engleski

Dense water generation in the North Adriatic Sea: the role of surface fluxes and river discharges

The analyses of winter thermohaline properties of the North Adriatic were performed at the transect Po-Rovinj in the 1967-2000 interval, based on the data of temperature and salinity collected primarily at two stations: the first positioned near the Po River mouth (station 5) and the second located close to the eastern shore (station 2). The analyses comprised single and double correlation analyses between temperature, salinity and sigma-t values in February as outputs to the surface fluxes (temperature versus heat flux, salinity versus water flux, density versus buoyancy flux) calculated for the North Adriatic and Po River discharge values as inputs. The February was chosen as the minimum in temperature and maximum in density have been measured then. Winter thermohaline properties are predominantly influenced both by Po River discharge and advection of warmer and saline waters from the southeast ; therefore, bottom temperature is always lower near the western shore whereas the salinity is higher close to the eastern flank in general, but such distribution can be reversed during the years when the Po River plume is detached from the shore. Correlation analyses indicate that bottom water properties in February are driven dominantly by fluxes in September (salinity versus water flux) and in June, October and December/January (temperature versus heat flux) at the station 2, and in February/March (salinity versus water flux and Po River discharge) and October (density versus buoyancy flux) at the station 5. The strongest influence on the west side has the pycnocline destruction that usually occurs in October, bringing warmer and less saline waters to the bottom. Correlation for sigma-t values is calculated to be significant at 99.99 % level, but correlation vanishes at station 2, due to the impact of the advective processes there. Correlation with February/March Po River discharges is a consequence of deepening of the waters influenced by Po River, which can be brought to the bottom during the period of vertical instability (February/March), then spreading in the bottom layer and reaching eastern side after a month (April). Finally, it should be pointed out that thermohaline properties at the bottom of the North Adriatic are not correlated to the dynamics that occurs at the zero phase lag (February) as one should expect, due to temporal characteristics of the fluxes and strong vertical stratification in January/February near the Po River delta.

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