DIATOMS AS PARTICULATE TRACERS IN THE WATER COLUMN IN THE EASTERN ENGLISH-CHANNEL

In the English Channel, diatoms constitute an important part of the su spended particulate matter (SPM). In this study, the diatom contents ( allochthonous and autochthonous) in surface waters are used as biogeni c tracers to define the sources of suspended material and the exchange of particles between the different water masses in the eastern Englis h Channel. Such an approach is especially worthwhile in this area wher e diatoms are very numerous. A factor analysis applied to the counts o f dead and living diatoms showed that the following zones could be dis tinguished in order of importance: a. a central zone in which primary production of marine planktonic diatoms is preponderant (autochthonous diatoms); b. a zone with numerous tychoplanktonic marine diatoms, eas ily resuspended in shallow waters (allochtonous diatoms); c. a deeper zone with a high ratio of marine to marine-brakish benthic diatoms, wh ich indicate particulate input from the Bay of the Seine and the Seine Estuary (allochthonous diatoms); and d. a coastal zone with numerious tidal-zone diatoms (allochthonous diatoms) which originate from litto ral erosion (especially along the French coast). The combined analysis of dead and living diatoms allows a description of the passive transp ort of particles. A spatial study during an annual survey within the S trait of Dover showed the reproducibility of the hydrodynamical respon se of the allochthonous diatom content for tracing SPM. Such a study i n the eastern English Channel allowed the detection of the flux of est uarine particulate input to the open sea.