CIRCULATION IN THE SURFACE AND INTERMEDIATE LAYERS OF THE BLACK-SEA

Circulation features of the Black Sea are presented based upon a basin-scale survey carried out in September-October 1990. The circulation pattern for the upper 300-400 dbar consists of a cyclonically meandering Rim Current, a series of anticyclonic eddies confined between the coast and the Rim Current, and a basin-wide, multi-centered cyclonic cell in the interior of the basin. In contrast to prior investigations, although the currents are much weaker as compared with those in the upper layer, the intermediate depth (defined here between 500 and 1000 dbar) circulations reveal considerable structural variability. This involves counter-currents, shift of eddy centers, coalescence of eddies, and associated sub-basin-scale recirculation cells separated by the meandering Mid-Basin Current system. A descriptive synthesis of the upper layer circulation, combining the present results with earlier findings, identifies the quasi-permanent and recurrent features even though the shape, position, strength of eddies and meander pattern, and the bifurcation structure of currents vary

MESOSCALE CIRCULATION AND THERMOHALINE STRUCTURE OF THE BLACK-SEA OBSERVED DURING HYDROBLACK-91

Results from nearly 300 hydrographic stations occupied during HydroBlack '91, a basin-wide survey performed during September 1991, reveal a complex, eddy-dominated three-dimensional circulation in the Black Sea. Except in the areas of anticyclonic eddies distributed around the periphery of the basin, the inshore portion of the Rim Current along the relatively smooth continental margin topography forms a narrow coastal jet characterized by small amplitude (approximately 20-30 km) undulations with a wavelength of approximately 125 km. The offshore margin of the Rim Current, however, exhibits large meanders, offshore filaments and dipole eddy structures. The Rim Current is accompanied by a strong frontal zone having cross-frontal temperature and salinity differences of approximately 1.0-degrees-C and approximately 0.5, respectively, near the surface. The circulation within the interior of the sea is composed of an interconnecting series of cyclonic eddies and gyres, varying in size and shape with depth. The mesoscale variability introduces a different scale of complexity to the general circulation at each pressure level, although larger and quasi-persistent features of the general circulation are fairly coherent down to 500 dbar. Important structural changes, however, take place in both large scale and mesoscale components of the circulation at 500 dbar and deeper, consistent with the findings of the September 1990 survey (OGUZ et al., Deep-Sea Research I, 40, 1597-1612). The circulation is strongest in the upper layer (approximately 150 dbar), where the calculated geostrophic currents have speeds of 0.2-0.3 ms-1 along the axis of the Rim Current. The strength, width, and frontal intensity of the Rim Current, however, reduce considerably below the permanent pycnocline

Experimental and field research: Vertical structure of the field of current velocities in the northwest part of the Black Sea based on the LADCP data for May 2004

The profiles of absolute current velocity obtained by using a lowered acoustic doppler current profiler (LADCP) are presented. In the course of the BSERP-3 expedition, the measurements were carried out in the regions of the Rim Current, anticyclonic eddy, and northwest shelf. In the core of the Rim Current, a unidirectional motion of waters is traced in layers below the main pycnocline down to depths greater than 500 m. Its characteristic velocity can be as high as 0.08 m/sec. It is shown that the direct action of the eddy is detected in the shelf region at distances larger than 20 km from the outer edge of the shelf in the zone bounded by an isobath of 100 m. The formation of multilayer vertical structures in the field of current velocities is revealed in the region of interaction of the anticyclonic eddy with irregularities of the bottom on the side of the shelf. A two-layer structure of currents with specific features in the layer of formed seasonal pycnocline is observed in the region of the shelf down to an isobath of 100 m. The profiles of the moduli of vertical shears of currents averaged over the casts ensemble are presented for the abyssal and shelf parts of the sea. It is shown that the shears induced by the geostrophic currents and wave processes in the region of the main pycnocline are comparable. Below the pycnocline, the shears are mainly determined by the wave processes. © 2008 Springer Science+Business Media, Inc