A representative number of sediment surface cores from the COMRA pioneer areas (tropical NE-Pacific) were analyzed for pore-water and solid-phase heavy-metal and nutrient concentrations, vane shear-strengths, and re-suspension re-sedimentation behavior, in comparison with similar cores from TUSCH study areas (Peru Basin, tropical E-Pacific). Geochemically, technical interventions in the NE-Pacific areas would cause less environmental changes because of significantly lower potential of pollutant release. Soil-mechanical conditions generally seem to be similar in both regions, except for locally higher variability in COMRA's Western Area.
Two of the world's most prospective manganese-nodule provinces are located in the tropical central and eastern Pacific Ocean, one of them between the Clarion and Clipperton Fracture Zones (CCFZ, 7°_ 17°NI120°·1600W), the other one in the Peru Basin (5°-100 S/85°92° W). The CCFZ province, also labeled "Manganese Nodule Belt" (e.g. Halbach et aI., 1988), has been extensively investigated during the 1970"s, primarily in order to develop the technical possibilities for deep-sea mining of the manganese nodules from water depths of 5000 m and more, e.g. by crawler/collector systems. At the same time, also the local and regional ecosystem responses to technical impacts on nodule fields were envisaged for the first time, the major issues involving physical and biological aspects, such as particle re-suspension and re-sedimentation processes, or disturbances to the benthic communities (e.g. Amos et al., 1973; Frank, 1976; Ozturgut et aI., 1978; U.S. Dept. Of Commerce et aI., 1981). Studies of geochemical changes in the abyssal environment, e.g. the release of dissolved heavy metals and nutrients from the pore water to the near bottom water by mining activities, were of subordinate importance then (e.g. Robertson & RanciteIli, 1973), as the dependence of seafloor subsurface redox environments on early diagenetic processes, i. e. on the accumulation and decomposition of organic matter, was still unknown in detail.
