Radioisotope constraints of Arctic deep water export to the North Atlantic

The export of deep water from the Arctic to the Atlantic contributes to the formation of North Atlantic Deep Water, a crucial component of global ocean circulation. Records of protactinium-231 (Pa-231) and thorium-230 (Th-230) in Arctic sediments can provide a measure of this export, but well-constrained sedimentary budgets of these isotopes have been difficult to achieve in the Arctic Ocean. Previous studies revealed a deficit of Pa-231 in central Arctic sediments, implying that some Pa-231 is either transported to the margins, where it may be removed in areas of higher particle flux, or exported from the Arctic via deep water advection. Here we investigate this "missing sink" of Arctic Pa-231 and find moderately increased Pa-231 deposition along Arctic margins. Nonetheless, we determine that most Pa-231 missing from the central basin must be lost via advection into the Nordic Seas, requiring deep water advection of 1.1 - 6.4Sv through Fram Strait. North Atlantic deep water (NADW) formation influences the climate and carbon cycle, but the contribution of Arctic waters is difficult to constrain. Here the authors use Pa/Th proxy measurements to determine the amount of Arctic Ocean water that flows through the Fram Strait and contributes to NADW.