The Geochemistry of Methane in Lake Fryxell, an Amictic, Permanently Ice-Covered, Antarctic Lake

• Published in: Biogeochemistry 1993-01, Vol.21 (2), p.95-115
• Main Authors: Smith, Richard L., Miller, Laurence G., Howes, Brian L.
• Format: Article
• Language: English
• Subjects: Acetates; Earth sciences; Earth, ocean, space; Exact sciences and technology; Isotope geochemistry; Isotope geochemistry. Geochronology; Lakes; Lentic systems; Marine and continental quaternary; Methane; Methane production; Oxidation; Quaternary ammonium compounds; Sediments; Sulfates; Surficial geology; Water consumption
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/bf00000873

The abundance and distribution of dissolved CH4 were determined from 1987-1990 in Lake Fryxell, Antarctica, an amictic, permanently ice-covered lake in which solute movement is controlled by diffusion. CH4 concentrations were < 1 μM in the upper oxic waters, but increased below the oxycline to 936 μM at 18 m. Sediment CH4 was 1100 μmol (1 sed)-1 in the 0-5 cm zone. Upward flux from the sediment was the source of the CH4, NH4+, and DOC in the water column; CH4 was 27% of the DOC + CH4 carbon at 18 m. Incubations with surficial sediments indicated that H14CO3- reduction was 0.4 μmol (1 sed)-1 day-1 or 4x the rate of acetate fermentation to CH4. There was no measurable CH4 production in the water column. However, depth profiles of CH4, NH4+, and DIC normalized to bottom water concentrations demonstrated that a significant CH4 sink was evident in the anoxic, sulfate-containing zone of the water column (10-18 m). The δ 13CH4 in this zone decreased from -72 ‰ at 18 m to -76 ‰ at 12 m, indicating that the consumption mechanism did not result in an isotopic enrichment of 13CH4. In contrast, δ 13CH4 increased to -55 ‰ at 9 m due to aerobic oxidation, though this was a minor aspect of the CH4 cycle. The water column CH4 profile was modeled by coupling diffusive flux with a first order consumption term; the best-fit rate constant for anaerobic CH4 consumption was 0.012 yr-1. On a total carbon basis, CH4 consumption in the anoxic water column exerted a major effect on the flux of carbonaceous material from the underlying sediments and serves to exemplify the importance of CH4 to carbon cycling in Lake Fryxell.