Seasonal rates of methane oxidation in anoxic marine sediments.

Methane concentrations and rates of methane oxidation were measured in intact sediment cores from an inshore marine sediment at Jutland, Denmark. The rates of methane oxidation, determined by the appearance of CO(2) from injected CH(4), varied with sediment depth and season. Most methane oxidation was anoxic, but oxygen may have contributed to methane oxidation at the sediment surface. Cumulative rates (0- to 12-cm depth) for methane oxidation at Kysing Fjord were 3.34, 3.48, 8.60, and 17.04 mumol m day for April (4 degrees C), May (13 degrees C), July (17 degrees C), and August (21 degrees C), respectively. If all of the methane was oxidized by sulfate, it would account for only 0.01 to 0.06% of the sulfate reduction. The data indicate that methane was produced, in addition to being oxidized, in the 0- to 18-cm sediment stratum.