Abstract or Keywords
The first full-scale deep-sea polymetallic nodule mining test in 44 years was carried out late 2022 in the Clarion-Clipperton Fracture Zone of the abyssal Pacific Ocean. Deep-sea mining generates sediment plumes, posing potential ecological risks to benthic communities. To understand these impacts it is crucial to define the spatial breadth and magnitude of these ambient collector plumes. This study utilizes X-ray fluorescence (XRF) and X-ray diffraction (XRD) techniques for monitoring deep-sea mining plumes to evaluate sediment deposition and removal in an area actively targeted for commercial mining. To obtain representative samples and spatial coverage, coring sites were selected based on their location in or adjacent to a modeled plume from this collector test. Ultimately six cores were chosen for evaluation based on model projections and distance from source - "track" sites were located within the path of the collector vehicle, 0.2 km East from track, 0.5 km East from track, 2 km East from track, and a control site 4 km away and to the northwest. After retrieval the cores were split, photographed, and frozen while aboard the research vessel for later transport and analysis in the lab. Elemental analysis was carried out in two phases. During phase one the frozen cores were scanned in 1-cm increments utilizing an XRF spectrometer and data were compiled in down-core concentrations per element. In phase two, five subsamples per core were selected based on the down-core data. The samples were then freeze-dried, finely ground (<65mu m), homogenized, and pressed into pucks for reanalysis by XRF to eliminate artifacts from in-situ scanning. Mineralogic analysis was conducted with a desktop XRD using the Crystallography Open Database (COD) for peak matching and Rietveld refinement for quantification. Initial results from down-core XRF data show correlative marker horizons among multiple cores and suggest a removal of the top approximately 4-5 cm of sediment from the collector track. Phase two XRF analysis eliminated variances in core surface scans and provided a more accurate quantification of elements in the top 3 cm. XRD analysis shows a mix of iron and manganese oxides with mainly silica clays and some carbonates. Spatial comparisons are in progress between the coring sites for Phase 2 XRF as well as XRD. This work is being performed by an undergraduate marine geology student at Eckerd College.