Patrick T. Schwing

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 proliferation of man-made and natural chemicals threatens coastal biota and human health, which is compounded by the potential for synergistic effects among chemicals, as well as the impacts of climate change and other significant environmental stressors. This project is studying a large urbanized estuary on the west coast of Florida, USA (Tampa Bay) to investigate all major classes of contaminants of emerging concern (CECs, e.g., PFAS, pharmaceuticals, UV filters), and a number of contaminants of known concern (CKCs, e.g., banned pesticides, PCBs, PAHs) This study aims to characterize their distribution, concentration, seasonality and the potential threats they pose to wildlife and humans. Target media for analyses include benthic invertebrates (oysters and barnacles), important recreationally caught finfishes (Spotted Sea Trout, Red Drum, Snook and Sheepshead), as well as Bay sediments and wastewaters. The project will pinpoint the sources, origins and fates of such chemicals, describe the decadal-scale depositional histories of contaminants into Bay sediments, and conduct surveys of human sub-populations that may be at particular risk from these chemical pollutants (e.g., subsistence-level fishers). The project also test novel technologies for remediating contaminants in wastewater effluent. These data will be used to inform human risk assessments for consumption of seafood harvested within the Bay. More broadly, results will be used by environmental managers to inform policy and regulatory decision-making with respect to point- and non-point source pollution abatement and the appropriateness of additional public health advisories.

The North Atlantic is an ocean basin with a diversity of deep-sea ecosystems. Here we provide a summary of the topography and oceanography of the North Atlantic including the Gulf of Mexico and Caribbean Sea, provide a brief overview of the history of scientific research therein, and review the current status of knowledge of each of 18 pelagic and benthic deep-sea ecosystems, with a particular focus on knowledge gaps. We analyse biodiversity data records across the North Atlantic and highlight spatial data gaps that could provide important foci for future expeditions. We note particular data gaps in EEZs of nations within and bordering the Caribbean Sea. Our data provide a baseline against which progress can be tracked into the future. We review human impacts caused by fishing, shipping, mineral extraction, introduction of substances, and climate change, and provide an overview of international, regional and national measures to protect ecosystems. We recommend that scientific research in the deep sea should focus on increasing knowledge of the distribution and the connectivity of key species and habitats, and increasing our understanding of the processes leading to the delivery of ecosystem services. These three pillars - distribution, connectivity, ecosystem function - will provide the knowledge required to implement conservation and management measures to ensure that any deep-sea development in the future is sustainable. Infrastructure and capacity are unevenly distributed and implementation of strategies that will lead to more equitable deep-sea science is required to ensure that essential science can be delivered.

Microplastic pollution is an increasingly alarming concern with widespread global distribution in aquatic environments. Spatial and temporal differences in microplastic abundance were evaluated in the Eastern Oyster, Crassostrea virginica, at six sites within Tampa Bay. Oyster tissue was digested using 30 % hydrogen peroxide (H 2 O 2) and microplastics were quantified using Nile Red stain and fluorescent particle excitement. A total of 3025 microplastics were found throughout six study sites over two seasons (winter 2021 and summer 2022) with varying site types. Microfragments (n=2867) made up the majority of microplastics, as compared to microfibers (n=158). Significant differences were observed among the sites studied, site type, and their location in the bay. Outflow and marina areas had significantly higher (p<0.01) amounts of microplastics compared to preserve areas, and the east bay had significantly higher (p<0.05) amounts than the west bay. Findings suggest micro-plastic contamination is associated with higher urbanization, proximity to drainage basins, and recreation.

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.

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.

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.

The 2010 Deepwater Horizon (DWH) oil well blowout in the Gulf of Mexico (GoM) was the largest and perhaps most consequential accidental marine oil spill in global history. This paper provides an overview of a Research Topic consisting of four additional papers that: (1) assemble time series data for ecosystem components in regions impacted by the spill, and (2) interpret temporal changes related to the vulnerability of species and ecosystems to DWH and the ensuing resilience to perturbation. Time series abundance data for many taxa pre-date DWH, often by decades, thus allowing an assessment of population- and community-level impacts. We divided the north central GoM into four interconnected “eco-types”: the coastal/nearshore, continental shelf, open-ocean pelagic and deep benthic. Key taxa in each eco-type were evaluated for their vulnerability to the circumstances of the DWH spill based on population overlap with oil, susceptibility to oil contamination, and other factors, as well their imputed resilience to population-level impacts, based on life history metrics, ecology and post-spill trajectories. Each taxon was scored as low, medium, or high for 13 vulnerability attributes and 11 resilience attributes to produce overall vulnerability and resilience scores, which themselves were also categorical (i.e., low, medium, or high). The resulting taxon-specific V-R scores provide important guidance on key species to consider and monitor in the event of future spills similar to DWH. Similar analyses may also guide resource allocation to collect baseline data on highly vulnerable taxa or those with low resilience potential in other ecosystems. For some species, even a decade of observation has been insufficient to document recovery given chronic, long-term exposure to DWH oil remaining in all eco-types and because of impacts to the reproductive output of long-lived species. Due to the ongoing threats of deep-water blowouts, continued surveillance of populations affected by DWH is warranted to document long-term recovery or change in system state. The level of population monitoring in the open-ocean and deep benthic eco-types has historically been low and is inconsistent with the continued migration of the oil industry to the ultra-deep (≥1,500 m) where the majority of leasing, exploration, and production now occurs.