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In the present study, lithogenic/biogenic and anthropogenic elements were determined in five sediment cores collected at the SW Iberian Continental Shelf in order to investigate the spatial and temporal heavy metal distribution and to associate them with specific continental influences/events.Elemental concentrations suggest a heavy metal (Cu, Zn and Pb) enrichment at the upper sections of all the cores. This enrichment is larger for cores localised closer to the coastline and probably exposed to a stronger continental influence. The geochemical regional background values for the studied elements are reached at ~25-30 cm for all the studied cores with one exception (core 8), which showed to be metal-enriched down to ~80 cm. It is worthnoting that core 8 is located closer to the coastal area, in a different fine sedimentary deposit, in which the deposition rates seem to be considerably higher. Enrichment factors (EF) calculated by using the natural background value determined at the deeper layers show that the EF values vary at the upper sections of cores, between 1.0 and 4.5 and the spatial distribution of the sediment cores show a similar behaviour in the heavy metal distribution patterns along this area of the continental shelf. Cu, Zn and Pb are heavy metals associated with mining exploitation along the Iberian Pyrite Belt, one of the most important mining areas of southwestern Europe, with massive orebodies of these metals. The combination of enrichment factors downcore profiles with sedimentation rate values signifies the beginning of heavy metal pollution in shelf sediments (~200-250 years ago) and is coincident with the mining exploitation reactivation during the XIX century.

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The present work aims to understand the origin of sediments deposited in the Galician coastal zone and continental shelf. Selected sediment cores were studied using different geochemical approaches: grain-size measurements, carbonate determinations and elemental analyses. Chemical analyses were carried out by multielemental techniques: energy dispersive X-ray fluorescence spectrometry (EDXRF) and instrumental neutron activation analysis (INAA). The grain-size distribution demonstrated that samples collected off the rias (Vigo and Pontevedra) contain higher percentages of silt and clay. The carbonate enrichment measured in some sediment samples with different locations and granulometries seems to indicate that the sediments might have distinct origins: biological fluvial productivity in sediments off the rias and marine biogenic activities for the deeper continental shelf sediments. Chemical analyses made it possible to distinguish different elemental sources: lithogenic, anthropogenic and biogenic. The downcore profiles of the elemental composition showed signs of a recent continental contamination for Zn and to a lesser extent for As, although there are no signs of exportation to the adjacent continental shelf. Other elements that can indicate anthropogenic activities were present in low concentrations compared with reference values. The Zr distribution determined in sediments collected along a straight line off Vigo Ria increases westwards, indicating an absence of recent exportation of this element from the continent.

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