Distribution and seasonal evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica

Abstract

Abstract. Supraglacial lakes (SGLs) enhance surface melting and can flex and fracture ice shelves when they grow and subsequently drain, potentially leading to ice shelf disintegration. However, the seasonal evolution of SGLs and their influence on ice shelf stability in East Antarctica remains poorly understood, despite some potentially vulnerable ice shelves having high densities of SGLs. Using optical satellite imagery, air temperature data from climate reanalysis products and surface melt predicted by a regional climate model, we present the first long-term record (2000–2020) of seasonal SGL evolution on Shackleton Ice Shelf, which is Antarctica's northernmost remaining ice shelf and buttresses Denman Glacier, a major outlet of the East Antarctic Ice Sheet. In a typical melt season, we find hundreds of SGLs with a mean area of 0.02 km2, a mean depth of 0.96 m and a mean total meltwater volume of 7.45×106 m3. At their most extensive, SGLs cover a cumulative area of 50.7 km2 and are clustered near to the grounding line, where densities approach 0.27 km2 km−2. Here, SGL development is linked to an albedo-lowering feedback associated with katabatic winds, together with the presence of blue ice and exposed rock. Although below-average seasonal (December–January–February, DJF) temperatures are associated with below-average peaks in total SGL area and volume, warmer seasonal temperatures do not necessarily result in higher SGL areas and volumes. Rather, peaks in total SGL area and volume show a much closer correspondence with short-lived high-magnitude snowmelt events. We therefore suggest seasonal lake evolution on this ice shelf is instead more sensitive to snowmelt intensity associated with katabatic-wind-driven melting. Our analysis provides important constraints on the boundary conditions of supraglacial hydrology models and numerical simulations of ice shelf stability.

Recent acceleration of Denman Glacier (1972–2017), East Antarctica, driven by grounding line retreat and changes in ice tongue configuration

“…Recent observations of grounding line migration at Denman have shown a 5 km retreat along its western flank between 1996 and 2017 (Brancato et al, 2020). However, over this time period there was a limited change in the speed of Denman (2001-2017; 3 ± 2 % acceleration; Fig.…”

“…3c). Reconstructions of the bed topography near the grounding line of Denman Glacier show that the western flank of Denman's grounding line was resting on a retrograde slope in 1996 a few kilometres behind a topographic ridge (Brancato et al, 2020). One possibility is that Denman's grounding line retreat initiated much earlier at some point in the 1970s in response to increased ocean temperatures enhancing melting of the ice tongue base.…”

“…Following the collapse of Larsen B in 2002, Shackleton is now the most northerly major ice shelf remaining in Antarctica, with most of the ice shelf lying outside the Antarctic Circle. Numerous surface meltwater features have been repeatedly reported on its surface (Kingslake et al, 2017;Stokes et al, 2019;Arthur et al, 2020). There is no evidence that these features currently have a detrimental impact on its stability, but there is a possibility that projected increases in surface melt (Trusel et al, 2015) could increase the ice shelves' vulnerability to meltwaterinduced hydrofracturing.…”

“…However, given our most recent understanding of bedrock topography in Wilkes Land, Denman Glacier (Fig. 1) provides the most direct pathway to the deep interior of the ASB (Gasson et al, 2015;Brancato et al, 2020;. Moreover, a recent mass balance estimate (Rignot et al, 2019) has shown that between 1979 and 2017 Denman Glacier's catchment may have lost an amount of ice (190 Gt) broadly comparable with Totten Glacier (236 Gt).…”

“…Moreover, a recent mass balance estimate (Rignot et al, 2019) has shown that between 1979 and 2017 Denman Glacier's catchment may have lost an amount of ice (190 Gt) broadly comparable with Totten Glacier (236 Gt). There have also been several reports of inland thinning of Denman's fast-flowing trunk (Flament and Remy, 2012;Helm et al, 2014;Young et al, 2015;Schröder et al, 2019), and its grounding line has retreated over the past 20 years (Brancato et al, 2020). However, unlike Totten and other large glaciers which drain marine basins in Antarctica, there has been no detailed study analysing any changes in its calving cycle, velocity or ice tongue structure.…”