Tiny shells of single-celled marine organisms (foraminifera) were measured for radiocarbon content from thirteen sediment cores over the past 20,000 years. Age models for the cores were based on correlating the percent of polar planktonic foraminifera to the Greenland ice core δ18O record and refined with thorium normalization. The radiocarbon reservoir ages (the difference between the age of the atmosphere and the carbon in the ocean surface water) was calculated. The data show consistent and large reservoir age increases of more than 1000 years from the last glacial maximum into Heinrich Stadial 1 (HS1), dropping abruptly back to approximately modern reservoir ages before the onset of the Bolling-Allerod. An intermediate complexity earth system model cGENIE was used to investigate the potential drivers of these reservoir age changes. The project found that sea ice, circulation and CO2 all play important roles in setting the reservoir age. Using these records, we showed that that Laurentide Heinrich Events were a response to stadial conditions, rather than their root cause.

Dr Andrea Burke (University of St Andrews) was PI with Co-I’s Prof. William Austin and Dr James Rae (St Andrews) and Prof. Paula Reimer and Dr Maarten Blaauw (QUB) and Postdoctoral research fellow Rosanna Greenop.