Sediment Oxygen Profiles in a Super-Oxygenated Antarctic Lake

Perenially ice-covered lakes are found in the McMurdo Dry Valleys of southern Victoria Land, Antarctica. In contrast to temperate lakes that have diurnal photic periods, antarctic (and arctic) lakes have a yearly photic period. An unusual feature of the antarctic lakes is the occurrence of $O_2$ at supersaturated levels in certain portions of the water column. Here we report the first sediment $O_2$ profiles obtained using a microelectrode from a perenially ice-covered antarctic lake. Sediment cores collected in January and october 1987 from Lake Hoare in Taylor Valley show oxygenation down to 15, and in some cases, 25 cm. The oxygenation of sediments several centimeters below the sediment-water interface is atypical for lake sediments and may be characteristic of perenially ice-covered lakes. There is a significant difference between the observed January and October sediment $O_2$ profiles. Several explanations may account for the difference, including seasonality. A time-dependent model is presented which tests the feasibility of a seasonal cycle resulting from the long photoperiod and benthic primary production in sediments overlain by a highly oxygenated water column.