The Eastern Mediterranean in the 80s and in the 90s: the big transition inthe intermediate and deep circulations

We present definitive observational evidence that the startling change of t he Eastern Mediterranean deep circulation observed in winter 1995 and docum ented by [Roether, W., Manca, B.B., Klein. B., Bregant, D., Georgopoulos, D ., Beitzel, V., Kovacevich, V., Luchetta, A., 1996. Recent changes in the E astern Mediterranean deep water. Science 271, 333-335.] actually started be fore October 1991. This change involved not only the deep water mass pathwa ys but also the origin and pathways of the water mass spreading in the inte rmediate layer. We carry out the first unified analysis of the POEMBC-O91 d ata set, which shows that, differently from the previous decade of the 80s, the Cretan/Aegean Sea was in 1991 the 'driving' engine of the intermediate , transitional and deep layer circulations, with Cretan Intermediate Water (CIW), transitional water and Cretan Deep Water (CDW) spreading out from th e Cretan Sea into the basin interior. The most important new results are. ( a) the Levantine Intermediate Water (LIW) formed inside or at the periphery of the Rhodes gyre is blocked in its traditional westbound route on its de nsity horizons sigma(theta) = 29.05 and 29.10 kg/m(3) by a three-lobe stron g anticyclonic structure in the Southern Levantine, which induces a substan tial LIW recirculation in the Levantine basin itself; (b) the CIW exiting f rom the Western Cretan Are Straits spreads into the Ionian interior on the sigma(theta) = 29.05-29.10 kg/m(3) isopycnal surfaces, thus replacing the L IW confined in the Levantine basin. A branch of CIW flows eastward in the C retan passage and is entrained by the Ierapetra anticyclone to flow again i nto the Cretan Sea through the Eastern Cretan Are Straits; (c) on the horiz ons sigma(theta) = 29.15 and 29.18 kg/m(3) a transitional water mass of Cre tan origin, denser than CIW, and CDW are observed to spread out massively f rom the Cretan Are Straits both into the Ionian and Levantine interiors. Th ese isopycnal surfaces rise to much shallower depths in 1991 than in 1987, increasing the salt content of the intermediate, transitional and deep laye rs. This leads to a massive salt increase in the Ionian below 1200 m, clear ly related to lateral advection of the new denser waters of Cretan/Aegean o rigin, thus contradicting the hypothesis of a vertical salt redistribution proposed by Roether et al. (C) 1999 Elsevier Science B.V. All rights reserv ed.