Effect of phytoplankton and microorganisms on the isotopic composition of organic carbon in the Russian Arctic seas

Abstract

Carbon isotope composition of suspended organic matter (CICSOM) and of organic carbon of the bottom sediments (CICBS) was studied in a series of expeditions (starting in 1993) to the White, Kara, Chukchi, and Barents seas in the Russian Arctic. For each sea, CICSOM and CICBS was found to depend primarily on the ratio of OM produced in the water and OM of terrigenous origin. While in the White Sea, where the primary production (PP) is 5.3 times higher than the yearly inflow of terrigenous OM, δ13C of SOM carbon is −29.1‰, in the Chukchi Sea, where PP is more than 300 times higher than the inflow of terrigenous OM, δ13C of SOM carbon is −21.8‰. In the Barents and Chukchi seas, a considerable effect of suspended material arriving with the currents from the neighboring seas on formation of the CICSOM was demonstrated. The difference between CIC OM of the bottom sediments form CICSOM, the main component of organic matter in the sediments of all shelf seas, was demonstrated for the first time for all the seas studied. This results from production of additional microbial OM due to CO2 assimilation at the water-sediment redox boundary or in near-bottom water.