WASHINGTONResearchers are exploring extreme conditions for life in a place not known for extremes.
As little as 20 meters (66 feet) below the surface of Lake Huron, the third largest of North America's Great Lakes, peculiar geological formationssinkholes made by water dissolving parts of an ancient underlying seabedharbor bizarre ecosystems where the fish typical of the huge freshwater lake are rarely to be seen. Instead, brilliant purple mats of cyanobacteriacousins of microbes found at the bottoms of permanently ice-covered lakes in Antarcticaand pallid, floating pony-tails of other microbial life thrive in the dense, salty water that's hostile to most familiar, larger forms of life because it lacks oxygen.
Groundwater from beneath Lake Huron is dissolving minerals from the defunct seabed and carrying them into the lake to form these exotic, extreme environments, says Bopaiah A. Biddanda of Grand Valley State University, in Muskegon, Mich., one of the leaders of a scientific team studying the sinkhole ecosystems. Those ecosystems are in a class not only with Antarctic lakes, but also with deep-sea, hydrothermal vents and cold seeps.
"You have this pristine fresh water lake that has what amounts to materials from 400 million years ago being pushed out into the lake," says team co-leader Steven A. Ruberg of the Great Lakes Environmental Research Laboratory of the National Oceanic and Atmospheric Administration (NOAA).
The researchers describe this little-known underwater habitat and their ongoing investigations of it in the current issue of Eos, the newspaper of the Earth and Space Sciences, published weekly by the American Geophysical Union (AGU). AGU is the world's largest organization of Earth and space scientists.
The scientists report that some deep sinkholes act as catch basins for dead and decaying plant and animal matter and collect a soft black sludge of sediment topped by a bacterial film. In the
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American Geophysical Union