Estimating the efficiency of open ocean alkalinization

The efficiency of open ocean alkalinization is estimated for four regions in the Atlantic: the subpolar North Atlantic, the northern subtropics, the equatorial region and the Southern Ocean. Therefore, a simple one-dimensional model is applied. First, observational based surface values of temperature, salinity, alkalinity, mixed layer depth (MLD), air-sea gas exchange velocity and pCO₂ for each region are derived from the ARMOR3D data set (Guinehut et al., 2012) and the surface pCO₂ data product by Landschützer et al. (2020). The model is run for 26 years, using the data from 1994 to 2019. Alkalinity is added to the mixed layer, which leads to enhanced oceanic carbon uptake, depending on the change in pCO₂ and the gas transfer velocity. When the mixed layer shallows, parts of the added substances remain in the deeper layer of the model (below the mixed layer). They can either be exported, or can be entrained into the mixed layer again when it deepens. In this way, the efficiency of alkalinization (mole of absorbed CO₂ per mole of added alkalinity) for the four regions and varying model parameters (alkalinity, pCO₂, gas transfer velocity, mixed layer depth, fraction of exported carbon/alkalinity) is computed. In addition, the cases with permanent and monthly alkalinity supply (repeated every year) are investigated.

Guinehut, S., A.-L. Dhomps, G.Larnicol and P.-Y. Le Traon (2012). High resolution 3-d temperature and salinity fields derived from in-situ and satellite observations, Ocean Sci., 8, 845–857, https://doi.org/10.5194/os-8-845-2012.

Landschützer, P., N. Gruber and D.C.E. Bakker (2020). An observation-based global monthly gridded sea surface pCO₂ and air-sea CO₂ flux product from 1982 onward and its monthly climatology (NCEI Accession 0160558). Version 6.6. NOAA National Centers for Environmental Information. Dataset. [2021-27-09]