Temporal trends in oceanic dissolved inorganic carbon (DIC) and δ 13 C‐DIC were reconstructed along five isopycnals in the upper 1000 m of the North Atlantic Ocean using a back‐calculation approach. The mean anthropogenic DIC increase was 1.21 ± 0.07 μmol kg −1 yr −1 and the mean 13 C decrease was −0.026 ± 0.002‰ yr −1 , both in good agreement with the results from previous studies. The observed δ 13 C‐DIC perturbation ratio is −0.024 ± 0.003‰ (μmol kg −1 ) −1 . Our results indicate that the North Atlantic is able to maintain equilibrium with the anthropogenic perturbation for DIC and follows it with decadal time lag for δ 13 C. A CFC‐calibrated one‐dimensional isopycnal advection‐diffusion model is used to evaluate temporal DIC and δ 13 C trends and perturbation ratios of the reconstructions. We investigate the time history of the air‐sea CO 2 and 13 C disequilibria in the North Atlantic and discuss the importance of physical and biological processes in maintaining them. We find evidence that the North Atlantic Ocean is characterized by enhanced uptake of anthropogenic CO 2 . Also, we use the model to examine how the time rate of change of δ 13 C depends on changes in the temporal evolution of δ 13 C in the atmosphere. The model evolution explains the curious result that the time rate of change of surface water δ 13 C in the North Atlantic Ocean can exceed that observed concurrently in the atmosphere. Finally we introduce a powerful way of estimating the global air‐sea p CO 2 disequilibrium based on the oceanic δ 13 C‐DIC perturbation ratio.
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Körtzinger et al. (2003) studied this question.