Core samples from subglacial lake sediments show surprising biological diversity
By Summit Voice
FRISCO — Burrowing 10 feet down into the primal muck at the edge of a receding ice sheet in Antarctica, scientists with the British Antarctic Survey found what they had long been looking for — traces of microbial life dating back nearly a hundred thousand years, including strands of DNA associated with previously unknown bacteria.
For decades, researchers speculated that so-called extremophiles might exist in the cold and dark lakes hidden deep beneath the Antarctic ice sheet. Organisms living in subglacial lakes could hold clues for how life might survive on other planets.
“This is the first time microbes have been identified living in the sediments of a subglacial Antarctic lake and indicates that life can exist and potentially thrive in environments we would consider too extreme,” said lead author David Pearce, who was with the British Antarctic Survey and is now at the University of Northumbria.
The DNA testing showed a surprising level of bacterial diversity in the subglacial environment, on the order of thousands to tens of thousands of different microbes.
“One would expect low diversity … it’s unusual for such a constrained environment,” Pearce said.
Polar researchers have long been trying to access the hidden lakes, but sampling them has been fraught with logistical challenges. So for this project, the scientists searched around the retreating margins of the ice sheet for subglacial lakes that are becoming exposed for the first time since they were buried more than 100,000 years ago.
The group targeted Lake Hodgson on the Antarctic Peninsula which was covered by more than 400 m of ice at the end of the last Ice Age, but is now considered to be an emerging subglacial lake. Just a relatively thin 10- to 15-foot layer of ice remains as parts of the ice sheet melt and retreat at unprecedented rates as the temperature rises at the poles.
Drilling through the ice they used clean coring techniques to delve into the sediments at the bottom of the lake ,which is 93 meters deep and about 1.5 km long by 1.5 km wide.
The lake was thought to be a harsh environment for any form of life but the layers of mud at the bottom of the lake represent a time capsule storing the DNA of the microbes which have lived there throughout the millennia.
The top few centimetres of the core contained current and recent organisms which inhabit the lake but once the core reached 3.2 m deep the microbes found most likely date back nearly 100,000 years.
“The fact these organisms have survived in such a unique environment could mean they have developed in unique ways which could lead to exciting discoveries for us. This is the early stage and we now need to do more work to further investigate these life forms.”
Some of the life discovered was in the form of fossil DNA showing that many different types of bacteria live there, including a range of extremophiles which are species adapted to the most extreme environments. These use a variety of chemical methods to sustain life both with and without oxygen.
One DNA sequence was related to the most ancient organisms known on Earth and parts of the DNA in twenty three percent has not been previously described. Finding as-yet unidentified strands of genetic material is not unusual in microbiological surveys, but in the Hodgson Lake sediments, the high percentage of unknown genetic material (up to 25 percent) was striking, Pearce said.
Many of the species are likely to be new to science, making clean exploration of the remote lakes isolated under the deeper parts of the ice sheet even more pressing.
Late last year a British expedition to drill into Lake Ellsworth was called off after technical difficulties. A US expedition sampled a subglacial environment near the edge of the ice sheet but has yet to report its findings, and a Russian led project has sampled ice near the surface of a subglacial lake and has reported finding signs of life.
The paper, Preliminary Analysis of Life within a Former Subglacial Lake Sediment in Antarctica has been published online in the Journal ‘Diversity’ as part of a special issue on Microbial Ecology and Diversity.