Long-term evolution and dynamics of a persistent warm core eddy in the Eastern Mediterranean Sea

Abstract

Shipboard data from seven cruises covering April 1988–October 1990 are analyzed to follow the dynamical evolution of a persistent warm core eddy located to the southeast of Cyprus. The eddt is characterized by an isothermal, isohaline lens of water wedged between the seasonal and permanent thermoclines. In the winter, this thermostad extends from the surface to a depth of nearly 400 m, while in other seasons it lies in the layer from 200 to 400 m. The data indicate that the temperature and salinity of the core of the eddy remained constant throughout most of 1989 and then increased abruptly (with a slight increase in σ_φ) in the winter of 1989–1990. The velocity jet usually appears between the surface and 200 m at a mean distance of 35 km from the center of the eddy. Speeds in the jets typically exceed 25 cm s⁻¹ and occasionally reach 50 cm s⁻¹. During 1989 the eddy spins down as indicated by a loss of kinetic energy. This weakening permits an abrupt renewal or exchange of core water during the winter of 1989–1990. The remnants of the previous core are apparently forced to sink into the permanent thermocline where the water may be free to spread laterally if the cross-isopycnal gradient of potential vorticity is weak. This process could explain the cycle of Levantine Intermediate Water formation in the centers of warm core eddies and its eventual lateral spreading. Finally the eddy slowly begins to spin up again in 1990.