Implementation and assessment of a model including mixotrophs and the carbonate cycle (Eco3M_MIX-CarbOx v1.0) in a highly dynamic Mediterranean coastal environment (Bay of Marseille, France) – Part 2: Towards a better representation of total alkalinity when modeling the carbonate system and air–sea CO$_2$ fluxes - Chimie des Environnements Marins
Article Dans Une Revue Geoscientific Model Development Année : 2024

Implementation and assessment of a model including mixotrophs and the carbonate cycle (Eco3M_MIX-CarbOx v1.0) in a highly dynamic Mediterranean coastal environment (Bay of Marseille, France) – Part 2: Towards a better representation of total alkalinity when modeling the carbonate system and air–sea CO$_2$ fluxes

Résumé

The Bay of Marseille (BoM), located in the northwestern Mediterranean Sea, is affected by various hydrodynamic processes (e.g., Rhône River intrusion and upwelling events) that result in a highly complex local carbonate system. In any complex environment, the use of models is advantageous since it allows us to identify the different environmental forcings, thereby facilitating a better understanding. By combining approaches from two biogeochemical ocean models and improving the formulation of total alkalinity, we develop a more realistic representation of the carbonate system variables at high temporal resolution, which enables us to study air–sea CO$_2$ fluxes and seawater pCO$_2$ variations more reliably. We apply this new formulation to two particular scenarios that are typical for the BoM: (i) summer upwelling and (ii) Rhône River intrusion events. In both scenarios, our model was able to correctly reproduce the observed patterns of pCO$_2$ variability. Summer upwelling events are typically associated with a pCO2 decrease that mainly results from decreasing near-surface temperatures. Furthermore, Rhône River intrusion events are typically associated with a pCO$_2$ decrease, although, in this case, the pCO2 decrease results from a decrease in salinity and an overall increase in total alkalinity. While we were able to correctly represent the daily range of air–sea CO$_2$ fluxes, the present configuration of Eco3M_MIX-CarbOx does not allow us to correctly reproduce the annual cycle of air–sea CO$_2$ fluxes observed in the area. This pattern directly impacts our estimates of the overall yearly air–sea CO$_2$ flux as, even if the model clearly identifies the bay as a CO$_2$ sink, its magnitude was underestimated, which may be an indication of the limitations inherent in dimensionless models for representing air–sea CO$_2$ fluxes.
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hal-04701283 , version 1 (18-09-2024)

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Lucille Barré, Frédéric Diaz, Thibaut Wagener, Camille Mazoyer, Christophe Yohia, et al.. Implementation and assessment of a model including mixotrophs and the carbonate cycle (Eco3M_MIX-CarbOx v1.0) in a highly dynamic Mediterranean coastal environment (Bay of Marseille, France) – Part 2: Towards a better representation of total alkalinity when modeling the carbonate system and air–sea CO$_2$ fluxes. Geoscientific Model Development, 2024, 17 (15), pp.5851-5882. ⟨10.5194/gmd-17-5851-2024⟩. ⟨hal-04701283⟩
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