Ocean alkalinization is an emerging marine Carbon Dioxide Removal (mCDR) approach that enhances the ocean's buffering capacity, promoting atmospheric CO₂ uptake and long-term storage as bicarbonates and carbonates. Despite its estimated removal potential of 0.1 to 1 GtCO₂/year, significant uncertainties remain regarding its large-scale effectiveness, posing challenges for its inclusion in emission reduction strategies. Establishing robust Measurement, Reporting, and Verification (MRV) mechanisms is therefore essential to accurately quantify the carbon fluxes induced by this method and assess potential ecosystem impacts.
Biogeochemical models (BGC) play a critical role in the MRV framework by providing numerical simulations to evaluate air-sea CO₂ fluxes and associated biogeochemical changes. However, current models, such as PISCES, exhibit systematic biases in simulating the seasonal variability of the partial pressure of CO₂ (pCO₂), particularly in high-latitude and carbon-cycle-sensitive regions. These limitations hinder their ability to precisely attribute the fraction of CO₂ uptake due to alkalinization relative to natural oceanic variability.
This postdoctoral research aims to improve the representation of seasonal pCO₂ cycles in the PISCES model by integrating observations from BGC-Argo floats. The approach will leverage data assimilation through a particle filter and ensemble-based parameter optimization to produce more accurate simulations and better constrain uncertainties associated with air-sea CO₂ fluxes. Building on a methodology developed for the North Atlantic, this project will extend its application to a global scale, targeting multiple oceanic bioprovinces to robustly quantify the alkalinization-attributable signal against natural carbon cycle fluctuations.

The postdoctoral researcher will be involved in the following activities:
• Assimilating BGC-Argo float data into the PISCES biogeochemical model using a particle filter approach.
• Optimizing model parameters to improve the simulation of seasonal CO₂ cycles.
• Producing ensemble simulations to quantify CO₂ fluxes with and without ocean alkalinization.
• Analyzing results and assessing uncertainties to strengthen the MRV framework for ocean alkalinization.
• Writing scientific articles and participating in international conferences.

The position will be based at Mercator Ocean in Toulouse, where the recruited person will work within the biogeochemical modeling team. Visits (twice a year) to the Villefranche Oceanography Laboratory will be planed to discuss with specialists in the carbon cycle and the BGC-Argo observation system. This two-year contract will offer a dynamic research environment, access to high-performance computing resources, and interactions with experts in ocean modeling and climate sciences