Glider transects in the Levantine Sea: Characteristics of the warm core Cyprus eddy

摘要

Beginning in March 2009, two gliders of the Oceanography Center of the University of Cyprus (OC-UCY) began occupying a hydrographic endurance line for measurements of temperature, salinity, dissolved oxygen, optical backscatter, and fluorescence in the Levantine Sea. The transects follow a butterfly pattern near the Eratosthenes Seamount, extending to a maximum depth of 1000 m. These operational transects represent the first in a time series of transects carried out by OC-UCY. In November 2009, a joint project, “Eye of the Levantine,” was carried out and in which 6 gliders were deployed to investigate the Cyprus warm core eddy observed earlier in the year by both glider and shipboard CTD. In December 2009, the TARA Oceans vessel was involved as well with CTD and water samples and the deployment of 4 surface drifters and 2 profiling floats in and around the eddy. Near the end of the experiment, the eddy was sampled again with shipboard CTD and ADCP by the Maria S. Merian in January 2010. At this time, only the OC-UCY glider continued its endurance line, which also passed through the eddy. It completed its mission in May 2010. About 2000 profiles down to 1000 m and 1000 profiles down to 200 m have been collected by the fleet of gliders including measurements of not only temperature and salinity, but also fluorescence (Chl a, CDOM) and backscatter (at 470 nm, 532 nm, 660 nm, 700 nm and 880 nm). The most recent mission (October 2010 to February 2011) revealed the same eddy approximately 80 km to the east. The Cyprus eddy is a permanent feature (since observations began), with radius of typically 45 km and tangential current speeds of approximately 0.30 m s⁻¹. It consists of an anticyclonic core of Levantine Intermediate Water to a depth of about 400 m. The surface signature is very weak, particularly in summer, however, it is visible in maps of absolute dynamic topography. Further analysis and modeling as well as continued observations-- of the eddy are required in order to determine how it is generated and what governs its evolution and decay.