Argon Saturation in a Suite of Coupled General Ocean Circulation Biogeochemical Models off Mauretania

Abstract. Numerical coupled ocean circulation biogeochemical modules are routinely employed in Earth System Models that provide projections into our warming future to the Intergovernmental Panel on Climate Change (IPCC). Previous studies have shown that a major source of uncertainties in the biogeochemical ocean component is the yet unacquainted vertical, or rather diapycnal, ocean mixing. The representation of diapycnal mixing in models is effected by several factors, among them are the (poorly constrained) parameter choices of the background diffusivity, the choice of the underlying advection numerics and the spatial discretization. This study adds to the discussion by exploring these effects in a suite of regional coupled ocean circulation biogeochemical model configurations. The configurations comprise the Atlantic Ocean off Mauretania – a region renown for its complex ocean circulation driven by seasonal wind patterns, coastal upwelling and peculiar mode water eddies featuring toxically low levels of dissolved oxygen. By exploiting simulated argon saturation as a proxy for effective mixing we show that the resolution effect beyond mesoscale on diapycnal mixing is comparable to other infamous spurious effects, such as the choice of advection numerics or a change of the background diffusivity within 20–40 %.