Biogeochemistry of a low-activity cold seep in the Larsen B area, western Weddell Sea, Antarctica

Abstract

Abstract. First videographic indication of an Antarctic cold seep ecosystem was recently obtained from the collapsed Larsen B ice shelf, western Weddell Sea (Domack et al., 2005). Within the framework of the R/V Polarstern expedition ANTXXIII-8, we revisited this area for geochemical, microbiological and further videographical examinations. During two dives with ROV Cherokee (MARUM, Bremen), several bivalve shell agglomerations of the seep-associated, chemosynthetic clam Calyptogena sp. were found in the trough of the Crane and Evans glacier. The absence of living clam specimens indicates that the flux of sulphide and hence the seepage activity is diminished at present. This impression was further substantiated by our geochemical observations. Concentrations of thermogenic methane were moderately elevated with 2 µM in surface sediments of a clam patch, increasing up to 9 µM at a sediment depth of about 1 m in the bottom sections of the sediment cores. This correlated with a moderate decrease in sulphate from about 28 mM at the surface down to 23.4 mM, an increase in sulphide to up to 1.43 mM and elevated rates of the anaerobic oxidation of methane (AOM) of up to 600 pmol cm −3 d −1 at about 1 m below the seafloor. Molecular analyses indicate that methanotrophic archaea related to ANME-3 are the most likely candidates mediating AOM in sediments of the Larsen B seep.

Interaction between hydrocarbon seepage, chemosynthetic communities, and bottom water redox at cold seeps of the Makran accretionary prism: insights from habitat-specific pore water sampling and modeling

“…Wallmann et al, 1997Wallmann et al, , 2006Suess et al, 1998;Tryon et al, 1999;Sahling et al, 2008;Niemann et al, 2009;Reitz et al, 2011). The upward supply of hydrocarbons towards and across the sediment/water interface produces steep geochemical gradients of pore water constituents, and typically stimulates high rates of anaerobic oxidation of methane (AOM) and other hydrocarbons with sulfate as an electron acceptor close to the sediment surface (Borowski et al, 1996;Treude et al, 2003).…”

“…Numerous studies have demonstrated that the flux of methane and sulfide towards the sediment/water interface determines the microbial and faunal community composition at cold seeps (e.g. Dando and Hovland, 1992;Barry et al, 1997;Sibuet and Olu, 1998;Sahling et al, 2002;Levin et al, 2003;Treude et al, 2003;van Dover et al, 2003;Arvidson et al, 2004;Levin, 2005;Niemann et al, 2006;Niemann et al, 2009;Lichtschlag et al, 2010a).…”

“…Gas flare imaging was conducted with the ship-mounted parametric echosounder system ATLAS PARASOUND as described by Nikolovska et al (2008). In this study the notation "Flare", as it has been adopted from onboard echosounder identification of potential sampling targets, will be used to specify a major locality.…”

“…Sahling et al, 2002;Niemann et al, 2009;Lichtschlag et al, 2010b Table 3). Sulfide fluxes of 3.3 mol m −2 yr −1 and 4.9 mol m −2 yr −1 were determined for white filamentous sulfur bacteria sites within the core-OMZ, which were unaffected by in-situ gas bubble ascend at the time of sampling.…”

Characterisation of the Nematode Community of a Low-Activity Cold Seep in the Recently Ice-Shelf Free Larsen B Area, Eastern Antarctic Peninsula

“…Such microbial mats are typical for active cold seeps where the anaerobic oxidation of methane leads to high sulphide concentrations near the sediment surface [8], [21]. An additional sign of cold-seep activity was present in the form of small mounds encrusted by bivalve shells belonging to the seep-associated vesicomyid clam Calyptogena sp., which lives in symbiosis with sulphur-oxidising bacteria [22].…”