Property distributions and transient-tracer ages in Levantine IntermediateWater in the Eastern Mediterranean

We present distributions of chlorofluorocarbons (CFCs) and ages derived fro m them, of carbontetrachloride, and of hydrographic properties, in Levantin e Intermediate Water (LIW) in the Eastern Mediterranean. The data originate from surveys of F/S METEOR in 1987 and 1995, which bracket the profound ch anges that have occurred in the Eastern Mediterranean deep waters, due to b ottom water formation from Aegean Sea overflow and related enhanced upwelli ng (Roether, W., Manca, B.B., Klein, B., Bregant, D., Georgopoulos, D., Bei tzel, V., Kovacevich, V., Luchetta, A., 1996a. Recent changes in Eastern Me diterranean deep waters. Science, 271, pp. 333-335). As a framework for an interpretation, classical knowledge on LIW is summarized. A density horizon of sigma(theta) = 29.05 is selected to characterize LIW, for which salinit ies and temperatures in 1995 were still similar to classical values. A prin cipal result derived from the CFC-age distributions is that the enhanced up welling of deep waters has been continuous up into the LIW layer. Newly for med LIW in both surveys is found to be distributed over an extended region which includes the Cretan Sea. The lowest CFC ages in LIW, amounting to sev eral years, are found in this region. Smaller but significant apparent CFC ages are present in the mixed layer in a winter situation (1995). The CFC d ata are compatible with a formation of LIW by open-ocean convection. Outcro pping of the isopycnal typical of young LIW was observed in the Aegean Sea in 1995, while to the east and southeast of the Rhodes Gyre no evidence of a major recent LIW formation was found. The CFC age distributions give an u pper limit for the apparent travel time of LIW up to the Strait of Sicily o f about 8 years. CCl4 is found to be chemically unstable in the Eastern Med iterranean (chemical lifetime in LIW < 5 years), but this feature allows us to use this tracer as a low-life age marker. The present work can serve as a basis for future data evaluation by Mediterranean circulation models. (C ) 1998 Elsevier Science B.V. All rights reserved.