Lake Untersee, a first isotope study of the largest freshwater lake in the interior of East Antarctica

Perennially ice-covered lakes partially bounded by glacier ice are common in some Antarctic coastal regions 1 but very rare inside the continent. Here we describe hydrological studies on the largest freshwater lake of interior Antarctica, Lake Untersee (71°20′ S/13°30′ E, surface area 10 km 2 , maximum depth >79 m) 2 , showing that the lake arose from a melt-water pond during climatic optimum periods in the Holocene. At present, the studied water body is thermally, hydrogeochemically and isotopically homogeneous because of thermal convection during the austral summer. Lake Untersee is fed throughout the year by underwater melting of the adjoining glacier ice. Isotope data suggest a permanent ice cover during its existence. The drainless lake is constantly losing water through sublimation on the surface of the more than 2.5-m-thick ice cover. The salt content suggests that the present water body is the remainder of an amount of melt water at least 50 times as great.