A lake divided. Lake Vostok has two deep basins, shown in dark blue, divided by a ridge (pale blue).

Two Ancient Lakes in One

Sealed beneath 4 kilometers of Antarctic ice, Lake Vostok doesn't yield its secrets easily. But researchers have recently unveiled a big one--a rocky ridge divides its waters into two basins. They likely have separate chemistries, the scientists say, and could yield unique insights into ancient Antarctic climate and the possibility of life in extreme conditions.

Lake Vostok has been essentially cut off from the world ever since it froze over around 30 million years ago. If anything lives in the lake's waters, it would have to survive using only the meltwater and particles dragged in from an overlying glacier, and possibly geothermal energy from below.

The lake's icy cover has made it hard for researchers to get a handle on some of its most basic features--including its precise temperature, dimensions, and even whether it's salty or fresh. To address some of those questions, Michael Studinger, a geophysicist at Columbia University, and colleagues flew over Lake Vostok and measured subtle variations in the gravitational pull of the ground below the lake. From these measurements, they inferred variations in density, which in turn enabled them to determine which regions were rock and which were water.

In the 19 June issue of Geophysical Research Letters, they report that Lake Vostok has two parts, separated by a ridge several hundred meters tall that probably disrupts water flow from the smaller northern basin to the larger southern basin. It's known that water melts from the glacier into the north end of the lake and freezes onto the underside of the glacier at the south end. If water flow between the two compartments is low, as Studinger and colleagues suggest, the northern basin may be significantly fresher, and sediments at its bottom would consist of what the glacier washes into the lake. The southern basin, on the other hand, would be much saltier, and the sediments there might be an untouched record of the climate in East Antarctica until the day it froze over. These different conditions may favor different types of bacteria.

"This is the most significant finding about Lake Vostok since its discovery," says glaciologist Martin Siegert of the University of Bristol, U.K. However, he says, until the lake is explored firsthand no one will really know how the water flows or what the two compartments are like. For now, Lake Vostok will keep that mystery to itself.

Related sites
A video of Vostok exploration, from NSF
Satellite pictures of Vostok and Antarctica
Studinger's Lake Vostok home page