* Astronomy

More than 145 lakes have been identified beneath the thick Antarctic ice sheet from ice-penetrating radar. Most of these lakes, captured between 3-4 kilometres of ice, are several kilometres long and are primarily located beneath the major ice divides.

Now two new lakes have been found beneath the Antarctic ice sheets.
The ancient lakes may contain ecosystems adapted to life beneath more than two miles of ice.

Geophysicists Robin Bell and Michael Studinger of Lamont-Doherty earth observatory used data from ice-penetrating radar, gravity surveys, satellite images, laser altimetry and records of a Soviet Antarctic Expedition that traversed the lakes in 1958-1959. The shorelines of the lakes appeared in satellite images of the region as perturbations in the surface of the East Antarctic ice sheet. In addition, because the ice is effectively floating on the surface of the lakes, the ice sheet exhibits slight depressions over the lakes that appear in radar and laser elevations.

The 90ºE Lake has a surface area of 2,000km2, and is second only to Lake Vostok's 14,000km2 surface area. Sovetskaya Lake was calculated to be about 1,600 km2. Both the lakes are sealed beneath more than two miles of ice.
The lake depths, estimated to be at least 900 meters, were calculated from gravity data taken during aerial surveys in 2000 and 2001. Because gravitational force is directly related to mass, a decrease in gravitational pull over the ice sheet corresponds to a decrease in mass beneath the ice.


MODIS satellite image showing location of Sovetskaya Antarctic research station and 90ºE Lake in relation to Lake Vostok.

"Over the lakes, the pull of gravity is much weaker, so we know there must be a big hole down there" - Robin Bell .



Detail of ice surface revealing outline of 90ºE lake (centre) and part of Sovetskaya Lake (beneath Sovetskaya research station). Data from 1958 Soviet study (coloured dots) revealed a noticeable drop in the Earth's gravitational pull above the two lakes. White triangles mark the locations of smaller lakes beneath the ice.

Their depth, along with the fact that they are parallel to each other and Lake Vostok, indicate that the lake system is tectonic in origin.
The combination of heat from below and a thick layer of insulating ice above keeps the water temperature at the top of 90ºE and Sovetskaya at –2 degrees Celsius, despite temperatures on the surface that can drop to –80 degrees Celsius in winter. Since the lakes are bounded by faults, it is likely the lakes receive flows of nutrients that could support unique ecosystems. Moreover, laser mapping of the ice sheet surface by NASA's Ice Cloud and Land Elevation Satellite (ICESat) revealed that this water-ice boundary, or ceiling, is tilted.

"Since the surface is tilted, we know that the ice sheet changes thickness over the lake and that will drive circulation in the lake. This will provide mixing and distribute whatever nutrients are in the lake, which is an important component of subglacial ecosystems" - Robin Bell.

This, along with the tectonic origin of the lakes, supports the idea that despite climate changes on the surface over the last 10 million to 35 million years, the volume of the lakes have remained remarkably constant, providing a stable, if inhospitable, environment that may harbour an ancient and alien ecosystem adapted to life beneath the ice sheet. However, just how, when or even whether scientists will risk the possibility of contaminating the lakes to confirm their suspicions remains the subject of an ongoing international debate.

http://www.ldeo.columbia.edu/