Rare earth elements and yttrium in seawater: ICP-MS determinations in the East Caroline, Coral Sea, and South Fiji basins of the western South Pacific Ocean

Using inductively coupled plasma mass spectrometry (ICP-MS), vertical profiles of yttrium and all the rare earth elements (REEs) in seawater were obtained at three locations in the western South Pacific (the East Caroline, Coral Sea, and South Fiji Basins). Based on the data, we have analyzed the inter-REE(III) relationships and found that REE(II)s heavier than Dy and particularly close neighbors show strong coherencies in their oceanic behavior. Considering that the heavy REE(III)s are less particle-reactive than the light and middle REE(III)s and that they have very tight correlations with regressions passing almost through the origin, the neighboring element ratios of the heavy REE(III)s behave virtually conservatively and are suitable as tracers of water masses. The Dy-Ho-Er system is practically good, because its dynamic range (signal-to-noise ratio) is large in the ocean. The highest Ho/Dy ratios (∼0.31) are found in intermediate and deep waters throughout the western South Pacific which overlie the Antarctic Bottom Water with a low Ho/Dy ratio (∼0.27). These high Ho/Dy waters are probably formed in the Polar and Subantarctic Frontal Zone and advect northward. REE(III) data provide better insights into the deep water recirculation in the South Pacific than those discussed based upon the regular oceanographic properties alone.