PRELIMINARY REPORT FOR THE SHALLOW-WATER MANGANESE NODULE FROM THE EAST SIBERIAN SEA SHELF

Manganese nodules are usually found on the seafloor and form manganese deposits with the manganese crust in the Pacific, Indian, and Atlantic Oceans. They have attracted attention as a near-future mineral resource because they are rich in Ni, Cu, Co, and rare earth elements, as well as Mn. During the 2021 ARA12B Expedition, 451 manganese nodules were acquired from two sites at water depths of 73 m (St58i) and 150 m (St52) on the East Siberian Sea Shelf in the Arctic Ocean. This study investigated the chemical composition, external form, size, weight, and internal texture of the nodules. Most nodules were non-spherical, similar to nodules from other areas in the Arctic Ocean, but their surface color considerably differed at each site. The nodules from site St52 were brown to black, while nodules from site St58i were yellow to light brown. Nodule size abundance at both sites was in the following order: medium (3–6 cm), large (> 6 cm), and small (< 3 cm). There were five groups based on external form; tabular, ellipsoidal, tube-shaped, and irregular types were common. The major axis and weight were positively correlated. Mn was abundant in dendritic and porous structures, while Fe and Co were abundant in the Fe-oxide layer. Manganese nodules from St58i had a lower Mn wt.% (avg. 9.4) with a higher Fe wt.% (avg. 13.5), while manganese nodules from St52 had a higher Mn wt.% (avg. 42.3) with a lower Fe wt.% (avg. 3.1). Based on Nd and Ce/Ce_PAAS, nearly all manganese nodules examined in this study were likely formed through a diagenetic process.