Sediment geochemistry and accumulation rates on the northeastern shelf of the Gulf of Cádiz (SW Iberian Peninsula)

Authors

  • Roberta Guerra Centro Interdipartimentale di Ricerca per le Scienze Ambientali (C.I.R.S.A.), University of Bologna - Department of Physics, University of Bologna
  • Enrico Dinelli Centro Interdipartimentale di Ricerca per le Scienze Ambientali (C.I.R.S.A.), University of Bologna - Department of Earth and Geological-Environmental Sciences, University of Bologna
  • Serena Righi Centro Interdipartimentale di Ricerca per le Scienze Ambientali (C.I.R.S.A.), University of Bologna - Department of Physics, University of Bologna
  • Jesús M. Forja Departamento de Química Física, Facultad Ciencias del Mar y Ambientales (CASEM)
  • Enrique García-Luque Departamento de Química Física, Facultad Ciencias del Mar y Ambientales (CASEM)

DOI:

https://doi.org/10.3989/scimar.2010.74s1067

Keywords:

radioactive tracers, 210Pb, 137Cs, g-spectrometry, mass accumulation rates, bioturbation, geochemistry, Gulf of Cádiz

Abstract


Geochemistry, total organic carbon and total nitrogen of three sediment cores collected in the Gulf of Cádiz and the Guadalquivir prodelta areas in Spain were investigated. The C/N ratio, mostly around 10, seems to indicate a predominantly marine origin for the sedimentary organic matter. Major and minor elements (Si, Ti, Al, Fe, Mg, Ca, K, Na, P, S) and trace elements (Mn, Sc, V, Cr, Ni, Cu, Zn, Rb, Sr, Y, Zr, Ba, Ce, Pb, Hg) showed significant differences in bulk chemical composition between the two areas. Despite the effects of bioturbation, vertical changes in downcore profiles of heavy metals occur only in the cores of the Cádiz area, although the concentrations keep to low levels. The relatively high concentrations of Zr and Y, elements commonly associated with the heavy minerals fraction, at the top of cores from the Cádiz area are attributed to an enrichment of heavy minerals related to selective transport that concentrates this fraction. 137Cs and 210Pb activities in one of the two sediment cores collected in the Gulf of Cádiz were also measured. The distribution of excess 210Pb was used to determine the modern (last 100 yr) mass accumulation rate and the depth of sediment mixing on the continental shelf of the gulf. Estimated sediment accumulation rate was 0.1 g cm-2 yr-1. The uppermost 4 cm had uniform excess 210Pb activity profiles above a region of steadily decreasing 210Pb activity, and this phenomenon was attributed to sediment mixing (bioturbation). 137Cs activity was lower than 3 Bq kg-1 and the profile does not show evidence of fallout peaks.

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Published

2010-12-30

How to Cite

1.
Guerra R, Dinelli E, Righi S, Forja JM, García-Luque E. Sediment geochemistry and accumulation rates on the northeastern shelf of the Gulf of Cádiz (SW Iberian Peninsula). scimar [Internet]. 2010Dec.30 [cited 2021Jan.22];74(S1):67-76. Available from: http://scientiamarina.revistas.csic.es/index.php/scientiamarina/article/view/1219

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