Geochemical features of Fe-Mn micronodules in deep-sea sediments around Minamitorishima Island: Implications for the formation process of extremely REY-rich mud

Abstract

We analyzed chemical compositions of Fe-Mn micronodules that were separated from deep-sea sediments, including the extremely REY-rich mud, around Minamitorishima Island in the western North Pacific Ocean. We also implemented k-means cluster analysis on the chemical composition data. Then the micronodules were classified into five groups based on their geochemical features. The stratigraphic variations of the clusters indicated that the characteristics of the micronodules varied from almost purely diagenetic to relatively hydrogenetic across the extremely REY-rich mud layer. This implies the changes in the supply of organic matter to the seafloor and the intensity of a bottom water current, which could be associated with an accumulation of fish debris as a host of REY in the sediments. These results support a previously proposed formation mechanism of the extremely REY-rich mud.