Rare-Earth distributions in the marine environment

Analyses for the rare-earth elements in sea water, in a phosphorite, and in a manganese nodule were made by neutron activation and X-ray fluorescence techniques. These marine samples showed a depletion, in the heavier rare-earth elements, relative to chondritic meteorites, beginning with samarium. Cerium was enriched in the manganese nodule, probably as a result of its oxidation to the 4+ valence state. The ratios of the rare-earth abundances in the two minerals to those of sea water go through a maximum in the vicinity of samarium. The europium concentration, often anomalous in terrestrial minerals, was normal relative to the other rare earths in all of the samples. The sea water showed four times the concentration of rare earths at a depth of 4000 meters as compared with surface values.