Radiocarbon Evidence of Ocean Circulation Change over the Last Deglaciation

Understanding the cause of the 90ppm difference in atmospheric CO2 during glacial versus interglacial periods remains a major challenge for palaeoclimate scientists. Whilst the cause is almost certainly related to a greater storage of carbon in the ocean, the mechanism remains unsolved. Radiocarbon derived ventilation ages may shed light on this problem as they help us to determine the distribution of carbon in the ocean as well as the partitioning of carbon between the ocean and the atmosphere. Here we use paired benthic and planktonic foraminifera radiocarbon ages to reconstruct the apparent ventilation age of intermediate-deep waters in both the Atlantic and the Pacific over the last deglaciation. Our data show a ventilation pulse of the entire deep Atlantic at the transition from Heinrich-Stadial1 to the Bølling-Allerød. A hint of this deep ventilation is also seen in the equatorial Pacific. This poses a conundrum for the deglacial carbon-cycle. A ventilation pulse would result in the release of old, radiocarbon depleted CO2 from the deep ocean to the atmosphere yet the pulse seems to occur during a plateau in the deglacial atmospheric CO2 increase and radiocarbon activity decrease.