Methane oxidation in permeable sediments at hydrocarbon seeps in the Santa Barbara Channel, California

摘要

A shallow-water area in the Santa Barbara Channel, California, knowncollectively as the Coal Oil Point seep field, is one of the largest naturalsubmarine hydrocarbon emission areas in the world. Both gas and oil areseeping constantly through a predominantly sandy seabed into the ocean. Thisstudy focused on the methanotrophic activity within the surface sediments(0–15 cm) of the permeable seabed in the so-called Brian Seep area at awater depth of ∼10 m. Detailed investigations of the sedimentbiogeochemistry of active gas vents indicated that it is driven by fastadvective transport of water through the sands, resulting in a deeppenetration of oxidants (oxygen, sulfate). Maxima of microbial methaneconsumption were found at the sediment-water interface and in deeper layersof the sediment, representing either aerobic or anaerobic oxidation ofmethane, respectively. Methane consumption was relatively low (0.6–8.7 mmol m?2 d-1) in comparison to gas hydrate-bearing fine-grainedsediments on the continental shelf. The low rates and the observation offree gas migrating through permeable coastal sediments indicate that asubstantial proportion of methane can escape the microbial methane filter incoastal sediments.