Lawrence Berkeley National Laboratory

We studied the distribution and speciation of Ce in a previously-characterized ferromanganese nodule from the South Pacific Gyre using X-ray microspectroscopy.We find Ce in three types of environment – diffusely in all parts of the nodule except the Fe-rich, Mn-poor “matrix”, fluorapatite grains with a negative Ce anomaly suggestive of an authigenic origin, and localized spots whose composition is consistent with a pseudobinary mixture of sorbed Ce4+ and a mix of sorbed Ce3+ and CeO2. In contrast with some other elements such as Ti, there is no clear correlation of the Ce concentration in the diffuse areas with either that of Mn, Fe or any linear combination of the two.We argue that the CeO2 came from oxidation of Ce3+ in the water column, while the Ce in the Mn-rich regions may have been initially deposited as Ce4+ and then partially reduced.