Planktic foraminifers in the outer Laptev Sea and the Fram Strait - Moderndistribution and ecology

Planktic foraminifers were studied in the Arctic Ocean in the outer Laptev Sea (76-80 degrees N, 100-150 degrees E) in 1995, in the Fram Strait (81-82 degrees N, 10 degrees W-15 degrees E) and in the western Barents Sea (76 d egrees N, 33 degrees E) in 1997, Five. depth intervals were sampled vertica lly between 500 m water depth and the sea surface, In the 125-250 mu m size class, highest abundances of living individuals were present in the wester n Fram Strait (17 ind/m(3)) and the Parents Sea (14 ind/m(3)), decreasing t o 4 ind/m(3) near Severnaya Zem-lya and less than 2 ind/m(3) at the eastern Laptev Sea continental margin, The most common species Neoglo-boquadrina p achyderma (sinistral coiling) occured in cold Polar water masses between 50 and 100 m water depth, where they accounted for >70% of all shells. A syno dic lunar reproductive cycle is demonstrated in all sampled areas, where re production takes place around full moon. In warmer Atlantic water masses of the West Spitzbergen Current and the Barents Sea, Turborotalita auinquelob a contributes >85% to the total assemblage. Most individuals were obtained between 50 and 200 m water depth. In the western Fram Strait affected by th e East Greenland Current and at the outer Laptev Sea relative abundances de crease to 2-10%, All other species combined make up only 5% of the total fa una, In general, empty tests are most abundant in water depths deeper than 200 m as a result of gametogenesis and due to high juvenile mortality. The strong gradient in absolute abundances seems to be determined by the availa bility of food, low salinity due to freshwater discharge from the Siberian rivers and the ice coverage of the Arctic Ocean. The relative abundances, h owever, reflect the complex hydrographic interaction between relatively war m Atlantic water inflow and cold polar water export in the Arctic Ocean.