BOUNDARY CURRENT INSTABILITIES, UPWELLING, SHELF MIXING AND EUTROPHICATION PROCESSES IN THE BLACK-SEA
PROGRESS IN OCEANOGRAPHY, 33 (4):
249--302 (1994)Abstract
Satellite and in situ data are utilized to investigate the mesoscale
dynamics of the Black Sea boundary current system with special emphasis
on aspects of transport and productivity. The satellite data are
especially helpful in capturing rapid sub-mesoscale motions insufficiently
resolved by the in situ measurements. Various forms of isolated features,
including dipole eddies and river plumes, are identified in the satellite
images. Unstable flow structures at these sites appear to transport
materials and momentum across the continental shelf. Species differentiation
and competition are evident along the boundary current system and
at the frontal regions during the development of early summer productivity.
A time series of Coastal Zone Colour Scanner (CZCS) images indicate
dynamical modulation of the springtime surface productivity in the
southern Black Sea. Unstable meandering motions generated at Sakarya
Canyon propagate east with speeds of approximately 10-15km d-1. Within
weeks, a turbulent jet is created which separates from the coast,
covering the entire southwestern sector. The nutrients driving the
phytoplankton production (mainly Emiliana huxleyi) of the current
system evidently originate from fluvial discharge entering from the
northwestern region including the Danube river. The productivity
pattern develops in early summer when the Danube inflow is at its
peak, and through meandering motions spreads into an area several
times wider than the continental shelf. In 1980, the CZCS data, and
in 1991 and 1992, the Advanced Very High Resolution Radiometer (AVHRR)
data indicate patches of upwelling along the west Anatolian coastline
between Sakarya Canyon and Cape Ince (Ince Burun) in summer. The
upwelling phenomenon is outstanding because it occurs on a coast
where normally the surface convergence near the coast implies downwelling,
and under conditions of unfavourable winds. In 1992, the hydrographic
data indicated the upwelling to be the result of a surface divergence
of the boundary current, and sequences of satellite data indicate
the role of transient dynamics. The in situ data showed the upwelling
centres to be devoid of phytoplankton as well as fish eggs and larvae.
The AVHRR and in situ hydrographic data in winter 1990 indicate cold
water is formed over the entire western Black Sea continental shelf.
The band of cold water decreases in width as it moves south and impinges
on the headland at Baba Burnu, where it undergoes a sudden expansion.
The maximum winter phytoplankton bloom sampled during the same period
indicates explosive populations of diatoms following the band of
cold water.