Simulated anthropogenic CO2 uptake and acidification of the Mediterranean Sea

Constraints on the Mediterranean Sea’s uptake of anthropogenic CO2 are limited, coming only from data-based approaches that disagree by more than a factor of two. Here we simulate this marginal sea’s anthropogenic carbon uptake by applying a perturbation approach in a high-resolution regional model. Our model simulates that between 1800 and 2001, basin-wide CO2 uptake by the Mediterranean Sea has increased by 1.0 Pg C, a lower limit based on the corresponding model evaluation with CFC-12, indicating inadequate simulated deep-water ventilation. Furthermore, by testing a data-based approach (Transit Time Distribution) in our model, comparing simulated anthropogenic CO2 to values computed from simulated CFC-12 and physical variables, we conclude that the associated basin-wide uptake of 1.7 Pg, published previously, must be an upper bound. Out of the total simulated uptake of 1.0 Pg C, 75% comes from air–sea exchange into the Mediterranean Sea and 25% comes from net transport from the Atlantic across the Strait of Gibraltar. Sensitivity tests indicate that the Mediterranean Sea’s higher total alkalinity, relative to the global-ocean mean, enhances the Mediterranean’s total inventory of anthropogenic carbon by 10%. Yet the corresponding average anthropogenic change in surface pH does not differ significantly from the global-ocean average, despite higher total alkalinity. In Mediterranean deep waters, the pH change is estimated to be between −0.005 and −0.06 pH units.

Palmiéri J., Orr J. C., Dutay J.-C., Béranger K., Schneider A., Beuvier J. & Somot S., 2014. Simulated anthropogenic CO2 uptake and acidification of the Mediterranean Sea. Biogeosciences Discussions 11:6461-6517. Article.

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