Physical features of the eastern Mediterranean resulting from the integration of POEM data with Russian Mediterranean Cruises

Two large-scale investigations of the eastern Mediterranean: POEM — an international cooperative effort, and GOIN — an initiative of the former USSR, were carried out between 1985 and 1995. The two projects were not coordinated and therefore the cruises of the two sometime overlap and sometime complement each other in time and in space. Statistical comparison between adjacent stations and comparisons between parameter maps indicated that there is no need to adjust any of the data and that the two data bases could be combined into a single POEM – GOIN data base (PGDB). The PGDB was employed for the description of winter and summer distributions of temperature and salinity in the eastern Mediterranean Sea. These appear to differ in some respects from the climatologies extracted from the MODB or from those extracted from the Naval Oceanographic Office gridded hydrographic data base. Since the MODB contains a large number of coastal cruises which were intended to monitor the Nile floods, the MODB salinity climatology reflects the conspicuous effects of those floods. However, this feature disappeared with the closure of the Aswan dam in 1965. On the other hand, some well-known mesoscale features of the eastern Mediterranean circulation do not appear in the climatological fields. We conclude that the differences are due to indiscriminate averaging, which does not produce a useful representative climatology. The PGDB also provided useful additional information in the southern region of the Ionian Sea, which was not covered by POEM cruises. Thus, details of the southern branch of the MAW, the branch that flows directly from the Sicily straits to the Cretan Passage, could be described. The PGDB allowed us to follow the history of the Irapetra Gyre and to show that, indeed, the gyre appeared only in the summer of 1987 and, apparently, lasted only until 1995. We describe the changes throughout this period, in intensity, size, and position of the Irapetra Gyre. The examination of previous cruises as well as a thorough search through the data of Med Atlas I indicated some occurrences of the Irapetra Gyre before its description by the POEM investigation, and therefore this gyre should be defined as a recurrent feature.