Differences in the morphology, geochemistry, and microbial communities of shallow-water Fe–Mn nodules with water depth

Abstract

Fe-Mn nodules are present in not only deep-sea abyssal plain but also shallow-water environment. We studied the morphology, geochemistry and microbial communities of 424 Fe–Mn nodules collected from two different water depths on the continental shelf of the East Siberian Sea. Fe–Mn nodules collected from St58i (water depth, 73 m) were commonly yellow-brown with a tabular shape and smooth surface texture, whereas those collected from St52 (water depth, 150 m) were predominantly brownish-black with tabular, tubular, or ellipsoidal shapes and rough surface texture. Nodules collected from St58i had lower Mn content and higher Fe content than those from St52. Based on their Nd content and (Ce/Ce*)PASS, the nodules examined in this study may have formed through a diagenetic process, regardless of the water depth at which they were collected. Radiolarians, diatoms, and bacteria, as well as unknown microorganisms were found at both sites. Pennate diatoms were present at both water depths, whereas centric diatoms were present only in deeper waters. The observed morphological, geochemical, and biological characteristics of the nodules clearly differed between the two sites, indicating that the aqueous conditions and formation processes of nodules in the Arctic Ocean vary with water depth. © 85th EAGE Annual Conference and Exhibition 2024.