PLANKTIC FORAMINIFERS IN THE OUTER LAPTEV SEA AND THE FRAM STRAIT--MODERN DISTRIBUTION AND ECOLOGY

Abstract

Planktic foraminifers were studied in the Arctic Ocean in the outer Laptev Sea (76–80°N, 100–150°E) in 1995, in the Fram Strait (81–82°N, 10°W–15°E) and in the western Barents Sea (76°N, 33°E) in 1997. Five depth intervals were sampled vertically between 500 m water depth and the sea surface. In the 125–250 μm size class, highest abundances of living individuals were present in the western Fram Strait (17 ind/m3) and the Barents Sea (14 ind/m3), decreasing to 4 ind/m3 near Severnaya Zemlya and less than 2 ind/m3 at the eastern Laptev Sea continental margin. The most common species Neogloboquadrina pachyderma (sinistral coiling) occured in cold Polar water masses between 50 and 100 m water depth, where they accounted for >70% of all shells. A synodic lunar reproductive cycle is demonstrated in all sampled areas, where reproduction takes place around full moon. In warmer Atlantic water masses of the West Spitzbergen Current and the Barents Sea, Turborotalita auinqueloba contributes >85% to the total assemblage. Most individuals were obtained between 50 and 200 m water depth. In the western Fram Strait affected by the East Greenland Current and at the outer Laptev Sea relative abundances decrease to 2–10%. All other species combined make up only 5% of the total fauna. 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 availability of food, low salinity due to freshwater discharge from the Siberian rivers and the ice coverage of the Arctic Ocean. The relative abundances, however, reflect the complex hydrographic interaction between relatively warm Atlantic water inflow and cold polar water export in the Arctic Ocean.