If one goes to the bottom of the Great Lakes, one can find huge sinkholes - just as on land - but the remarkable thing is that the sinkholes may be filled with brine. Not freshwater - saline brine which forms when water percolates out from the bedrock saturated with minerals.
Now, researchers are discovering that these unusual sinkholes are home to extraordinary communities of microscopic bacteria. The organisms are not new to science, but preliminary genetic analysis is showing that they are relatives of bacteria that live in the subglacial lakes of Antarctica. Others are functionally similar to the extremophile bacteria living on the black smokers of the deep ocean.
The sinkholes were discovered in 2001, when a sonar expedition searching for shipwrecks found deep pits, up to 100 metres across, in the lake floor. The underwater pits have formed in places where an ancient underlying seabed is dissolving.
As groundwater water rises through the carbonate bedrock, it dissolves minerals and carries them into the lake. "You have this pristine fresh water lake that has what amounts to materials from 400 million years ago being pushed out into [it]," says Steven Ruberg of the National Oceanic and Atmospheric Administration (NOAA).
Ruberg is part of a team of researchers who are studying the chemistry and biology of these odd pockets of life. So far, they have found that the water inside them is chemically very different to the overlying lake water. For starters, it is rich in sulphates and low in oxygen. It is also significantly more acidic, contains more chloride, less dissolved organic carbon, and supports entirely different life forms to the rest of the lake.
Via the excellent science blog NAACAL.