Manganese nodules in the EEZ's of island countries in the southwestern equatorial Pacific

Abstract

Studies on polymetallic manganese nodules in south equatorial Pacific EEZ's between 0 and 20°S show that Ni and Cu reach their greatest combined abundances of over 2% between 2° and 8°S on the southern margin of the equatorial zone of high biological productivity in the Cook, Line and Phoenix Island areas, as a result of biological fluxing of Ni and Cu to the nodules at and just below the calcium carbonate compensation depth (CCD). By contrast, Co reaches its greatest abundance of 0.6% south of 8°S in the Cook Islands area in what are believed to be slowly growing nodules on non-biogenic clays well below the CCD where little biological Co supply is likely. Nodule abundances are greatest (up to 30 kg/m 2) in the Co-rich area, in part due to Antarctic Bottom Water (AABW) flow, giving highest overall metal quantities per square metre in the nodules there, particularly of Co. Ellice Islands nodules are different from those found in the other island groups studied in that they show features more typical of hydrogenetic ferromanganese oxide crusts than of diagenetically influenced nodules. There are approximately 110 × 10 6t of combined Ni+Cu+Co expressed as Ni equivalent in the Cook Islands EEZ nodules, approximately 12 × 10 6t in Phoenix Islands nodules and approximately 1.4 × 10 6t in Ellice Islands nodules, in areas of 5kg/m 2 nodule abundance.