The vertical changes driven by eddy-wind interaction in the Southern Ocean

Hajoon Song, Yonsei University, Department of Atmospheric Sciences, Seoul, South Korea, John C Marshall, MIT, Cambridge, MA, United States, Dennis Joseph McGillicuddy Jr, Woods Hole Oeanographic Institution, Woods Hole, MA, United States and Hyodae Seo, WHOI, Woods Hole, United States
Abstract:
Momentum input from the predominantly eastward-blowing winds over the Southern Ocean (SO) is continuously modified by the eastward-flowing Circumpolar Current, through modulation of the relative speed of winds and currents. Mesoscale patterns of surface currents associated with eddies and meanders also add complexity to this momentum transfer. Here, using an eddy-resolving 1/20 degree model, we evaluate the impact of eddy-wind interaction (EWI) on vertical processes and mesoscale eddies near the Drake Passage in the SO.
Although we find that the net change of wind-driven upwelling is small, there is a considerable modification on both linear and nonlinear wind-driven Ekman pumping contributions that are compensating each other.
Moreover, EWI enhances the stratification below the mixed layer and suppresses coherent eddies by reducing their number by half. Wind-driven upwelling is enhanced in anticyclones, which tends to transform them to mode water eddies exhibiting a convex isopycnal lens shape. In contrast, net downward motion in cyclones leads them to become cyclonic thinnies. These EWI-driven changes have the potential to alter biogeochemical processes including nutrient supply, biological productivity and air-sea carbon dioxide exchange.