On the continuous functioning of an internal mechanism that drives the Eastern Mediterranean thermohaline circulation: The recent activation of the Aegean Sea as a dense water source area

Abstract

The scientific interest in Eastern Mediterranean (EMed) processes of major importance has been revived in recent years due to the predominance of internal variability manifested in a decadal time scale leading to the alternating activation of the two dense water sources (i.e. the Adriatic and Aegean Seas). Analysis of available hydrographic data during the 2003–2012 period reveals an anticorrelated almost decadal oscillation in the thermohaline properties of the upper and intermediate water masses in both the Ionian and the Levantine/Aegean Seas. This event is the manifestation of an ongoing internal mechanism initially introduced by Theocharis et al. (in press) which periodically disturbs the upper thermohaline EMed conveyor belt and changes the respective water mass pathways, thus driving the alternating activation of the two dense water sources through salinity preconditioning. Since 2004–2005, the salinity of the upper/intermediate layer in the eastern part of the EMed gradually increased up to 2010, while at the same time it decreased in the North Ionian Sea. During the same period we observed the activation of the Aegean Sea as a Dense Water Formation area even though the atmospheric forcing conditions were not favorable. After 2010 the salinity trend reversed in both regions. This suggests that in the near future the salinity preconditioning of the Adriatic Sea will be favored again following the respective water mass pathway changes.