On the Circulation and Thermohaline Properties of the Eastern Mediterranean Sea

Abstract

The circulation of the Eastern Mediterranean Sea is characterized by numerous recurrent or permanent anticyclonic structures, which modulate the pathway of the main currents and the exchange of the water masses in the basin. This work aims to describe the main circulation structures and thermohaline properties of the Eastern Mediterranean with particular focus on two anticyclones, the Pelops and the Cyprus gyres, using in-situ (drifters and Argo floats) and satellite (altimetry) data. The Pelops gyre is involved in the circulation and exchange of Levantine origin surface and intermediate waters and in their flow toward the Ionian and the Adriatic Sea. The Cyprus Gyre presents a marked interannual variability related to the presence/absence of waters of Atlantic origin in its interior. These anticyclones are characterized by double diffusive instability and winter mixing phenomena driven by salty surface waters of Levantine origin. Conditions for the salt finger regime occur steadily and dominantly within the Eastern Mediterranean anticyclones. The winter mixing is usually observed in December–January, characterized by instability conditions in the water column, a gradual deepening of the mixed layer depth and the consequent downward doming of the isohalines. The mixing generally involves the first 200 m of the water column (but occasionally can affect also the intermediate layer) forming a water mass with well-defined thermohaline characteristics. Conditions for salt fingers also occur during mixing events in the layer below the mixed layer.

Climatic, Decadal, and Interannual Variability in the Upper Layer of the Mediterranean Sea Using Remotely Sensed and In-Situ Data

“…It is interesting to note that salinity values in the surface layer of the South Levantine sector are lower than the other sectors (red circles in Figure 10C), whereas in the intermediate layer they are in line and occasionally larger than the values collected in the other sectors (red circles in Figure 10D). These salinity values confirm the inflow of the AW in the surface layer of the Southern Levantine, in agreement with the results of Techtmann et al [93] and Menna et al [24]. The largest surface layer salinities are observed in the Cyprus sector during the anticyclonic periods (black crosses in Figure 10C) and in the Cretan sector during the cyclonic periods (blue triangles in Figure 10D).…”

“…The EMED was identified as a case study not only because it is the best sampled by Argo floats compared to the other sub-basins, but also because it is the perfect region to appreciate the salinity variations of the Levantine surface water and LIW formed in its interior [92]. These variations affect the variability of the whole MED [4,24,52].…”

“…Moreover, these variations show prominent long-term trends, which however differ between various sub-basins [11,14,15,17]. These differences are probably due to the local circulation [18][19][20][21], thermohaline changes [22][23][24], and relatively short time-series where it has been calculated from [25,26]. A quick summary of the trend analysis recently conducted in the Mediterranean describes a scenario of increasing freshwater deficit [27], sea surface temperature (SST) and sea level [11,[14][15][16], and a basin-scale multi-decadal salinification [11,23,[28][29][30].…”

The hydrodynamic theory of the Cyprus Eddy

“…In the north, these gyres are flanked by the AMC, while in the south by the meandering eastward Mid Mediterranean Jet (MMJ). The MMJ transfers the waters to the south of Cyprus, flowing along the northern periphery of a warm anticyclonic feature located in the Eratosthenes seamount broad area (Menna et al 2021). This unusual relatively permanent eddy south of Cyprus was first identified as the warm Cyprus Eddy in Brenner (1989).…”

“…The general circulation of the Eastern Mediterranean Levantine Basin is predominantly counterclockwise (Nielsen 1912), consisting of a complicated system of strong currents, meandering jets, mesoscale eddies, and gyres. The knowledge of the Eastern Mediterranean surface circulation is steadily improving (Ovchinnikov 1966;Ovchinnikov et al 1976;Robinson et al 1991Robinson et al , 2001Pinardi et al 2006;Hamad et al 2006;Schroeder et al 2012;Menna et al 2012;Akpinar et al 2016;Menna et al 2021).…”