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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 12
Biogeosciences, 14, 2929-2953, 2017
https://doi.org/10.5194/bg-14-2929-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Climate–carbon–cryosphere interactions in the...

Biogeosciences, 14, 2929-2953, 2017
https://doi.org/10.5194/bg-14-2929-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 20 Jun 2017

Research article | 20 Jun 2017

Pore water geochemistry along continental slopes north of the East Siberian Sea: inference of low methane concentrations

Clint M. Miller1, Gerald R. Dickens1, Martin Jakobsson2, Carina Johansson2, Andrey Koshurnikov3, Matt O'Regan2, Francesco Muschitiello4, Christian Stranne2, and Carl-Magnus Mörth2 Clint M. Miller et al.
  • 1Department of Earth Science, Rice University, Houston, TX 77005, USA
  • 2Department of Geological Sciences, Stockholm University, 106 91 Stockholm, Sweden
  • 3Moscow State University, Geophysics, Moscow, Russian Federation
  • 4Lamont–Doherty Earth Observatory, Columbia University, Palisades, NY, USA

Abstract. Continental slopes north of the East Siberian Sea potentially hold large amounts of methane (CH4) in sediments as gas hydrate and free gas. Although release of this CH4 to the ocean and atmosphere has become a topic of discussion, the region remains sparingly explored. Here we present pore water chemistry results from 32 sediment cores taken during Leg 2 of the 2014 joint Swedish–Russian–US Arctic Ocean Investigation of Climate–Cryosphere–Carbon Interactions (SWERUS-C3) expedition. The cores come from depth transects across the slope and rise extending between the Mendeleev and the Lomonosov ridges, north of Wrangel Island and the New Siberian Islands, respectively. Upward CH4 flux towards the seafloor, as inferred from profiles of dissolved sulfate (SO42−), alkalinity, and the δ13C of dissolved inorganic carbon (DIC), is negligible at all stations east of 143° E longitude. In the upper 8 m of these cores, downward SO42− flux never exceeds 6.2 mol m−2 kyr−1, the upward alkalinity flux never exceeds 6.8 mol m−2 kyr−1, and δ13C composition of DIC (δ13C-DIC) only moderately decreases with depth (−3.6 ‰ m−1 on average). Moreover, upon addition of Zn acetate to pore water samples, ZnS did not precipitate, indicating a lack of dissolved H2S. Phosphate, ammonium, and metal profiles reveal that metal oxide reduction by organic carbon dominates the geochemical environment and supports very low organic carbon turnover rates. A single core on the Lomonosov Ridge differs, as diffusive fluxes for SO42− and alkalinity were 13.9 and 11.3 mol m−2 kyr−1, respectively, the δ13C-DIC gradient was 5.6 ‰ m−1, and Mn2+ reduction terminated within 1.3 m of the seafloor. These are among the first pore water results generated from this vast climatically sensitive region, and they imply that abundant CH4, including gas hydrates, do not characterize the East Siberian Sea slope or rise along the investigated depth transects. This contradicts previous modeling and discussions, which due to the lack of data are almost entirely based on assumption.

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Continental slopes north of the East Siberian Sea are assumed to hold large amounts of methane. We present pore water chemistry from the 2014 SWERUS-C3 expedition. These are among the first results generated from this vast climatically sensitive region, and they imply that abundant methane, including gas hydrates, do not characterize the East Siberian Sea slope or rise. This contradicts previous modeling and discussions, which due to the lack of data are almost entirely based assumption.
Continental slopes north of the East Siberian Sea are assumed to hold large amounts of methane....
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