Anthropogenic trace metals in the sedimentary record of the Llobregat continental shelf and adjacent Foix Submarine Canyon (northwestern Mediterranean)

Anthropogenic trace-metal concentrations and inventories were studied on the Llobregat continental margin, from the Llobregat river mouth to the Foix submarine canyon. A prodelta sedimentary depocentre was identified along with a previously known canyon depocentre. Significant upward increases in trace-metal contents were detected in sediment cores of the prodelta and upper part of the canyon (down to 860 m depth). Metal enrichment factors ranged between 1.8 and 10 on the continental shelf and between 1.2 and 2.7 in the submarine canyon. These metal enrichments occurred during the 20th century and can be correlated with the period of maximum increase of population and industrial activities in the Barcelona area and the consequent anthropogenic metal inputs. Maximum trace-metal enrichments are located in the prodelta depocentre and significant enrichments were also measured in the southern prodelta and in the Foix upper canyon as a consequence of efficient shelf–canyon sediment and metal transfer. Deeper in the canyon, at 1370 m depth, no metal enrichments were detected, probably because of particle dispersion and dilution with uncontaminated sediment within the canyon. This study shows that, in some Mediterranean sedimentation systems, anthropogenic trace metal contamination is affecting not only the littoral and the continental shelf, but also the adjacent continental slope sediments through submarine canyons.