ALBERT

Beschreibung: A compilation of published and unpublished chemical analyses of samples of ferromanganese deposits from the ocean floor reveals that only in relatively few areas of the world are the copper and nickel contents sufficiently high for the nodules to represent a potential source of metals. The North and South Atlantic and Indian Oceans are characterized by deposits whose metal content (Cu, Ni, Mn and Co) are well below the minimum values necessary for economic exploitation. The situation is more favorable in the Pacific Ocean and most encouraging in the North Pacific. In the South Pacific, nodules containing over 1% Ni and lesser amounts of copper occur in the Peru Basin, in deep waters east of the Marquesas Islands and Tuamotu Plateau, and within the Southwest Pacific Basin. The relatively low Cu and Ni values obtained in these areas may eliminate them as prospective mining sites. Only in the North Pacific do the analyses consistently show values greater than 1% Cu and 1% Ni, and these nodules, therefore, are the immediate target of the ocean mining industry. The deposits of interest lie north of the equator in a broad band between 6° 30' N and 20° N and stretching from 110° W to 180° W. Maximum copper and nickel values occur along a line 8° N to 10° 30'N and 131°3 0'W to 145° W.

Beschreibung: Siliceous skeletons were investigated in two core profiles (9 cores), one off Cap de Sines, Portugal and the other off Cap de Mazagan, Morocco. Total number of skeletons was determined per gram of dried sediment at different core depths of the fraction 〉21 µ. Results are compared with a core profile from the Arabian Sea. Diatoms are of four groups: (A) marine-planktonic, B) marine-benthic, (C) freshwater and (D) Tertiary species (Trinacria e.g.). Species from groups (B), (C) and (D) are redeposited in all cores taken at a water depth of greater than 100 m. Small numbers of Silicoflagellates and Radiolarians were found throughout the cores from the Ibero-Moroccan shelf. In the Arabian Sea core, Radiolarians were concentrated in distinct horizons in which Tertiary material was redeposited (40-50, 140-150, 250-260 cm). The number of siliceous skeletons per gram of dried sediment decreases more or less rapidly with increasing depth in all cores. Whereas about 2500 skeletons were found in sediments close to the surface, approximately 100 skeletons only were found in deeper (〉40 cm) layers. Deeper horizons with more than 100 specimens were interpreted as redeposited material. This sediment contained robust skeletons, resistant against dissolution, as well as benthic and Tertiary material. The decrease of siliceous skeletons relative to core depth depends upon the sedimentation rate. Where the sedimentation rate is high, the opal dissolution zone extends down to 30-60 cm, where the sedimentation rate is low, it is located at 10-30 cm. Below these depths opals disappears. These zones also have approximately the same age (4000 years) everywhere. Siliceous skeletons dissolve differentially, first the Silicoflagellates disappear, second the Diatoms, third the Radiolarians, and fourth the Sponge Spicules. Surface structure of skeletons from near the opal dissolution zones are similar to those of skeletons treated with NaOH. Tertiary diatoms (Trinacria e. g.) and benthic diatoms (Campylodiscus e.g.) dissolve less rapidly than skeletons of modern planktonic diatoms (Coscinodiscus e.g.). The time control of the opal dissolution zones appeared rather independent of various oceanic influences. No evidence was found for effects from upwelling either off Portugal or off Morocco. No difference in dissolution rates was recorded between the abyssal plains lying off these two areas. Likewise, there was no change in solution rates from Pleistocene to Holocene within either one of the abyssal plains. The Mediterranean outflow, which is enriched in dissolved silica, apparently had no effect on dissolution rates of siliceous skeletons in the sediment.