Abstract
Observations of dense water formation on the shelf of the Gulf of Thermaikos (North Aegean) are presented, based mainly on continuous monitoring of temperature and currents, during the winter of 2001–2002, at an instrumented mooring and a CTD survey carried out in early February 2002. A 2.5-month realistic simulation, corresponding to the period of observation, was performed to investigate the processes of dense water formation and cascading. The simulation is first compared to the main characteristics of the dense water, time variation of bottom temperature and spatial distribution of the dense water on the shelf. Subsequently, the simulation is used (a) to show that the formation of dense water takes place within the semi-enclosed Thessaloniki Bay and (b) to explain the intermittence of cascading out of the bay in relation to wind variations. The pathways of the dense water through the shelf are investigated with an emphasis on the role of the bottom slope and friction in the Ekman layer. The export of dense water towards the open sea occurs primarily along the slope bounding the western coast.
Highlights
Thermaikos Gulf in the Northern Aegean Sea (Fig. 1), the Adriatic Sea and the Gulf of Lions are regions of the northern Mediterranean that are characterised by a large continental shelf, exposed to strong and frequent winds blowing from the continent
During the February 1998 cruise, the lowest temperatures (o121) were observed in the bottom layers of the northern stations, i.e. in northern Thermaikos Gulf and in Thessaloniki Bay, which is a semi-enclosed area located at the northern extremity of the main gulf (Fig. 1)
Shallow waters which allow rapid cooling under the action of cold wind; this characteristic is shared by the whole of the coastal band within the gulf. It was established from the meteorological model that total heat losses are stronger along the western coast than in Thessaloniki Bay; this is due to increasing wind, from North to South
Summary
Thermaikos Gulf in the Northern Aegean Sea (Fig. 1), the Adriatic Sea and the Gulf of Lions are regions of the northern Mediterranean that are characterised by a large continental shelf, exposed to strong and frequent winds blowing from the continent. During the February 1998 cruise, the lowest temperatures (o121) were observed in the bottom layers of the northern stations, i.e. in northern Thermaikos Gulf and in Thessaloniki Bay, which is a semi-enclosed area located at the northern extremity of the main gulf (Fig. 1). These cold water masses, formed by intense winter cooling, were observed in May 1997, indicating a very slow bottom water exchange rate in the northernmost part of the gulf (Kontoyiannis et al, 2003). Thermaikos Gulf appears to be a region of dense water formation of the Mediterranean Sea, as is the case for the Gulf of Lions (Fieux, 1974) and the northern Adriatic Sea (Manca et al, 2002; Vilibic, 2003)
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