An improved sample preparation method for the accurate determination of manganese redox state of microparticles in deep-sea oxic sediment

Abstract

Manganese (Mn) is a crucial element in global metallic cycling owing to its redox-sensitive dynamics; however, determining the redox state of abundant Mn-microparticles in deep-sea oxic sediments is challenging because of high-energy beam irradiation sample processing, such as focused-ion-beam and/or electron beam processing. Our study demonstrates an improved sample preparation method for accurately determining the redox state of Mn-microparticles in deep-sea oxic sediments. We could enrich Mn-microparticles without altering their redox state by employing a novel beam-free approach, as confirmed by scanning transmission X-ray microscopy (STXM) analyses. Our methodological advancements revealed that the Mn-microparticles predominantly existed in the Mn⁴⁺ oxidation state. The new technique, which allows us to accurately determine the redox state of Mn in these particles, provides critical insights into the geochemical processes of Mn oxide precipitation and the environmental conditions that favor its formation and preservation, thereby highlighting the potential of these particles as indicators of oxic conditions in geological environments.