Diagnosing Effective Mixing in Ocean Models

Ocean mixing plays a critical role in distributing heat and biogeochemical tracers, yet its representation in ocean circulation models remains fraught with challenges. Especially in coastal domains - where topographic interactions, tidal currents, and nearshore processes put models under extreme tests - diapycnal mixing is poorly constrained and highly sensitive to parameter choices, with spurious effects from advection numerics further complicating results. In this study, we explore the benefits of introducing argon saturation as an additional tracer to circulation models, leveraging its oversaturation state as a diagnostic indicator for diabatic/diapycnal mixing. The approach sucessfully ranks the impact of horizontal resolution against numerical effects associated with the choice of advection schemes in a suite of regional model setups in the North Atlantic off Mauritania. By providing a quantitative method to compare diffusivities in model configurations, our framework may help to develop more robust coastal models.