Dense water formation in the Aegean Sea: Numerical simulations during the Eastern Mediterranean Transient

Abstract

[1] Dense water formation processes in the Aegean Sea (eastern Mediterranean) are studied using a three-dimensional numerical ocean model. The simulations cover the period 1979-1994 during which major changes that affected the thermohaline circulation of the whole Mediterranean Sea were recorded. Sensitivity studies that focus on the role of freshwater budget are presented, and the results are evaluated against available hydrological data of the same period. The very cold winters of 1987, 1992, and 1993 and the extended dry period 1989-1993 that affected the whole eastern Mediterranean Sea are the main driving mechanisms, corresponding to 50% and 32%, respectively, of the excessive deepwater volume formed in the Aegean after 1987. The reduced Black Sea Water outflow during the same dry period was another important forcing mechanism, contributing 18% to the total formation, while the increased inflow of saline waters from the Levantine Sea after 1992 was an additional preconditioning factor. The locations and mechanisms of water formation processes are identified with combined analysis of data from the March 1987 oceanographic cruise in the Aegean Sea and the respective model results for that period. Deep water is found to be formed mainly through open ocean convection in the central and north Aegean Sea, while the contribution of shelf areas is limited. Intermediate water is also formed through open ocean convection in the southern Aegean Sea during cold winters as well as in the central and northern Aegean during mild winters. The total volume of dense water formed during 1979-1994 corresponds to an annual formation rate of 0.24 Sv for deep water and 0.34 Sv for intermediate water.

Dense intermediate water outflow from the Cretan Sea: A salinity driven, recurrent phenomenon, connected to thermohaline circulation changes

“…Zervakis et al [2000] argues that there was such a reduction during the 1992-1993 winters which contributed to surface buoyancy loss. A numerical study by Nittis et al, [2003] showed that a BSW inflow reduction of 25% during 1989-1990 and 15% during 1992-1993 could correspond to 18% of the total deep water formed in the Aegean Sea during the EMT, but this would only correspond to almost half of the E-P increase impact on deep water formation during the same period. [Vervatis et al, 2013], suggests that changes in the Dardanelles BSW inflow during the EMT played a minor role in the salinity increase in the North-Central Aegean Sea, which was largely controlled by the intrusion of saline water masses of Levantine origin in the area.…”

On the response of the Aegean Sea to climatic variability: a review

“…Turkish data suggest that in 1987 the surface salinity of the Marmara Sea reached very high values (33)(34)(35)Emin Ozsoy,unpublished data,personal communication), a fact suggesting a greatly reduced Dardanelles buoyancy input to the north Aegean, thus facilitating the 1987 dense-water formation event. Nittis et al (2003), through numerical experiments, have shown that the north Aegean dense-water formation could significantly increase the outflow of Aegean water through the Cretan Arc Straits, despite the fact that they introduce the Dardanelles buoyancy flux anomaly in 1989 instead of 1987. We should point out that massive dense-water formation in the north Aegean is consistent with the salt redistribution scenario, as the former accelerates the Aegean thermohaline conveyor belt (Tragou et al, 2003), thus enhancing the intrusion of high-salinity LIW into the south and north Aegean basins.…”

“…were the first to sketch the general circulation of the Aegean Sea, and Ovchinnikov (1966) produced maps of its seasonal variability. Since then, a large number of national and international studies have revealed the characteristics of the general circulation in more detail (Georgopoulos et al, 1989(Georgopoulos et al, , 1992Lascaratos, 1992;Theocharis et al, , 1999aZodiatis, 1993a,b;Zodiatis and Balopoulos, 1993;Stergiou et al, 1997;Balopoulos et al, 1999;Kontoyiannis et al, 1999;Tsimplis et al, 1999;Lykousis et al, 2002;Zervakis and Georgopoulos, 2002;Nittis et al, 2003). All studies agree on a cyclonic general circulation, with several sub-basin-scale permanent and recurrent eddies containing most of the kinetic energy.…”

“…However, considering that there are areas of the Aegean that are known as dense-water formation sites, we loosely use the term Aegean conveyor belt to refer to the branch of the thermohaline circulation of the eastern Mediterranean that extends to the Aegean basin. Several sites of deep-water formation have been identified, both through direct observations and more sophisticated analyses (Lacombe and Tchernia, 1960;Plakhin, 1971Plakhin, , 1972Georgopoulos et al, 1989Georgopoulos et al, , 1992Gertman et al, 1990;Ovchinnikov et al, 1990;Theocharis et al, 1998Theocharis et al, , 1999bLascaratos et al, 1999;Zervakis et al, 2000;Boscolo and Bryden, 2001;Stratford and Haines, 2002;Nittis et al, 2003). Sites of the Aegean where deep-water formation takes place are the shelves of the north Aegean and the Cyclades plateau (Nittis et al, 2003).…”

Correlation between air-sea heat fluxes over the Aegean Sea and the total precipitable water over Europe and North Africa

“…The latter affect the thermohaline circulation of the Eastern Mediterranean Sea (Roether et al, 1996;Nittis et al, 2003). This vital process for the renewal and oxygenation of near bottom water layers is directly related to the surface heat exchange regime.…”