Atmospheric CO2 concentrations declined markedly about 70,000 years ago, when the Earth’s climate descended into the last glaciation. Much of the carbon removed from the atmosphere has been suspected to have entered the deep oceans, but evidence for increased carbon storage remains elusive. Here we use the B/Ca ratios of benthic foraminifera from several sites across the Atlantic Ocean to reconstruct changes in the carbonate ion concentration and hence the carbon inventory of the deep Atlantic across this transition. We find that deep Atlantic carbonate ion concentration declined by around 25 μmol kg−1 between ∼80,000 and 65,000 years ago. This drop implies that the deep Atlantic carbon inventory increased by at least 50 Gt around the same time as the amount of atmospheric carbon dropped by about 60 Gt. From a comparison with proxy records of deep circulation and climate model simulations, we infer that the carbon sequestration coincided with a shoaling of the Atlantic meridional overturning circulation. We thus conclude that changes in the Atlantic Ocean circulation may have played an important role in reductions of atmospheric CO2 concentrations during the last glaciation, by increasing the carbon storage in the deep Atlantic.
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We thank J. McManus, D. Sigman and B. Anderson for insightful and constructive discussions and comments, and L. Kinsley and L. Rodriguez-Sanz for laboratory assistance. This work is supported by ARC Discovery Project (DP140101393) and Future Fellowship (FT140100993) to J.Y., CAS/SAFEA International Partnership Program for Creative Research Teams to J.Y. and Z.D.J., DECRA (DE150100107) to L.M., UK NERC grant NE/J008133/1 to S.B., and by Australian Laureate Fellowship (FL120100050) to E.J.R. Core materials were kindly provided by LDEO (N. Anest), NOC (G. Rothwell), GEREGE (N. Thouveny), and WHOI (E. Roosen/D. Oppo) core repositories. Model experiments were performed on a computational cluster owned by the Faculty of Science of the University of New South Wales as well as on a cluster from the NCI National Facility at the Australian National University.
The authors declare no competing financial interests.
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Yu, J., Menviel, L., Jin, Z. et al. Sequestration of carbon in the deep Atlantic during the last glaciation. Nature Geosci 9, 319–324 (2016) doi:10.1038/ngeo2657
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