Patrick T. Schwing

Sediment cores were collected in the Gulf of Mexico (GoM) to investigate the sediment record of synthetic based drilling mud (SBM) and evaluate the scope of the Deepwater Horizon (DwH) oil spill. Synthetic drilling mud containing barium sulfate is used at oil drilling sites to control the temperature and pressure inside the well during drilling activities. On April 20, 2010, the DwH oil spill triggered the release of over 4 million barrels of oil in the ocean. Attempts were made to stop the flow of oil from the well, including pumping synthetic barium sulfate (barite) drilling mud into the well. This failed to stop or reduce the oil flow and nearly 30,000 barrels of drilling mud were dispersed onto the seafloor. Due to the unique characteristics and uses of SBMs, they may be used as tracers in deep-sea sediments to investigate the environmental implications of barium from oil drilling and assist with the evaluation of the implications of barium increases in benthic environments. The objectives of this research are as follows: (I) Determine if there is variability of barium in sediments in northeast the GoM, (II) If yes, determine if this can be attributed to oil drilling activities and/or other anthropogenic activities. Sediment cores were analyzed by X-ray Fluorescence (XRF) spectroscopy to determine the elemental composition of sediment samples and evaluate variability in Ba concentrations. Short lived radioisotope analyses ( (super 210) Pb) were conducted to provide age control over the past approximately 100 years to determine timing of Ba input. Preliminary findings indicate that sediment surrounding the DwH site exhibit increased concentrations of Ba at the surface, likely due to the DwH event. Samples collected from areas of active drilling exhibit spikes in Ba concentrations at various intensities possibly indicating drilling activities from surrounding wells. This research can be used to evaluate the effectiveness of regulations on synthetic drilling mud put in place to prevent contamination and toxicity to benthic communities, as well as provide a potentially more persistent tracer of oil spill events. This will help further determine the spatial extent of the DwH event on the seafloor as well as its preservation in the sedimentary record.

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.