Neodymium and Hafnium Isotope and Rare Earth Element Geochemical Cycling and Fluxes from the Amazon to the tropical western Atlantic

Continental margins are a dynamic interface linking the terrestrial lithosphere and oceanic hydrosphere, thus controlling fluxes of terrigenous materials from land to ocean. In particular, estuaries are places channeling vast amounts of minerals, nutrients, organic matter and trace elements (TEs) in dissolved and particulate forms into the oceans. As many TEs are essential nutrients for phytoplankton growth, their concentrations ([TEs]) together with macronutrients in surface waters influence marine primary productivity, thereby impacting ocean ecosystems and carbon cycling. However, before entering the oceans, terrigenous TEs are modified at continental margins by various processes including removal, release and recycling. Consequently, studying geochemical cycling of TEs at continental margins is crucial for discerning their sources and processes that determine TE fluxes to oceans. Radiogenic neodymium (Nd) and hafnium (Hf) isotopic compositions, expressed as εNd and εHf, respectively are sensitive tracers of the origin and mixing of water masses and seawater-particle interactions at the continent-ocean interface. In this thesis a detailed investigation of the distributions of radiogenic Nd and Hf isotopes as well as rare earth elements and yttrium (REY) is performed across the Amazon freshwater plume, the Amazonian mangrove belt and the Amazon shelf and slope as part of the GEOTRACES GApr11 cruise. The objective is to investigate the sources and processes influencing the TE supplies, Nd and Hf isotope distributions and their fluxes to the western Atlantic Ocean.


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