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Atlantic Ocean CO2 uptake reduced by weakening of the meridional overturning circulation

Nature Geoscience volume 6, pages 146152 (2013) | Download Citation

Abstract

Uptake of atmospheric carbon dioxide in the subpolar North Atlantic Ocean declined rapidly between 1990 and 2006. This reduction in carbon dioxide uptake was related to warming at the sea surface, which—according to model simulations—coincided with a reduction in the Atlantic meridional overturning circulation. The extent to which the slowdown of this circulation system—which transports warm surface waters to the northern high latitudes, and cool deep waters south—contributed to the reduction in carbon uptake has remained uncertain. Here, we use data on the oceanic transport of volume, heat and carbon dioxide to track carbon dioxide uptake in the subtropical and subpolar regions of the North Atlantic Ocean over the past two decades. We separate anthropogenic carbon from natural carbon by assuming that the latter corresponds to a pre-industrial atmosphere, whereas the remaining is anthropogenic. We find that the uptake of anthropogenic carbon dioxide—released by human activities—occurred almost exclusively in the subtropical gyre. In contrast, natural carbon dioxide uptake—which results from natural Earth system processes—dominated in the subpolar gyre. We attribute the weakening of contemporary carbon dioxide uptake in the subpolar North Atlantic to a reduction in the natural component. We show that the slowdown of the meridional overturning circulation was largely responsible for the reduction in carbon uptake, through a reduction of oceanic heat loss to the atmosphere, and for the concomitant decline in anthropogenic CO2 storage in subpolar waters.

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Acknowledgements

This work was supported by the Spanish Ministry of Sciences and Innovation and co-funded by the Fondo Europeo de Desarrollo Regional 2007–2012 (FEDER) through the CATARINA project (CTM2010-17141) and through EU FP7 project CARBOCHANGE ‘Changes in carbon uptake and emissions by oceans in a changing climate’, which received funding from the European Commission’s seventh Framework Programme EU under grant agreement no. 264879. The OVIDE research project was co-funded by the IFREMER, CNRS/INSU and LEFE. H.M. was supported by CNRS and P.L. by IFREMER. M.V-R. was funded by the CSIC I3P Predoctoral Grant program (I3P-BPD2005).

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Affiliations

  1. Instituto de Investigaciones Marinas, IIM-CSIC, 36208 Vigo, Spain

    • Fiz F. Pérez
    • , Marcos Vázquez-Rodríguez
    • , Anton Velo
    • , Paula C. Pardo
    •  & Aida F. Ríos
  2. CNRS, Laboratoire de Physique des Océans, UMR6523, CNRS, Ifremer, IRD, UBO, 29280 Plouzané, France

    • Herlé Mercier
  3. Ifremer, Laboratoire de Physique des Océans, UMR6523, CNRS, Ifremer, IRD, UBO, 29280 Plouzané, France

    • Pascale Lherminier
  4. Faculty of Marine Sciences, University of Vigo, Campus Lagoas-Marcosende, 36200 Vigo, Spain

    • Gabriel Rosón

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Contributions

All authors contributed extensively to the work presented in this paper. F.F.P., H.M. and A.F.R. designed the research. F.F.P., H.M., M.V-R., A.V., P.L. and A.F.R. analysed the physical and chemical data. H.M. and P.L. estimated the currents and thermohaline fields. F.F.P., M.V-R., A.V. and G.R. determined the anthropogenic CO2 concentrations and storage rates. H.M., F.F.P., P.L. and A.F.R. estimated the uncertainties. F.F.P., H.M., M.V-R., P.C.P. and A.F.R wrote the paper. All authors discussed the results and implications and commented on the manuscript at all stages.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Fiz F. Pérez.

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https://doi.org/10.1038/ngeo1680

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