Antarctica's Deep Frozen “Lakes”

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Science  25 Mar 2011:
Vol. 331, Issue 6024, pp. 1524-1525
DOI: 10.1126/science.1202888

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The Antarctic ice sheet is made of meteoric ice formed by compression and recrystallization of snow. On page 1592 of this issue, Bell et al. (1) report new radar data that shows that this ostensibly obvious statement is not fully correct. They demonstrate that over a large fraction of East Antarctica the deepest section of the ice sheet contains thick basal accreted ice. This ice did not originate as surface snow but developed when subglacial meltwater was frozen onto the underside of the ice sheet to form frozen analogs of Antarctic subglacial lakes. These accreted ice masses expose the existence of an internal hydrological system, which accomplishes appreciable redistribution of mass and heat within the Antarctic ice sheet. Because basal accreted ice does not develop from surface snow, it does not contain direct records of past climates. Hence, its unexpectedly high abundance in the interior of Antarctica will affect the ongoing search for the oldest ice on Earth. Frozen-on basal ice layers provide, however, a new, exciting archive of spatial and temporal dynamics in subglacial hydrology and microbial life habitats. Accreted basal ice may be softer than regular glacial ice; its widespread existence may make the Antarctic ice sheet more susceptible to changes in velocity and mass balance than current models recognize.