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Surface Methane Concentrations Along the Mid‐Atlantic Bight Driven by Aerobic Subsurface Production Rather Than Seafloor Gas Seeps
Author(s) -
Leonte Mihai,
Ruppel Carolyn D.,
RuizAngulo Angel,
Kessler John D.
Publication year - 2020
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2019jc015989
Subject(s) - methane , water column , methanogenesis , seafloor spreading , greenhouse gas , sink (geography) , anaerobic oxidation of methane , geology , atmospheric methane , environmental chemistry , oceanography , surface water , environmental science , chemistry , cartography , organic chemistry , environmental engineering , geography
Relatively minor amounts of methane, a potent greenhouse gas, are currently emitted from the oceans to the atmosphere, but such methane emissions have been hypothesized to increase as oceans warm. Here, we investigate the source, distribution, and fate of methane released from the upper continental slope of the U.S. Mid‐Atlantic Bight, where hundreds of gas seeps have been discovered between the shelf break and ~1,600 m water depth. Using physical, chemical, and isotopic analyses, we identify two main sources of methane in the water column: seafloor gas seeps and in situ aerobic methanogenesis which primarily occurs at 100–200 m depth in the water column. Stable isotopic analyses reveal that water samples collected at all depths were significantly impacted by aerobic methane oxidation, the dominant methane sink in this region, with the average fraction of methane oxidized being 50%. Due to methane oxidation in the deeper water column, below 200 m depth, surface concentrations of methane are influenced more by methane sources found near the surface (0–10 m depth) and in the subsurface (10–200 m depth), rather than seafloor emissions at greater depths.