On Steady Response of a Ventilated Thermocline to Enhanced Ekman Pumping

Atsushi Kubokawa and Shang-Ping Xie

Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, Japan

J. Oceanography, 58, 565-575.

Abstract. Steady response of the ventilated thermocline to an increase in Ekman pumping is investigated, with a focus on the effect of the mixed layer depth distribution on the subsurface density anomaly. The mixed layer is assumed to be deep in the northwest and shallow elsewhere with a narrow transition zone separating the deep and shallow mixed layer regions. At the intersection of this narrow transition zone and the outcrop line, low potential vorticity fluid is subducted and ventilated into the thermocline. In such a situation, an enhancement of the Ekman pumping confined to the northern subtropical gyre leads to pronounced subsurface cold anomalies in the southern subtropics that is free of anomalous forcing. These density anomalies are much greater than those when either the mixed layer depth is zonally uniform or the Ekman pumping is enhanced in the whole subtropical gyre. They are caused by anomalous changes in the trajectory of the low potential vorticity fluid in response to anomalous Sverdrup flow.