The interplay between ocean circulation and biological productivity affects atmospheric CO2 levels and marine oxygen concentrations. During the warming of the last deglaciation, the North Pacific experienced a peak in productivity and widespread hypoxia, with changes in circulation, iron supply and light limitation all proposed as potential drivers. Here we use the boron-isotope composition of planktic foraminifera from a sediment core in the western North Pacific to reconstruct pH and dissolved CO2 concentrations from 24,000 to 8,000 years ago. We find that the productivity peak during the Bølling–Allerød warm interval, 14,700 to 12,900 years ago, was associated with a decrease in near-surface pH and an increase in pCO2, and must therefore have been driven by increased supply of nutrient- and CO2-rich waters. In a climate model ensemble (PMIP3), the presence of large ice sheets over North America results in high rates of wind-driven upwelling within the subpolar North Pacific. We suggest that this process, combined with collapse of North Pacific Intermediate Water formation at the onset of the Bølling–Allerød, led to high rates of upwelling of water rich in nutrients and CO2, and supported the peak in productivity. The respiration of this organic matter, along with poor ventilation, probably caused the regional hypoxia. We suggest that CO2 outgassing from the North Pacific helped to maintain high atmospheric CO2 concentrations during the Bølling–Allerød and contributed to the deglacial CO2 rise.

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We thank M. Sarnthein for providing core material and stimulating discussions, the ‘B-team’ for their accommodation in the National Oceanography Centre Southampton’s laboratories, A. Mortes-Ródenas for assistance with ICP-MS analysis at Cardiff University, and J. Holmes for support throughout the project. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling for the coordination of CMIP and thank the climate modelling groups for producing and making available their model output (https://esgf-node.llnl.gov/search/cmip5/). This work was funded by NERC studentship NE/I528185/1 awarded to W.R.G., NERC studentship NE/1492942/1 to B.T., NERC grant NE/N011716/1 awarded to J.W.B.R and A.B., and NERC grant NE/I013377/1 awarded to A.E.S.

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  1. Department of Geography, University College London, London, UK

    • William R. Gray
  2. School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK

    • William R. Gray
    • , James W. B. Rae
    • , Ben Taylor
    •  & Andrea Burke
  3. Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA

    • Robert C. J. Wills
  4. Department of Earth Sciences, University College London, London, UK

    • Amelia E. Shevenell
  5. College of Marine Science, University of South Florida, St Petersberg, FL, USA

    • Amelia E. Shevenell
  6. Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton, UK

    • Gavin L. Foster
  7. School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK

    • Caroline H. Lear


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W.R.G. and J.W.B.R. designed the study and wrote the manuscript. W.R.G., J.W.B.R, G.L.F., C.H.L., B.T. and A.E.S. were involved in the generation of the trace element and δ11B data; R.C.J.W. analysed climate model output; all authors contributed to the interpretation and preparation of the final manuscript.

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The authors declare no competing interests.

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Correspondence to William R. Gray.

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