HR: 0830h
AN: C31B-0394    [PDF]
TI: Estimating the Depth and Shape of Lake Vostok's Water Cavity from Aerogravity Data
AU: * Studinger, M
EM: mstuding@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, POBox 100, Palisades, NY 10964 United States
AU: Bell, R E
EM: robinb@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, POBox 100, Palisades, NY 10964 United States
AU: Tikku, A A
EM: ani@ori.u-tokyo.ac.jp
AF: Lamont-Doherty Earth Observatory, POBox 100, Palisades, NY 10964 United States
AU: Tikku, A A
EM: ani@ori.u-tokyo.ac.jp
AF: Ocean Research Institute University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8639 Japan
AB: The water circulation within Lake Vostok provides a viable mechanism for transporting mass and energy through the lake, enhancing the potential for the support of biota. The circulation pattern depends primarily on the geometry of the lake bathymetry. Water in shallow regions will warm more from the geothermal heat flux than in deeper parts, resulting in subtle lateral changes of water density. This temperature-induced change in water density is the primary driving force for the horizontal circulation within the lake. To date, only a few seismic soundings have provided estimates of the water depth of Lake Vostok. To determine the depth and shape of the water cavity over the entire lake we use gravity data acquired along a grid of flight lines traversing the region. The free-air gravity anomaly field reflects density variations related to both major geological and topographic structures and changes in the water depth of the lake. The gravity contribution from the deeper geological structures can be removed from the free-air anomaly by low-pass filtering of the data. The subglacial topography outside the lake and the geometry of the overlying ice sheet are well constrained from ice-penetrating radar measurements. The unknown parameter that dominates the filtered gravity anomaly is the relief of the bedrock-water interface. Assuming a constant density contrast across this boundary, the gravity data can be inverted for the bathymetry of the lake. The results show that Lake Vostok consists of two sub-basins, a northern and southern. The southern sub-basin is much deeper and approximately double the spatial area of the smaller northern sub-basin. The two sub-basins are separated by a saddle with very shallow water depths. The separation of Lake Vostok in two distinct sub-basins has important ramifications for the water circulation within the lake. The lake volume estimated from the inversion of gravity data is 5200 cubic km, three times bigger than previously thought. The melting and freezing pattern observed from ice-penetrating radar data is intimately linked to the bathymetric structure of the lake. Over the northern basin, basal melting is dominating while over the southern basin, basal freezing dominates the lake/ice interaction. For a fresh-water scenario, basal meltwater in the northern basin would sink to the bottom. For this reason the water exchange between the two basins is probably very limited and raises the possibility that the two separate basins have different chemical and maybe biological compositions. Sediments released by basal meting are likely to accumulate in the northern basin while pre-glacial sediments are more likely to be found in the southern, deeper basin.
DE: 0920 Gravity methods
DE: 1827 Glaciology (1863)
DE: 3010 Gravity
DE: 3260 Inverse theory
DE: 9310 Antarctica
SC: Cryosphere [C]
MN: 2003 Fall Meeting