Mesoscale atmospheric forcing leads to mixed layer deepening in the North Pacific

The net impact of air-sea exchange on large-scale ocean circulation is accomplished by the transfer of heat, momentum and other properties across the mixed layer (ML) base. Understanding the governors of mixed-layer depth (MLD) is therefore key to understanding climate variability. Though substantial efforts have been made toward improving MLD simulations, the impact of mesoscale atmospheric forcing on the MLD remains unclear. We vary the atmospheric forcing resolution in eddying ocean simulations to demonstrate that including mesoscale atmospheric features can deepen the MLD in most parts of the North Pacific. The dominant mechanism driving the time-mean ML deepening is wind-induced mixing due to increased wind-stress magnitude arising from the higher forcing resolution and the nonlinear dependence of wind stress on wind speed. Buoyancyforcing change is a secondary mechanism, and Ekman pumping change is negligible. Our results indicate that the horizontalatmospheric resolution should be carefully chosen in climate simulations to ensure physically plausible upper-ocean mixing.