Ronald E. Sweeney

Ice cover, landscape setting, and geological framework of Lake Vostok, East Antarctica

Abstract Lake Vostok, located beneath more than 4 km of ice in the middle of East Antarctica, is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment. Melting and freezing at the base of the ice sheet, which slowly flows across the lake, controls the flux of water, biota and sediment particles through the lake. The influx of thermal energy, however, is limited to contributions from below. Thus the geological origin of Lake Vostok is a critical boundary condition for the subglacial ecosystem. We present the first comprehensive maps of ice surface, ice thickness and subglacial topography around Lake Vostok. The ice flow across the lake and the landscape setting are closely linked to the geological origin of Lake Vostok. Our data show that Lake Vostok is located along a major geological boundary. Magnetic and gravity data are distinct east and west of the lake, as is the roughness of the subglacial topography. The physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake’s circulation. Lake Vostok is a tectonically controlled subglacial lake. The tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small, but significant amounts of thermal energy into the lake.

GRAVITY ANOMALY MAP OF NORTH AMERICA

The Gravity Anomaly Map of North America is the product of a 12-year international effort to compile, critically edit and merge gravity anomaly data on a continental and global scale. This color‐pixel map, printed on four quadrant sheets at a scale of 1:5 000 000 and including a fifth sheet showing a color index map with data references, is the first such map at this large scale to include several hundreds of thousands of precise surface data of the United States, Canada, Mexico and Central America as well as other high‐quality surface data from neighboring continental and oceanic areas. The map, which shows Bouguer gravity anomalies on land and free‐air gravity anomalies over oceans, is remarkable for its detail. Sixty‐six colors or shadings have been used in a carefully conceived nonlinear scheme to show anomalies at a 5 or 10 mGal interval over a dynamic range from about −300 mGal to +130 mGal.