Subduction

Subduction is the transfer of surface water into the stratified ocean interior, where it moves along isopycnals as it leaves the directly forced mixed layer. It occurs where the Ekman pumping is downward and where the wintertime mixed layer shoals in spring, so water set at the late-winter mixed-layer base is capped and isolated from the atmosphere. The subduction rate combines vertical pumping and lateral induction across the sloping mixed-layer base. Subduction forms the mode waters and ventilates the main thermocline, setting how surface heat, carbon, and oxygen anomalies enter the interior on decadal timescales.