The Biogoechemistry of the East Siberian Sea and its Impact on the Upper Waters of the Deep Arctic Ocean

The Siberian shelf seas is a very biogeochemical dynamic region which receives a lot of river runoff (containing nutrients and dissolved and particulate organic matter), exchange waters with the deep Arctic Ocean, exchange gases with the atmosphere and has an extensive biological activity. These processes impact the concentrations of chemical constituents that set the frame for the magnitude of the fluxes. In the summer 2008 we studied the biogeochemistry of the waters in the eastern Laptev Sea, the East Siberian Sea and the western Chukchi Sea during the International Siberian Shelf Study 2008 (ISSS-08). The findings reveal substantial differences from close to the coast as well as between the western and eastern regions. Close to the coast the signature is influenced by mixing between the river runoff and the seawater, while the outer regions show a more typical marine signature. Overlaying this pattern is the impact by microbial decay of organic matter, in the west dominated by terrestrial OM and in the east by marine OM. The microbial decay results in low oxygen levels, reaching as low as 40% in the shallow areas. The deficit in reactive nitrogen relative to phosphate suggests that also nitrate is used as electron acceptor during microbial decay, likely very close to the sediment or at the sediment surface. A result of this use of several electron acceptors is that there is no clear phosphate to oxygen relationship and it deviates from the classic RKR ratio. On the other hand there is a rather close correlation between silicate and oxygen that likely is not due to a common process but rather that the low oxygen waters close to the waters also gets enriched by silicate by leakage from the sediment surface. The processes behind the chemical distribution will be discussed as well as its impact on the upper waters of the deep central Arctic Ocean, which for instance support the findings by Nishino et al. (2009) that the East Siberian Sea is a source of two different silica maxima with variable salinities. Ref: Nishino, S., Shimada, K., Itoh, M, Chiba, S. J. Oceanogr., 65, 871-883, 2009.