Trace Metals in the Surface Sediments of the South China Sea, Area I: Gulf of Thailand and East Coast of Peninsular Malaysia

Abstract

The trace metal distribution in the surface sediments of the Gulf of Thailand and the South China Sea were studied. Samples were obtained from two cruises of the MV SEAFDEC Total metal content were measured in the 63mm fraction of dried sediment. For the first cruise (Pre-Northeast monsoon) results, metal concentration ranges were between 0.41- 0.19mgg^-1Cd, 10-36mgg^-1Cu, 7.02-27.8mgg-1Pb, 15.3-352mgg-1Zn, 20.5-122mgg^-1 Cr, 209-720mgg^-1Mn, 0.79-5.96%Al and 0.71-2.82%Fe. Similar results were obtained for the second cruise (Post-Northeast monsoon) results, with metal concentrations in the range of 0.10-0.94 mgg^-1Cd, 10.3-61.4 mgg^-1Cu, 5.24-78.2 mgg^-1Pb, 18.1-98 mgg^-1Zn, 21.1-101 mgg^-1Cr, 117-797 mgg^-1Mn, 1.89-7.22 %Al and 0.70-2.38 %Fe. The concentrations of Al, Cr, Cu and Mn were significantly higher in the Gulf of Thailand in the pre-monsoon while concentrations of Fe, Cd and Zn were similar for both areas. For the postmonsoon Al, Cu and Mn concentrations were higher in Gulf sediments. Differences in metal concentrations were noted between the pre- and the post monsoon samples. Fe, Cr and Mn concentrations were generally higher in the pre-monsoon period for both areas but the distribution of Pb was higher in the post-monsoon while Zn and Cu distribution differed between the Gulf and the South China Sea areas. However normalisation of the metal data to aluminium content of the sediment showed generally uniform concentration of the metals studied over most of the area studied. Some enrichment by Cu in sediments from two sampling stations in the upper Gulf of Thailand is indicated by Cu:Al ratios exceeding normal crustal abundances of these metals. However low Cu:Al ratios in sediments from some areas of the South China Sea may indicate depletion of Cu in the sediments.