MEPS 264:1-14 (2003)  -  doi:10.3354/meps264001

Anaerobic oxidation of methane above gas hydrates at Hydrate Ridge, NE Pacific Ocean

Tina Treude1,*, Antje Boetius1,2,3, Katrin Knittel1, Klaus Wallmann4, Bo Barker Jørgensen1

1Max Planck Institute for Marine Microbiology, Department of Biogeochemistry, Celsiusstrasse 1, 28359 Bremen, Germany
2Alfred Wegener Institute for Polar and Marine Research, Department of Geochemistry, Am Handelshafen 12, 27515 Bremerhaven, Germany
3International University Bremen, Research II, Campusring 1, 28759 Bremen, Germany
4GEOMAR, Research Center for Marine Geosciences, Wischhofstrasse 1-3, 24148 Kiel, Germany

ABSTRACT: At Hydrate Ridge (HR), Cascadia convergent margin, surface sediments contain massive gas hydrates formed from methane that ascends together with fluids along faults from deeper reservoirs. Anaerobic oxidation of methane (AOM), mediated by a microbial consortium of archaea and sulfate-reducing bacteria, generates high concentrations of hydrogen sulfide in the surface sediments. The production of sulfide supports chemosynthetic communities that gain energy from sulfide oxidation. Depending on fluid flow, the surface communities are dominated either by the filamentous sulfur bacteria Beggiatoa (high advective flow), the clam Calyptogena (low advective flow), or the bivalve Acharax (diffusive flow). We analyzed surface sediments (0 to 10 cm) populated by chemosynthetic communities for AOM, sulfate reduction (SR) and the distribution of the microbial consortium mediating AOM. Highest AOM rates were found at the Beggiatoa field with an average rate of 99 mmol m-2 d-1 integrated over 0 to 10 cm. These rates are among the highest AOM rates ever observed in methane-bearing marine sediments. At the Calyptogena field, AOM rates were lower (56 mmol m-2 d-1). At the Acharax field, methane oxidation was extremely low (2.1 mmol m-2 d-1) and was probably due to aerobic methane oxidation. SR was fueled largely by methane at flow-impacted sites, but exceeded AOM in some cases, most likely due to sediment heterogeneity. At the Acharax field, SR was decoupled from methane oxidation and showed low activity. Aggregates of the AOM consortium were abundant at the fluid-impacted sites (between 5.1 × 1012 and 7.9 × 1012 aggregates m-2) but showed low numbers at the Acharax field (0.4 × 1012 aggregates m-2). A transport-reaction model was applied to estimate AOM at Beggiatoa fields. The model agreed with the measured depth integrated AOM rates and the vertical distribution. AOM represents an important methane sink in the surface sediments of HR, consuming between 50 and 100% of the methane transported by advection.

KEY WORDS: Anaerobic oxidation of methane · Methanotrophic archaea · Sulfate reduction · Gas hydrate · Fluid flow · Chemoautotrophy · Cold seep · Modeling

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