Lakes that lie beneath Antarctica’s vast ice sheets may hold clues to the Earth’s past climate, ice sheet history and the evolution of life — how do we know?
Since the 1970’s scientists have used radar, seismic and satellite technologies to discover over 400 lakes locked beneath Antarctica’s vast ice sheets. These range from large stable lakes, such as Lake Vostok under the East Antarctic Ice Sheet, to small ephemeral waterbodies at the ice sheet margins and under fast-flowing ice streams. The water beneath the ice remains liquid because of small levels of geothermal heat from the Earth’s core coming up through bedrock, and from the insulating effect of several kilometres of ice above.
How long have they been under the ice?
Some lakes under land-based sectors of the ice sheet may be up to 15 million years old. The age of the water within these lakes will be as old as the overlying ice that melts into them, which in East Antarctica is around 1.5 million years. Lakes present under marine based sectors of the ice sheet (which includes much of West Antarctica), have formed since the last expansion of the ice sheet over these areas, which could be less than 100 thousand years ago. However, frequent changes in the configuration of subglacial hydrological networks means some of the lakes maybe present over much shorter timescales.
Why are Antarctica’s lakes important?
There are three main questions that can be addressed by studying subglacial lakes:
- Did the West Antarctic Ice Sheet collapse, or persist, during recent interglacial periods, when Antarctic conditions resembled future conditions under CO2 warming? Radar surveys show that some of the lakes have accumulated 10-100s meters of sediments which likely contain evidence of past ice sheet configurations, which is particularly important to understand under the marine based part of the ice sheet. Under the land-based ice the oldest lakes could preserve climate and ice sheet records dating back millions of years.
- How does the presence of water beneath the ice sheet influence its stability? Near the edge of the ice sheet and under fast flowing ice streams the lakes are important parts of the hydrological network; the water acts as a lubricant to the ice above influencing how fast the ice sheet flows.
- What life is present and how has survived isolated from the atmosphere and ocean for thousands to millions of years? The older, stable lakes are thought to be extreme yet viable habitats for unusual lifeforms that have evolved to use energy derived from inorganic chemicals from the rocks whilst surviving with no light and under extreme pressure from the overlying ice.
Answering these questions requires direct access and sampling of the lakes.
Is it possible to drill through the ice to sample the water and sediments?
Accessing the subglacial environment is a huge technical challenge. BAS has developed hot water drills that have been used to access the bed more than 2.1 km beneath the ice surface. This is a technology that provides rapid access to the bed, and a short window in which to carry out scientific experiments.
Geophysical surveys have identified several subglacial lakes under the main bodies of the East and West Antarctic Ice Sheets with stable water columns and sediments that are suited to addressing the major scientific questions cited above. A network of international collaborations and partnerships is being developed to access these lakes, building on successful drilling campaigns at the margins.
- There are over 400 subglacial lakes known in Antarctica.
- They exist in most parts of the continent because low levels of geothermal heat from the Earth’s interior is enough to melt the base of the ice sheet.
- The melted water is part of a hydrological network under the ice sheet which includes lakes, ‘river’ channels and ‘estuarine’ environments just as it does on the land surface.
- The movement of water through the networks, and from lake to lake can sometimes be tracked by satellites which measure raising and lowering of the surface of the ice sheet as the lakes fill-up and drain.
- The Scientific Committee for Antarctic Research has developed a Code of Conduct on subglacial access experiments, which was accepted at the 2011 ATCM (held in Buenos Aires) and in revised form in at the 2017 ATCM (in Beijing).