Development of rare earth elements and neodymium isotope analysis of organic materials in sediments

Abstract

The river-sea interfaces, continental margins, are the major source of a number of elements and materials including oxide fraction, organic matter and detrital mass. Organic matter (OM) has an important function on exchange process between the atmosphere, hydrosphere and geosphere and biogeochemical. The OM in natural waters are usually derived from photosynthetic processes. In the river-sea interface systems, a significant fraction of OM in sea water may have a continental origin which delivered via rivers and atmospheric input. Minor fraction of OM can reach the seafloor and undergo early diagenetic processes. The neodymium (Nd) contained in the accumulated OM does not undergo isotopic fractionation and can be a useful tool to see the recorded information at the time of OM formation. Despite the potential importance of OM in hydro-geochemistry, distribution of OM and its Nd isotope have not been actively studied in Korea. In this study, we developed an experimental method to extract OM and separate Nd from Fe-Mn oxides and detrital fraction in sediments. Furthermore, Nd isotope analysis of OM in various river and ocean sediment reference materials are in process. We collected sediment samples from two distinct river-sea interface system. In the Geum River-Yellow Sea interface, sediments were collected from six locations, from the inside of the dam to the outer sea, which is the boundary between river and sea. In the opened Sumjin River-South Sea interface without dams, sediments were collected at five sites from the river to the sea. Its OM extraction and Nd isotope analysis are undergoing. A comparison of these two systems is expected to make a meaningful insight of the behavior of OM.