Influence of Deep Water Circulation and Sea Floor Morphology on the Abundance and Grade of Central South Pacific Manganese Nodules

Abstract

Analyses of polymetallic nodules from the central south Pacific and from the underlying sediments indicate that nodule abundance is at least partly related to the degree of carbonate dissolution, which, itself, is strongly influenced by the flow of the Antarctic Bottom Water. The greatest nodule abundance is generally encountered in a 300 to 400 meter thick water layer situated between the lysocline and the calcite compensation depth levels. This range of depth is ~Ie first and main controlling factor of abundance. Inside this range, the bathymetry represents a secondary factor influencing both abundance and grade. Some correlations appear locally between nodule grade and abundance. Nodule grade seems to be generally related to the bottom morphology. Ni, Cu and Mn grades are positively correlated and are highest in topographic lows. On the contrary, Co and Cu are negatively correlated and Co presents higher grade on topographi c hi ghs.

Influence of regional and local topography on the distribution of polymetallic nodules in Central Indian Ocean Basin

“…There is inverse relationship between grade and abundance of the polymetalic nodules (Menard and Frazer 1978). The abundance increases with depth and is high on the periphery and the flanks of abyssal hills and low in the troughs (Peutot and Melguen 1979).…”

Manganese nodule distribution in different topographic domains of the Central Indian Basin

“…Regarding grade, an inverse relationship of topography with abundance has been established (Menard & Frazer, 1978). Abundance increases with depth and is high on periphery and flanks of abyssal hills and low in troughs (Peutot & Melguen, 1979). In the Atlantic Ocean, higher abundance of nodules is reported on rugged topographic terrains; however, the nodule distribution is patchy (Ewing et al, 1973).…”

Analysis of the world distribution of metal-rich subsea manganese nodules

“…The publicly available data on concentration of manganese nodules are insufficient, especially outside of the Pacific, to support any firm conclusions, but, in tiie population shown in figure 13, all but one of the stations having more than about 13 kg of nodules per square meter occur at depths greater than about 3,700 m. Analysis of hundreds of freefall grab samples collected by the Centre National pour ITExploitation des Oceans-SoeietS Le Nickel and the Association Francaise pour ITStude et la Recherche des Nodules Polymetalliques led Pautot and Melguen (1979) to conclude that the greatest concentrations of nodules are restricted to an interval of 300 to 400 m, the lower limit of which varies from basin to basin but falls within the range of 4,350 to 5,200 m-close to the carbonate compensation depth in each basin. Skornyakova (1979) also reported that the highest concentrations are confined to depths below the carbonate concentration depth.…”