Mixing Inferred from an Ocean Climatology and Surface Fluxes

This study provides observation-based estimates, determined by inverse methods, of horizontal and isopycnal eddy diffusion coefficients K H and K I , respectively, the small-scale mixing coefficient D , and the diathermohaline streamfunction Ψ. The inverse solution of Ψ represents the ocean circulation in Absolute Salinity S A and Conservative Temperature Θ coordinates. The authors suggest that the observation-based estimate of Ψ will be useful for comparison with equivalent diagnostics from numerical climate models. The estimates of K H and K I represent horizontal eddy mixing in the mixed layer and isopycnal eddy mixing in the ocean interior, respectively. This study finds that the solution for D and K H are comparable to existing estimates. The solution for K I is one of the first observation-based global and full-depth constrained estimates of isopycnal mixing and indicates that K I is an order of magnitude smaller than K H . This suggests that there is a large vertical variation in the eddy mixing coefficient, which is generally not included in ocean models. With ocean models being very sensitive to the choice of isopycnal mixing, this result suggests that further investigation of the spatial structure of isopycnal eddy mixing from observations is required.