Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 3
Biogeosciences, 12, 781-802, 2015
https://doi.org/10.5194/bg-12-781-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 12, 781-802, 2015
https://doi.org/10.5194/bg-12-781-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Feb 2015

Research article | 10 Feb 2015

Simulated anthropogenic CO2 storage and acidification of the Mediterranean Sea

J. Palmiéri1,2, J. C. Orr1, J.-C. Dutay1, K. Béranger2, A. Schneider3, J. Beuvier4,5, and S. Somot5 J. Palmiéri et al.
  • 1LSCE/IPSL, Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
  • 2ENSTA-ParisTech, Palaiseau, France
  • 3GEOMAR; Helmholtz-Zentrum für Ozeanforschung Kiel, Germany
  • 4Mercator Ocean, Ramonville Saint-Agne, France
  • 5CNRM/Météo-France, Toulouse, France

Abstract. Constraints on the Mediterranean Sea's storage 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 storage by applying a perturbation approach in a high-resolution regional model. Our model simulates that, between 1800 and 2001, basin-wide CO2 storage by the Mediterranean Sea has increased by 1.0 Pg C, a lower limit based on the model's weak deep-water ventilation, as revealed by evaluation with CFC-12. 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 storage of 1.7 Pg, published previously, must be an upper bound. Out of the total simulated storage of 1.0 Pg C, 75% comes from the air–sea flux 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.

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Different observational-based estimates of CO2 uptake and resulting acidification of the Mediterranean Sea vary widely. A new study finds that even the smallest of those are an upper limit because the approach used assumes air-sea CO2 equilibrium. Then with a lower limit from new fine-scale numerical model simulations, the authors bracket Mediterranean Sea CO2 uptake and acidification rates. They conclude that its rate of surface acidifcation is much like that for typical ocean waters.
Different observational-based estimates of CO2 uptake and resulting acidification of the...
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