We are applying a new framework for diagnosing mixing in stratified flows based on Available Potential Energy (APE) (Scotti and White 2013) to study the energy cycle of the global ocean circulation. Graduate student Varvara Zemskova has calculated the full ocean energy budget based on surface heat flux data from the Woods Hole Oceanographic Institution OAFlux project and model output from a 17-year run of the eddy-permitting global ocean-state estimate ECCO2 based on the MIT global climate model (MITgcm). The results clarified the relative roles of wind forcing around Antarctica and deep polar convection in energetically driving the MOC and in determining the nature of the heat transferred from the atmosphere to the ocean over seasonal to decadal time scales (Zemskova et al. 2015). This project was funded by NSF.

 

Figure8Global distribution of vertical buoyancy flux due to mean currents. The dominant contribution is in the Southern Ocean where Ekman suction generates enough upwelling to raise APE in the mean. This upwelling is globally balanced by the eddy field which decreases APE. Whereas small-scale processes and mixing have typically been thought to drive a net downward heat transport to counteract deep convection at the poles, the ECCO2 energy cycle suggests that wind-driven upwelling is so strong that small-scale processes work in reverse, transporting dense fluid downward.