Deep ocean ventilation in the Central Fram Strait during the past 35 kyr

Ocean ventilation in the Arctic Mediterranean via transformation of northward inflowing warm Atlantic surface water into cold deep water affects regional climate, large-scale atmospheric circulation and carbon storage in the deep ocean. Radiocarbon dating of benthic foraminifera has been used to suggest a near-cessation of Arctic Ocean ventilation during the Last Glacial Maximum. During the last deglaciation episodic surges of this Arctic `aged' glacial deep water into the Nordic Seas and the subpolar North Atlantic Ocean may have occurred (Thornalley et al., 2011, 2015; Science). A recent study from the SE Norwegian Sea and the Iceland Basin has revealed large radiocarbon age differences between different benthic foraminiferal species during the last deglaciation (Ezat et al., 2017; Paleoceanography), which arguments for a re-evaluation of previous bottom-water radiocarbon ventilation age reconstructions from the region. Here, we present new species-specific benthic and planktic foraminiferal radiocarbon dates from the central Fram Strait and the SE Norwegian Sea for the past 35 kyr. Several lines of evidence in this new dataset demonstrate that the previously suggested `extreme aging' of >6000 14C years in the Arctic Mediterranean is most likely erroneous. In addition, benthic-planktic age offsets in the deep central Fram Strait display a remarkable decrease from 1300-2300 14C years in late Marine Isotope Stage (MIS) 3 to 0-500 14C year in MIS 2, which correlates with a decrease in benthic d13C and reduction in the benthic-planktic d18O gradient. We are in the process of compiling/screening published ventilation age reconstructions from the Arctic Mediterranean and the subpolar North Atlantic in the light of our new results in order to establish a basin-scale evolution of ocean ventilation since late MIS 3 in this region.