Diurnal thermocline oscillations driven by tidal flow around an island in the Middle Adriatic

Oceanographic data collected between February and September 2006 have been examined in order to detect and interpret different physical processes in the Adriatic shelf break area. One of the main objectives was to gain more information on internal tides. The work comprised thermistor measurements carried out at the islands of Bisevo, Susac and Lastovo at 10 equidistant depths, between 4 and 40 m, on submarine cliffs opened to the southeast. Significant diurnal temperature oscillations were detected at Lastovo. The strongest variations were driven by the sea/land breezes (middle of July 2006). However, during several episodes between June and August 2006 diurnal wind forcing was not significant, whereas barotropic currents at an ADCP station close to Lastovo, as well as sea levels at Split and Dubrovnik, contained a pronounced diurnal signal. The wind and tidal influences on the temperature variability were separated by applying a multiple cross-wavelet spectral analysis with the hourly pseudo wind stress and sea level (or barotropic current) data treated as the inputs and the isotherm heights at Lastovo considered as the output. The analysis confirmed that significant correlation between tides and thermocline oscillations existed at the end of June, at the end of July and in August 2006. Diurnal internal tidal observations were consistent with simple theoretical near-resonant interaction of tidal flow with the island of Lastovo under stratified conditions, resulting in the generation of baroclinic island-trapped waves. This study revealed that even in a shallow area of high bathymetric complexity subjected to micro-tides, large amplitude internal waves at diurnal tidal frequency could be generated. (C) 2009 Elsevier B.V. All rights reserved.