Two transects across the Celtic Sea and adjacent continental slope in August 1985 and August 1988 illustrate the importance of dynamic physical processes on dissolved trace metal distributions (Cd, Ni, Cu, Pb, Co, Fe, Mn). The influence of a coastal frontal zone can be seen in the 1985 transect, while an intrusion of open ocean waters into the shelf environment is the main factor influencing the horizontal distribution of trace metals in 1988. A third transect across the continental slope bordering the Porcupine Seabight (May 1984) reveals marked horizontal fronts in the concentrations of Fe, Mn and Cu at the shelf edge (over a 21 km distance, concentrations fall from 3 to 1 nM for Fe, from 2 to 0.5 nM for Mn, from 2 to 1 nM for Cu) which are unaccompanied by any coincident hydrographic features. In transects 85 & 88, variations of metal concentrations versus salinity can be represented as two linear segments intersecting within the coastal frontal zone and at the leading edge of the oceanic intrusion, respectively. We propose that benthic inputs of metals to these waters are less important than previously assumed. By contrast, the remobilization of Fe, Mn and Cu from shelf edge sediments does provide the most plausible explanation for the presence of some unusual metal fronts observed at the Celtic shelf edge in 1984. The 1984 transect indicates not only a common benthic source of Fe, Mn and Cu in that particular area but also similarities in their cycling through the water column. These similarities are interpreted in terms of the photoreductive dissolution of oxidized forms of Fe and Mn, coinciding with the enhanced organic complexation of Cu. None of the elements investigated shows any large scale perturbation of concentration by biological activity, even though nutrient concentrations are low where sigma(theta) is less than 27.00, i.e. in surface waters as well as landward of the isohaline coastal fronts. However, the 1985 transect suggests that some oxidative removal of Mn is probably taking place throughout the Celtic Sea and that dissolved Co and Pb are removed in places by uptake onto suspended solids.
How to cite this document:Muller Fll, Tappin Ad, Statham Pj, Burton Jd, Hydes Dj (1994). Trace-metal fronts in waters of the celtic sea. Oceanologica Acta, 17(4), 383-396. Open Access version : http://archimer.ifremer.fr/doc/00098/20899/