ORIGIN, DISTRIBUTION, AND SIGNIFICANCE OF BRINE IN THE SUBSURFACE OF ANTARCTICA

Cryogenic brine is a prominent feature of the McMurdo region of Antarctica. In the McMurdo Dry Valleys, it has been documented below the Taylor Glacier, in numerous ice-covered lakes, and, in the Taylor Valley, in an extensive, seaward-flowing groundwater system. A much larger and less studied body of brine exists offshore in the McMurdo Sound subsurface, where it saturates the porosity and has precipitated large volumes of intergranular cement in Neogene glaciomarine strata of the Victoria Land Basin. This review examines nature and distribution of brine in the McMurdo region to assess its volume, genesis, and significance with regard to climate and glacial processes. Constraints on subsurface fluid migration patterns are considered in context of available data. Geochemical data indicate that the brine is the product of seawater freezing. The large volume of brine, in excess of 27,000 km³, records the concentration of c. 3.5-6 times this amount of seawater via freezing before it infiltrated the subsurface as brine. Geochemical data are consistent with a genetic relationship between brine in the Taylor Valley and offshore in the Victoria Land Basin subsurface. Chronostratigraphic constraints point toward a scenario involving flooding of the McMurdo Dry Valleys during Neogene periods of relative warmth to form fjord-like systems, which were then cut off or over-ridden during subsequent cooling and ice sheet growth. Isolated bodies of seawater were concentrated via freezing to form brine, which percolated into the subsurface and flowed seaward. Among the enduring features that may record the presence of brine in the geologic record, brine cement phases hold the most promise.