An early to mid-Pleistocene deep Arctic Ocean ostracode fauna with North Atlantic affinities

•A new Pleistocene ostracode fauna was discovered in the western Arctic Ocean.•Early to mid-Pleistocene ostracodes exhibit affinities to North Atlantic taxa.•Several species now extinct in the Arctic Ocean were found.•Faunal turnovers occurred with the Mid-Pleistocene Transition and Mid-Brunhes Event.•Ostracodes track Pleistocene Arctic sea ice development.

An early to middle Pleistocene ostracode fauna was discovered in sediment core P1-93-AR-23 (P23, 76.95°N, 155.07°W) from 951 meter water depth from the Northwind Ridge, western Arctic Ocean. Piston core P23 yielded more than 30,000 specimens and a total of about 30 species. Several early to mid-Pleistocene species in the genera Krithe, Echinocythereis, Pterygocythereis, and Arcacythere are now extinct in the Arctic and show taxonomic affinities to North Atlantic Ocean species. Our results suggest that there was a major ostracode faunal turnover during the global climate transitions known as the Mid-Pleistocene Transition (MPT, ~ 1.2 to 0.7 Ma) and the Mid-Brunhes Event (MBE, ~ 400 ka) reflecting the development of perennial sea ice during interglacial periods and large ice shelves during glacial periods over the last 400,000 years.