North Atlantic radiocarbon constraints on ocean circulation over the last deglaciation

Paleoclimate records from the North Atlantic show some of the most iconic records of abrupt climate change during the ice ages. Here we use radiocarbon as a tracer of ocean circulation and air-sea gas exchange to investigate potential mechanisms for the abrupt climate changes seen in the North Atlantic over the last deglaciation. We have created a stack of surface radiocarbon reservoir ages over the past 20,000 years from the North Atlantic, using new synchronized age models from thirteen sediment cores refined with thorium normalization between tie-points. This stack shows consistent and large reservoir age increases of more than 1000 years from the LGM into HS1, dropping abruptly back to approximately modern reservoir ages before the onset of the Bolling-Allerod. We use the intermediate complexity earth system model cGENIE to investigate the potential drivers of these reservoir age changes in order to further our understanding of the climatic changes occurring at these times and improve regional radiocarbon calibration. We find that the background state of overturning circulation influences the response of surface reservoir ages to fresh water hosing in the North Atlantic and caution against a straightforward interpretation of radiocarbon in terms of ventilation.