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Hydrographic conditions in the northern Adriatic in relation to surface fluxes and Po river discharge rates (1966-1992)

Background and purpose: The northern Adriatic is a site of dense water formation and an area in which near anoxia or mucilage events are periodically observed. To understand both phenomena it is important to understand mechanism of seasonal and long-term changes of hydrographic conditions in the region. In this paper we describe seasonal cycles and year-to-year variability (1966-1992) of temperature, salinity and density in surface and in bottom layer in the northern Adriatic and relate them to changes in surface fluxes and in Po river discharge rates. Material and methods: This analysis is based on sea temperature and salinity data collected monthly to seasonally in the 1966-1992 interval at a station in the northern Adriatic. Results and conclusion: The seasonal changes in temperature and salinity in the northern Adriatic were found to be related to air-sea surface fluxes and to the Po river discharge. The Po influence was important only in spring and summer. The year-to-year changes in surface temperature and salinity were induced primarily by changes in air-sea heat and water fluxes during winter and were highly dependant on freshwater input in summer. The seasonal and year-to-year changes of temperature and salinity in the bottom layer were primarily controlled by processes of vertical mixing. The seasonal changes of density were primarily driven by seasonal changes in temperature while the year-to-year density changes were dependant on both salinity and temperature. It seems that temperature of both surface and bottom layer was somewhat higher in late eighties and early nineties that during other years of the 1966-1992 interval. The values of salinity and sigma-t were lower during seventies and early nineties than during sixties or eighties.

hydrographic conditions; northern Adriatic; long-term change

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