Microbes living beneath Antarctica鈥檚 ice sheet may survive on methane generated by geothermal heat rising from deep below Earth鈥檚 surface. The discovery could have implications for assessing the potential for life to survive on icy worlds beyond Earth.
鈥淭hese could be hotspots for microbes that are adapted to live in these areas,鈥� says at Brown University in Rhode Island.
We already know that there is methane beneath Antarctica鈥檚 ice sheet. Other researchers have identified the gas in subglacial lakes and sediment cores, and found microbes feeding on it. However, that methane was generated by other microbes breaking down organic matter in the top few metres of sediment underneath the ice.
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Piccione and his colleagues have now identified that some of the methane beneath the ice sheet comes from a different source: geothermal heat slowly breaking down organic matter buried at a greater depth beneath the ice sheet 鈥� potentially up to about a kilometre down in the ground on which the ice sits. It is then thought to seep up through the ground as a warm gas.
They gathered this evidence by analysing carbon isotopes in gravel collected from two different sites in East Antarctica. The gravel had once been buried underneath the ice sheet, but had been pushed to the surface as the ice ground against mountains, making it possible to get samples. 鈥淎ccess to the rock record in Antarctica is extremely difficult,鈥� says Piccione.
The carbon isotopes within minerals extracted from these gravels indicated they had formed from geothermally generated methane at temperatures of around 20掳C (68掳F). 鈥淭hat鈥檚 way, way too hot for any subglacial water,鈥� says Piccione. The chemistry of the minerals further indicated that anaerobic microbes used such methane as an energy source.
Geothermally generated methane has been detected below other ice sheets and glaciers, but this is the first evidence that it forms under the Antarctic ice sheet. 鈥淲hat it probably means is that any estimate we have of how much methane is underneath the ice is probably too low,鈥� says at the University of Florida, who wasn鈥檛 involved with the research. That could expand the potential size of the habitable zone for microbes beneath the ice, he says. 鈥淯nderneath an ice sheet, the options for energy are really limited.鈥�
Such geothermally sustained habitats could be used to understand how life might survive in similar environments beyond Earth 鈥� for instance, on Jupiter鈥檚 frozen moon Europa. Antarctica 鈥渋s our best analogue for what might be happening with life on another icy world鈥�, says Piccione.
EarthArXiv
