CONCENTRATIONS, DISTRIBUTIONS AND SEASONAL VARIABILITY OF DISSOLVED CD, CO, CU, MN, NI, PB AND ZN IN THE ENGLISH-CHANNEL

Open ocean studies have shown that dissolved manganese, cobalt and lea d exhibit vertical profiles that reflect external sources and short re sidence times due to scavenging on to particle surfaces. In contrast, dissolved cadmium, copper, nickel and zinc mirror, to different degree s, the profiles of the nutrients. The work reported here for three cru ises (November-December 1985, May and July-August 1986) in a shallow s helf sea shows that seasonal variations are shown by metals of the sca venged group, whereas the metals whose cycling in the open ocean paral lels those of the nutients, do not show these correlations and, in fac t, show no measurable seasonal variability. Concentrations of manganes e increased progressively from winter to summer [2.3 +/- 0.7 (mean +/- 1sigma) to 5.0 +/- 3.0 nmol l-1]. A surface enrichment in the upper m ixed layer of the western Channel during summer was also observed. Con centrations of cobalt increased from winter to spring (from less-than- or-equal-to 0.02-0.50 to 0.08-0.71 nmol l-1), paralleling those of man ganese, but then decreased into summer (to less-than-or-equal-to 0.08- 0.56 nmol l-1). The regional distribution of lead changed during the s pring, possibly reflecting removal by diatoms and decreased river inpu ts, although overall mean concentrations remained similar throughout t he year (0.22 nmol l-1). Concentrations of cadmium (0.20 nmol l-1), co pper (3.2 nmol l-1), nickel (3.8 nmol l-1) and zinc (7.6 nmol l-1), an d their regional distributions, remained relatively uniform over the p eriod of the observations.