Rare earth elements and yttrium along eastern Atlantic estuaries

Abstract

Rare earth elements (REE) are widely used as tracers of geochemical and anthropogenic processes across diverse environments. We investigated the abundances, sources, and fractionation of REE and Y in 12 estuaries along the Southwest Atlantic Coast. Additionally, we assessed the concentrations of Al, Fe, Mn, and organic carbon (OC) to elucidate the influence of diagenetic remobilization and facilitate comparison between estuaries. The ƩREEY varied widely, ranging from 6 mg kg-1 (Santa Cruz Channel; > 90% sand) to 337 mg kg-1 (Piraquê-Açú; 30% silt+clay). Normalized REE abundances relative to post-Archean Australian shale (PAAS) revealed enrichment of light REE (LREE) over heavy REE (HREE). Moreover, the northern estuaries of the Todos os Santos Bay (São Paulo, Mataripe, Subaé), Vitória Bay, and the Doce River exhibited enrichment of medium REE (MREE) over HREE. Positive correlation between ƩREEY and Al, Fe, and Mn were observed in 5 of the studied estuaries. LREE showed a positive correlation with Al (r2 > 0.7) and Fe (r2 > 0.8) across most of the areas studied. Additionally, REE were significantly correlated with Mn (r2 > 0.8) in only 5 out of the 12 estuaries, while a positive correlation with OC (r2 > 0.8) was observed in 8 estuaries. The concentration of REEY, Al, Mn, Fe, and OC depends on the bottom types and position along the estuarine zones. The observed REEY abundances contribute to the characterization of estuaries along the east coast of Brazil and can serve as a baseline reference for the region.