Award: OCE-2048831

Project Outcomes and Findings. The goal of this project is to understand how dissolved organic carbon is transformed at methane seeps. We used ultra-high resolution mass spectrometry to characterize the components of the dissolved organic carbon in profiles of cores taken near seeps and compared with cores taken far from methane seeps (i.e. reference cores) to understand the unique chemical transformations that occur during methane oxidation near the sediment-water interface. Lignin is a structural component of plant cell walls and one of the most abundant biological materials on our planet. It has a complex aromatic structure that has generally been considered to be difficult to breakdown by microorganisms in the environment. At our study site, Astoria Canyon off the coast of Oregon, the most likely source of lignin is terrestrial runoff from the Columbia River. Because of its resistance to decay it is generally thought that lignin will accumulate in deep sediments contributing to the deposition of organic carbon. Our results are consistent with this mechanism at the reference site. Surprisingly, however, our analysis of the organic carbon demonstrates that lignin is consumed at the methane seep site, contrary to the expectation that lignin is difficult to degrade. Our project further demonstrates that the metabolic diversity of the microbial community at the seep site is relatively narrow, while microbial metabolisms at the reference site are diverse, likely because of the comparatively small amount of energy-rich resources at the non-seep locations. Our results have implications for the accumulation of organic carbon in deep marine sediments and the potential for contribution of terrestrial carbon (e.g. lignin) to the deep marine biosphere. Products of this Project Documentary: Part of this project was to fund an educational documentary about methane seeps and the work we do in collaboration with WFSU Public Media. This documentary and associated learning materials will also be made available to public school teachers free of charge via PBS Learning Media for inclusion in lesson plans. The documentary by WFSU Public Media, Secrets of the Seep, was completed with an airdate currently being scheduled. The documentary will also stream at the first time it airs on local public television. Datasets: Dataset of FTCIR-MS results available via Zenodo: 10.5281/zenodo.15119966 Conference Presentations: This project contributed to four presentations at the American Geophysical Union Conference in Washington DC held Dec 9-13 2024: Sources, age, production, and fate of seep-derived dissolved organic carbon at methane seeps in Astoria Canyon: An overview of recent and ongoing studies. John Pohlman, Laura L. Lapham, Rachel Wilson, Jeffrey Seewald, Ellen Lalk, Anna Hildebrand, Karen G Lloyd, Leketha Williams, Mario Veloso, Tim Weiss, Jens Greinert, Kun Ma, Susan Q Lang, Lennart Stock and Marcus Elvert, The bioavailability of dissolved organic carbon from methane seeps in the deep sea. Ellen Lalk, John W. Pohlman, Rachel Wilson, Laura L. Lapham, Jeffrey Seewald, Julie A. Huber, Margrethe Serres, and Michael Casso Anaerobic oxidation of methane as a mechanism for producing sedimentary dissolved organic carbon. Anna Hildebrand, John Pohlman, Karen G. Lloyd, Jeffrey Seewald, Rachel M (Wilson) Younge, Maureen Strauss, Laura Lapham Quantifying temporal variability of methane and dissolved organic carbon from sediments surrounding hydrocarbon seeps. Laura L. Lapham, Maureen Strauss, Anna Hildebrand, Ellen Lalk, John W. Pohlman, Rachel Wilson, Jeff Seewald Scientific Manuscripts Wilson, RM, L. Wiliams, K. Lloyd, A. Hildebrand, E. Lalk, J. Pohlman and L.L. Lapham. (2025) Transformation of organic matter during methane oxidation at high flux seeps. Frontiers in Marine Science, in preparation. Last Modified: 04/01/2025 Submitted by: RachelMWilson