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[1] Dense water formation processes in the Aegean Sea (eastern Mediterranean) are studied using a three-dimensional numerical ocean model. The simulations cover the period 1979-1994 during which major changes that affected the thermohaline circulation of the whole Mediterranean Sea were recorded. Sensitivity studies that focus on the role of freshwater budget are presented, and the results are evaluated against available hydrological data of the same period. The very cold winters of 1987, 1992, and 1993 and the extended dry period 1989-1993 that affected the whole eastern Mediterranean Sea are the main driving mechanisms, corresponding to 50% and 32%, respectively, of the excessive deepwater volume formed in the Aegean after 1987. The reduced Black Sea Water outflow during the same dry period was another important forcing mechanism, contributing 18% to the total formation, while the increased inflow of saline waters from the Levantine Sea after 1992 was an additional preconditioning factor. The locations and mechanisms of water formation processes are identified with combined analysis of data from the March 1987 oceanographic cruise in the Aegean Sea and the respective model results for that period. Deep water is found to be formed mainly through open ocean convection in the central and north Aegean Sea, while the contribution of shelf areas is limited. Intermediate water is also formed through open ocean convection in the southern Aegean Sea during cold winters as well as in the central and northern Aegean during mild winters. The total volume of dense water formed during 1979-1994 corresponds to an annual formation rate of 0.24 Sv for deep water and 0.34 Sv for intermediate water.

Data collected from different platforms in the Cretan Sea during the 2000s decade present evidence of gradually increasing salinity in the intermediate and deep intermediate layers after the middle of the decade. The observed gradual salt transport toward the deeper layers indicates contributions of dense water masses formed in various Aegean Sea subbasins. The accumulation of these saline and dense water masses in the Cretan Sea finally led to outflow from both Cretan Straits, with density greater than typical Levantine/Cretan Intermediate water but not dense enough to penetrate into the deep layers of the Eastern Mediterranean. We name this outflowing water mass as dense Cretan Intermediate Water (dCIW). A retrospective analysis of in situ data and literature references during the last four decades shows that similar events have occurred in the past in two occasions: (a) in the 1970s and (b) during the Eastern Mediterranean Transient (EMT) onset (1987)(1988)(1989)(1990)(1991). We argue that these salinity-driven Aegean outflows are mostly attributed to recurrent changes of the Eastern Mediterranean upper thermohaline circulation that create favorable dense water formation conditions in the Aegean Sea through salinity preconditioning. We identify these phenomena as ''EMT-like'' events and argue that in these cases internal thermohaline mechanisms dominate over atmospheric forcing in dense water production. However, intense atmospheric forcing over an already salinity preconditioned basin is indispensable for creating massive deep water outflow from the Cretan Sea, such as the EMT event.

Abstract. We use a three-dimensional primitive equation ocean model to study the formation of Levantine Intermediate Water (LIW), the characteristic intermediate water mass of the Mediterranean Sea. The model is forced by atmospheric monthly climatological values and incorporates a realistic air-sea interaction scheme. The cyclonic Rhodes gyre, a permanent general circulation feature of the Levantine basin, is found to be the unique formation site under these mean climatological conditions. The convection event has a duration of 2 months (February-March), and the estimated annual mean formation rate is 1.2 Sv. Using two different horizontal resolutions, an eddy-resolving (5.5 km) and a non-eddy-resolving (11 km) grid, we are able to make comparative experiments on the influence of eddy dynamics on the convection process. The results indicate that baroclinic eddies formed at the periphery of the cyclonic convection area control the formation process through horizontal advection of buoyant water from the periphery toward the center of the gyre. This mechanism reduces the extent and duration of the LIW formation event. The large number of small-scale and mesoscale baroclinic eddies that dominate the flow field at intermediate depths, together with the Asia Minor Current, are responsible for the spreading of the newly formed LIW, mainly in zonal direction.

Abstract. This paper describes the first evaluation of the quality of the forecast and analyses produced at the basin scale by the Mediterranean ocean Forecasting System (MFS)