Until recently, Lake Vostok, with its surface area of 14,000 square kilometers,
held claim to being the only defined large lake under Antarctic ice. The subglacial
lake may harbor forms of life that evolved, isolated from the elements, for
more than tens of millions of years long before the Antarctic ice sheets
first formed more than 30 million years ago. Now, however, geologists say that
Vostok is not alone. Two great lakes, each more than 1,000 square
kilometers in area and buried deep under the Antarctic ice, are giving scientists
a new view of the continent and how such large lakes formed there.
|Because tectonic-controlled lakes are so deep and quite old, they probably have diverse ecosystems.|
Past work had identified the lakes based on the flatness of the ice above them,
but their sizes and origins remained unexplored, says Michael Studinger, a geophysicist
at Columbia Universitys Lamont-Doherty Earth Observatory in New York.
To define these deep hidden lakes, Studinger and his co-workers took surveys
from 1958 and 1970 and added new measurements from modern satellites that track
ice profiles and thickness, as well as from flyovers in a 2000 to 2001 survey
of Lake Vostok.
As published in the Jan. 25 Geophysical Research Letters (GRL), the team found that one lake, called 90°E, rivals the area of Rhode Island, at about 2,000 square kilometers. The second lake, newly dubbed Lake Sovetskaya, named for the Russian base that once stood on the flat ice above, is about 1,600 square kilometers. Geophysical measurements show that both lakes could be as deep as 900 meters or more (Vostok is probably much deeper). The 90°E lake may have a volume of about 1,800 cubic kilometers, compared to Vostoks 5,400 cubic kilometers.
Elsewhere, lakes that size generally occur when tectonic forces are at play, from large-scale movements of faults that are big enough to split continents, such as Lake Tanganyika in the African Rift Zone or even Lake Tahoe in Californias Sierra Nevada. Large glacier-carved lakes tend to be much shallower.
Similar tectonic forces may be involved in the formation of the Antarctic lakes through a series of large faults, Studinger says. Geophysical gravity data show that the lakes are bounded by steep walls and formed parallel lengthwise, likely the result of processes controlling the formation of the paralleling Transverse Mountains.
Because tectonic-controlled lakes are so deep and quite old, they probably have diverse ecosystems, says David Karl, a microbial ecologist at the University of Hawaii in Honolulu. A group of scientists, including Karl, is hoping to explore the life forms potentially present in Vostok in a drilling project, but such work is only in the preliminary planning stages.
The two new lakes complicate the ecological investigation of Vostok, however, as the three lakes could be interconnected, says Karl, who reviewed the paper for GRL. This has implications for sampling: If we contaminate one, we contaminate several of them.
Interconnectedness also has implications for how the ice above the lakes moves locally, if not on larger scales, Studinger and co-authors say. The new surveys show that the ice sheet, which actually floats atop these subglacial lakes, takes on a wedge shape over the water.
Tipping those ice wedges by accumulating ice or snow on top, or melting ice from geothermal processes below, could cause spillover into other connected lakes beneath the ice, says Frank Pattyn, a glacier modeler at the French Free University in Brussels, who says that exactly how the Antarctic ice sheet and great lakes interact remains uncertain. Draining between the lakes, Pattyn says, could lubricate the ice sheet, accelerating and redirecting its movements.
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