverage in 2020 was unprecedented, and consequently whether this represented a notable increase in GVIIS's vulnerability.…”

Seasonal evolution of Antarctic supraglacial lakes in 2015–2021 and links to environmental controls

“…Of these, three are situated on the southwest API and three are distributed around the margin of the EAIS. The choice of study regions was made in agreement with known supraglacial lake occurrences across different glaciological and climatic settings (Banwell et al, 2021;Dell et al, 2020;Dirscherl et al, 2021;Kingslake et al, 2017;Spergel et al, 2021) as well as satellite data availability. The study regions on https://doi.org/10.5194/tc-2021-203 Preprint.…”

“…Separated by Alexander Island (71°00' S, 70°00' W), these ice shelves stretch over an area of ~23 370 km 2 , ~4540 km 2 , and ~11 144 km 2 , respectively (Cook and Vaughan, 2010;Holt et al, 2013a). While Bach and Wilkins Ice Shelf are fed by several inlets from Alexander Island and have comparatively broad calving fronts with respect to their total extent, the structural setting of George VI Ice Shelf is far more complex (Banwell et al, 2021). Stretching over ~450 km along its centreline and up to ~75 km at its northern and southern calving fronts in Marguerite Bay and Ronne Entrance, George VI Ice Shelf is located within a narrow channel between Alexander Island and Palmer Land (Holt et al, 2013b).…”

Surface meltwater drainage and ponding on Amery Ice Shelf, East Antarctica, 1973–2019

“…Satellite observations highlight large interannual variability in the maximum size of drainage systems (e.g. Liang and others, 2012;Langley and others, 2016;Lenaerts and others, 2017;Dell and others, 2020;Banwell and others, 2021)). It is unclear if this variability can be explained by or is linked to seasonal meltwater production or whether more complex glaciohydrological coupling is at play.…”