Large δ13C Gradients in the Preindustrial North Atlantic Revealed

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Science  29 Oct 2010:
Vol. 330, Issue 6004, pp. 658-659
DOI: 10.1126/science.1193769

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Changes in ocean circulation are commonly inferred by differences between the distribution of carbon isotopes in the past and now, but making such comparisons neglects the fact that modern fossil fuel burning has modified the carbon isotopic composition of the ocean. This in turn obscures details about recent mass movement of water. Olsen and Ninnemann (p. 658) correct for this effect in the North Atlantic and show that the natural distribution of carbon isotopes has more detail and is clearly related to water mass distributions. The results change some important ideas about glacial-interglacial ocean variations within the context of modern climate variability.


The carbon isotopic composition (13C/12C, expressed as δ13C) of fossil foraminifera is the primary tracer used to infer changes in past ocean ventilation, and its variations are interpreted by using the modern oceanic δ13C distribution as a framework. However, the present ocean δ13C distribution is strongly overprinted by isotopically light anthropogenic carbon dioxide. A correction for this oceanic C-13 Suess effect in the North Atlantic (NA) shows that the pristine NA δ13C distribution has a richer and more detailed structure that is more clearly related to water mass distributions. Our results revise some fundamental perceptions regarding glacial-interglacial ocean δ13C differences and allow paleo-δ13C variations to be understood within the context of modern climate variability.

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