Scientia Marina, Vol 74, No S1 (2010)

Temporal clustering of metals in a short sediment core of the Cascais Canyon (Portuguese Margin)


https://doi.org/10.3989/scimar.2010.74s1089

Mário Mil-Homens
Laboratório Nacional de Energia e Geologia, I.P., Unidade de Geologia Marinha , Portugal

Ana M. Costa
Laboratório Nacional de Energia e Geologia, I.P., Unidade de Geologia Marinha , Portugal

Susana M. Lebreiro
Geological Survey of Spain, Dept. of Geosciences Research and Prediction , Spain

João Canário
Instituto National de Recursos Biológicos, Instituto de Investigação das Pescas e do Mar (IPIMAR) , Portugal

Cristina Lopes
Laboratório Nacional de Energia e Geologia, I.P., Unidade de Geologia Marinha , Portugal

Filomena Mouro
Laboratório Nacional de Energia e Geologia, I.P., Laboratório de Análises Químicas , Portugal

Manuela Mateus
Laboratório Nacional de Energia e Geologia, I.P., Laboratório de Análises Químicas , Portugal

Henko de Stigter
Royal Netherlands Institute for Sea Research, Department of Marine Chemistry and Geology , Netherlands

Thomas Richter
Royal Netherlands Institute for Sea Research, Department of Marine Chemistry and Geology , Netherlands

Vasco Branco
Instituto National de Recursos Biológicos, Instituto de Investigação das Pescas e do Mar (IPIMAR) , Portugal

M. Ascensão Trancoso
Laboratório Nacional de Energia e Geologia, I.P., Laboratório de Análises Químicas , Portugal

Zenaida Melo
Laboratório Nacional de Energia e Geologia, I.P., Laboratório de Análises Químicas , Portugal

Wim Boer
Royal Netherlands Institute for Sea Research, Department of Marine Chemistry and Geology , Netherlands

Abstract


The Cascais Canyon delivers contaminated sediments from the shelf to the deep marine environment. Multi-core PE252-32, located at 2100 m water depth in the canyon, records the latest 300 years of sedimentation. It was dated by 210Pb and analyzed texturally and geochemically for major elements and selected trace metals (Cu, Cr, Hg, Li, Ni, Pb and Zn). Cluster analysis performed on the down-core geochemical data identified four groups of variables related by grain-size, geochemical source and composition. Mercury, Pb and Zn were grouped in a cluster representing the anthropogenic component. Cluster analysis was applied again particularly to the latter cluster relatively to depth, in order to constrain the onset and temporal evolution of anthropogenic contamination. A second clustering, made on the basis of Hg, Pb and Zn, grouped samples by age and degree of anthropogenic contamination. One cluster contained relatively uncontaminated samples older than 1900 AD, and another cluster samples younger than 1900 AD with distinct metal enrichment. Maximum enrichments occurred during the early 1980s, followed by a slight recovery from the mid-1980s to the present. Mercury was the element with the highest enrichment factor (EFHg=5). Despite relatively low accumulation rates at this core location, our results show the importance of the Cascais Canyon as a transport route for contaminated sediments from the Tagus prodelta into the deep regions of the Portuguese Margin.

Keywords


Portuguese Margin; Cascais Canyon; sediment; heavy metals; cluster analysis; enrichment factors

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