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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 non-geological 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.
Ideas and perspectives: A strategic assessment of methane and nitrous oxide measurements in the marine environmentnull (Ed.)Abstract. In the current era of rapid climate change, accuratecharacterization of climate-relevant gas dynamics – namely production,consumption, and net emissions – is required for all biomes, especially thoseecosystems most susceptible to the impact of change. Marine environmentsinclude regions that act as net sources or sinks for numerous climate-activetrace gases including methane (CH4) and nitrous oxide (N2O). Thetemporal and spatial distributions of CH4 and N2O are controlledby the interaction of complex biogeochemical and physical processes. Toevaluate and quantify how these mechanisms affect marine CH4 andN2O cycling requires a combination of traditional scientificdisciplines including oceanography, microbiology, and numerical modeling.Fundamental to these efforts is ensuring that the datasets produced byindependent scientists are comparable and interoperable. Equally critical istransparent communication within the research community about the technicalimprovements required to increase our collective understanding of marineCH4 and N2O. A workshop sponsored by Ocean Carbon and Biogeochemistry (OCB)was organized to enhance dialogue and collaborations pertaining tomarine CH4 and N2O. Here, we summarize the outcomes from theworkshop to describe the challenges and opportunities for near-futureCH4 and N2O research in the marine environment.