THE ISOTOPIC COMPOSITION OF NEODYMIUM IN THE MARINE ENVIRONMENT: INVESTIGATIONS OF THE SOURCES AND TRANSPORT OF RARE EARTH ELEMENTS IN THE OCEANS.

摘要

The isotopic compositions of neodymium has been determined for a variety of ferromanganese sediments, seawater, and submarine hydrothermal solutions in an effort to determine the sources and transport of rare earth elements in the marine environment. Large variations in ('143)Nd/('144)Nd are observed which exhibit a clear separation of the ocean basins. Within an ocean basin, ('143)Nd/('144)Nd falls within a relatively small, well defined range which is characteristic of the ocean basin sampled. In (epsilon) notation, the average ('143)Nd/('144)Nd values for the major ocean basins are: Atlantic, (epsilon)(,Nd)(0) (DBLTURN) -12; Indian, (epsilon)(,Nd)(0) (DBLTURN) -8; Pacific, (epsilon)(,Nd)(0) (DBLTURN) -3. These isotopic data indicate that the REE supply to the oceans is dominated by continental sources. In addition to isotopic variations between ocean basins, distinct isotopic variations are often observed in the water column within an ocean basin providing evidence of substantial lateral transport of REE in the oceans. In general, Nd concentrations exhibit a regular increase in concentration with depth (from (TURN)2 to 4 x 10('-12)g/g) indicating that REE distributions in the water column may in part be associated with particle transport.; Direct measurements of Nd isotopic compositions and concentrations in water column profiles provide important contributions to the understanding of trace element transport in the oceans. First, Nd isotopic differences in the water column clearly indicate that transport of Nd from the surface to the deep ocean cannot account for the observed increase in concentration of Nd with depth. These isotopic differences must be maintained by lateral transport of the REE and indicates that concentration gradients of REE and possibly other trace elements may also be related in part to lateral transport processes. Second, a close correlation is observed between changes in Nd isotopic compositions and temperature-salinity relationships in the water column indicating that lateral transport of REE in the oceans is directly related to the origin and flow of water masses. Thus, the isotopic composition of Nd in seawater is shown to be a useful tracer for studying the sources and transport of trace elements in the oceans.; The concentrations and isotopic compositions of Nd and Sr were determined in hydrothermal solutions emanating from hot springs on the crest of the East Pacific Rise at 21(DEGREES)N and at Guaymas Basin, Gulf of California. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI