Methane production in meromictic Ace Lake, Antarctica

Abstract

Methane occurred in the monimolimnion, at depths greater than 11 m, of an antarctic meromictic lake, Ace Lake (depth 24.7 m). Although the water of the lake was of approximate marine salinity, bottom waters were depleted in sulfate (less than 1 mmol 1−1). The temperature of the bottom waters of the lake were constantly between 1 °C and 2 °C. Rates of methanogenesis from 14C-labelled precursors (bicarbonate, formate and acetate) were determined in time course experiments with the detection of 14CH4 produced by a gas chromatography-gas proportional counting system. Rates of 14CH4 production were difficult to determine as the reactions were always near our limit of detection. Reliable determinations of rates of methanogenesis at some depths using some precursors were obtained, the fastest rate being 2.5 µmol kg−1 day−1 at depth 20 m. Assuming constant rates of methanogenesis with time, this would equate to a turnover of methane in the lake every two years. The slow rate of methanogenesis suggests that the methanogens in Ace Lake may be working at well below their optimum temperature although definitive statements regarding the presence of psychrophilic methanogens in this antarctic lake must await isolation attempts or longer field studies using alternative methodologies.