Subglacial lakes are bodies of liquid water hidden beneath vast ice sheets and glaciers. Shielded by kilometers of ice, these environments are extreme and isolated. They represent a significant portion of the planet’s liquid freshwater, with estimates suggesting that Antarctic subglacial lakes alone contain about 15% of Earth’s total liquid freshwater supply, roughly 10,000 cubic kilometers.
Formation and Characteristics
Subglacial lakes form through a combination of geothermal heat from the Earth’s interior and the insulating properties of the overlying ice. Geothermal heat warms the base of the ice sheet, causing a slow melting process at a rate of a few millimeters per year. The immense pressure exerted by the thick ice sheet also lowers the melting point of water, allowing it to remain liquid even at temperatures below 0 degrees Celsius.
This meltwater then collects in depressions and troughs in the bedrock beneath the ice. These accumulations form subglacial lakes, which can range widely in size. Lake Vostok in Antarctica, the largest known subglacial lake, is approximately 240 kilometers long and 50 kilometers wide, holding about 5,400 cubic kilometers of water. These lakes can remain isolated for millions of years, creating stable ecosystems.
Discovery and Exploration
The existence of subglacial lakes was first detected using radar technology, specifically airborne radio-echo sounding (RES). This technique involves sending radio waves from an aircraft, which then reflect off the interfaces between different materials, such as ice, water, and sediment. Subglacial lakes appear as distinct, strong, and flat reflections on the radar data, indicating the presence of smooth, liquid surfaces beneath the ice.
The initial observation of a subglacial lake occurred in 1969 near Sovetskaya Station in East Antarctica. The first inventory of 17 Antarctic subglacial lakes was compiled in 1973, with Lake Vostok discovered between 1974 and 1975. Exploring these environments requires innovative methods to access and sample them without contamination. Scientists employ hot water drills and sterile techniques to prevent introducing foreign microbes. Direct sampling efforts have accessed lakes like Lake Whillans in 2013 and Lake Mercer in 2018, both at the edge of the West Antarctic ice sheet.
Life and Climate Insights
Subglacial lakes offer unique opportunities for studying extremophile life and ancient climate records. Characterized by perpetual darkness, high pressure, and limited nutrient availability, these environments support active microbial communities. These extremophiles provide insights into the potential for life in similar extraterrestrial environments.
The trapped water and sediments within these lakes act as natural archives of past climates and atmospheric conditions. Sediments at the lake beds can contain records of subglacial processes and ice-sheet history dating back millions of years. By studying these sediments and the chemical composition of the lake water, scientists can reconstruct Earth’s past climate, offering valuable data for understanding long-term environmental changes.
Impact on Ice Flow
Subglacial lakes influence the dynamics of the overlying ice sheets. They act as a lubricating layer at the ice-bed interface, reducing friction and allowing the ice to flow more rapidly towards the ocean. Water-saturated sediments beneath the ice sheets also contribute to this lubrication, facilitating basal sliding even at low driving stresses.
The filling and draining cycles of these lakes can directly alter ice sheet movement. Active subglacial lakes, which periodically store and release water, can trigger short-term accelerations in ice flow. For instance, the drainage of some lakes has been linked to a temporary increase in ice flow rates, such as a 10% acceleration observed in the Byrd Glacier system for over a year. These dynamic interactions have implications for understanding and predicting future sea level rise.