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Fluffy Layer Suspended Matter (FLSM) is a layer of fairly concentrated suspended matter resting on the sea floor. Its passage to the depositional basins in the Pomeranian Bay - Arkona Deep System of the Baltic Sea is estimated to take around six months. In the course of this migration, the properties of FLSM change as a result of ageing and the influx of fresh particles from the water column, and possibly also because of mass exchange with the uppermost sediment layers. Measurements of radioisotopes (210Po, 210Pb, 137Cs) have demonstrated that in shallow water this topmost layer of sediments, from 8 cm to 3 cm in thickness, is subject to mixing. This creates redox profiles favourable to biota and bioturbation. Basing on 210Pb/210Po disequilibria and the 210Po excess, it was estimated that under steady state conditions from 1.5 to 2.2% of fine fraction (FSF) in the mixed layer of sediments is freshly imported from FLSM. This implies replacement of FSF from the sediments and its incorporation into FLSM. On the assumption that the surface density of FLSM is 10 mg cm-2, FSF freshly exported from sediments actually comprises up to 15% of FLSM. Therefore, the properties of FLSM are strongly influenced by the processes taking place in the sediments, although FLSM by definition is independent of sediments.
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