engleski

Periodic upwelling/downwelling observed in the Adriatic Sea

Between February and September 2006 extensive measurements were carried out in the Adriatic shelf-break area in the framework of the Internal Tidal Hydrodynamics and Ambient Characteristics of the Adriatic (ITHACA) project. During the experiment (1) meteorological conditions were documented by several permanent stations (Split-Marjan, Dubrovnik, Komiza, Hvar and Palagruza), (2) optical surveys were performed on two occasions at three stations, (3) shipboard CTD surveys were carried out on four occasions at an along-basin transect comprising thirteen closely spaced stations, (4) thermistor time series were collected on the islands of Lastovo, Susac and Bisevo utilizing 3 x 10 sensors deployed on steep cliffs opened to the southeast, (5) ADCP measurements were continuously performed at three stations using trawl-resistant bottom mounts (called barnys), and (6) surface tides were monitored at the permanent Split and Dubrovnik stations and at one of the ADCP stations. Preliminary analysis of the data collected has revealed subsurface temperature oscillations, characterized by the 24, 12 and 8 h periods, at one of the islands (Lastovo). The corresponding baroclinic current variability was largest at a nearby ADCP station and was bottom-intensified. Whereas the signal was partly related to internal tides, pronounced diurnal oscillations recorded between 14 and 19 July 2006 were obviously driven by sea/land breezes that occasionally reached 10 m/s. The range of thermocline variability surpassed 20 m, implying that the excitation of upwelling/downwelling events was near-resonant. The thermocline was lowest at about 6 am and was highest at about 4 and 10 pm - the two maxima probably signaling nonlinear interaction between the diurnal, semidiurnal and terdiurnal wind-driven constituents.

Adriatic; upwelling; downwelling

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