Mean Circulation and Internal Variability in an Ocean Primitive Equation Model

A primitive equation World Ocean model has been integrated with restoring boundary conditions to reach a steady state. The global distribution of potential temperature, salinity and meridional streamfunction are consistent with observations. In steady state, the effective freshwater fluxes were diagnosed, and the model has been integrated further prescribing these freshwater fluxes. The ocean circulation undergoes self-sustained oscillations over a wide range of time-scales, ranging from decadal to millennium. Most pronounced are self-sustained oscillations with a 20, 300 and 1000 year timescale. The latter two oscillations are coupled. They consist of density (salinity) anomalies that circulate through the global Conveyor Belt, periodically enhancing convection in the Southern Ocean and limiting convection in the northern North Atlantic. The timescale is set by the vertical diffusion which destabilizes the stratification in the Southern Ocean when convection is weak. The 20 year oscillation is a coupled salinity and sea-ice thickness anomaly propagating around Antarctica. (orig.)