MEAN CIRCULATION AND INTERNAL VARIABILITY IN AN OCEAN PRIMITIVE EQUATION MODEL

A primitive equation World Ocean model has been integrated with restor ing boundary conditions to reach a steady state. The global distributi on of potential temperature, salinity, and meridional streamfunction a re consistent with observations. In steady state, the effective freshw ater fluxes were diagnosed, and the model has been integrated further prescribing these freshwater fluxes. The ocean circulation undergoes s elf-sustained oscillations over a wide range of timescales, ranging fr om decadal to millennium. Most pronounced are self-sustained oscillati ons with a timescale of 20, 300, and 1000 years. The latter two oscill ations are coupled. They consist of density (salinity) anomalies that circulate through the global conveyor belt, periodically enhancing con vection 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-yr oscillation is a coupled salinity and sea ice thick ness anomaly propagating around Antarctica.