During the CIESM workshop (Monaco, 22-24 April 2002) entitled "Monitoring Hydrolouical Trends in the Mediterranean", the review of existing data sets and analyses has revealed important variability in the dynamics and hydrological characteristics, in the past century, ranging from interannual to decadal time scales. These variations are related mainly to local forcing and larger scale atmospheric parameters (NAO, ENSO, Indian monsoon). Moreover, abrupt events contribute to modification of the Mediterranean conveyor belt, also influencing the biogeochemical environment and the Mediterranean outflow in the Atlantic Ocean. The participating scientists have agreed on the need of a sustained multi-component long-term monitoring system based on both oceanographic and atmospheric observations and modelling. The group also proposed an expansion and strengthening of the ongoing relevant large operational programs by a "climatic approach" component.

In this paper we revisit, with a thorough in-depth analysis, the dataset collected in the hydrographic surveys of the international collaborative programme POEM (Physical Oceanography of the Eastern Mediterranean) in the period 1986-1987. The work has two major objectives. The first is to refine the dynamic picture of the Ionian upper thermocline sub-basin scale circulation, rather less definitive than the dynamic picture of the Levantine Sea circulation. The second is to identify the pathways of the major water masses of the basin not only in the near-surface, but also in the intermediate and deep layers. To our knowledge, this is the first work defining the pathways of the Levantine Intermediate Water (LIW) and of the Adriatic Deep Water (ADW)/Eastern Mediterranean Deep Water (EMDW) that characterize the intermediate and deep circulations.The major novel results can be summarized as follows. In the upper thermocline: (1) The Atlantic Ionian Stream (AIS) jet entering the Sicily Straits bifurcates into two main branches at 37 degrees N, similar to 17 degrees E. It advects the Modified Atlantic Water (MAW) into the Ionian Sea interior. The first branch turning directly southward encloses an overall anticyclonic area comprising multiple centers around which the MAW is advected. (2) The second AIS branch extends further into the northeastern Ionian, where it too turns southward before crossing the entire Ionian Sea meridionally, advecting MAW on its left side and Ionian Surface Water (ISW) on its right. This branch of the jet is confined to the Ionian margin and does not pass around the Pelops gyre. (3) A new water mass, the LSW, is formed in the Levantine basin and enters the Cretan passage, then is first veered cyclonically south of Crete by the Cretan gyre and successively is entrained anticyclonically around the Pelops gyre, and then enters the Aegean Sea. (4) A permanent cyclone located in the northeastern Ionian determines the pathway of mixed Adriatic Surface Water/Ionian Surface Water (ASW/ISW). (5) A permanent cyclone is found in all the surveys near the tip of the Italian boot.This novel analysis of the LIW pathways shows that: (I) The major source of intermediate LIW during the period 1986-1987 was actually in the Levantine Sea. LIW formed there entered the Cretan passage, was veered cyclonically by the Cretan gyre south of Crete and then entered the southern Ionian Sea. The major LIW pathway was westward directly to the Sicilian Straits. (2) Secondary important LIW pathways were determined by the interior structures. The strong Pelops anticyclone was entraining LIW around its periphery and was determining the LIW northward pathway that closely followed the eastern Greek coastline, It was along this pathway that LIW entered the Otranto Strait. A further branch of LIW was entrained and recirculated around the multiple Ionian Anticyclones (IA) of the western Ionian Sea. (3) The Cretan cyclone is a feature confined to the upper thermocline-intermediate layer. It disappears at similar to 400 dbar while the Pelops anticyclone is strongly barotropic below the upper 100 dbar and penetrates quite intense down to 800 dbar. (4) A further completely novel result concerns the new water mass found in the deep layer that spreads on the 29.15 kg/m(3) isopycnal surface. This water mass, characterized by high salinity and high oxygen content, is formed inside the Aegean Sea and is observed to spread out all around the Cretan Are Straits.The final fully novel result is the demonstration of a second pathway for the ADW exiting from the Otranto Strait that is transformed into EMDW and occupies the abyssal layers of the Ionian Sea interior. The traditional pathway for EMDW is along the isobaths along the western side of Italy but ADW was observed to be exiting from the Otranto Strait in the eastern Hellenic trench at 39.5 degrees N, both during POEM-ON86 and POEM-AS87. This second pathway for EMDW follows isobath contours along the western side of Greece. The two EMDW routes converge and merge between 36 degrees N and 35 degrees N, so producing a deep layer of EMDW that occupies uniformly the abyssal plain of the interior of the Ionian Sea. (C) 1997 Elsevier Science Ltd. All rights reserved.

Waters of the eastern Mediterranean portray an unusual pattern of stable isotope composition compared with other evaporitic systems: an increase in 18O concentration up to value of δ18O = +2.2‰ is not matched by a commensurate increase of deuterium. It is shown that this unusual pattern is an expression of the “medi‐terranean” location of the sea, where the air‐sea interaction with relatively dry and isotopically depleted continental air masses dominates the evaporation process in winter and where the diluting meteoric waters are extremely depleted in the heavy isotopes. As a result, the slope of the evaporation line in δ(2H)‐δ(18O) space is lower than in other marine systems, whereas the mixing line between the meteoric waters and the seawater is very steep. This pattern provides an independent method for the estimation of the evaporation E and freshwater influx terms M of the water balance of the Mediterranean Sea. In winter, the ratio of evaporation to freshwater input is found to be E/M = 1.20, whereas in summer this ratio E/M = 1.83.

During the last decade the oceanography community has focused much attention on the Mediterranean Sea. One reason for the growing interest is that the Mediterranean's impact on the Northern Atlantic Ocean is more significant than previously realized. The warm, salty Mediterranean water tongue exits the Gibraltar Straits and spreads throughout the North Atlantic at all depths between 1000 and 2500 m. The second reason for the surge in interest is the well‐recognized role of the Mediterranean Sea as a laboratory for studying ocean processes that are important in global climate dynamics [Malanotte‐Rizzoli and Robinson, 1991; Malanotte‐Rizzoli and Robinson, 1994].

In the framework of the major multinational coordinated POEM-II-86 (March-April 1986) and POEM-V-87 (September-October 1987) cruises in the Eastern Mediterranean, high resolution hydrographic (CTD) data were collected by R.V. Aegaio in the eastern Ionian Sea, south Aegean Sea and northwest Levantine Basin. The intercalibrated data sets were analyzed objectively for an optimal estimation of the basin's circulation in two different seasons. The analysis reveals a rather complex general circulation pattern consisting of basin, sub-basin and mesoscale features during both study periods. The major results concern the advection of the Modified Atlantic Water (MAW) along its eastward route, the spreading of the Levantine Intermediate Water (LIW) and its trapping by the eddy fields; the interaction between the south Aegean Sea and the eastern Mediterranean; and the reverse circulation in the Cretan Sea during winter and summer. From the hydrography and the dynamic height maps, synthetic schemes show the main circulation features in the two seasons.

A novel description of the phenomenology of the Eastern Mediterranean is presented based upon a comprehensive pooled hydrographic data base collected during 1985–1987 and analyzed by cooperating scientists from several institutions and nations (the POEM project). Related dynamical process and modeling studies are also overviewed. The circulation and its variabilities consist of three predominant and interacting scales: basin scale, subbasin scale, and mesoscale. Highly resolved and unbiased maps of the basin wide circulation in the thermocline layer are presented which provide a new depiction of the main thermocline general circulation, composed of subbasin scale gyres interconnected by intense jets and meandering currents. Semipermanent features exist but important subbasin scale variabilities also occur on many time scales. Mesoscale variabilities modulate the subbasin scale and small mesoscale eddies populate the open sea, especially the south-eastern Levantine basin. Clear evidence indicates Levantine Intermediate Water (LIW) to be present over most of the Levantine Basin, implying that formation of LIW is not localized but rather is ubiquitous. The Ionian and Levantine basins are confirmed to form one deep thermohaline cell with deep water of Adriatic origin and to have a turnover time of one and a quarter centuries. Prognostic, inverse, box and data assimilative modeling results are presented based on both climatological and POEM data. The subbasin scale elements of the general circulation are stable and robust to the dynamical adjustment process. These findings bear importantly on a broad range of problems in ocean science and marine technology that depend upon knowledge of the general circulation and water mass structure, including biogeochemical fluxes, regional climate, coastal interactions, pollution and environmental management. Of global ocean scientific significance are the fundamental processes of water mass formations, transformations and dispersion which occur in the basin.