Synthesis of environmental impacts of deep seabed mining

A synthesis of environmental data compiled over the past 25 years is review ed and organized. We describe the anticipated activities associated with ex ploration for commercial deposits, with engineering tests of recovery and m ining systems, and with basic metallurgical processing. Basic description o f the manganese nodule oceanographic environment is presented, including th e occurrence of nodule deposits, relative sediment properties, benthic curr ents, and biological community. Environmental impacts from previous studies are summarized. Studies to date support the original concerns for environm ental impact identified in the DOMES research, including impact on the bent hic community where nodules are removed; impacts of the discharged plume on the near-surface biota; and impacts on the benthos due to deposition of su spended sediment. Future studies should address the establishment of quanti tative relationships between resedimented thickness and benthic community r esponse; integration of mining-related research efforts on benthic communit ies; establishment of clear guidelines for monitoring of precommercial mini ng test; and comparison of impacts from deep seabed mining with alternative land-based mining scenarios.