Hydrocarbon seeps release fossil methane into the marine environment, but emission of this seep-derived methane to the atmosphere is challenging to constrain. Here, we measure the concentration and radiocarbon content of dissolved methane in seawater above seeps in the northern Gulf of Mexico that have previously been linked to considerable atmospheric emissions. In bottom waters above the seeps, methane radiocarbon content is close to zero, confirming the release of fossil seep methane. However, radiocarbon signatures approach modern values at shallower depths, indicating that only ~21% of the methane in surface waters is sourced from seeps. We observe a mid-depth methane concentration maximum and radiocarbon minimum at ~200m below the surface, but this likely reflects lateral advection of fossil methane from shallower seep fields. Our findings are consistent with previous radiocarbon fingerprinting in coastal regions, and suggest that seeps deeper than ~400m are not a major contributor to atmospheric methane emissions.

- Author (Pusan National University): DongJoo Joung (Deapartment of Oceanography, G-LAMP) 

- Title of original paper: Deep Gulf of Mexico seeps are not a significant source of methane to the atmosphere

- Journal: Communications Earth and Environment

- Web link: https://www.nature.com/articles/s43247-025-03027-0 

- Contact e-mail: dongjoo.joung@usan.ac.kr