Radiocarbon evidence for enhanced respired carbon storage in the Atlantic at the Last Glacial Maximum.

The influence of ocean circulation changes on atmospheric CO2 hinges primarily on the ability to alter the ocean interior's respired nutrient inventory. Here we investigate the Atlantic overturning circulation at the Last Glacial Maximum and its impact on respired carbon storage using radiocarbon and stable carbon isotope data from the Brazil and Iberian Margins. The data demonstrate the existence of a shallow well-ventilated northern-sourced cell overlying a poorly ventilated, predominantly southern-sourced cell at the Last Glacial Maximum. We also find that organic carbon remineralization rates in the deep Atlantic remained broadly similar to modern, but that ventilation ages in the southern-sourced overturning cell were significantly increased. Respired carbon storage in the deep Atlantic was therefore enhanced during the last glacial period, primarily due to an increase in the residence time of carbon in the deep ocean, rather than an increase in biological carbon export.This work was made possible by NERC support for the cruise that collected the JC89-SHAK cores (NE/J00653X/1) and by NERC grant NE/L006421/1, as well as support from the Royal Society and the Isaac Newton Trust. MD09 cores were collected on board R/V Marion Dufresne during RETRO cruise III, supported by ESF EUROMARC project RETRO, IPEV, and ANR project ANR-09-BLAN-0347. CW acknowledges support from the European Research Council grant ACCLIMATE/no 339108. This is LSCE contribution 5579.This is the final version of the article. It first appeared from Nature Publishing Group via https://doi.org/10.1038/ncomms1199