Surface Methane Concentrations Along the Mid-Atlantic Bight Driven by Aerobic Subsurface Production Rather Than Seafloor Gas Seeps

Mihai Leonte*, Carolyn D. Ruppel, Angel Ruiz-Angulo, John D. Kessler

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)

Abstract

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.

Original languageEnglish
Article numbere2019JC015989
JournalJournal of Geophysical Research: Oceans
Volume125
Issue number5
DOIs
Publication statusPublished - 1 May 2020

Bibliographical note

Funding Information:
We thank the crew and marine operations staff of the R/V Hugh R. Sharp. Water current velocity measurements were facilitated by USGS staff G. Hatcher at sea and M. Martini and J. Borden onshore. Assistance with shipboard sampling was provided by Zach Bunnell, Lillian Henderson, Allison Laubach, and Ben Young. Additional assistance with GC-FID analysis was provided by Zach Bunnell, Lillian Henderson, and Allison Laubach. We want to thank N. Prouty for reviewing this manuscript and two additional anonymous reviewers. CTD data measured on this cruise along with methane concentrations, isotopic ratios, and the fraction of methane oxidized can be accessed here (https://accession.nodc.noaa.gov/0209090). Geophysical data used to identify gas seeps can be accessed here (https://doi.org/10.5066/P9Y1MSTN). LADCP data can be accessed here (https://accession.nodc.noaa.gov/0209236). This research was supported by DOE Grant (DE-FE0028980) to J. K. and by DOE-USGS Interagency Agreement DE-FE0026195. Any use of trade, firm, or product name is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Funding Information:
We thank the crew and marine operations staff of the R/V . . Water current velocity measurements were facilitated by USGS staff G. Hatcher at sea and M. Martini and J. Borden onshore. Assistance with shipboard sampling was provided by Zach Bunnell, Lillian Henderson, Allison Laubach, and Ben Young. Additional assistance with GC‐FID analysis was provided by Zach Bunnell, Lillian Henderson, and Allison Laubach. We want to thank N. Prouty for reviewing this manuscript and two additional anonymous reviewers. CTD data measured on this cruise along with methane concentrations, isotopic ratios, and the fraction of methane oxidized can be accessed here ( https://accession.nodc.noaa.gov/0209090 ). Geophysical data used to identify gas seeps can be accessed here ( https://doi.org/10.5066/P9Y1MSTN ). LADCP data can be accessed here (https://accession.nodc.noaa.gov/0209236). This research was supported by DOE Grant (DE‐FE0028980) to J. K. and by DOE‐USGS Interagency Agreement DE‐FE0026195. Any use of trade, firm, or product name is for descriptive purposes only and does not imply endorsement by the U.S. Government. Hugh R Sharp

Publisher Copyright:
©2020. American Geophysical Union. All Rights Reserved.

Other keywords

  • gas seeps
  • isotopes
  • methane
  • mid Atlantic bight
  • ocean
  • oxidation

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