Observations on the circulation of the Saronikos Gulf: A Mediterranean embayment sea border of Athens, Greece

The Saronikos Gulf three-dimensional flow structure is mapped by objective analysis in 12 acoustic Doppler current profiler surveys (4 seasonal surveys per period for the periods May 1998-May 1999, May 2000-May 2001, May 2003-May 2004) under various winds. Robust seasonal flows throughout the Gulf are basically induced by thermohaline effects (winter water subduction, different responses to atmospheric heating of shallow and deeper areas of the Gulf) and density contrasts with inflowing Aegean waters. Inner Gulf observations show that the seasonal flows are modified by the wind, while recurrent structures (cyclonic and anticyclonic) appear between the seasonal flows and the coast of Attica. In summer an anticyclonic and a cyclonic flow exists throughout the Gulf above and below the pycnocline, respectively, with a jet observed to meander within the Inner Gulf. In winter and early spring an anticyclonic flow prevails in the upper similar to 100 m. In late spring-early summer cyclonic and anticyclonic flow occurs in the upper (similar to 0-40 m) and deeper (similar to 60-100 m) layers, respectively. The predominant northerly winds in summer and winter push the Inner Gulf eastward seasonal jet to the south and favor the formation of a recurrent cyclonic upwelling structure between this jet and Attica. Northwesterly, westerly, and southerly winds favor the northward meandering of the seasonal jet in the Inner Gulf and no recurrent structures appear in the limited space between this jet and Attica. In the southeast area of the Inner Gulf, the wind-driven flow fluctuations at 30 m have time scales of 3.5-4 days. Observed meandering period is similar to 13 days; meandering characteristics are close to instability predictions. Time scales of flows due to recurrent structures are similar to 8 days.