Patrick T. Schwing

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.

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.

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.

This study estimated the total ecosystem carbon stock (TECS) and
sediment carbon sequestration rate through burial for fragmented
mangrove habitats of Kochi, south-west coast of India. The mean TECS of
Kochi mangroves was estimated at 335.33 +/- 184.47 t C ha -1, with above
ground biomass of 171.68 +/- 104.42 t C ha -1, below -ground biomass of
83.30 +/- 41.98 t C ha- 1, litterfall carbon as dead biomass of 7.12 +/-
2.81 t C ha- 1 and soil carbon stock of 73.22 +/- 39.40 t C ha -1. The
average historical soil carbon sequestration rate of Kochi mangroves was
also estimated as 2.95 t C ha- 1 yr- 1. The study revealed that there
was significant variability in TECS and sediment carbon burial rate
among riverine, estuarine and marine mangrove habitats and it appears
that, the biological factors especially mangrove plant structure,
species, age, litterfall production, crab density, mangrove conversion
to aquaculture ponds and other urban pressure played major roles in
driving the variability in carbon stocks and storage. While the sediment
particle size, bulk density and the environmental settings played a
sec-ondary role. Very low TECS and soil carbon sequestration rate was
found in aquaculture converted mangrove habitat. The CO2e of ecosystem
carbon stock (496311.20 t CO2 e) and soil CO2 burial (10.62 t CO2 e ha-
1 yr- 1 respectively) of mangroves of Kochi, revealed that even with
high urban pressure and anthropogenic activities which resulted in
fragmented distribution, they are still potent in long term carbon
sequestration unless it is not further disturbed. Therefore,
conservation and restoration of mangrove habitats based on understanding
of the regional controlling factors of carbon stock and carbon burial is
a need for scientific climate change mitigation efforts. The study will
also contribute to fill the gaps in global mangrove carbon stock
assessments for avoiding uncertainties.

The majority of observations and discrete samplings for Karenia brevis blooms and related impacts are focused in the neritic zone since blooms occur throughout the water column. Far less sampling in the benthic zone has been conducted, thus the role of the benthos in bloom initiation and other key dynamics remains unknown. Recent evidence that similar species, including Karenia mikimotoi, produce resting stages has led to an increased interest in understanding the life cycle of K. brevis and thus the role that the benthic environment plays on initiation and termination of bloom events. This collaborative effort involves working directly with the Florida Fish and Wildlife Conservation Commission-Fish and Wildlife Research Institute's Harmful Algal Bloom (FWRI-HAB) group to investigate K brevis bloom and benthic coupling with the goals of 1) providing environmental context (sedimentology) of the benthos; 2 ) establishing baselines of K brevis bloom impacts/conditions in benthic environments (benthic foraminifera assessments); and 3) evaluating the historical context and flux rates (short lived radioisotopes). These collective goals are critical for laying the groundwork for a cyst or benthos monitoring program to aid in forecasting bloom dynamics, especially initiation and termination. Samples were collected by FWRI and collaborators on directed and routine FWRI-HAB sampling efforts, and analyses were performed at Eckerd College Galbraith Marine Science Laboratory which include the examination of surficial sediments, sediment trap material, and sediment cores. These efforts are critical to the advancement and enhancement of bloom modeling and prediction capabilities.