Impact of Current-Wind Interaction on Vertical Processes in the Southern Ocean

Abstract

Momentum input from westerly winds blowing over the Southern Ocean can be modulated by mesoscale surface currents and result in changes in large-scale ocean circulation. Here, using an eddy-resolving 1/20 degree ocean model configured near Drake Passage, we evaluate the impact of current-wind interaction on vertical processes. We find a reduction in momentum input from the wind, reduced eddy kinetic energy, and a modification of Ekman pumping rates. Wind stress curl resulting from current-wind interaction leads to net upward motion, while the nonlinear Ekman pumping term associated with horizontal gradients of relative vorticity induces net downward motion. The spatially averaged mixed layer depth estimated using a density criteria is shoaled slightly by current-wind interaction. Current-wind interaction, on the other hand, enhances the stratification in the thermocline below the mixed layer. Such changes have the potential to alter biogeochemical processes including nutrient supply, biological productivity, and air-sea carbon dioxide exchange.