Abstract
Abstract. Seasonal and year-to-year time evolution of the thermal structure, including the heat content change in the upper water column and its relationship with the surface net heat fluxes, have been studied at five locations in the central Mediterranean Sea. The study is based on temperature profiles collected during XBT surveys (eXpendable Bathy-Thermograph) carried out on ships of opportunity, in the framework of the MFSPP (Mediterranean Forecasting System Pilot Project), between September 1999 and May 2001. The five investigated zones are located in the southern Adriatic, NW Ionian, southern and northern Tyrrhenian, and Ligurian Sea. Gradual erosion of the thermocline in autumn, formation of a mixed layer in winter, and the onset of the stratification in spring, are common properties of the temporal evolution of thermal structures at all five locations. Moreover, in the southern Adriatic, a deep convection took place down to about 600 m in winter 1999/2000. On the other hand, mild climatic conditions and small surface heat loss in autumn and winter 2000/2001 drastically reduced a mixing/convection depth which hardly reached 200 m. Simultaneously, the NW Ionian remained slightly stratified throughout the winter period. The heat storage rate in the upper portion of the water column (down to 450 m) is compared with the air-sea net heat flux at a monthly scale. A heat content decrease is determined by the surface heat loss, and the processes such as lateral advection, or upwelling of the colder waters through the base of the water column (for example, in the southern Adriatic and Ionian Seas). Elsewhere (for example, in the northern Tyrrhenian and Ligurian Seas), the upwelling does not contribute significantly to the heat balance within the water column, since the vertical temperature gradients in deeper layers are negligible. Key words. Oceanography: general (climate and interannual variability; descriptive and regional oceanography) – Oceanography: physical (air-sea interactions)
Highlights
A ship-of-opportunity programme developed in the framework of the MFSPP enabled us to collect XBT profiles in the Mediterranean Sea, on monthly and bi-weekly time scales, starting from September 1999 (Manzella et al, 2001)
The temperature profiles collected by the Italian participants of the OGS and the ENEA along the tracks depicted in Fig. 1 are used for the description of the temporal evolution of the thermal structures at some locations in the southern Adriatic, in the northwestern (NW) Ionian, in the Ligurian, and in the Tyrrhenian, for the entire measurement period
The temporal evolution of the thermal structure was studied for the five locations in the central Mediterranean, namely the southern Adriatic, the NW Ionian, the southern and northern Tyrrhenian Seas, and the Ligurian Sea
Summary
A ship-of-opportunity programme developed in the framework of the MFSPP enabled us to collect XBT profiles in the Mediterranean Sea, on monthly and bi-weekly time scales, starting from September 1999 (Manzella et al, 2001). The temperature profiles collected by the Italian participants of the OGS (on board vessel “Lipa”) and the ENEA (on board “Excelsior”) along the tracks depicted in Fig. 1 are used for the description of the temporal evolution of the thermal structures at some locations in the southern Adriatic, in the northwestern (NW) Ionian, in the Ligurian, and in the Tyrrhenian, for the entire measurement period. They are used for estimating the heat content change in the water column, which is related to heat fluxes at the airsea interface. In the southern Adriatic in particular, these phenomena induce dense water formation, which outflows across the Strait of Otranto (Artegiani et al, 1997; Manca et al, 2002), taking part in a deep thermohaline circulation belt of the eastern Mediterranean
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