Ice Motion over Lake Vostok

Ice motion over Lake Vostok is measured using repeat-pass Synthetic Aperture Radar (SAR) interferometry. The coverage of the lake and the components of the vector field are resolved using ten overlapping data takes from ascending and descending look directions. Seventy-day temporal baselines provide the sensitivity required to observe the range of ice motion (0-6 m/yr) over the lake and the adjacent ice sheet. It is remarkable that the scattering field remained coherent over these time separations. This is critical for interferometric analysis and can be attributed to the low surface accumulation and low air temperature at this elevation. The regional flow of the ice sheet around Lake Vostok is from West to East, perpendicular to the surface elevation contours. As the ice flows pass the grounding line, a southward component of motion that is correlated with the North-South surface slope along the length of the lake. The motion profile increases slowly from the northern tip of the lake and then more rapidly south of 77's. At Vostok Station, the ice motion is 4.2 d y r. Across the lake and away from the boundary effects, the down-lake flow pattern takes on parabolic profile with maximum velocity close to the center line of the lake. The overall influence of the subglacial lake is the addition of a down-lake motion component to the prevailing west-east motion of the ice sheet. As a result, we estimate 10 % of the mass flowing onto the lake is diverted south. Reconstruction of the origins of the Vostok ice core indicates that it was grounded upglacier approximately 5000 years ago. This suggest a minimum freezing rate of 4 cm/yr for the subglacial accretion ice, ten times greater than that inferred from thermodynamic modeling of the upper 2 km of the ice core