A paleoclimate reference record spanning the last 1 million years from the Fram Strait (Sites U1621 and U1623, IODP Expedition 403)

As the main gateway to the Arctic Ocean, the Fram Strait (FS) plays a critical role in regulating central Arctic–Atlantic water exchange and global climate dynamics. Paleoclimate reconstructions from this key region remain particularly challenging due to the scarcity of continuous, well-positioned and high-resolution sedimentary records. During International Ocean Discovery Program (IODP) Expedition 403 (Eastern Fram Strait Paleo-Archive), Sites U1621 and U1623 were cored in the Bellsund Drift, southeastern Fram Strait. This study presents detailed calcareous nannofossil data from Holes U1621A and U1623A, documenting an unprecedented record of key Quaternary calcifying phytoplankton groups in the region. Intercalibrated with shipboard magnetostratigraphic data, these records establish the first chronological framework for the Bellsund Drift sediments, spanning the last ∼1 million years. Increases in nannofossil abundances—defined as Nannofossil Abundance (NA) events—are identified at both sites and closely correlate with peak enhancements in Ca/Ti and Sr/Ti ratios recorded in X-ray fluorescence (XRF) data. This biogenic-geochemical covariance provides compelling evidence of fluctuations in primary productivity and sedimentary calcium carbonate (CaCO3) concentration, linked to orbitally driven changes in local conditions across glacial–interglacial (G/IG) cycles. These signals likely reflect ecological variability driven by changes in North Atlantic water inflow along the Fram Strait. The timing and structure of NA events show strong similarities with records from the palaeoceanographically connected lower-latitude Norwegian Seas. Within the structure of our record, we identify evidence of key transitions during the Pleistocene, the Mid-Pleistocene Transition (MPT) and the Mid-Brunhes Event (MBE), as well as the evolution of the interglacial phases Marine Isotope Stages (MIS) 31, 19, 15–9, 5 and the Holocene. Globally recognizable features, such as the increased pelagic production during the mid-Brunhes interval, are also observed. This study underscores the exceptional value of the Bellsund Drift as providing high-resolution records for the reconstruction of orbital scale paleoceanographic and paleocelimate variability from the key Fram Strait region during the last ∼1 million years.