Concentration and stable carbon isotopic composition (δ13C) of CH4 are determined in a water column of an 327 m deep oxic oligotrophic crater lake, Lake Towada in Japan. The results of CTD measurements show relatively high temperature and high conductivity in the lower part of the column, possibly derived from hot springs at the crater wall approximately 150 m deep. The vertical profile of CH4 concentration shows two sharp maxima of 68 and 69 nmol/kg at depths of 20 and 150 m, respectively. The δ13C value of CH4 at 20 m is -55‰PDB, suggesting microbial production in and around the lake. In contrast, the δ13C value of CH4 at 150 m is +11‰PDB, which suggests some secondary isotopic alternation processes peculiar to hot spring-derived CH4 in the oxic water column, such as rapid aerobic microbial oxidation.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology