The distribution and abundance of planktonic foraminifera under summer sea-ice in the Arctic Ocean

Abstract. Planktonic foraminifera are calcifying protists that represent a minor yet important part of the pelagic microzooplankton. They are found in all of Earth’s ocean basins and are widely studied in sediment records to reconstruct climatic and environmental changes throughout geological time. The Arctic Ocean is currently being transformed in response to modern climate change, yet the effect on planktonic foraminiferal populations is virtually unknown. Here we provide the first systematic sampling of planktonic foraminifera communities in the ‘high’ Arctic Ocean – here defined as areas north of 80° N – in a broad region located between northern Greenland (Lincoln Sea with adjoining fjords and the Morris Jesup Rise), the Yermak Plateau, and the North Pole. Stratified depth tows down to 1000 m using a multinet were performed to reveal the species composition and spatial variability of these communities below the summer sea-ice. The average abundance in the top 200 m ranged between 15–65 ind.m-3 in the central Arctic Ocean and was <0.3 ind.m-3 in the shelf area of the Lincoln Sea. At all stations, except one site at the Yermak Plateau, assemblages consisted solely of the polar specialist Neogloboquadrina pachyderma. It predominated in the top 100 m, where it was likely feeding on phytoplankton below the ice. Near the Yermak Plateau, at the outer edge of the pack ice, rare specimens of Turborotalita quinqueloba occurred that appeared to be associated with the inflowing Atlantic Water layer. Our results indicate that the anticipated turnover from polar to subpolar planktonic species in the Arctic Ocean has not yet occurred, in agreement with recent studies from the Fram Strait. The dataset will be a valuable reference for continued monitoring of the abundance and composition of planktonic foraminifera communities as they respond to the ongoing sea-ice decline and the ‘Atlantification’ of the Arctic Ocean basin. Additionally, the results can be used to assist paleoceanographic interpretations, based on sedimented foraminifera assemblages.