Eastern Mediterranean Transient studied with Lagrangian diagnostics applied to a Mediterranean OGCM forced by satellite SST and ECMWF wind stress for the years 1988-1993

Abstract

In this work, we estimate deep and intermediate water mass dispersal in the different phases of the Eastern Mediterranean Transient by means of the Lagrangian analysis of a Mediterranean ocean general circulation model (OGCM) run, forced by daily European Centre for Medium-Range Weather Forecasts (ECMWF) wind stress and satellite sea surface temperature (SST) over the years from 1988 to 1993. While in a first phase (1989-1991) major modifications of the intermediate salty waters path are observed, during 1992 and 1993 the general mechanism of the transient is reproduced in the deep Ionian basin, where the Cretan overflow replaces Adriatic deep water that uplifting of several hundred meters freshens in the intermediate layers. Analysis of the water mass formation rates shows that dense water production during 1993 is twice the climatological values in the eastern subbasins of the Mediterranean and that the densest water is formed in the Cretan Sea. From 1988 to 1993, about 1.3 × 1014 m3 of water flows over the Cretan Arcs (see the caption of Figure 1 for a definition of the Cretan Arcs) to sink deeper than 600 m in the eastern Mediterranean, which is roughly half of the value estimated by Roether et al. [1996]. About 60% of this deep outflow (∼0.8 × 1014 m3) occurs in a few months, during the cold winters of 1992 and 1993, when the overflow of Cretan dense water in the Antikithera Strait reaches 1.5 Sv and rapidly propagates in the deep Ionian basin, developing very energetic coherent structures. We study the characteristic times of the relaxation of the system toward the climatology, and finally, we estimate the rate and the geographical distribution of the upwelling in the intermediate and subsurface layers.