Sediment Geochemistry and Diatom Distribution in the Chukchi Sea: APPLICATION FOR BIOPRODUCTIVITY AND PALEOCEANOGRAPHY

One goal of the first decade of the Russian-American Long-term Census of the Arctic (RUSALCA) program was to characterize benthic composition in the Chukchi and East Siberian Seas in order to understand the geological history of productivity and paleoclimatological changes in this region. To this end, our team analyzed total chemical composition; content of biogenic elements including organic carbon, opal, and chlorin; and the distribution and species composition of the diatom thanatocoenosis in surface sediment samples. Increased calcium content (Ca/Al > 0.22) and dominance of the diatoms Paralia sulcata and Thalassiosira nordenskioeldii indicate transport pathways of warm Pacific water within the Chukchi Sea. Areas of greatest ice cover are characterized by sediments with low calcium content (Ca/Al < 0.15) and the presence of strontium, and dominance of the diatom Thalassiosira antarctica. Distributions of elements produced by phytoplankton such as opal, chlorin, and organic carbon are less informative as indicators of water masses, bioproductivity, and ice conditions because the phytoplankton are transported by currents and they accumulate in seafloor depressions. On the Chukchi Sea shelf, these depressions usually coincide with neotectonic structures. Specific sedimentation environments within the grabenrift system of the Chukchi Sea may be created by hydrothermal vents and cold seeps, where hydrochemical conditions promote preservation of biogenic remains in the sediment and anomalous accumulation of many metals (Fe, Mn, Mo, V, Zn, Ni, Ag, Hg).