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Elevated levels of dimethylated‐sulfur compounds in Lake Bonney, a poorly ventilated Antarctic lake

Lake Bonney is a permanently ice‐covered lake in the McMurdo Dry Valleys, Antarctica. The lake has two chemically stratified lobes (referred to as the east and west lobes), each with distinct biogenic sulfur profiles. Dimethylsulfoniopropionate (DMSPp) and dimethylsulfoxide (DMSOp) exceeded 32 and 2 nmol L−1, respectively, in the photic surface waters of the lake. Maximum DMSPp levels occurred in the deep‐chlorophyll layer of both lobes, a zone dominated by chrysophytes and chlorophytes, which are thought to be the source of dimethylated sulfur in the deep waters of the lake following sedimentation and biogeochemical processing. Waters beneath the chemoclines of both lobes are cold (<0°C), saline (>3 times seawater), suboxic, and devoid of phytoplankton biomass and activity. Dimethylsulfide (DMS) levels (>330 nmol L−1) in the deep west lobe are among the highest recorded in a natural aquatic ecosystem. In contrast, saline waters of the deep east lobe contain relatively little DMS (<70 nmol L−1) but high DMSOd (270 nmol L−1), with the latter being the highest observed in any natural aquatic ecosystem. We argue that the differences in the biogenic sulfur profiles between the deep waters of the two lobes arise principally from subtle differences in the redox conditions found in each lobe.