Diatom distribution in surface sediments of the Kara Sea

Diatom assemblages in 62 surface sediment samples from the outer Ob and Yenisei estuaries and the adjacent inner Kara Sea shelf were examined in relation to environmental conditions. Concentrations of diatoms reflect the biological productivity of surface waters along with specific water mass processes of diatom valve deposition in the zone of intermixing of riverine and marine waters. An inverse relationship between total concentration of diatom valves in sediments and surface water salinity is found. Extremely high abundances of diatom valves (up to 82.4 million valves/g sediment) are observed in the outer Ob and Yenisei estuaries (salinity < 5) and are related to a zone with rapid deposition of riverine organic matter. The overall distribution pattern of freshwater diatoms indicates the inflow of river water onto the shelf and follows the general pattern in surface water salinity. A linear regression between average summer surface water salinity and relative proportions of freshwater diatoms reveals a correlation coefficient of r = 0.86 for a salinity range of ~ 5 to 20. The distribution of sea-ice diatoms in the surface sediments generally reflects the sea-ice conditions during spring and summer time. Steep increases in their relative abundances (>10-20%) correspond to the mean interannual location of the winter polynya corroborating previously obtained results from the Laptev Sea.