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Carbon dioxide release from the North Pacific abyss during the last deglaciation


Atmospheric carbon dioxide concentrations were significantly lower during glacial periods than during intervening interglacial periods, but the mechanisms responsible for this difference remain uncertain. Many recent explanations call on greater carbon storage in a poorly ventilated deep ocean during glacial periods1,2,3,4,5, but direct evidence regarding the ventilation and respired carbon content of the glacial deep ocean is sparse and often equivocal6. Here we present sedimentary geochemical records from sites spanning the deep subarctic Pacific that—together with previously published results7—show that a poorly ventilated water mass containing a high concentration of respired carbon dioxide occupied the North Pacific abyss during the Last Glacial Maximum. Despite an inferred increase in deep Southern Ocean ventilation during the first step of the deglaciation (18,000–15,000 years ago)4,8, we find no evidence for improved ventilation in the abyssal subarctic Pacific until a rapid transition 14,600 years ago: this change was accompanied by an acceleration of export production from the surface waters above but only a small increase in atmospheric carbon dioxide concentration8. We speculate that these changes were mechanistically linked to a roughly coeval increase in deep water formation in the North Atlantic9,10,11, which flushed respired carbon dioxide from northern abyssal waters, but also increased the supply of nutrients to the upper ocean, leading to greater carbon dioxide sequestration at mid-depths and stalling the rise of atmospheric carbon dioxide concentrations. Our findings are qualitatively consistent with hypotheses invoking a deglacial flushing of respired carbon dioxide from an isolated, deep ocean reservoir1,2,3,4,5,12, but suggest that the reservoir may have been released in stages, as vigorous deep water ventilation switched between North Atlantic and Southern Ocean source regions.

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Figure 1: Dissolved oxygen, phosphate and radiocarbon in the present-day North Pacific.
Figure 2: Apparent age differences between paired benthic and planktonic foraminifera at intermediate and deep sites in the North Pacific over the past 25 kyr.
Figure 3: Multi-proxy sedimentary records from the subarctic Pacific spanning 5 to 30 kyr ago.

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We thank A. de Vernal, J. Leduc, P. Dulski, M. Soon and K. Gordon for analytical assistance, and J. Sarmiento, R. Toggweiler, M. Kienast, L. Keigwin and S. Calvert for intellectual and practical support. R. Schlitzer’s program Ocean Data View was used to generate Fig. 1. E.D.G., T.F.P. and R.F. were supported by the Natural Sciences and Engineering Research Council of Canada and the Canadian Foundation for Climate and Atmospheric Sciences, S.L.J. by a Swiss National Foundation post-doctoral fellowship, D.M.S. by US NSF, and by BP and Ford Motor Company through the Princeton Carbon Mitigation Initiative, and G.H.H. by Deutsche Forschungsgemeinschaft.

Author Contributions E.D.G. and S.L.J. contributed equally to this work. T.F.P. and G.H.H. initiated and guided the project. E.D.G. prepared samples and picked foraminifera from ODP Site 887, S.L.J. prepared and analysed samples from site ODP Site 882. R.F. and S.L.J. made the 230Th measurements and J.R.S. made the radiocarbon measurements. M.C. contributed to the 14C analysis. E.D.G., S.L.J. and D.M.S. wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Eric D. Galbraith.

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Supplementary information

Supplementary Information

The file Supplementary Methods; Supplementary Figures S1-S4 and Legends; Supplementary Tables S1-S2 and additional references. This file contains additional notes related to the main text, regarding modern North Pacific hydrography, foraminiferal sampling methods, reservoir ages, comparison to previous Pacific radiocarbon measurements, calcium carbonate stratigraphy, foraminiferal carbon isotope interpretations, and 230-Th results, with four supplementary figures. It also contains tables of the foraminiferal 14C measurements and age constraints for ODP 887. (PDF 671 kb)

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Galbraith, E., Jaccard, S., Pedersen, T. et al. Carbon dioxide release from the North Pacific abyss during the last deglaciation. Nature 449, 890–893 (2007).

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