ALBERT

Description: A reconnaissance cruise by the NZOI research vessel TANGAROA has defined limits of manganese nodule occurrence in portions of the Southwestern Pacific Basin. Bottom samples were collected at 46 stations between New Zealand and Rarotonga (in the Cook Islands), using pipe dredges, gravity corers and free fall grabs. Manganese nodules were recovered at 9 stations southwest of Rarotonga, at distances of 130 to 1000 km from the island, and in depths of 4700 to 5700 meters. Dense concentrations, up to 100% (as seen in bottom photographs), occur in a more restricted area, 220 to 745 km southwest of Rarotonga. A free fall grab yielded 20 kg/m^ of nodules at one station in this area. Most of the nodules are spheroidal, and range in size from 1-9 cm. Nodules were recovered at 15 stations in two areas south of Rarotonga, 45 to 1270 km and 1580 to 2090 km south of the island, and in depths of 3970 to 5590 meters. Compared to the nodules collected southwest of Rarotonga, nodules from the areas south of Rarotonga show a wider range of sizes (0.5-11 cm) and shapes (discoidal, botryoidal, spheroidal with equatorial "skirts", and more irregular forms in addition to many spheroidal nodules). Considering the entire study area, where different nodule morphologies occur at a single station, the smaller nodules tend to be more spheroidal. Surface textures of the nodules are generally uniformly granular. Nodules from all areas in the basin occur on light brown to dark brown silty clay; the coarse fraction of the sediment invariably includes volcanic fragments (pumice, tuff, and basalt), and often sharks' teeth. Areas devoid of nodules have little coarse fraction in the sediment. Sedimentation rates and availability of nuclei are presumed to govern nodule distribution.