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Convergence of atmospheric and North Atlantic carbon dioxide trends on multidecadal timescales


Oceanic uptake of carbon dioxide substantially reduces the rate at which anthropogenic carbon accumulates in the atmosphere1, slowing global climate change. Some studies suggest that the rate at which the oceans take up carbon has significantly decreased in recent years2,3,4,5,6,7,8. Others suggest that decadal variability confounds the detection of long-term trends9,10,11. Here, we examine trends in the partial pressure of carbon dioxide in the surface waters of three large biogeographic regions in the North Atlantic, using observational data collected between 1981 and 2009. We compare these oceanic observations with trends in atmospheric carbon dioxide levels, taken from a global observational network. We show that trends in oceanic carbon dioxide concentrations are variable on a decadal timescale, often diverging from trends in atmospheric carbon dioxide. However, when the entire 29-year period is considered, oceanic trends converge with atmospheric trends in all three regions; it takes 25 years for this long-term trend to emerge and overcome the influence of decadal-scale variability. Furthermore, in the southernmost biome, the data suggest that warming—driven by a multidecadal climate oscillation and anthropogenic forcing12,13—has started to reduce oceanic uptake of carbon in recent years.

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Figure 1: Trend in oceanic pCO2 compared to atmospheric pCO2 trend20 for a multidecadal and a decadal period.
Figure 2: Trend in oceanic pCO2 versus atmospheric pCO2, variable years.


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G.A.M. and A.R.F. acknowledge funding from NASA (07-NIP07-0036). The SURATLANT Project is supported by Institut National des Sciences de l’Univers (INSU, as contribution of the ORE SSS) and Institut Paul Emile Victor (IPEV) in France. This work was also supported by French program LEFE/FlamenCO2, a component of SOLAS-France and European Integrated Project CARBOOCEAN (511176). T.T. is supported by a NOAA grant (NA080AR4320754).

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G.A.M designed the study and wrote the manuscript. A.R.F. did the data analysis. T.T. developed the oceanic pCO2 database. N.M. synthesized the SURATLANT data. All authors discussed and revised the manuscript.

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Correspondence to Galen A. McKinley.

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The authors declare no competing financial interests.

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McKinley, G., Fay, A., Takahashi, T. et al. Convergence of atmospheric and North Atlantic carbon dioxide trends on multidecadal timescales. Nature Geosci 4, 606–610 (2011).

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