Evolution of dynamics in the eastern Mediterranean affecting water mass structures and properties in the Ionian and Adriatic Seas

Basin‐wide hydrographic observations performed in the eastern Mediterranean during the past 2 decades attest changes in the thermohaline circulation as well as new aspects concerning the onset and the follow up of the major transient event that occurred at the beginning of the 1990s, i.e., the change of the dense water formation site from the Adriatic to the Aegean Sea. Since 1999, the upper thermohaline circulation has indicated the restoring of the opposite flows of the Atlantic Water and the Levantine Intermediate Water, which were greatly reduced in the period 1987–1995. In the deep layer the comparison between water mass structures observed in 1995, during the mature status of the transient, and those observed in 1999 shows a damping of the event and a regained role of the Adriatic Sea as a primary source of dense waters. Separate calculations of the salt content in the Ionian and in the Levantine Seas show an overall salt redistribution. During 1987–1995 a salt loss of about 25 × 1012 kg was computed for the upper 800 m, constituting only 27% of the salt gain in the deep layer over most of the eastern Mediterranean. On the contrary, during 1995–1999 the restored upper thermohaline circulation caused a salt redistribution between the two basins of about the same amount, but in the opposite sense, while an extra quantity of 12 × 1012 kg was deposited in the deep layer. In addition, calculations of the salt concentration in the convection region of the southern Adriatic reveal a remarkable amount of the salt, not yet totally transferred into the deep layers by its interior dynamics because of mild winters.