MEAN CIRCULATION OF THE HAMBURG LSG OGCM AND ITS SENSITIVITY TO THE THERMOHALINE SURFACE FORCING

The sensitivity of the global ocean circulation to changes in surface heat flux forcing is studied using the Hamburg Large Scale Geostrophic (LSG) ocean circulation model. The simulated mean ocean circulation f or appropriately chosen surface forcing fields reproduces the principa l water mass properties, residence times, and large-scale transport pr operties of the observed ocean circulation quite realistically within the constraints of the model resolution. However, rather minor changes in the formulation of the high-latitude air-sea heat flux can produce dramatic changes in the structure of the ocean circulation. These str ongly affect the deep-ocean over-turning rates and residence times, th e oceanic heat transport, and the rate of oceanic uptake Of CO2. The s ensitivity is largely controlled by the mechanism of deep-water format ion in high latitudes. The experiments support similar findings by oth er authors on the sensitivity of the ocean circulation to changes in t he fresh-water flux and are consistent with the existence of multiequi libria circulation states with a relatively low transition threshold.