Northern Adriatic general circulation behaviour induced by heat fluxes variations due to possible climatic changes

Abstract

Summary. — The thermohaline circulation of the central-north Adriatic basin is investigated by means of a 3D hydrodynamic numerical model. Three diferent runs —where the surface heat fluxes annual average is respectively negative, slightly pos- itive and slightly negative—are performed; the general circulation patterns are then discussed and depicted, also with the aid of the trajectories of numerical particles released during the integrations. Results confirm that surface heat fluxes can start and trigger the general circulation in the basin (both vertically and horizontally), even without prescribing other forcings. Particularly, when the annual budget of the heat fluxes is negative (i.e. the basin loses heat to the atmosphere) a horizontal cyclonic surface circulation is generated, characterized by a northward flow along the eastern coast and a southward return current system along the western one. From the vertical point of view, an antiestuarine circulation is established. A sim- ilar circulation pattern is depicted when the surface fluxes have a slightly negative annual budget. On the other hand, when the annual fluxes balance is positive the vertical circulation switches to estuarine and, as expected, the integrated circulation becomes anticyclonic. A modification in the heat fluxes budget is strictly related to a change in the water column turnover time of the Jabuka pit, the deepest meso- Adriatic depression: when the annual heat fluxes balance is negative but close to zero, the dense-water residence time in the pit becomes minimum and the water has a shorter turnover time, denoting a faster renewal compared to those exhibited in the other experiments.