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Ann. Geophys., 21, 63-73, 2003
www.ann-geophys.net/21/63/2003/
© European Geosciences Union 2003
Temporal evolution of thermal structures and winter heat content change from VOS-XBT data in the central Mediterranean Sea
V. Kovačević1, M. Gačić1, G. Fusco2, and V. Cardin1
1OGS, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Trieste, Italy
2ENEA, Marine Environmental Research Centre, La Spezia, Italy
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)
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