Sub-inertial variability in the Cretan Sea from the M3A buoy

V. Cardin,K. Nittis,V. Kovačević,M. Gačić,L. Perini

doi:10.5194/angeo-21-89-2003

Abstract

Abstract. One year of continuous records of temperature, salinity data at various depths, and currents obtained from by an upward looking acoustic Doppler current profiler (ADCP) moored at a site in the Cretan Sea were analyzed. Temperature and salinity data revealed the influence of a multi-scale circulation pattern prevailing in this area. This pattern consists of mesoscale cyclonic and anticyclonic vortices moving together as a dipole, and inducing downwelling and upwelling in the water column. The dipole movements, which control the circulation in the area, have been evidenced from horizontal current variability in the upper 250 m. The basin-scale circulation also shows a prominent seasonal variability. The Empirical Orthogonal Function analysis applied to either zonal or meridional components of the currents, confirmed the prevalence of a depth-independent mode over the baroclinic-like one for the whole period of measurements and for both current components. Nevertheless, the depth-dependent structure indicated the out-of-phase behaviour of the upper 250 m layer with respect to the deeper one. The first mode of the temperature EOF analysis, which accounts for most of the variance, represents the seasonal heating of the water column being principally associated with the surface mixed layer at the level of the seasonal thermocline. Key words. Oceanography: physical (currents, eddies and mesoscale processes, general circulation)

Highlights

Continuous measurements of some oceanographic parameters and their transmission in real time have been one of the main requirements for running an operational forecasting system
The beginning of the seawater heating leads to the onset of the seasonal thermocline and the stratification of the upper layer in a rather short time
We have investigated the structure of spatial and temporal variability using Empirical Orthogonal Function analysis (EOF), applied separately to the u and v components of the current and to the temperature data along the water column down to 450 m (Preisendorfer, 1988; Kundu et al, 1975; Kundu and Allen, 1976)

Summary

Introduction

Continuous measurements of some oceanographic parameters and their transmission in real time have been one of the main requirements for running an operational forecasting system. There are several criteria for the selection of the mooring site, among them the biogeochemical characteristics of an open ocean oligotrophic area of the Mediterranean Sea. The Cretan Sea is characterised by complex dynamical features, and plays a significant role in the hydrology of the Eastern Mediterranean, as it is a site where both intermediate and deep-water masses are formed (Georgopoulos et al, 1989; Roether et al, 1996). The Cretan Sea is characterised by complex dynamical features, and plays a significant role in the hydrology of the Eastern Mediterranean, as it is a site where both intermediate and deep-water masses are formed (Georgopoulos et al, 1989; Roether et al, 1996) It is considered the source of recent changes in the deep thermohaline circulation in the Eastern Mediterranean (Theocharis et al, 1992; Theocharis et al, 1996). It is bounded to the north by the Kiklades Plateau with a depth of 400 m and to the south by the Cretan Arc Islands

Methods

Results

Discussion

Conclusion