The Levantine Intermediate Water Experiment (LIWEX) Group: Levantine basin—A laboratory for multiple water mass formation processes

Abstract

In winter 1995 the last major field work of the Physical Oceanography of the Eastern Mediterranean (POEM) program was carried out, the Levantine Intermediate Water Experiment (LIWEX). In this study a thorough analysis is presented of the data set collected during three successive surveys in January, February, and March–April 1995. The major overall result is that the Levantine basin is shown to be the site for multiple, and different, water mass formation processes. Levantine Deep Water (LDW) was formed in the Rhodes gyre, with the preconditioning phase starting in December 1994. In late January the chimney was ventilating to the atmosphere. In February the strong mixing phase is documented by the convective cell vertically homogeneous to 900 m depth. In March–April, recapping has occurred in the upper 200 m. LDW remained confined inside the Rhodes gyre cyclonic circulation. Levantine Intermediate Water (LIW) is instead deeply affected by the upper thermocline circulation. Shallow ventilating chimneys with the LIW thermostads were found in the January survey inside the cyclonic region of the northern Levantine. The formation process of LIW does not involve deep penetrative convection. Winter surface cooling and evaporation are sufficient to produce a surface mixed layer 100 m deep with LIW characteristics. At the mixed layer basis, LIW subducts and spreads along isopycnal surfaces along pathways determined by the cyclonic/anticyclonic structures of the upper thermocline circulation.