Les nodules du pacifique central dans leur environnement géologique CAMPAGNES COPANO - 1979

The cruises named COPANO have been undertaken during the summer 1979 on the R. V. Le Suroit of the CNEXO, as a part of an international research program I.C.I.M.E. The objective of this project was to study relatively small zones (a few km2) and to establish a relationship between characteristics of the manganese nodules and their environment. During the COPANO cruises, five zones have been studied: two in the northern Pacific, two in the southern Pacific and finally one in the equatorial Pacific. All the zones are centered on the longitude 134° Wand therefore their symmetry to the highly productive equatorial zone may be tested. As one of the results of the cruises is the relation between nodules and the bottom soil, established by sediment-sampling and a large number of photographic pictures of the sea bottom. In this way for each zone a schematic «geological» or rather «pedological» map could be drawn. Geochemical analysis demonstrate an inverted symmetry between the metal content of the sediments (Mn, Cu, Ni) and the associated nodules. The metal content of the sediments increases with the distance from the Equator whereas in the nodules the metal content diminishes. The organic production followed by dissolution and diagenesis is most likely the dominant phenomenon governing the enrichment of the nodules. The physical properties of the nodules : their density of the bottom, their size and appearance seems to be related to the deep water circulation. The most favourable zones for nodule exploration are the flanks of the deep submarine valleys.