Widespread movement of meltwater onto and across Antarctic ice shelves

Abstract

Surface meltwater drains across ice sheets, forming melt ponds that can trigger ice-shelf collapse 1, 2 , acceleration of grounded ice flow and increased sea-level rise 3, 4, 5 . Numerical models of the Antarctic Ice Sheet that incorporate meltwater's impact on ice shelves, but ignore the movement of water across the ice surface, predict a metre of global sea-level rise this century 5 in response to atmospheric warming 6 . To understand the impact of water moving across the ice surface a broad quantification of surface meltwater and its drainage is needed. Yet, despite extensive research in Greenland 7, 8, 9, 10 and observations of individual drainage systems in Antarctica 10, 11, 12, 13, 14, 15, 16, 17, we have little understanding of Antarctic-wide surface hydrology or how it will evolve. Here we show widespread drainage of meltwater across the surface of the ice sheet through surface streams and ponds (hereafter 'surface drainage') as far south as 85° S and as high as 1,300 metres above sea level. Our findings are based on satellite imagery from 1973 onwards and aerial photography from 1947 onwards. Surface drainage has persisted for decades, transporting water up to 120 kilometres from grounded ice onto and across ice shelves, feeding vast melt ponds up to 80 kilometres long. Large-scale surface drainage could deliver water to areas of ice shelves vulnerable to collapse, as melt rates increase this century. While Antarctic surface melt ponds are relatively well documented on some ice shelves, we have discovered that ponds often form part of widespread, large-scale surface drainage systems. In a warming climate, enhanced surface drainage could accelerate future ice-mass loss from Antarctic, potentially via positive feedbacks between the extent of exposed rock, melting and thinning of the ice sheet.

Channelized Melting Drives Thinning Under a Rapidly Melting Antarctic Ice Shelf

“…A comparison of DIS's velocity structure in 2015 with that of 2008 (Figure S9) shows that changes in ice divergence could not be the cause of the observed signal in the altimetry data and hence that the observed surface lowering does not have an ice‐dynamic origin. We also eliminate any explanation that invokes surface processes, because the magnitudes of changes related to surface processes are small here (Figure S8) and no evidence of surface melt has been recorded (Kingslake et al, ). We propose that the most likely explanation for the observed surface lowering is thinning caused by melting at the base of the ice shelf.…”

Intense Winter Surface Melt on an Antarctic Ice Shelf

“…Current mass loss of the Antarctic Ice Sheet is made up almost entirely of ice shelf basal melting and iceberg calving (Depoorter et al, ). Although supraglacial and englacial runoff has been widely observed, especially in regions of low albedo such as blue ice and bare rock (Bell et al, ; Kingslake et al, ; Lenaerts et al, ), models suggest that only a small fraction (<%) of the ∼115 Gt (1 Gt = 10 12 kg) of surface meltwater produced annually (Trusel et al, ; Van Wessem et al, ) runs off directly into the ocean. Instead, it is refrozen within underlying snow and firn layers (Kuipers Munneke, Picard, et al, ).…”

Antarctic Supraglacial Lake Identification Using Landsat-8 Image Classification

“…Antarctic supraglacial lakes have been mapped on individual ice shelves using band thresholding methods [44,54,69,70] but have only recently gained wide appreciation. Kingslake et al [71] were the first to note widespread surface lakes across Antarctica by manually mapping meltwater features across a temporal composite of cloud-free Landsat imagery. Stokes et al [72] also mapped lakes in East Antarctica from a composite of cloud-free Landsat imagery, and provided a minimum estimate of lake area during one month of a high-melt summer (January 2017) using a normalized difference water index threshold.…”