WP3 will investigate geochemical and biogeochemical conditions and processes in the surface sediments, quantify solute fluxes across the sediment-water interface and trophic interactions including the flow of energy and the bioaccumulation of metals and other toxicants.
For the first time this will allow a holistic assessment of the biogeochemistry and ecosystem functioning of nodule areas including feedbacks between biological and geochemical processes, how they are affected by the mining impact and what time is required to establish a new equilibrium after the disturbance by mining activities. These investigations are possible by combining a broad range of disciplines and methodologies including state-of-the-art geochemical and ecotoxicological analyses, in situ biogeochemical sensing and incubations, as well as advanced stable isotope studies based on natural isotope ratios and process studies with labelled material.
Progress in scientific instrumentation for targeted sampling, in situ measurements and manipulation in deep-sea areas that has mostly been achieved after the last investigation of the DISCOL mining area (cruise SO106 in 1996) is key to the proposed investigations. Technologies applied for the WP3 work involve video-guided sampling equipment, ROV- and lander-deployed microprofilers and benthic enclosures as well as small-scale, short-term disturbance experiments. The results on biogeochemical conditions and benthic food web interactions will be used to validate and improve numerical diagenetic and food web models. The combination of newly collected data from sites with different levels of disturbance with data obtained at the DISCOL site during the SO106 cruise 18 years ago will improve prognostic simulations of the mining impact and the ecosystem recovery. Biogeochemical investigations will be carried out at both, the DISCOL area in the Peru Basin and the CCZ, while in situ studies on biogeochemical processes and ecosystem functions will be focused at DISCOL, where higher benthic activities allow for short-term measurements and where areas with different levels of disturbance can be compared. For both areas, investigations within WP3 will greatly improve our understanding of biogeochemistry and ecosystem function. For both, DISCOL and CCZ areas, we will improve baseline biogeochemical studies, which were underrepresented in the exploratory work carried out previously. Connecting the findings from both sites will provide us with an understanding of the range of biogeochemical responses expected for nodule mining at sites underlying oligotrophic and highly productive surface waters – and appropriate technologies to assess these impacts. This knowledge is of highest relevance for nodule exploration and mining guidelines provided by the International Seabed Authority (ISA) and will feed into WP5.
The main aims of WP3 are to:
- Determine the short-term and long-term impact of a deep-sea mining event on geochemical and biogeochemical processes and ecosystem functions along a disturbance gradient within the DISCOL area, and assess the time required to establish a new equilibrium.
- Assess the biogeochemical conditions and processes within the nodule belt of the CCZ as baseline information for future mining activities and for comparison with conditions of the more productive Peru Basin.