Large δ13C Gradients in the Preindustrial North Atlantic Revealed

The carbon isotopic composition (C-13/C-12, expressed as delta C-13) 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 delta C-13 distribution as a framework. However, the present ocean delta C-13 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 delta C-13 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 delta C-13 differences and allow paleo-delta C-13 variations to be understood within the context of modern climate variability.