Ferromanganese nodules, individually up to a few ten of centimetres across, occur in vast quantities on the deep ocean floor south of New Zealand. Composed largely of iron and manganese, the nodules also contain the strategic metals Ni, Cu and Co, as well as rare earth elements. They occur below the carbon compensation depth, where both the rate of sediment deposition is very low, and current flow is strong (c. 10 cm/s). Most are smoothly spherical, and form by direct precipitation of metals from seawater, perhaps aided by metal-ingesting micro-organisms. Such nodules grow very slowly, a few mm/Myr (as determined by (super 10) Be dating). Other nodules have irregular or botryoidal morphology, and form within the top few centimetres of seafloor sediment. South of New Zealand, the extensive Campbell Nodule Field began to form about 15 million years ago beneath the global Pacific Deep Western Boundary Current (DWBC). Seafloor mapping, photography and dredging indicates a dramatic change in the character of the seafloor west to east across, and perpendicular to, the DWBC flow. To the west, a thick layer of biogenic ooze covers the relatively shallow Campbell Plateau. Next to this, on the upper Campbell Slope, a thin layer of sediment-the 'Campbell Skin Drift'-is littered with boulders and occasional whale bones coated in ferromanganese. Recently drilled at ODP 181, Site 1121, this unit contains buried nodules at several stratigraphic horizons, where they have been trapped by periods of faster sedimentation. The main nodule field abuts the base of the Campbell Slope at water depths of 4000-4500 m, and narrows northward from c. 300 km wide, to less than 100 km wide where the field divides around the Bollons Seamount. There are no nodules on the 5000 m deep clay-rich abyssal plain of the Southwest Pacific Basin, which stretches away to the southeast. The density of nodules on the ocean floor is thus highly variable, being greatest (up to 90% coverage) beneath the main DWB current flow, and diminishing laterally where the current weakens, and where increasing amounts of sediment cover hinder nodule formation. The composition of the nodules also varies widely, with Mn/Fe ratios ranging from 0.4 to 1.8, Cu + Ni ranging up to 1.3%, and Co ranging up to 0.5%. Internally, the nodules show broad compositional changes, with Mn/Fe and Cu + Ni increasing, and Co decreasing from core to rim. These trends are interpreted to reflect changes in the physical and chemical characteristics of the DWBC in response to environmental changes in its source area, Antarctica. The relatively low Cu, Ni and Co contents of the nodules, and their high recovery costs, make them only marginally economic to mine at present-day commodity prices. However, they still represent an immense resource of strategic metals for the future. A conservative estimate of the total amount of metal contained in those nodules within New Zealand's EEZ and extended continental shelf is c. 10 million tonnes.

West: 176.5952 East: 176.5952 North: -50.5353 South: -50.5353

Expedition: 181

Site: 181-1121

Provider: SEDIS Publication Catalogue

Data set link: http://sedis.iodp.org/pub-catalogue/index.php?id=2012-046188 (c.f. for more detailed metadata)

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