SALE-UNITED - Research at the subglacial lakes of Antarctica
Scientists of the Commission for Glaciology at the Bavarian Academy of Sciences and Humanities in Munich and colleagues of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven investigate the physical and dynamical conditions of the subglacial Lake Vostok in the Antarctic. These activities are a contribution to the IPY project SALE-UNITED (Subglacial Antarctic Lake Environments – Unified International Team for Exploration and Discovery).
Focus of the research is the detailed investigation of the water circulation and the melt and freeze processes within subglacial Lake Vostok. A numerical circulation model was adapted for this purpose to the specific lake conditions and new results from field measurements (ice thickness, ice velocities and lake boundaries) are included in the model setup.
There exists a pronounced water circulation within the lake which enables melt water from the ice/lake interface to mix with the lake water underneath. This process also allows a continuous discharge of nutrients, salts, dust and potentially microbes into the lake, after they completed a long journey of more than 420000 years through the ice sheet.
Our investigations demonstrate that there is a net-gain of water from ice melt and refreeze. This imbalance is mainly influenced by the geothermal heat flux and the heat transport from the lake into the ice. In contrast, the water circulation is rather stable in respect to changes in heat content and the low content of soluble salts in the lake. The distribution of the refrozen water mainly depends on the ice transport across the lake and the slope of the ice sheet/lake interface. About 11000 km2, or 64% of the lake surface is covered by refrozen lake water. The mean thickness of this layer is about 90 m, but reaches approximately 200 m in the region of the Vostok drill site. The volume of the refrozen water layer is almost 1000 km3 which is after all similar to 8 times the estimated ice volume of all glaciers in the Alps. Only 36% of the lakes´ surface is in contact with meteoric ice from the ice sheet. This is especially important for sedimentation processes, the availability of nutrients and plans for future sampling of the lake. So far, the results show that it takes about 30000 year for a complete overturning of the water volume. Thus, the entire lake water was exchanged many times since the start of the lake evolution several million years ago.
