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Biogeochemistry of methane in the permanently ice‐covered Lake Untersee, central Dronning Maud Land, East Antarctica
Author(s) -
Wand Ulrich,
Samarkin Vladimir A.,
Nitzsche Horst-Michael,
Hubberten Hans-Wolfgang
Publication year - 2006
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2006.51.2.1180
Subject(s) - methanogenesis , water column , anoxic waters , sulfate , methane , biogeochemistry , anaerobic oxidation of methane , oceanography , environmental chemistry , geology , stable isotope ratio , isotopes of carbon , total organic carbon , chemistry , physics , organic chemistry , quantum mechanics
We found unprecedentedly high abundances of microbially produced CH 4 in the anoxic deep waters of Lake Untersee, an oligotrophic, perennially ice‐covered Antarctic freshwater lake. The maximum CH 4 concentration (approaching 21.8 ± 1.4 mmol L −1 ) is one of the highest observed so far in a natural aquatic ecosystem. Although surficial lake sediments are the predominant source of CH 4 in Lake Untersee, methanogenesis occurs also within the anoxic waters. Radiocarbon labeling experiments show that H 2 /CO 2 reduction is the predominant methanogenic pathway (90–100%) both in the sediments and the water column, whereas acetate is only a minor CH 4 precursor. This result is consistent with the stable carbon isotope fractionation between coexisting CH 4 and CO 2 . In the water column, CH 4 is partly consumed by both aerobic and anaerobic microbial oxidation as evidenced by CH 4 concentration patterns, stable isotope analyses ( 13 C, 2 H), and 14 C‐CH 4 assays. Dissimilatory sulfate reduction also occurs and peaks at 84 m water depth (1.83 µmol SO 4 L −1 d −1 ). Intense methanogenesis in surficial lake sediments, diffusion of CH 4 from sediments to the water column, additional CH 4 production in the water column, gross CH 4 production higher than CH 4 consumption, and lack of mixing because of the permanent ice cover cause the exceptionally high CH 4 concentration in the lake. Our studies demonstrate that H 2 /CO 2 reduction may sometimes be the major pathway of methanogenesis in low‐sulfate freshwater environments even at low temperatures. This pathway is obviously more important in Antarctic lakes than hitherto assumed.