AMAZON ESTUARY - ASSESSMENT OF TRACE-ELEMENTS IN SEABED SEDIMENTS

The interactive processes operating on the continental shelf adjacent to the river mouth control the amount and the characteristics of the A mazon discharge reaching the Atlantic Ocean. In this study, the distri bution of trace elemental concentrations, with emphasis to the rare-ea rth elements, in sediment cores collected at several stations from the Amazon continental shelf during the falling water period was investig ated by instrumental neutron activation analysis. Cores from the terri genous and blue water zones have relatively uniform REE concentrations throughout the profile. Cerium anomalies for samples of the upper sec tion of the eight stations are consistently positive and of high Value s (normally >2). Similar variation in the elemental concentration rati os between the seabed sediments and Amazon River suspended sediments w as seen for stations located in the biogenic and blue water zones, wit h an enrichment for Ce, Sm, Fe, Th, and Sc and a depletion for the La, Eu, Tb, Yb, Co, Cr, Cs, Hf, Ta, and Zn. The shale-normalized REE patt erns from shelf sediments are enriched in LREE relative to HREE, with enrichment factors varying from 1.5 for stations near the river mouth (terrigenous zone) to 1.9 for stations located far in the blue water z one. Published data for the Amazon River suspended sediment agree rema rkably well with this observation of LREE-enrichment.