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- Title
Radiocarbon in Marine Methane Reveals Patchy Impact of Seeps on Surface Waters.
- Authors
Joung, DongJoo; Leonte, Mihai; Valentine, David L.; Sparrow, Katy J.; Weber, Thomas; Kessler, John D.
- Abstract
Geological sources of methane (CH4), such as hydrocarbon seeps, are significant yet poorly constrained sources of CH4 to seawater and the overlying atmosphere. We investigate the radiocarbon content (14C) and concentrations of dissolved CH4 in surface waters from the Coal Oil Point seep field to test the hypothesis that geological sources can dominate the regional background signal of CH4. We find that surface waters with elevated CH4 concentration were populated with seep‐CH4 and that lower concentrations of CH4 were well explained by mixing with the regional background of nongeological CH4. Substantial differences in concentration and 14C‐CH4 were observed over distances <5 km, demonstrating that surface currents mix background‐CH4 into the seep field. These results indicate that even a prolific seep region like the Santa Barbara Basin exerts limited influence on the regional background of CH4 in the surface layer but is a significant driver of patchiness in oceanic CH4 biogeochemistry. Plain Language Summary: Methane is a greenhouse gas whose concentration in the atmosphere is currently increasing. Natural hydrocarbon seeps are one potential contributor to this increase. Here, we investigate the dynamics of methane dissolved in surface waters from the world's most prolific seep field, Coal Oil Point in the Santa Barbara Basin, California, USA. We found strong spatial gradients of concentration and radiocarbon values of methane dissolved in surface waters and determine that mixing between more open ocean and seep‐impacted waters is the main driver of these spatial variations. Key Points: Distributions of radiocarbon content and dissolved methane concentrations in surface waters of the Coal Oil Point seep fields were studiedStrong spatial gradients of concentration and isotopic values of methane were observed within short distancesMixing of open‐ocean and seep‐impacted waters facilitated by currents was the key mechanism for reducing dissolved CH4 in the seep fields
- Subjects
CALIFORNIA; WATER; CARBON isotopes; METHANE; OIL seepage; WATER currents; BIOGEOCHEMISTRY
- Publication
Geophysical Research Letters, 2020, Vol 47, Issue 20, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2020GL089516