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

摘要

The Cascais Canyon delivers contaminated sediments from the shelf to the deep marine environment Multi core PE252 32 located it 2100 m water depth in the canyon records the latest 300 years of sedimentation It was dated by Pb-210 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 tour 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 ad Zn grouped samples by age mod degree of anthropogenic contamination One cluster cont.-lined 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