Gregg R. Brooks

Deep-sea mining for polymetallic nodules is currently exploratory, but commercial-scale operations require indicators of environmental change to support regulatory thresholds and inform adaptive management. In the Clarion-Clipperton Zone, where background sedimentation rates are low, seafloor imagery has validated mining plume deposition but cannot resolve repeated sedimentation as nodules become buried. Thorium-234 (
Th), a naturally occurring radionuclide with a 24.1-day half-life and strong particle reactivity, serves as a high-resolution geochemical tracer. Here we apply sedimentary
Th to identify the spatial extent of plume deposition following the NORI-D mining test. Excess
Th (
Th
) activity was low at baseline but elevated after mining and declined to background within 1-2 km of the directly mined area. Results suggest that mining plumes scavenge and redistribute
Th
, establishing a geochemical benchmark for plume extent and an operational tool for tracing recent sedimentation under future commercial-scale mining scenarios.

The Gulf of Mexico (GoM) is a unique ecosystem due to its physical characteristics, being influenced by the Mississippi River in the north and the Loop Current from the south, resulting in a gradient of organic to carbonate sediment composition from north to south. The continental slope of the northern and southwestern portions of the GoM are generally well studied; however, less is known about the southeastern GoM along the slope of Cuba. To fill this knowledge gap, sediment cores were collected in 2017 at nine stations (974–1580 m depth) to determine abiotic controls on the deep-sea benthic macrofauna community. Oceanographic data indicated a stratified water column typical of an oligotrophic ocean and no evidence of hypoxia. Sediment texture and composition indicated a west-east gradient likely determined by downslope transport of terrigenous material in the eastern part with a high proportion of carbonate in the west. Heavy metals (Cu, Hg, Pb, and Zn) at concentrations known to cause adverse benthic effects were present in the east near the city of Havana, with the macrofauna community showing characteristics indicative of environmental stress. Overall, this region supported a diverse community of macrofauna families of low abundance, typically only 1–2 animals, and high variability among replicates within stations. Rarefaction curves revealed higher biodiversity per number of individuals in the samples from Cuba compared to those from the nGoM at similar depths, though more samples would be needed to better reveal the true diversity. The major factors influencing macrofauna communities in the continental slope off northwestern Cuba are most likely the lack of organic-rich sediment and low sediment deposition rates, both of which can be attributed to the strong currents and lack of major terrigenous input, along with the regular natural disturbances which prevents domination.
•Along the Cuban slope, there was a total of 275 macrofauna collected from 65 families and 9 phyla in 25 cores.•Evidence of toxic levels of heavy metals and adverse community impacts were observed from the station offshore of Havana.•Southeast GoM has low abundance, but higher diversity and evenness compared to northern GoM samples from comparable depths.•Highly heterogenous habitat along Cuban slope resulting in large variation in macrofauna communities.

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.

Microplastics have accumulated in the environment since plastic production began, with present-day observations that range from marine trenches to mountains. However, research on microplastics has only recently begun so it is unclear how they have changed over time in many oceanic regions. Our study addressed this gap by quantifying the temporal and spatial dynamics of microplastics in two deep-water regions of the Gulf of Mexico (GOM). We isolated agglutinated foraminifera from sediment cores and assessed microplastics that were incorporated into their tests. Our results indicated that microplastics were incorporated by agglutinated foraminifera after plastic production began. Microplastics were higher at deep-water sites and closer to the Mississippi River. This study confirms the presence of microplastic incorporation into agglutinated foraminifera tests and investigates microplastics in deep-water sediments in the GOM. Additional work is needed to fully identify the distribution of microplastics across the GOM and other oceanic basins.

This dataset includes CTD and environmental data for four stations collected onboard R/V Weatherbird II cruise WB-0522 in the Gulf of Mexico from 2022-05-16 to 2022-05-19. The dataset includes 4 profiles/casts of temperature, salinity, conductivity, chlorophyll-a and colored dissolved organic matter fluorescence, turbidity, oxygen saturation, sound velocity, altimetry and Photosynthetically Available Radiation (PAR). R/V Weatherbird II cruise WB-0522 was led by chief scientists Dr. Patrick Schwing, Dr. Rebekka Larson, and Dr. Gregg Brooks. Processed data are in text format.

This dataset includes CTD and environmental data for four stations collected onboard R/V Weatherbird II cruise WB-0523 in the Gulf of Mexico from 2023-05-23 to 2023-05-31. The dataset includes profiles/casts of temperature, salinity, conductivity, chlorophyll-a and colored dissolved organic matter fluorescence, turbidity, oxygen saturation, sound velocity, altimetry and Photosynthetically Available Radiation (PAR). R/V Weatherbird II cruise WB-0523 was led by chief scientists Dr. Patrick Schwing, Dr. Rebekka Larson, and Dr. Gregg Brooks. Processed data are in CNV fromat.

As the deep-sea mining industry expands, it is crucial to develop sensitive indicators to measure the footprint of an ambient sediment plume from a collector vehicle (PCV). This study introduces a novel technique using Thorium-234, a short-lived radioisotope (half-life: 24.5 days), as a high-resolution indicator for tracking event-driven sedimentation, examining resuspended sediment particles' ability to re-scavenge thorium in the water column, and delineating the spatial extent of an ambient plume created by a PCV from the first full-scale collector test in over 40 years. Multicores were collected for baseline Thorium-234 activity from the NORI-D lease area in the Clarion Clipperton Zone (CCZ) in 2021 and were subsampled at 0.5-1.0 cm intervals. Pre-collector test samples were collected August-September, 2022 and Post-collector test samples were collected November-December of 2022. Thorium-234 activities were determined for each sediment subsample. Pre-collector surface (0-1 cm) excess Thorium-234 activities across all sites ranged from 0.31-1.9 dpm/g. Post-collector surface (0-1 cm) excess Thorium-234 activities across all sites ranged from 0.23-6.31 dpm/g. Our findings highlighted the highest Thorium concentrations 0.5 km away from the test site, which returned to background levels at 1 km away. This study provides insight into the spatial extent of the sedimentation footprint of fine-grained particles and can be used to verify plume models as well as provide a potential threshold for sedimentation.

The Deep Water Horizon (DWH) oil spill occurred in the Northern Gulf of Mexico (NGoM) in 2010. Over 700 million liters of oil spilled into the NGoM in the 87 days the wellhead was actively leaking. Samples were taken from sites annually to semi-annually from 2010-2023 to provide a spatial and temporal benthic assessment for the NGoM. Reference conditions provide an ecological snapshot of the marine environment and allow for quantitative assessment of impact and response in the case of future oil spills. Benthic foraminifera, which are single-celled, testate organisms that inhabit the seafloor have proven to be excellent indicators and records of ecological change. Stable carbon isotopes in benthic foraminifera shells (tests) have also proven to be effective indicators of petroleum carbon incorporation into the benthic system. Seafloor sediment cores were most recently collected in 2023, at specific time series sites in the NGoM, as a part of the Scientist-At-Sea program. The sediment cores were subsampled at 2 mm increments. Calcareous foraminifera species, Cibicidoides pachyderma and C. wuellerstorfi, were isolated for stable isotope (oxygen and carbon) analysis using a stable isotope ratio mass spectrometer (SIRMS). Stable isotopes from benthic foraminifera from two of the time-series sites have been measured continually from 2010 to 2017. This study will provide a comparison of the latest benthic foraminifera stable carbon isotopes profiles with previous collections to determine long-term recovery of the system, gain insight into natural variability, and establish long-term preservation of the DWH signal in fossil (downcore) benthic foraminifera tests. These records will continue to aid in the understanding of natural seafloor carbon cycling, and also in the event of future pollution events such as oil spills.

Scientific advancements in isotope geochemistry and sedimentary geochronology have allowed for high-resolution sampling of radioisotope activities in marine sediments. Given the recent advances in deep sea mining, the ability to understand the nature of radioisotope scavenging on resuspended sediments could provide essential insights into the impacts it may have on benthic environments. Sediment plumes from collector vehicles used in deep sea mining often spread their footprint over the seafloor and sensitive indicators such as radioisotopes are critical to their further investigation. This pilot study attempts to replicate the natural process of radioactive isotope scavenging of resuspended sediments in a laboratory setting. Radioisotopes, such as (super 210) Pb and (super 234) Th, are valuable tools for evaluating human and natural impacts recorded in the sediment record. Radioisotopes adsorb to sediment particles and remain until they are deposited on the ocean floor and begin to decay. The known decay rate of (super 234) Th and (super 210) Pb allows for the calculation of a date of deposition and also for the determination of the spatial extent of the resuspended sediment in the surface sediments. A tank replicating the deep sea sedimentary environment was constructed for this study and filled with 4.5kg of sediment. This sediment was known to have been deposited over 100 years ago, thereby no longer showing any excess radioisotope activity. Roughly 100 liters of seawater flowed through the tank at one liter per minute as the sediments were resuspended every twenty minutes for thirty-second intervals. Gamma spectrometric analysis of post-experiment samples revealed that (super 234) Th adsorbed to the resuspended sediment during the experiment and supported the constant rate of supply age model. Results from the radioisotope (super 210) Pb, however, were inconclusive and require further testing. This pilot study only scratches the surface of the questions about the implications of resuspended radioisotope adsorption in deep sea settings. Radioisotope scavenging has high utility for determination of the spatial extent of ambient sediment plumes caused by deep sea mining. Further research into methods of artificial resuspension and adsorption are critical to fully understanding this process.

In the context of climate regulation and anthropogenic waste detoxification (e.g. oil spills), estimates of deep ocean sedimentation and carbon sequestration are of the utmost importance. Radiocarbon (14C) is a common radioisotope that can be used to establish millennial scale sediment accumulation rates. The objectives of this study were to: 1) establish ages for co-occurring total organic carbon (TOC) and planktic foraminifera (carbonate) in the northeastern Gulf of Mexico (GoM), 2) use these ages to estimate accumulation rates independently, 3) identify any evidence of redistribution, and 4) examine any offset between TOC and carbonate 14C ages as a tool to potentially identify selective TOC transport. Sediment samples were collected in May 2018 from the RV Point Sur using an Ocean Instruments MC-800 multi corer. Radiocarbon measurements of both planktic foraminifera and TOC subsamples were made at the National Ocean Science Accelerator Mass Spectrometry Facility (NOSAMS). Radiocarbon ages, calibrated using the OxCal 4.4, ranged from recent to 6407 BP. Linear (LAR: 4–24 cm/kyr) and mass accumulation rates (MAR: 1.5–11.5 g/cm2/kyr) were generally consistent with those reported by other recent studies in the GoM. At two sites, C14 ages decreased from the surface to the second sampling increment which was consistent with sediment redistribution. The TOC-carbonate offsets, which are indicative of lateral advection and organic matter aging, were lower than those found in the majority of other regions, which was consistent with less lateral transport or a more oligotrophic setting. The magnitude in radiocarbon age offsets with depth could potentially be used as a relative aging or transport assessment tool in areas with little resuspension. •Total organic carbon and planktic foraminifera 14C ages established for sites in the Gulf of Mexico.•Total organic carbon and carbonate 14C age offsets are indicative of advection and aging.•14C age offsets with depth could be used as relative aging or transport assessment tool.