Recent and Expected Future Changes in the Hydrography, Ecology, and Circulation of the Eastern Mediterranean

Abstract

The classical view of the thermohaline circulation (THZ) of the Eastern Mediterranean has been that relatively less saline near-surface waters intruding from the Western Mediterranean through the Strait of Sicily were converted into more saline (i.e., denser) waters essentially in two regions. These are the northwestern Levantine Sea, where a high-salinity intermediate water mass is formed (Levantine Intermediate Water, LIW) which feeds a subsurface outflow into the Western Mediterranean, and the Adriatic, from which all the deeper waters were replenished (Wüst, 1961). The dominant role of the Adriatic was manifest in a rather uniform salinity of the deep waters. Observations that go back to 1910 indicate persistence of the classical situation since at least then. The Aegean Sea, which was known to be capable of also producing dense waters, was mostly seen as playing but a minor role in the THZ of the sea. But around 1990 the situation changed in that the Aegean suddenly formed large volumes of particularly dense water, which by 1995 had replaced approximately 20% of the waters below 1500 m and had influenced most of the deep and intermediate waters (Roether et al., 1996, Roether et al., 1998; Klein et al., 1999; Lascaratos et al., 2000). The changes were apparent in deep water salinities being markedly raised compared to the classical situation, with maximum effects in the waters adjoining the Aegean Sea. Whereas previously salinity and temperature decreased continuously below the LIW depth range down to the sea floor, there were now inversions in both properties (in 1995, inversion at about 1500 m depth).