title: Geochemistry, faunal composition and trophic structure in reducing sediments on the southwest South Georgia margin.
abstract: Despite a number of studies in areas of focused methane seepage, the extent of transitional sediments of more diffuse methane seepage, and their influence upon biological communities is poorly understood. We investigated an area of reducing sediments with elevated levels of methane on the South Georgia margin around 250 m depth and report data from a series of geochemical and biological analyses. Here, the geochemical signatures were consistent with weak methane seepage and the role of sub-surface methane consumption was clearly very important, preventing gas emissions into bottom waters. As a result, the contribution of methane-derived carbon to the microbial and metazoan food webs was very limited, although sulfur isotopic signatures indicated a wider range of dietary contributions than was apparent from carbon isotope ratios. Macrofaunal assemblages had high dominance and were indicative of reducing sediments, with many taxa common to other similar environments and no seep-endemic fauna, indicating transitional assemblages. Also similar to other cold seep areas, there were samples of authigenic carbonate, but rather than occurring as pavements or sedimentary concretions, these carbonates were restricted to patches on the shells ofAxinulus antarcticus(Bivalvia, Thyasiridae), which is suggestive of microbe-metazoan interactions.
authors.affiliation: School of Geography and Water@Leeds, University of Leeds, Leeds LS2 9JT, UK; Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: James B
authors.identifier: 0000-0002-6145-5821
authors.initials: JB
authors.lastname: Bell
authors.affiliation: Ocean and Earth Science, National Oceanography Centre Southampton , University of Southampton , Southampton SO14 3ZH , UK.
authors.forename: Alfred
authors.initials: A
authors.lastname: Aquilina
authors.affiliation: School of Geography and Water@Leeds , University of Leeds , Leeds LS2 9JT , UK.
authors.forename: Clare
authors.initials: C
authors.lastname: Woulds
authors.affiliation: Life Sciences, Natural History Museum , Cromwell Road, London SW7 5BD , UK.
authors.forename: Adrian G
authors.initials: AG
authors.lastname: Glover
authors.affiliation: School of Earth and Environment , University of Leeds , Leeds LS2 9JT , UK.
authors.forename: Crispin T S
authors.initials: CT
authors.lastname: Little
authors.affiliation: School of Biology , Newcastle University , Ridley Building, NE1 7RU , UK.
authors.forename: William D K
authors.identifier: 0000-0003-0190-0425
authors.initials: WD
authors.lastname: Reid
authors.affiliation: Ocean and Earth Science, National Oceanography Centre Southampton , University of Southampton , Southampton SO14 3ZH , UK.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Hepburn
authors.affiliation: NERC Life Sciences Mass Spectrometry Facility , SUERC , East Kilbride G75 0QF , UK.
authors.forename: Jason
authors.initials: J
authors.lastname: Newton
authors.affiliation: Ocean and Earth Science, National Oceanography Centre Southampton , University of Southampton , Southampton SO14 3ZH , UK.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Mills
keywords: Southern Ocean; assemblage composition; authigenic carbonates; ecology; methane; trophodynamics