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Abstract:
Adriatic is not widely acknowledged as region of significant upwelling. Short episodes occur under strong synoptic-scale wind - bora on the eastern or sirocco on the western coast. However, historic observations, summer satellite SST fields and existence of unexpectedly rich benthic vegetation at specific sites on the eastern edge of Jabuka Pit indicate that during summer more persistent upwelling occurs at offshore islands of the eastern Middle Adriatic. Temperature data along water column recorded continuously for seven years at Blitvenica are analyzed together with wind field and results from ROMS ocean model to ascertain existence of upwelling, determine its temporal scale, intensity and interannual variability. Temperature data document distinct midsummer cooling by some 3 to 5 °C, recurring from June to August each year with changing intensity. The cooling is occasionally interrupted by short warming events. Predominant wind circulation in summer is northwest, upwelling-favorable etesian airflow, but sporadic short episodes of strong cross-shore bora intensify surface cooling while gale downwelling-favorable sirocco produces abrupt brief warming. The general midsummer cooling is realized in a series of episodes, each lasting some three days. Vertical velocity related to Ekman transport, estimated from wind field, reaches 10 m/day (20 m/day) during strong upwelling (downwelling). Wind curl around Blitvenica is nearly always positive but Ekman suction velocities are usually much smaller. Finally, time evolution of cooling/heating within water column closely agrees with the vertical velocity except during episodes of strong surface heat flux, providing firm evidence of seasonal upwelling along eastern side of Middle Adriatic.
