School of Engineering and Science - Jacobs University

feature was not recognized in early studies due to the negative anomaly present for
neighboring Ce (e.g., de Baar et al., 1983). Positive Gd and Lu anomalies are also
present in seawater REY patterns, though the magnitude of these anomalies are
significantly smaller (see Fig. 6). The presence of positive La, Gd, and Lu anomalies
was originally postulated to arise from a greater stability of the solution complexes for
these elements, which presumably resulted from the exactly empty, half-filled, and
completely filled 4f electron shell configurations for La, Gd, and Lu, respectively (de
Baar et al., 1985b). Early work by Cantrell and Byrne (1987), as shown in Fig. 7,
predicted no anomalous behavior for these elements, though this study reported
experimental data for only a few REY (e.g., Ce, Eu, Tb), which were then extrapolated
across the entire REY series. More recent experimental studies (Luo and Byrne, 2004)
determined equilibrium formation constants for carbonate complexes of all 15 REY,
and these results are shown in Figure 9. Equilibrium constants for the formation of
monocarbonate REY complexes in high ionic strength solutions mimicking seawater do
not vary smoothly across the REY series, with La, Gd, Y, and Lu showing the greatest
deviations. Predominance diagrams for mono- and dicarbonate REY complexes in
seawater also predict that La, Gd, Y, and Lu should fractionate from their immediate
neighbors (Fig. 9).
It is also likely that the observed positive La and Gd anomalies in seawater are to
some degree generated during adsorption/desorption processes on scavenging particle
surfaces. The authors Byrne and Kim (1990) and Lee and Byrne (1993) suggested that
organic ligands on particle surfaces (e.g., carboxylate) should discriminate against La
and Gd, producing an enrichment of these elements in seawater. This would be
consistent with the conclusions of Bau et al. (1999) regarding REY surface
complexation on hydrous Fe-Mn oxides in seawater. It therefore appears that the La,
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