Geochemical characterization of sediment cores from the continental shelf off the western rias area (NW Iberian Peninsula)

Abstract

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.

Palaeoproductivity changes and upwelling variability in the Galicia Mud Patch during the last 5000 years: geochemical and microfloral evidence

“…Ba excess is commonly used as a tool for the reconstruction of paleoproductivity although some authors have discussed its validity (e.g., Anderson and Winckler 2005). In core high (Araújo et al, 2002;Corredeira et al, 2005). Two strong peaks are observed around 2000 cal.…”

Chapter 8 The NW Iberian continental shelf

“…However, in spite of the heavy metal contamination detected in the downstream region of some of the rivers draining the NW coastal area, including the Ave and the Duero rivers (the major source of fine-grained shelf sediments), no significant metal enrichments were detected in shelf sediments (Araújo et al 1998(Araújo et al , 2002Corredeira et al 2005Corredeira et al , 2009Mil-Homens et al 2006). However, in spite of the heavy metal contamination detected in the downstream region of some of the rivers draining the NW coastal area, including the Ave and the Duero rivers (the major source of fine-grained shelf sediments), no significant metal enrichments were detected in shelf sediments (Araújo et al 1998(Araújo et al , 2002Corredeira et al 2005Corredeira et al , 2009Mil-Homens et al 2006).…”

“…However, in spite of the heavy metal contamination detected in the downstream region of some of the rivers draining the NW coastal area, including the Ave and the Duero rivers (the major source of fine-grained shelf sediments), no significant metal enrichments were detected in shelf sediments (Araújo et al 1998(Araújo et al , 2002Corredeira et al 2005Corredeira et al , 2009Mil-Homens et al 2006). Rubio et al 2000;Corredeira et al 2005Corredeira et al , 2009Á lvarez-Iglesias et al 2006;Á lvarez-Iglesias & Rubio 2009b;Rubio et al 2010) but they are confined to only the uppermost layers of the cores, representing about half of the last century. Both factors depend on the textural and compositional variability of the different sediment types present in the study area.…”

Atomic spectrometry update—X-ray fluorescence spectrometry

“…Pepelnik et al 264 showed that despite biogenous decalcification one year later, which led to increased organic matter, the concentrations of Bi, Cd and W in 2002 and 2003 sediment samples were still higher than those measured in 1998. A Spanish language paper 265 reported XRF and INAA data to assist in the geochemical characterisation of sediment cores from the continental shelf off the north-western Iberian Peninsula. The down-core profiles showed evidence of recent contamination by As and Zn, although there was no evidence of exportation to the adjacent continental shelf.…”