The dimensions and topographic setting of Antarctic subglacial lakes and implications for large-scale water storage beneath continental ice sheets
Radio-echo sounding (RES) at 60 MHz has penetrated to the ice-sheet bed on about 400 000 km of flight track covering more than 50% of the 13.5 x 106 km2 Antarctic ice sheet. About 70 subglacial lakes have been identified by characteristic strong, mirror-like, and very flat RES reflectors. Most are located in the ice-sheet interior, where numerical modeling predicts basal melting, and 33% are within 100 km of the ice crest. Mean ice thickness above the lakes is about 3000 m. About 75% of lakes have radio-echo lengths of 30 km. The largest is Vostok Lake, which is 230 km long, 14 000 km2 in area, and has a water volume of about 2000 km3. More than 60% of lakes have maximum local bedrock elevations of <400 m and bed gradients of <0.1 adjacent to their margins. Extrapolating the observed side-slope topography implies water depths from tens to several hundred meters in a few cases. About 20 000 km2 of subglacial lakes are inferred from RES, which can be doubled for the entire ice sheet to yield an estimated total area of about 40 000 km2, excluding Vostok Lake. Assuming average lake depths between 50 and 250 m, and including the 2000 km3 of water stored within Vostok Lake, we calculate an envelope of about 4000 to 12 000 km3 for the likely volume of water stored in modern Antarctic subglacial lakes, equivalent to 10–35 mm of global sea-level rise. In these volume calculations it is assumed that no subglacial lakes the size of Lake Vostok remain to be discovered and that RES length measurements along single transects are representative of overall lake dimensions. Our estimates of the total water volume of Antarctic subglacial lakes, which may be a suitable analogue for full glacial Quaternary ice sheets, do not necessarily conflict with the possible significance of large meltwater floods during the deglaciation of former midlatitude ice sheets.