engleski

Two aspects of winter hydrographic conditions in the northern Adriatic

The northern Adriatic is one of the most productive regions in the Mediterranean Sea. It is also the place where the densest Mediterranean water can be formed. A long term analysis (1966-2000) of February thermohaline properties at a transect between the Po River delta and Rovinj showed that two types of winter hydrographic conditions can occur in this region: type "A", when bottom salinity and density are higher in the eastern than in the western part of it, and type "B", when values for these parameters are higher in its western than in its eastern part. In winters of type "B" the average density of bottom waters at the in transect was higher than in winters of type "A". A more detailed study based on hydrographic data collected in the winters of 2000 (type "B") and 2001 (type "A") at a larger area showed that A and B winters are different in dynamics as well. Eastward of the Po River delta there was a cyclonic gyre in 2000 and an anticyclonic gyre in 2001. Winter oceanographic conditions of both A and B types turned out to be persistent: hydrographic and dynamic conditions observed in February were already present in the earlier months. We hypothesize that atmospheric conditions during the autumn drive the appearance of A or B winter type, regardless of winter conditions. This hypothesis has been further explored using a numerical model (ROMS). In future, implications of A and B winter types (a) on primary and secondary production in the Adriatic, and (b) for the characteristics of Mediterranean dense waters formed in the Adriatic should be investigated. Our preliminary research indicate that in February of the "A" type, phytoplankton production in the northern Adriatic is much higher than in February of the "B" type.

northern Adriatic ; geostrophic currents ; winter

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