Circulation in Lake Vostok: A laboratory analogue study

The waters of sub-glacial Lake Vostok are thought to represent a unique biological habitat that has been out of contact with the atmosphere for millions of years. Although the water circulation within the lake will determine how nutrients are redistributed and hence where life may exist, the handful of existing studies conflict regarding whether the lake is stratified or well mixed, whether there is a clockwise or anti-clockwise circulation, or whether the sloping roof leads to a flow intensified along the eastern boundary. Here, an experimental analogue model of Lake Vostok is used to show a qualitatively different mode of circulation than described previously. The dominant mode of dispersion, and hence bio- and chemical redistribution, is controlled by the presence of columnar vortex structures that arise from rotating convection. This form of circulation does not occur in any other lake on Earth. We estimate that a water parcel takes 20-30 days to travel from the base to the roof of Lake Vostok and will experience minimal lateral mixing during this time. As the nutrient supply to the lake via melting ice is predicted to be less than that required for active growth within the entire lake, we speculate that this form of slow columnar convection would lead to the presence of thin biological boundary layers within the waters of the lake. This has important implications for the interpretation of any direct water samples taken near the roof of Lake Vostok.