Similarly, a cyclonic gyre exists at the entrance of the Thermaikos Gulf, transporting water inwards along the eastern coastline and outwards along the western coast of this gulf (Zervakis et al., 2005 and Olson et al., 2007).

The current work presents collected hydrographic data and examines the surface distribution of water parameters (temperature, salinity, density and geopotential anomaly) during the summer periods of 1998–2001 with the aim of studying meteorological influences on the surface water patterns of the North Aegean Sea. In this work, special emphasis was placed on the BSW plume expansion, the BSW-LIW frontal characteristics and the variability of permanent and transient sub-basin gyre features. The North Aegean Sea was visited DAPT molecular weight during the summer IWR-1 solubility dmso periods in 1998–2001, on board the fishing trawler ‘Evagelistria’, for the conducting of experimental fishery research within the framework of the MEDITS (Mediterranean International Trawling Survey) programme. The area covered represents the whole North Aegean Sea and the northern part of the Central Aegean Sea, between 38–41°N and 22.5–26.3°E. Table 1 presents the starting and ending dates of each MEDITS summer cruise, together with the number of stations sampled per year. Standard hydrographic measurements were undertaken using a Seabird Electronics SBE 19 plus CTD. Sensor accuracy was 0.01°C for temperature

and 0.01 mS cm−1 for conductivity. A total of 360 CTD casts were obtained during summers 1998–2001. The 1998 and 1999 cruises commenced from the Thracian Sea coastline (northern Aegean Sea border), DNA ligase followed

a meridian transect through Lemnos, Lesvos and Chios Islands, and then moved north-westwards to the Sporades Islands, where the cruise ended. The 2000 and 2001 cruises followed a similar track, but extended to the northern Evoikos, Thermaikos and Strymonikos Gulfs (Figure 2). The 2000 and 2001 castings were limited to the first 200 m of the water column depth, to monitor surface dynamics and associate the collected data with the distribution of the ichthyofauna, which was sampled concurrently using a bongo net (0–50 m depth). The 1999 survey profiles were limited to 50 m depth. The raw data were filtered and processed according to the SBE software manual to derive water temperature and salinity as a 1-dbar bin average, together with potential temperature and density (σt-values). Standard routines (SeaMat library, available at http://woodshole.er.usgs.gov) were used to produce geopotential anomaly values (dynamic height in m multiplied by the acceleration due to gravity, expressed in J kg−1 or m2 s−2) at 5 dbars relative to 40 (ΔФ5/40) and 100 dbars (ΔФ5/100). Based on these values, geostrophic velocity vectors were then produced. Although a deeper reference level may be desirable (e.g.