Abstract
At the end of the Last Glacial Maximum (19,000 to 11,000 years ago), atmospheric carbon dioxide concentrations rose while the Δ14C of atmospheric carbon dioxide declined1,2. These changes have been attributed to an injection of carbon dioxide with low radiocarbon activity from an oceanic abyssal reservoir that was isolated from the atmosphere for several thousand years before deglaciation3. The current understanding points to the Southern Ocean as the main area of exchange between these reservoirs4. Intermediate water formed in the Southern Ocean surrounding Antarctica would have then carried the old carbon dioxide signature to the lower-latitude oceans5,6. Here we reconstruct the Δ14C signature of Antarctic Intermediate Water off the coast of Chile for the past 20,000 years, using paired 14C ages of benthic and planktonic foraminifera. In contrast to the above scenario, we find that the Δ14C signature of the Antarctic Intermediate Water closely matches the modelled surface ocean Δ14C, precluding the influence of an old carbon source. We suggest that if the abyssal ocean is indeed the source of the radiocarbon-depleted carbon dioxide, an alternative path for the mixing and propagation of its carbon dioxide may be required to explain the observed changes in atmospheric carbon dioxide concentration and radiocarbon activity.
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Acknowledgements
We thank M. Carman and the National Ocean Science Accelerator Mass Spectrometer Facility and Keck Carbon Cycle Accelerator Mass Spectrometer staff for technical support. Financial support for this work came from the NSF grant OCE-0751643. R.D.P.-H. was supported by the Cooperative Institute for Climate and Ocean Research (CICOR) postdoctoral fellowship at the Woods Hole Oceanographic Institution.
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R.D.P.-H. and L.K. conceived the study. R.D.P.-H. collected the foraminifera and wrote the paper with the help of all the co-authors. J.S. supplied ideas that shaped the final version. D.H. and M.M. collected the core material and provided the samples. Core SO161-SL22 was retrieved for M.M. doctoral thesis work. All authors contributed to the writing of this manuscript.
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De Pol-Holz, R., Keigwin, L., Southon, J. et al. No signature of abyssal carbon in intermediate waters off Chile during deglaciation. Nature Geosci 3, 192–195 (2010). https://doi.org/10.1038/ngeo745
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DOI: https://doi.org/10.1038/ngeo745
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