Quantifying the contribution of ocean advection and surface flux to the upper-ocean salinity variability resolved by climate model simulations

This study examines the impact of ocean advection and surface freshwater flux on the non-seasonal, upper-ocean salinity variability in two climate model simulations with eddy-resolving and eddy-parameterized ocean components (HR and LR, respectively). We assess the realism of each simulation by comparing their sea surface salinity (SSS) variance with satellite and Argo float estimates. In the extratropics, the HR variance is about five times larger than that in LR and agrees with Argo. In turn, the extratropical satellite SSS variance is smaller than that from HR and Argo by about a factor of two, potentially caused by the insufficient resolution of radiometers to capture mesoscale features and their low sensitivity to SSS in cold waters. Using a simplified salinity conservation equation for the upper-50-m ocean, we find that the advection-driven variance in HR is, on average, 10 times larger than the surface flux-driven variance, reflecting the action of mesoscale processes.