Abstract. Drastic changes have occurred in the vertical structure of the deep waters of the eastern Mediterranean in the early 1990s, as dense water of Aegean origin has displaced lighter waters of Adriatic origin at the bottom of the deep basins. This work suggests that the initiation of this process took place in the North Aegean in the winter of 1986/1987 and was intensified by another formation event in 1992/1993. The available observations from the North Aegean support such a scenario. Furthermore, we propose that the outflow of Black Sea waters into the Aegean through the Dardanelles could act as an insulator of the deeper layer from the atmosphere, thus absorbing a large part of the heat and salt exchange; despite this fact, the existence of the densest bottom water of the Mediterranean in the North Aegean, and the continuation of density increase for a large period of time, suggests that it is a region of formation, thus that the insulation layer may at times be penetrated. We suggest that reduced Black Sea outflow into the North Aegean could facilitate dense water formation during the passage of cold atmospheric fronts in the winter.

The combination of two research projects offered us the opportunity to perform a comprehensive study of the seasonal evolution of the hydrological structure and the circulation of the North Aegean Sea, at the northern extremes of the eastern Mediterranean. The combination of brackish water inflow from the Dardanelles and the sea-bottom relief dictate the significant differences between the North and South Aegean water columns. The relatively warm and highly saline South Aegean waters enter the North Aegean through the dominant cyclonic circulation of the basin. In the North Aegean, three layers of distinct water masses of very different properties are observed: The 20-50 m thick surface layer is occupied mainly by Black Sea Water, modified on its way through the Bosphorus, the Sea of Marmara and the Dardanelles. Below the surface layer there is warm and highly saline water originating in the South Aegean and the Levantine, extending down to 350-400 m depth. Below this layer, the deeper-than-400 m basins of the North Aegean contain locally formed, very dense water with different ı/S characteristics at each subbasin. The circulation is characterised by a series of permanent, semi-permanent and transient mesoscale features, overlaid on the general slow cyclonic circulation of the Aegean. The mesoscale activity, while not necessarily important in enhancing isopycnal mixing in the region, in combination with the very high stratification of the upper layers, however, increases the residence time of the water of the upper layers in the general area of the North Aegean. As a result, water having out-flowed from the Black Sea in the winter, forms a separate distinct layer in the region in spring (lying between "younger" BSW and the Levantine origin water), and is still traceable in the water column in late summer.

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High Frequency Radar (HFR) is a land-based remote sensing instrument offering a unique insight to coastal ocean variability, by providing synoptic, high frequency and high resolution data at the ocean atmosphere interface. HFRs have become invaluable tools in the field of operational oceanography for measuring surface currents, waves and winds, with direct applications in different sectors and an unprecedented potential for the integrated management of the coastal zone. In Europe, the number of HFR networks has been showing a significant growth over the past 10 years, with over 50 HFRs currently deployed and a number in the planning stage. There is also a growing literature concerning the use of this technology in research and operational oceanography. A big effort is made in Europe toward a coordinated development of coastal HFR technology and its products within the framework of different European and international initiatives. One recent initiative has been to make an up-to-date inventory of the existing HFR operational systems in Europe, describing the characteristics of the systems, their operational products and applications. This paper offers a comprehensive review on the present status of European HFR network, and discusses the next steps toward the integration of HFR platforms as operational components of the European Ocean Observing System, designed to align and integrate Europe's ocean observing capacity for a truly integrated end-to-end observing system for the European coasts.

Abstract. During the period 1998–2000, the Mediterranean Forecasting System Pilot Project, aiming to build a forecasting system for the physical state of the sea, has been carried out. A ship-of-opportunity programme sampled the Mediterranean upper ocean thermal structure by means of eXpendable Bathy-Thermographs (XBTs), along seven tracks, from September 1999 to May 2000. The tracks were designed to detect some of the main circulation features, such as the stream of surface Atlantic water flowing from the Alboran Sea to the Eastern Levantine Basin. The cyclonic gyres in the Liguro-Provenal Basin, the southern Adriatic and Ionian Seas and the anticyclonic gyres in the Levantine Basin were also features to be detected. The monitoring system confirmed a long-term persistence of structures (at least during the entire observing period), which were previously thought to be transient features. In particular, in the Levantine Basin anticyclonic Shikmona and Ierapetra Gyres have been observed during the monitoring period. In order to identify the major changes in the thermal structures and the dynamical implications, the XBT data are compared with historical measurements collected in the 1980s and 1990s. The results indicate that some thermal features are being restored to the situation that existed in the 1980s, after the changes induced by the so-called "Eastern Mediterranean Transient". Key words. Oceanography: physical (eddies and mesoscale processes; general circulation; instruments and techniques)

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Abstract. The evolution of the upper thermocline on a section across the eastern Mediterranean was recorded bi-weekly through a series of XBT transects from Piraeus, Greece to Alexandria, Egypt, extending from October 1999 to October 2000 on board Voluntary Observing Ships in the framework of the Mediterranean Forecasting System Pilot Project. The data acquired provided valuable information on the seasonal variability of the upper ocean thermal structure at three different regions of the eastern Mediterranean: the Myrtoan, Cretan and Levantine Seas. Furthermore, the horizontal distance (~12 miles) between successive profiles provides enough spatial resolution to analyze mesoscale features, while the temporal distance between successive expeditions (2–4 weeks) allows us to study their evolution. Sub-basin scale features are identified using contemporaneous sea surface temperature satellite images. The cross-transect geostrophic velocity field and corresponding volume fluxes for several sub-basin scale features of the Levantine Sea are estimated by exploiting monthly q / S diagrams from operational runs of the Princeton Ocean Model in use at NCMR. A southwestward transport in the proximity of the southeast tip of Crete was estimated between 1–3 Sv. The transport increases after the winter formation of dense intermediate water in the Cretan Sea strengthens the pressure gradient across the Cretan Straits. The Mersah-Matruh anticyclone was identified as a closed gyre carrying about 2–6 Sv. This feature was stable throughout the stratified period and disappeared from our records in March 2000. Finally, our data reveal the existence of an eastward-flowing coastal current along the North African coast, transporting a minimum of 1–2 Sv. Key words. Oceanography: physical (eddies and mesoscale processes; currents; marginal and semi-closed seas)