A priori estimates of mixing and circulation in the hard-to-reach water body of Lake Vostok

Lake Vostok in Eastern Antarctica is covered by a similar to 4000 m thick ice sheet that glides over the subglacial water body on a time scale of similar to 20 000 years. As a basis for "pre-expedition'' planning, a priori estimates are made for water temperature, heat flux and currents. Whereas vertical temperature gradients are predicted to be extremely small due to geothermally driven convective turbulence, horizontal temperature gradients are expected to be present due to the horizontal gradient of the pressure-dependent freezing point at the base of the sloped ice ceiling. Except at the lake's deepest location, where a thin strati red layer may develop, the vertical in situ temperature profile will be near the adiabatic lapse rate. Based on internal heat fluxes associated with observed melting and re-freezing at the base of the ice sheet we calculate internal currents by assuming geostrophic balance. Vertical and horizontal motions are both expected to lie in the range of fractions of mm/s. Ice plasticity (hydrostatic adjustment) and water-ice heat exchanges are predicted to flatten the ice-cover quickly to a remarkably smooth terrain while the ice moves over the lake. These results corroborate well with the recent finding that only the upper part of accreted lake water, retrieved from the Vostok ice-core, contains particles. Our predictions are discussed with respect to uncertainties and the experimental challenges to be met. (C) 2000 Elsevier Science Ltd. All rights reserved.