Time-dependent response of the overturning circulation and pycnocline depth to Southern Ocean surface wind stress changes

Abstract Changes in the Southern Ocean (SO) surface wind stress influence both meridional overturning circulation (MOC) and stratification not only SO but global oceans, which can take multiple millennia to fully equilibrate. We use a hierarchy of models investigate time-dependent response MOC low-latitude pycnocline depth (which quantifies stratification) changes: two-layer analytical theory, multi-column model (PyMOC), an idealized general (GCM). find that GCM PyMOC, has multi-decadal adjustment timescale while multi-centennial timescale. The theory instead predicts adjust on same, argue this discrepancy arises because depends bulk stratification, amplitude is sensitive mostly isopycnals within cell. reconcile by interpreting “pycnocline depth” as specific isopycnal near maximum MOC. also stationary eddies respond very quickly sudden change, compensating for most change Ekman-driven This effect missing where eddy-induced follows depth. Our results emphasize importance depth-dependence oceans’ transient changes boundary conditions, distinct role played SO.