PRECONDITIONING THE GREENLAND SEA FOR DEEP CONVECTION - ICE FORMATIONAND ICE DRIFT

The role of sea ice in preconditioning the mixed layers of the central Greenland Sea for deep convection is investigated, with particular em phasis on the formation of the ''Nordbukta.'' The opening of the ice f ree bay in late January 1989 indicated that the upper layer was well p reconditioned for deep convection which reached down to 1500 m depth i n March 1989. We propose that the ice free bay occurred due to diminis hing new ice formation without extensive ice melt. A key process is wi nd-driven ice drift to the southwest, as observed by upward looking ac oustic Doppler current profilers, which will alter the upper ocean fre shwater budget when an ice volume gradient along the ice-drift directi on exists. We investigated the importance and effects of such an ice-d rift-induced freshwater loss on upper ocean properties using an ice-oc ean mixed-layer model. Observed temperature and salt profiles from Dec ember 1988 served as initial conditions, and the model was integrated over the winter season. Given the one-dimensional physics and climatol ogical surface fluxes, the model was not able to produce a reasonable ice and mixed-layer evolution. However, allowing ice drift to reduce t he local ice thickness improved the ice-ocean model performance dramat ically. An average ice export of 5-8 mm d(-1) was needed to be consist ent with the observed evolution of mixed-layer properties and ice cove r. Using the same fluxes and ice export, but initial conditions from t he ''Is Odden'' region, yielded ice cover throughout the winter over a shallow mixed layer, both of which are consistent with the observatio ns from the Odden region.