ESTABLISHING BENTHIC RADIOCHEMICAL BASELINES IN THE CLARION CLIPPERTON FRACTURE ZONE (CCZ)

Found in the abyssal plains of large gyre systems, polymetallic nodules are formed when manganese-rich pore water combines with aqueous oxygen to form manganese dioxide “pearls” that are rich in economically sought-after dissolved metals. Due to an increase in demand for renewable technology, there has been a rise in interest in deepwater polymetallic nodule mining along the Clarion Clipperton Fracture Zone (CCZ) in the North Pacific Gyre. To effectively assess and minimize sediment plume impact on the benthic boundary layer, baseline radiochemical values need to be established. Such parameters can be used as the foundation for determining sedimentation rates and bioturbation depths at collector sites as well as determining the depositional boundaries of sediment plumes caused by nodule collection. The goal of this study is to provide an analysis of 234Th & 210Pb activity level profiles between the pre-nodule collector test and post-nodule collector test sediment samples at various mining sites in the CCZ. Pre-collector test samples were collected from late August to early September of 2022 and Post-collector test samples were collected from mid-November to early December of 2022. Background and excess 234Th concentrations range from (0.44-1.87 dpm/g) and (0.0-0.57 dpm/g), respectively. Post-collector test samples are currently being measured and will be presented to determine any changes in the radioisotope activities related to the test collection. These results will serve as proof of concept to utilize these radioisotope methods to quantitatively assess the impact for monitoring and mitigation of deep sea mining efforts in the future.

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