At the end of the last Ice Age, Lake Hodgson lay buried under more than 400 metres of ice. Today only a 3–4 metre ice lid covers it, and in 2013 a British-led team reported that the mud on its floor holds a rich community of microbes, likely dating back nearly 100,000 years. It was the first microbiological analysis of a sediment sample from this former subglacial lake.
Lake Hodgson: a subglacial lake coming back to light
Lake Hodgson lies on southern Alexander Island, off the Antarctic Peninsula. As glaciers retreated, it emerged from beneath the ice sheet, one of several subglacial lakes now reappearing at the margins of Antarctica as deglaciation resumes. That makes it a natural laboratory: scientists can sample sediments that formed under thick ice without drilling through kilometres of it.
What the scientists found in the sediment
The study, “Preliminary Analysis of Life within a Former Subglacial Lake Sediment in Antarctica”, was published in the journal Diversity in September 2013 by D. A. Pearce, D. A. Hodgson, M. A. S. Thorne, G. Burns and C. S. Cockell. Analysing DNA from a sediment core, they found bacterial diversity dominated by four groups: Actinobacteria (about 23.8%), Proteobacteria (21.6%), Planctomycetes (20.2%) and Chloroflexi (11.6%). Around 23% of the sequences matched nothing previously described and could only be classed as “unidentified bacterium”.
“What was surprising was the high biomass and diversity we found,” said lead author David Pearce. The common sequences were not specifically polar, cold-adapted, freshwater or marine types, which leaves open questions about how this community arrived and survived. The researchers presented the work as a first step that calls for further analysis.
Antarctica’s hidden lakes
More than 400 subglacial lakes have been found beneath the Antarctic ice sheet. They stay liquid because geothermal heat from below balances the heat lost through the ice, and because the enormous pressure of the overlying glacier lowers the melting point of water below 0 °C. The largest known is Lake Vostok, where the ice above the lake is even thicker than the surrounding ice sheet.
Lake Hodgson’s results arrived during a busy period for this research. In December 2012 a UK team tried to reach Lake Ellsworth with a clean hot-water drill, but the mission was called off after equipment failure. In January 2013 the US WISSARD project drilled into Lake Whillans, beneath the West Antarctic Ice Sheet, and found about 130,000 microbial cells per millilitre and thousands of bacterial species, active organisms living on ammonia, methane and sulfur in sediments some 120,000 years old.
Why life under the ice matters
Subglacial lakes are some of the most isolated habitats on Earth: dark, cold and cut off from the atmosphere for many thousands of years. Finding abundant life there widens our picture of where organisms can survive, and it helps scientists design clean sampling methods for other extreme environments, including icy worlds beyond Earth. Clean coring matters because any contamination from the surface would blur which microbes truly belong to the lake.
Further information: British Antarctic Survey publication record.
Explore more: fieldwork in the McMurdo Dry Valleys; radar revealing a different hidden polar landscape.
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