The impacts of ocean physics on the efficiency of ocean alkalinity enhancement in a one-dimensional model

We use a one-dimensional diffusion model to examine the relative effects of air-sea gas exchange and interior mixing on the efficiency of ocean alkalinity enhancements in drawing down atmospheric CO2 under a range of oceanic conditions. First, a series of highly idealized simulations are run to explore the impacts of deployment depth, wind speed, mixed layer depth, interior diffusivities and seasonality on the efficiency of CO2 uptake following an alkalinity addition. For additions made within the mixed layer subject to typical wind speeds and diffusivity profiles, we find efficiencies one year after deployment of around 50%, with wind speeds playing a dominant role in determining efficiency compared to mixed layer depth or interior diffusivities. Next, we use wind speeds, surface buoyancy and momentum fluxes from reanalysis to produce realistic, time varying diffusivities that we use to drive the model, producing estimates of efficiencies at different global locations over one annual cycle. Our simulations lend insight into the underlying processes that determine OAE efficiency and aid in the interpretation of similar calculations that have been performed using more complex models.