Distribution of planktic foraminifera at the ice margin in the Arctic (Fram Strait)

Abstract

Planktic foraminifera were collected in net tows (>63 μm) along two east-west transects at 78 ° and 80 °N in the Fram Strait (northern Nordic Seas) at five concurrent depth intervals in the upper 200 m of the water column. In the ice-free zone, absolute abundances in the upper 200 m of the water column up to 500 individuals/m 3 were obtained. Along the ice margin the absolute abundances reached up to 1250 ind/m 3, while in the ice-covered areas not more than 50 ind/m 3 have been found. Surprisingly, these strong variations in abundance are not accompanied by significant changes in faunal assemblages between the ice-free and the ice-covered regions. Neogloboquadrina pachyderma is the dominant species in most samples, making up to 60% of the total faunal assemblage. Globigerina quinqueloba contributes 38%, and all other species combined make up only 2% of the total fauna. Both, absolute and relative abundances of the collected foraminifera are strongly dependent on the mesh size used. Using smaller mesh sizes provides a wider species spectrum, which is of special interest for paleoceanographic reconstructions in the Nordic Seas, where fossil assemblages >150 μm often consist of only one species. The specific hydrographic conditions in the Fram Strait, with warm Atlantic waters underlying cold Polar surface waters, result in a rather atypical depth distribution of the planktic foraminifera. All species seem to prefer the temperate Atlantic waters (between 50 m and 200 m). Thus, the species composition as well as geochemical tracers do not reflect the surface ocean conditions, which again has potentially interesting implications for paleoceanographic reconstructions.