Controlling factors of seabed manganese nodule genesis in the northest Pacific manganese nodule belt

Abstract

For better understanding of controlling factors of seabed manganese nodule genesis, two blocks located in the southern (9°N~11°N) (KR5) and northern parts (16°N~17°N) (KR2) of the Clarion-Clipperton fracture zone along 130°W ~ 133°W meridian were investigated for nodule and sediment characteristics. Nevertheless of relatively short latitudinal distance of ~ 400 miles, two blocks show different origin nodule associations with distinctive chemical compositions and textures. KR2 block is dominated by irregular and poly-type nodules of hydrogenetic origin with low Mn/Fe, Cu, and Ni contents and high Fe and Co contents, while KR5 block is dominated by discoidal and ellipsoidal nodules of diagenetic origin with high Mn/Fe, Cu, and Ni contents and low Fe and Co contents. In addition, nodules from two blocks show different surface textures: smooth and transitional in KR2 and dimorphic and rough in KR5. Nodule genesis is affected by supply of biogenic, terrigenous, and hydrogenetic materials to the sediment and nodules, thus high sedimentation rate is known to be favorable to diagenetic nodule formation. However, the estimated sedimentation rates were found lower in the southern block dominated by diagenetic nodules nevertheless of its proximity to equator. It could be due to the decomposition of organic components that are enriched in low latitude sediments, resulting in lower sedimentation rate in sediment records. Alternatively, the distribution of different nodule association might be attributed to different sediment distributions in the studied two blocks. The northern block is characterized by thick (<250cm) metal-poor sediment distribution at the surface, which likely prevents the supply of metals remobilized from underlying metal-rich sediments by precipitating micro-nodules within sediment column. On the contrary, the metal-poor surface sediments distributes thin (<12cm) in the southern block, which coveys metals from the underlying metal-rich sediments to the