Long-term changes in hydrographic conditions in northern Adriatic and its relationship to hydrological and atmospheric processes

N Supić,I Vilibić,I Ivančić,B Grbec

doi:10.5194/angeo-22-733-2004

Abstract

Abstract. A very long data series (1921–2000) of hydrographic parameters (temperature, salinity and density) collected in surface and bottom layers at a station in the coastal zone in the northeastern Adriatic was analyzed. Seasonal and interannual variability of the three parameters is described on the basis of monthly and yearly averages. The seasonal cycles obtained were found to be typical for the northern Adriatic. Interannual analysis showed that there was no trend in temperature, salinity and density in the region during the interval analyzed. The long-term series of yearly means of hydrographic parameters were related to the long-term series of yearly means of several hydrological/atmospheric parameters using different time lags of between 0 and 4 years. These parameters are surface heat flux gained by insolation Qs computed for Trieste, precipitation P in Trieste, Po River discharge rate R and two atmospheric oscillation indexes, a Mediterranean Oscillation (MO) index and North Atlantic Oscillation (NAO) index. At zero time lag the interannual changes at the surface were found to be significantly related to changes in the Qs and NAO index (temperature) and R (salinity and density). At the same time lag the changes in the bottom were found to be related to the MO index (temperature, salinity and density). Additionally, bottom salinity and density were significantly related to R at a time lag of 1 year. Key words. Oceanography: Physical (air-sea interactions; hydrography)

Highlights

It is generally known that the hydrographic characteristics of the northern Adriatic are under the influence of air-sea fluxes and the Po River discharge rates
In the middle Adriatic, inflow of very saline water from the Mediterranean is considered to be connected to the sea-level pressure difference between the mid North Atlantic and southeast Mediterranean, named the Mediterranean Oscillation index (MO index; Grbec et al, 2003)
The analysis of data from the period 1966–1992 showed that seasonal and interannual variations of hydrographic conditions in the northern Adriatic are related to the corresponding changes in surface fluxes and in the Po River discharge rate (Supicet al., 1997; Supicand Ivancic, 2002)

Summary

Introduction

It is generally known that the hydrographic characteristics (e.g. temperature, salinity and density) of the northern Adriatic are under the influence of air-sea fluxes (e.g. under the influence of air-sea heat flux Q and air-sea water flux W) and the Po River discharge rates (e.g. Franco and Michelato, 1992; Orlicet al., 1992). Franco and Michelato, 1992; Orlicet al., 1992) They are influenced by periodical inflow of more saline water of Mediterranean origin The North Atlantic Oscillation (NAO) is a large-scale mode of natural climate variability having large impacts on weather and climate in the North Atlantic region and over Europe It is often defined through an oscillation index as the sea-level pressure difference between the polar low and the subtropical high. The analysis of data from the period 1966–1992 showed that seasonal and interannual variations of hydrographic conditions in the northern Adriatic are related to the corresponding changes in surface fluxes (air-sea heat flux, air-sea water flux, air-sea buoyancy flux) and in the Po River discharge rate (Supicet al., 1997; Supicand Ivancic, 2002). The impact of long-term changes in the MO and NAO indexes on hydrographic conditions of the region has not been analysed to date

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