Submitted as: model description paper
05 May 2023
Submitted as: model description paper |  | 05 May 2023
Status: this preprint is currently under review for the journal GMD.

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. II): Towards a better representation of total alkalinity when modelling the carbonate system and air-sea CO2 fluxes

Lucille Barré, Frédéric Diaz, Thibaut Wagener, Camille Mazoyer, Christophe Yohia, and Christel Pinazo

Abstract. The Bay of Marseille (BoM), located in the north-western 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 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 study air-sea CO2 fluxes and seawater pCO2 variations more reliably. We apply this new formulation to two particular scenarios, 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 pCO2 variability. Summer upwelling events are typically associated with pCO2 decrease that mainly results from decreasing near-surface temperatures. Furthermore, Rhône River intrusion events are typically associated with pCO2 decrease, although in this case the pCO2 decrease results from a decrease in salinity and an overall increase in total alkalinity. While our model was able to correctly represent the daily range of air-sea CO2 fluxes, we were unable to correctly estimate the yearly total air-sea CO2 flux. Although the model consistent with observations, predicted the BoM to be a sink of CO2 on a yearly basis, the magnitude of this CO2 sink was underestimated which may be an indication of the limitations inherent in dimensionless models for representing air-sea CO2 fluxes.

Lucille Barré et al.

Status: open (until 08 Jul 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Lucille Barré et al.

Lucille Barré et al.


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Short summary
Carbonate system is typically studied using measurements, yet modelling can contribute valuable insights. Using a biogeochemical model, we propose a new representation of total alkalinity, dissolved inorganic carbon, pCO2 and pH in a highly dynamic Mediterranean coastal area: the Bay of Marseille, a useful addition to measurements. Through a detailed analysis of pCO2 and air-sea CO2 fluxes we show that their variations are strongly impacted by the hydrodynamic processes that affect the bay.