Suspended particulate matter and nepheloid layers over the southern marginof the Cretan Sea (NE Mediterranean): seasonal distribution and dynamics

Seawater along the southern margin of the Cretan Sea (May 1994-September 19 95) has been found to have light transmission values ranging from 79% to 94 %, corresponding to SPM values ranging from 1.5 mg 1(-1) to 0.2 mg 1(-1). T he highest SPM concentrations (mostly of terrigenous origin) were found clo se to the sea-bed over the shelf-break and upper slope. The origins of SPM in the surface waters (<150 m) is principally biogenic. The occurrence of n epheloid layers at intermediate depths within the upper water column is mos tly a result of density stratification. The dynamics of SPM distributions a re governed by the 2-gyre system which induces a general onslope flow; and so inhibits the seaward dispersion of the relatively more turbid coastal/sh elf waters. This is in agreement with the virtual absence of suspensates of terrigenous origin offshore of the shelf-break. Near bottom nepheloid laye rs (BNL) and detached intermediate nepheloid layers occur in the vicinity o f the shelf-break and over upper slope region; these may be explained by re suspension induced by near-bed current activity and breaking of internal wa ves. High concentrations of SPM near the seabed may be caused by anthropoge nic (trawling) activity. Occasionally, the formation of BNL may result from local seismic activity resulting in gravity-driven mass movements. (C) 200 0 Elsevier Science Ltd. All rights reserved.