Tiki Basin (South-central Pacific); relationships between nodule composition and distribution and ocean floor topography

The Tiki basin is in the south central Pacific, south of the Marquesas Islands and east of the Tuamotu archipelago. It is bounded nothwards by the Marquesas Fracture Zone and divided in two parts by the topographic heights cunstituting the end to the Tuamotu Fracture Zone. One hundred stations with nodule sampling were occupied by the Group CNEXO-SLN in this area (scale 1O X 10 degrees). The nodule abundance at each station is determined from the weight of nodules brought back by free fall grabs. Chemical analysis were made on each sample (three by station) and the values presented here are the mean values. The parameters : abundance, Ni grade, Cu grade and Mn grade are compared with water depth and topographic features of the area. The main results are : - no nodules or very few between 0 and 3900 meters water depth ; - the maximum abundance of nodules (up to 4 kg/m²) is found at or close an average water depth of 4240 meters ; - the abundance classes between 0.1 and 4 kg/m² show that abundance increases with depth in the range 3900 to 4300 meters ; - the Mn maximum grade is represented by a swarm of values near 4230 meters water depth ; - the highest Ni values are situated near 4200 meters, Ni grade also increases with depth ; - a comparable evolution is shown by Cu : most of the higher values occur close to 4245 meters. In this area, there is thus a noteworthy convergence between abundance and high grade between 4200 and 4250 meters water depth. Classes of nodule concentration and grade are reported on a detailed map of the area and correlations with the topographic framework are discussed. [NOT CONTROLLED OCR]