Water exchange between the subglacial Lake Vostok and the overlying ice sheet

It has now been known for several years that a 200-km-long lake, called Lak e Vostok, lies beneath the ice sheet on which sits Vostok Station in Antarc tica(1-5), The conditions at the base of the ice sheet above this subglacia l lake can provide information about the environment within the lake, inclu ding the likelihood that it supports life(2). Here we present an analysis o f the ice-sheet structure from airborne 60-MHz radar studies, which indicat es that distinct zones of basal ice loss and accretion occur at the ice-wat er interface. Subglacial melting and net ice loss occur in the north of the lake and across its 200-km-long western margin, whereas about 150 m of ice is gained by subglacial freezing in the south. This indicates that signifi cant quantities of water are exchanged between the base of the ice sheet an d the lake waters, which will enrich the lake with gas hydrates, cause sedi ment deposition and encourage circulation of the lake water.