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A Coupled Riverine-Marine Fractionation Model for Dissolved Rare Earths and Yttrium

Authors:

Institution:

(1) Department of Marine Science, University of South Florida, 140 Seventh Avenue South, St. Petersburg, FL, 33701, U.S.A

Abstract:

Fractionation of yttrium (Y) and the rare earth elements (REEs) begins in riverine systems and continues in estuaries and the ocean. Models of yttrium and rare earth (YREE) distributions in seawater must therefore consider the fractionation of these elements in both marine and riverine systems. In this work we develop a coupled riverine/marine fractionation model for dissolved rare earths and yttrium, and apply this model to calculations of marine YREE fractionation for a simple two-box (riverine/marine) geochemical system. Shale-normalized YREE concentrations in seawater can be expressed in terms of fractionation factors ( lambda

_ij) appropriate to riverine environments ( $\lambda _{ij}^{river}$ ) and seawater ( $\lambda _{ij}^{ocean}$ ):

$\log \frac{{\left( {M_i } \right)_T^{ocean} }}{{\left( Y \right)_T^{ocean} }} = log\lambda _{ij}^{ocean} + ((\lambda _{ij}^{river} )^{ - 1} - 1)log\frac{{Y]_T^{river} }}{{Y^0 ]_T^{river} }}$

where $\left( {M_i } \right)_T^{ocean}$ and $\left( Y \right)_T^{ocean}$ are input-normalized total metal concentrations in seawater and $Y]_T^{river} /Y^0 ]_T^{river}$ is the ratio of total dissolved Y in riverwater before $(Y^0 ]_T^{river} )$ and after $(Y]_T^{river} )$ commencement of riverine metal scavenging processes. The fractionation factors ( lambda

_ij) are calculated relative to the reference element, yttrium, and reflect a balance between solution and surface complexation of the rare earths and yttrium.

Keywords:

Rare earth Rare earth fractionation model riverine oceanic estuarine

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