Recent Ostracoda from the Laptev Sea (Arctic Siberia): species assemblages and some environmental relationships

Ostracod assemblages from coretop sediments collected at 26 localities at different depths of the Laptev Sea shelf and upper continental slope were investigated for assemblage studies. A total of 41 species belonging to 19 genera and 12 families have been identified. Three assemblages have been established that could be linked to environmental factors such as water depth, bottom salinities, water mass circulation and sea-ice transportation. The species-rich and abundant assemblages of the western and central Laptev Sea were related to the Atlantic waters occupying the upper continental slope. These include relatively deep-water forms that show clear affinities to North Atlantic and Arctic Ocean assemblages (Cytheropteron biconvexa, C. testudo, C. simplex, C. nodosoalatum, C. inflatum, C. porterae, Krithe glacialis, K. minima, Pseudocythere caudata, Polycope punctata, P. orbicularis). In the eastern middle shelf region, the assemblage is comprised of Acanthocythereis dunelmensis together with other normal marine species (Semicytherura complanata, Elofsonella concinna, Cluthia cluthae). This assemblage seems connected to the winter flaw polynya which is believed to be the main area of sediment entrainment into sea ice. The inner shelf assemblage of the southern Laptev Sea is dominated by shallow-water euryhaline species (Paracyprideis pseudopunctillata and Heterocyprideis sorbyana) with admixture of the brackish-water species Roundstonia macchesneyi. The unusual occurrence of a number of shallow-water ostracod species on the upper continental slope may be explained by ice-rafting which these ostracods are probably able to survive.