THE ADRIATIC SEA GENERAL-CIRCULATION .1. AIR-SEA INTERACTIONS AND WATER MASS STRUCTURE

A comprehensive historical hydrographic dataset for the overall Adriat ic Sea basin is analyzed in order to define the open ocean seasonal cl imatology of the basin. The authors also define the regional climatolo gical seasons computing the average monthly values of heat fluxes and heat storage from a variety of atmospheric datasets. The long term mea n surface heat balance corresponds to a heat loss of 19-22 W m(-2). Th us, in steady state, the Adriatic should import about the same amount of heat from the northern Ionian Sea through the Otranto Channel. The freshwater balance of the Adriatic Sea is defined by computing the ave rage monthly values of evaporation, precipitation, and river runoff, o btaining an annual average gain of 1.14 m. The distribution of heat ma rks the difference between eastern and western Adriatic areas, showing the winter heat losses in different parts of the basin. Climatologica l water masses are defined for three regions of the Adriatic: (i) the northern Adriatic where Seasonal variations in temperature penetrate t o the bottom; deep water (NAdDW) with sigma(t) > 29.2 kg m(-3) is prod uced and salinity is greatly affected by river discharges; (ii) the mi ddle Adriatic where a pool of modified NAdDW is stored during the summ er season after being renewed in winter and modified Levantine Interme diate Water (MLIW) intrudes from the southern regions between spring a nd autumn; and (iii) the southern Adriatic where homogeneous water pro perties are found below 150 m (the local maximum depth of the seasonal thermocline) and a different deep water mass (SAdDW) is found with si gma(t) > 29.1 kg m(-3), T approximate to 13.5 degrees C, and S approxi mate to 38.6 psu. Due to river runoff waters, the surface layers of al l three regions are freshened during the spring-summer seasons. The ve rtical distributions of dissolved oxygen vary quantitatively in the th ree regions showing a spring-summer subsurface maximum due to the bala nce between phytoplankton growth in the euphotic zone and low vertical mixing in the water column. This behavior can be reconciled with open ocean conditions except for the northernmost part of the Adriatic whe re well-mixed oxygen conditions prevail throughout the year. Large int erannual anomalies of both temperature and salinity are found at the g eographical center of the basin in surface and deep waters (100 m).