SUBGLACIAL LAKE

A discrete body of water between the substrate and an ice sheet or glacier, where the bed is at the pressure melting point. Subglacial lakes are normally found at ice divides where ice-flow velocity is low, in the onset zones of ice streams, within subglacial basins where ice velocity is comparatively high and in volcanically active areas with locally high geothermal heat fluxes. Approximately 280 lakes have been discovered under the Antarctic Ice Sheet, a majority of which are in east Antarctica. The largest is Lake Vostok with an area of 14,000 km2 and a maximum depth of 1,200 m. This lake has a closed hydrological system where ice is at the pressure melting point in some areas, while refreezing and build-up of accretionary ice takes place in others. However, many lakes receive water from areas of warm-based ice, where basal melting occurs particularly at ice-stream onset zones and tributaries, and can fill and drain via subglacial drainage pathways linking several lakes together. These relatively abrupt changes in water volume at the bed can change ice velocity over annual or shorter periods and have significant dynamic implications for the overall ice sheet.

In Iceland, glacier-volcano interactions below ice caps produce meltwater lakes that drain catastrophically at times, as jökulhlaups, sometimes during volcanic eruptions. Microbial life has been discovered in these Icelandic subglacial lakes, and there is currently a significant effort under way to sample the subglacial lakes in Antarctica to discover whether they also contain specially adapted, unique microbial ecosystems. Additionally, the lake-floor sediments may contain records of ice-sheet and climatic history.

[See alsoice-sheet dynamics]