engleski

The Levantine Intermediate Water (LIW) pathways in the northern Adriatic and their relation to bora events

Long-term (1967-2000) changes of February bottom salinity (30 m) at two stations in the northern Adriatic have been analysed in order to detect winters in which advection events of modified Levantine Intermediate Water (LIW) from the south occurred. The stations are located in open waters of the eastern (station 1) and western (station 2) part of the Po River delta-Rovinj profile. Although the surface layer in the region is generally affected by fresh waters, the bottom salinity varied within a relatively small interval (37.4-38.6). The bottom values were on average slightly higher at station 1 (38.1 0.2) than at station 2 (38.0 0.3). High salinity values (>38.3) were ascribed to modified Levantine Intermediate Water (LIW). They were observed in 1981, 1989, 1990 and 2000. Data collected monthly along the Po river delta-Rovinj profile in the winter season of 1999/2000, as well as computed geostrophic currents relative to 30 m depth, indicate that LIW entered the northern Adriatic by the end of 1999. On 18 December 1999 a strong inflow (with currents up to 6 cm/s) of high salinity water (38.4) was observed in a water band extending from the surface to the bottom in the western part of the section. As the Adriatic circulation is cyclonic, with an inflow across the eastern coast (EAC, East Adriatic Current), the December 1999 event supports the hypothesis that the EAC is on some occasions deflected towards the west, entering the northern Adriatic in its central/western part. Such LIW pathway may be a result of bora- induced circulation which favours strong currents emerging from the Bay of Kvarner and forming tranversal frontal zone, preventing EAC to enter the northern Adriatic along the eastern coast. Actually, strong bora occurred just two days before, on 16 December 1999, with daily averaged wind speed of 13.4 m/s measured at coastal Pula station. Data collected across the Po river delta-Rovinj profile on 5 January show the presence of modified LIW in a band extending from the surface to the bottom in the eastern part of the section, and in deep layers close to the Po delta. On the 21 February cruise modified LIW was observed only in bottom layers of the western Adriatic, and during the 17-21 March cruise it was not observed at all. After several very strong bora events in the second part of December (with daily averaged wind speed up to 18.9 m/s at Pula station) the wind decreased and during January, February and March it was generally moderate, blowing mainly from the NE. Therefore, the circulation retain to a normal, with LIW inflow along the eastern coast observed in January, whereas lower salinity in March is probably a result of vertical mixing and replenishment of LIW in the wider area.

water masses ; salinity ; northern Adriatic

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