Some aspects of vanadium and chromium chemistry in the English Channel

Dissolved and particulate vanadium and chromium concentrations along a tran sect between Cherbourg and the Isle of Wight were investigated in the Engli sh Channel. Seawater samples were collected at two different depths (surfac e and bottom) at five sampling stations during five cruises carried out bet ween September 1994 and September 1995. Calculated mass flows through this Channel section were 7600 T yr(-1) for vanadium (about 66% was in the disso lved phase) and 1650 T yr(-1) for chromium (about 50% was in the dissolved phase). Dissolved chromium concentrations do not vary significantly along t he transect. Seasonal variations in chromium distribution linked to biotic parameters were noted during the September 1994 cruise, when a significant relationship between particulate chromium and algal organic carbon was foun d. In addition, dissolved Cr (III) and Cr (VI) were well correlated with bo th algal and terrestrial organic matter. In the May cruise, during phytopla nktonic decay, particulate chromium was correlated with the detritic and ba cterial organic fractions. These observations suggest interactions between chromium and biotic material. During the winter period, no relationship bet ween chromium and POC was found. Dissolved and particulate vanadium concent rations varied, respectively, between 15 and 28 nmol l(-1) and 2-32 nmol l( -1). Values of dissolved vanadium showed depletion in the Channel with resp ect to oceanic waters. This loss in dissolved vanadium was higher near the English coast, but was compensated for by the increase in the particulate v anadium. There was no clear relationship between dissolved vanadium and alg al organic carbon and it is inferred that the vanadium transfer cannot be e xplained by trapping with biotic material. On the other hand, the dissolved vanadium depletion could be attributed to the presence of ferric oxyhydrox ide phases in particles, which have strong adsorbing properties for a range of dissolved metal ions. (C) 1999 Elsevier Science Ltd. All rights reserve d.