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A. Artegiani, E. Paschini, A. Russo, D. Bregant, F. Raicich, and N. Pinardi

Abstract

A comprehensive historical hydrographic dataset for the overall Adriatic Sea basin is analyzed in order to define the open ocean seasonal climatology of the basin. The authors also define the regional climatological seasons computing the average monthly values of heat fluxes and heat storage from a variety of atmospheric datasets. The long term mean surface heat balance corresponds to a heat loss of 19–22 W m−2. Thus, 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 average monthly values of evaporation, precipitation, and river runoff, obtaining an annual average gain of 1.14 m. The distribution of heat marks the difference between eastern and western Adriatic areas, showing the winter heat losses in different parts of the basin.

Climatological water masses are defined for three regions of the Adriatic: (i) the northern Adriatic where seasonal variations in temperature penetrate to the bottom; deep water (NAdDW) with σ t > 29.2 kg m−3 is produced and salinity is greatly affected by river discharges; (ii) the middle Adriatic where a pool of modified NAdDW is stored during the summer season after being renewed in winter and modified Levantine Intermediate Water (MLIW) intrudes from the southern regions between spring and autumn; and (iii) the southern Adriatic where homogeneous water properties are found below 150 m (the local maximum depth of the seasonal thermocline) and a different deep water mass (SAdDW) is found with σ t > 29.1 kg m−3, T ≈ 13.5°C, and S ≈ 38.6 psu. Due to river runoff waters, the surface layers of all three regions are freshened during the spring–summer seasons. The vertical distributions of dissolved oxygen vary quantitatively in the three regions showing a spring–summer subsurface maximum due to the balance 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 where well-mixed oxygen conditions prevail throughout the year.

Large interannual anomalies of both temperature and salinity are found at the geographical center of the basin in surface and deep waters (100 m).

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A. Artegiani, E. Paschini, A. Russo, D. Bregant, F. Raicich, and N. Pinardi

Abstract

In the second part of the paper dedicated to the Adriatic Sea general circulation, the horizontal structure of the hydrographic parameters and dissolved oxygen fields is described on a seasonal timescale.

Maps of temperature and salinity climatological fields reveal the enhanced seasonal variability of the Adriatic Sea, which at the surface is associated with the major dilution effects of river runoff.

The density and derived dynamic height fields show for the first time the baroclinic geostrophic structure of the general circulation. Winter is dominated by compensation effects between temperature and salinity fronts along the western coastline. The resulting baroclinic circulation is weak and suggests the presence of barotropic current components not accessible by the dataset. Spring and summer seasons have the smallest spatial scales in the temperature and salinity fields and stronger subbasin-scale gyres and current systems, which have been classified in a schematic representation of the circulation. The Adriatic Sea general circulation comprises boundary currents and jets that strengthen and change spatial scales in different seasons. Two separate cyclonic gyres clearly exist in the middle and southern Adriatic except during winter.

The rates of formation of the northern Adriatic deep waters and southern Adriatic deep waters are estimated to be 0.07 and 0.36 Sv (Sv ≡ 106 m3 s−1), respectively. Likely driving mechanisms of the circulation are discussed.

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