Diatoms as particulate tracers in the water column in the eastern english channel

Abstract

In the English Channel, diatoms constitute an important part of the suspended particulate matter (SPM). In this study, the diatom contents (allochthonous and autochthonous) in surface waters are used as biogenic tracers to define the sources of suspended material and the exchange of particles between the different water masses in the eastern English Channel. Such an approach is especially worthwhile in this area where diatoms are very numerous. A factor analysis applied to the counts of dead and living diatoms showed that the following zones could be distinguished 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, easily resuspended in shallow waters (allochthonous diatoms); c. a deeper zone with a high ratio of marine to marine-brackish benthic diatoms, which indicate particulate input from the Bay of the Seine and the Seine Estuary (allochthonous diatoms); and d. a coastal zone with numerous tidal-zone diatoms (allochthonous diatoms) which originate from littoral erosion (especially along the French coast). The combined analysis of dead and living diatoms allows a description of the passive transport of particles. A spatial study during an annual survey within the Strait of Dover showed the reproducibility of the hydrodynamical response of the allochthonous diatom content for tracing SPM. Such a study in the eastern English Channel allowed the detection of the flux of estuarine particulate input to the open sea.