Geotechnical and sedimentological investigations of deep-sea sediments from a manganese nodule field of the Peru Basin

Deep-sea mining of manganese nodules will significantly modify the surface layer of deep sea. Surface sediments are mechanically disturbed, and a cloud of sediment particles suspended and re-deposited. Assessment of sedimentological and soil mechanical characteristics of undisturbed top layer sediments from a manganese nodule field of the Peru Basin are necessary to provide baseline data for soil mechanical estimations and for the physical and numerical modelling of environmental impacts of future ocean mining activities. This will assist the International Seabed Authority to make decisions on how to formulate the mining code, and will increase our understanding of sedimentation processes in the Peru Basin. The deployment of a new sampling device (maxicorer) guaranteed undisturbed sediment samples in which soil mechanics-related parameters were measured including sediment density, water content, shear strength, and penetration force. Data evaluation show a close relationship between the soil mechanical parameters and various sedimentological properties such as grain-size distribution, mineral composition and micro-structure. From the results it can be concluded that in the worst case a deep-sea nodule mining vehicle would sink about 15–20 cm into the sea bed.