Rare earth element distribution in Caribbean seawater: Continental inputs versus lateral transport of distinct REE compositions in subsurface water masses

Abstract

The rare earth element (REE) concentrations of full water column profiles from ten stations in the Caribbean, the Gulf of Mexico, and the Florida Straits, as well as of surface waters close to the mouth of the Orinoco River have been analyzed. The results show a high concentration of REEs in surface waters, in particular close to the mouth of the Orinoco, and a middle-REE-enrichment that is strongest in the south and east of the study area suggesting that fluvial inputs are the main sources rather than REEs supplied by Saharan dust. The surface waters close to the Orinoco are heavy REE enriched compared to the potential fluvial sources, emphasizing the importance of processes in the estuaries and the surface ocean that preferentially remove light- and middle-REEs. Relatively small heavy-REE enrichments in near-bottom water samples at the mouth of the Orinoco may be the result of preferential release of light REEs from river-transported sediments. The REE patterns of distinct subsurface water masses are largely coherent across the Caribbean basin, suggesting that the lateral transport of preformed compositions is not significantly influenced by vertical processes of scavenging and release. In particular, low Dy/Er molar ratios are associated with Antarctic Intermediate Water and have most likely been advected into the Caribbean from the Southern Ocean. In contrast, deep waters in the Caribbean are enriched in light and middle REEs compared to incoming Upper North Atlantic Deep Water suggesting that release from sinking particles or from sediments is an important source of these REEs in the deep ocean, in particular when deep water residence times are long.