AbstractThis 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.