Subglacial lake
A subglacial lake is a lake that is found under a glacier, typically beneath an ice cap or ice sheet. Subglacial lakes form at the boundary between ice and the underlying bedrock, where gravitational pressure decreases the pressure melting point of ice. Over time, the overlying ice gradually melts at a rate of a few millimeters per year. Meltwater flows from regions of high to low hydraulic pressure under the ice and pools, creating a body of liquid water that can be isolated from the external environment for millions of years. There are about 140 subglacial lakes within the Antarctic, and about 400 in the world (including Iceland and Greenland). These lakes contain a substantial proportion of Earth's liquid freshwater, with the volume of Antarctic subglacial lakes alone estimated to be about 10,000 km3, or about 15% of all liquid freshwater on Earth.
As ecosystems isolated from Earth's atmosphere, subglacial lakes are influenced by interactions between ice, water, sediments, and organisms. They contain active biological communities of extremophilic microbes that are adapted to cold, low-nutrient conditions and facilitate biogeochemical cycles independent of energy inputs from the sun. These lakes and their inhabitants are of particular interest in the field of astrobiology and the search for extraterrestrial life.
Among the subglacial lakes of Westarctica is Lake Mercer.