Abstract
Methane seepage at the seafloor can form gas hydrate and sustain chemosynthetic communities of deep-sea animals. Most known hydrate seeps occur shallower than 2000 m on continental slopes, whereas hydrothermal vents are found at greater depths along active spreading centres. Here we report the discovery of hydrate mounds with cold-seep fauna at 3640 m deep on the Molloy Ridge. The mounds display seafloor morphologies resulting from progressive stages of hydrate dissociation. Gas bubbles from the mounds rise to within 300 m of the ocean surface, and isotopic analysis shows the hydrates contain thermogenic gas. Crude oil sampled from the hydrate deposits indicates a young Miocene source rock formed in a fresh-brackish water paleo-environment. The hydrate mounds are inhabited by taxa including siboglinid and maldanid tubeworms, skeneid and rissoid snails, and melitid amphipods. Family-level composition of the fauna is similar to that of Arctic hydrothermal vents at similar depths, including the Jøtul vent field on the Knipovich Ridge, and less similar to nearby methane seeps at shallower depths. The overlap between seep and vent fauna in the Arctic has implications for understanding ecological connectivity across deep-sea habitats and assessing their vulnerability to future impacts from seafloor resource extraction in the region.
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Long-distance migration and venting of methane from the base of the hydrate stability zone
Negligible atmospheric release of methane from decomposing hydrates in mid-latitude oceans
Discovery of the first hydrothermal field along the 500-km-long Knipovich Ridge offshore Svalbard (the Jøtul field)
Data availability
All the data generated and or analysed in the study are included in the main text and in the Supplementary Information file. The species identified at the Freya gas hydrate mounds, the ROV frame showing the Freya gas hydrate mounds and the gas hydrate sampling on which the biological and geochemical analyses for this paper, the n-Alkanes chromatograms of the oil from Freya gas hydrate mounds, the source rock proxies, the oil maturity proxies, all-pairwise faunal similarity matrix (Sørensen Index values) for high-Arctic (>72 °N) cold seeps and hydrothermal vents, calculated from family presence/absence data using faunal records from this study and published literature (see Supplementary Data 1 for data sources), and the Fledermaus plot showing where the flares originate on the topography as processed with Qimera and acoustic backscatter processed with FMMidwater using the shipboard MBES at the Freya gas hydrate mounds are provided in the Supplementary Information. A video showing methane bubbles in this study is provided as Supplementary Movie 1.
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Acknowledgements
UiT The Arctic University of Norway, Ocean Census, and REV Ocean supported our research and the Deep Arctic – EXTREME24 expedition. Ocean Census acknowledges the funding of The Nippon Foundation, which supported this expedition. K.L. is part of the British Antarctic Survey Polar Science for Planet Earth Programme and funded by the UK’s Natural Environment Research Council. The RV Kronprins Haakon officers and crew, the ROV Aurora team, and Steve Killops are deeply acknowledged.
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Open access funding provided by UiT The Arctic University of Norway (incl University Hospital of North Norway).
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G.P.: conceptualisation, methodology, writing, original draft preparation, funding acquisition. J.T.C.: conceptualisation, methodology, writing. K.L.: methodology, writing. V.N.: methodology, writing. E.R.-L.: methodology, writing. C.A.: data visualisation, methodology. B.F.: data visualisation, writing. A.D.R.: conceptualisation, methodology, writing, funding acquisition. AD-E24 team: methodology.
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Panieri, G., Copley, J.T., Linse, K. et al. Deep-sea gas hydrate mounds and chemosynthetic fauna discovered at 3640 m on the Molloy Ridge, Greenland Sea.
Nat Commun (2025). https://doi.org/10.1038/s41467-025-67165-x
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DOI: https://doi.org/10.1038/s41467-025-67165-x
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