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

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