Distribution spatio-temporelle des éléments Fe, Al, Mn, Ca, Mg, Ti et V particulaires dans le détroit du Pas-de-Calais

Within the framework of the European Fluxmanche programme, 92 samplings of suspended particulate matter were collected during eight cruises through the Dover Strait. The mean concentrations obtained for Al (44.3 mg/g), Fe (27.4 mg/g) and Ca (110 mg/g) are comparable to those obtained by Nolting and Eisma in January 1980. However, the concentrations of Mn (0.585 mg/g) Ti (3.14 mg/g) and V (0.225 mg/g) are twice as large. An important gradient of concentration is observed between the coastal and offshore waters, reflecting coastal erosion and human activities. Detailed examination of the contents of the major elements indicates that these remain practically constant in the particulate matter during a tidal cycle. On the other hand, the concentrations of heavy metals (Mn, V, etc.) vary notably and the use of models simulating the dispersion of the contaminants confirms these observations. The study of the Fe/Al ratio permits a distinction between the two surveys: that carried out in November 1990, where high values are obtained because of the presence of a low-density alumino silicate phase and of diatoms; and that carried out in May 1991, to which the influence is added of a planktonic bloom, together with a fluvial contribution along the English coast and the effects of coastal erosion along the French coast.