Methane budget of the down-current plume from Coal Oil Point seep field, Santa Barbara Channel, California
Abstract
Previous research indicates that 5.5-9.6 x 106 mol/d (90-150 t/d) of methane are emitted from the seafloor into the coastal ocean near Coal Oil Point (COP), Santa Barbara Channel (SBC), California. Methane concentrations and biologically-mediated oxidation rates were quantified at 12 stations in a 198 km2 area down-current from COP during the SEEPS"07-Cruise with the R/V Atlantis. A ship-board Acoustic Doppler Current Profiler (ADCP) recorded current velocity patterns simultaneously with water sampling. The observed methane distribution matches the cyclonic gyre which is the normal current flow in this part of the Santa Barbara Channel - pushing water to the shore near the seep field and then broadening the plume while the water turns offshore further from the source. A methane budget was calculated using a box model, with budget terms including methane burden, sea-air flux, oxidative loss, and flux in and out of the 51 km3 box. The results indicate a 0.6% loss via sea-air exchange and a 1.5% loss due to microbial oxidation. The majority of the methane is advected in and out of the box. This data enables a calculation of the amount of dissolved methane emitted from the COP seep field, and when combined with published measurements of bubble flux, allows for a revision of the total methane flux from the COP seeps. Revised estimates for the dissolved methane flux for COP are 5.5 x 106 mol/d, raising the total COP methane release to 7.4-11.5 x 106 mol/d (120-180 t/d). These results represent a snapshot, but serve as a base for the first complete dissolved methane budget of the water column above a seep site in the marine realm.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMOS33A1310M
- Keywords:
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- 1615 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0414;
- 0793;
- 4805;
- 4912);
- 3004 Gas and hydrate systems;
- 4806 Carbon cycling (0428);
- 4820 Gases;
- 4851 Oxidation/reduction reactions (0471)