In situ fluxes and zonation of microbial activity in surface sediments of the Ha˚kon

• Main Authors: Mosby Mud Volcano, Dirk De Beer, Eberhard Sauter, Helge Niemann, Norbert Kaul, Ursula Witte, Michael Schlüter, Antje Boetius
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Barents Sea; Kon
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.322.6576; http://222.aslo.org/lo/toc/vol_51/issue_3/1315.pdf

From the Ha˚kon Mosby Mud Volcano (HMMV) on the southwest Barents Sea shelf, gas and fluids are expelled by active mud volcanism. We studied the mass transfer phenomena and microbial conversions in the surface layers using in situ microsensor measurements and on retrieved cores. The HMMV consists of three concentric habitats: a central area with gray mud, a surrounding area covered by white mats of big sulfide oxidizing filamentous bacteria (Beggiatoa), and a peripheral area colonized by symbiontic tube worms (Pogonophora). A fourth habitat comprised gray microbial mats near gas seeps. The differences between these four methane-fueled habitats are best explained by different transport rates of sulfate into the sediments and porewater upflow rates. The upflow velocities were estimated by two independent methods at 3–6 m yr21 in the central area and 0.3–1 m yr21 in Beggiatoa mats. In the central area no sulfide was found, indicating that the rapidly rising sulfate-free fluids caused sulfate limitation that inhibited anaerobic oxidation of methane (AOM). Under Beggiatoa mats a steep sulfide peak was found at 2 to 3 cm below the seafloor (bsf), most likely due to AOM. All sulfide was oxidized anaerobically, possibly through nitrate reduction by Beggiatoa. The Beggiatoa mats were dominated by a single filamentous morphotype with a diameter of 10 mm and abundant sulfur