An analysis of dense water production on the North Adriatic shelf

Abstract

The aim of this paper is to investigate the mechanism of dense water formation in the northern shelf region of the Adriatic Sea and its spreading towards the Middle and South Adriatic. The analyses encompass temperature, salinity, sigma- t and dissolved oxygen data collected during 1951–1989 interval in the deep trench located in the middle of the Adriatic. Hydrographic sections as well as current and temperature time series collected in the North and Middle Adriatic were analysed, too. The data outline linear trends of salinity by +0.0036±0.0017 year −1 and of dissolved oxygen content by −0.022±0.008 ml l −1 year −1, whereas temperature data reveal three periods having different attributes: strong fluctuations (1951–1962), higher (1966–1980) and lower (1981–1989) temperature values. Two types of North Adriatic Dense Water (NAdDW) formation result from the analysis: the first with rather low temperatures (high rates of surface buoyancy losses, e.g. 1956, 1981, 1984) and the second with high salinity (large inflow of Levantine Intermediate Water—LIW, e.g. 1955, 1968). After formation on the shelf, NAdDW can bifurcate and goes close to the western (main branch) and/or eastern (secondary branch) flanks. By correlating hydrological data collected at the bottom of the trench with the North Adriatic surface buoyancy fluxes and the Po River discharges, main NAdDW current velocity is calculated to be higher than 8 cm s −1, therefore reaching the Jabuka Pit about 1 month after generation, whereas the secondary branch arrives there about 1 month later. NAdDW current lasted for about 2 months (spring 1984). Preconditionings favourable for the NAdDW formation are achieved too, by correlating both surface buoyancy fluxes and the Po River discharges with temperature data measured at the bottom of the Jabuka Pit.