Methane oxidation in permeable sediments at hydrocarbon seeps in the Santa Barbara Channel, California
Titel:
Methane oxidation in permeable sediments at hydrocarbon seeps in the Santa Barbara Channel, California
Auteur:
T. Treude W. Ziebis
Verschenen in:
Biogeosciences discussions
Paginering:
Jaargang 7 (2010) nr. 2 pagina's 1905-1933
Jaar:
2010
Inhoud:
A shallow-water area in the Santa Barbara Channel (California), known collectively as the Coal Oil Point seep field, is one the largest natural submarine oil and gas emission areas in the world. Both gas and oil are seeping constantly through a predominantly sandy seabed into the ocean. This study focused on the methanotrophic activity within the surface sediments (0–15 cm) of the permeable seabed in the so-called Brian Seep area at a water depth ~10 m. Detailed investigations of biogeochemical parameters in the sediment surrounding active gas vents indicated that methane seepage through the permeable seabed induces a convective transport of fluids within the surface sediment layer, which results in a deeper penetration of oxidants (oxygen, sulfate) into the sediment, as well as in a faster removal of potentially inhibiting reduced end products (e.g. hydrogen sulfide). Methanotrophic activity was often found close to the sediment-water interface, indicating the involvement of aerobic bacteria. However, biogeochemical data suggests that the majority of methane is consumed by anaerobic oxidation of methane (AOM) coupled to sulfate reduction below the surface layer (>15 cm), where sulfate is still available in high concentrations. This subsurface maximum of AOM activity in permeable sands is in contrast to known deep-sea seep habitats, where upward fluid advection through more fine-grained sediments leads to an accumulation of AOM activity within the top 10 cm of the sediments, because sulfate is rapidly depleted.
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