Developing Systematic Evaluation Methods of Acid Reductive Leaching for Paleoceanographic Proxies: a Case Study using Pacific Marine Sediment.

Acid reductive leaching of sediment has been applied to many paleoceanographic and biogeochemical studies, however the results and reproducibility of these leaching analyses vary based on methods and sediment lithology. We set out to evaluate the reproducibility and fidelity of the Hydroxylamine Hydrochloride (HH) leach commonly applied to marine sediment for Nd and Pb isotopic analysis. Previous work has highlighted the challenges of interpreting and evaluating isotopic leach data across varying lithogies, especially in the Pacific where Nd isotopic compositions can be relatively homogeneous between water column and sediment signatures (McKinley et al 2019). Therefore, we set out to develop a procedure that could evaluate and augment our existing methods. We leached a suite of marine sediment of different lithogenic compositions from well characterized drill sites in the Pacific, IODP Site U1370 and ODP Site 1149, in addition to standard reference material MAG-1 and a solid in house standard. We measured both the isotopic composition and Trace, Major and Rare Earth Element concentrations of each leach step. We present a collection of calculations to assess reproducibility of this leach procedure as a) recovery calculations from elemental concentrations, b) recovery calculations from total element masses available to leach, c) comparison of isotopic compositions across phases. Our goal is to present lessons learned and recommendations both for analyses that include leaching and for future evaluations of leach procedures.