Summary

The neodymium isotope composition of authigenic phases from marine sediments is used as a proxy to study ocean circulation in the past. However, extracting Nd from authigenic phases remains challenging, and recent studies show that that authigenic phases may not simply record bottom water Nd isotope composition. In this study we investigate systematically how various experimental parameters affect the extraction and design a method that is capable of avoiding signficant detrital contamination using a suite of core-top sediment samples from the Gulf of Alaska. We show that the extraced Nd using this method is indeed sourced from authigenic Fe-Mn phases, but the resulting isotope composition differs from that of local bottom water. We further show that this difference was attributed to in situ contribution of likely radiogenic volcanic materials to pore water and authigenic Nd in sediments. We therefore propose a new model to explain how authigenic phases aquire their Nd isotope signatures, and an alterantive frameword of using authigenic Nd isotopes to study ocean circulation.

This study was published in Geochimica et Cosmochimica Acta:
Neodymium isotopes in authigenic phases, bottom waters and detrital sediments in the Gulf of Alaska and their implications for paleo-circulation reconstruction