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Negligible atmospheric release of methane from decomposing hydrates in mid-latitude oceans

October 17, 2022

Naturally occurring gas hydrates may contribute to a positive feedback for global warming because they sequester large amounts of the potent greenhouse gas methane in ice-like deposits that could be destabilized by increasing ocean/atmospheric temperatures. Most hydrates occur within marine sediments; gas liberated during the decomposition of seafloor hydrates or originating with other methane pools can feed methane emissions at cold seeps. Regardless of the origin of seep methane, all previous measurements of methane emitted from seeps have shown it to have a unique fossil radiocarbon signature, contrasting with other sources of marine methane. Here we present the concentration and natural radiocarbon content of methane dissolved in the water column from the seafloor to the sea surface at seep fields along the US Atlantic and Pacific margins. For shallower water columns, where the seafloor is not within the hydrate stability zone, we do document seep CH4 in some surface-water samples. However, measurements in deeper water columns along the US Atlantic margin reveal no evidence of seep CH4 reaching surface waters when the water-column depth is greater than 430 ± 90 m. Gas hydrates exist only at water depths greater than ~550 m in this region, suggesting that the source of methane escaping to the atmosphere is not from hydrate decomposition.

Publication Year 2022
Title Negligible atmospheric release of methane from decomposing hydrates in mid-latitude oceans
DOI 10.1038/s41561-022-01044-8
Authors DongJoo Joung, Carolyn D. Ruppel, John R. Southon, Thomas Weber, John D. Kessler
Publication Type Article
Publication Subtype Journal Article
Series Title Nature Geoscience
Index ID 70237656
Record Source USGS Publications Warehouse
USGS Organization Woods Hole Coastal and Marine Science Center