The 2010 Deepwater Horizon (DwH) oil spill was responsible for dispersing an estimated 4.9 million barrels of oil into the northeastern Gulf of Mexico. Much was transported rapidly to the seafloor during a sediment pulse, but the ultimate fate of the oiled sediments remains unknown. This study investigates the potential for bottom sediments within the initial DwH impact zone to be mobilized and redeposited in down-slope depocenters. Sediment cores were collected from 31 sites up to 250km down-slope (SE) of the initial seafloor impact zone to search for evidence of sediment redistribution, and whether the sediment source area(s) included the initial impact zone. Twenty-seven of the 31sites contained sedimentary structures indicative of sediment redistribution, primarily by low density turbidity currents. Other evidence of sediment redistribution includes elevated benthic foraminiferal fracture percentage, rapid and pulsed accumulation rates and the paucity of extensive pelagic deposition. Sediments consist dominantly of siliciclastic muds, with subordinate carbonate sandy muds. The most likely source for siliciclastic muds is the Mississippi River Delta and adjacent continental margin as it is immediately up-slope from the study area. This area includes the DwH seafloor impact zone. DwH oil residues were detected in sediments deposited at different times (post 2010), at 13 core sites, up to 96km SE of the impact zone, which is consistent with multiple redistribution episodes capable of transporting oiled sediments long distances. Results of this study are not only important for developing mitigation strategies for future contaminant spills, but as sediment redistribution processes can be quite destructive, information regarding process type and frequency can be vital for planning future activities on the sea floor.

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.

Deep-sea offshore northwestern Cuba is the less studied zone of the Gulf of Mexico (GoM). Our study aimed to set an environmental baseline and investigate a potential west-east gradient of sediment properties and nematode diversity along the northwestern Cuba. Sediments were collected by multicorer at nine sites in the insular slope between 974 and 1682 m depth. Sediment texture and composition showed a west-east gradient caused likely by narrowing of shelf width and increasing of downslope transport of terrigenous material. We found clear signatures of heavy metal pollution likely derived from Havana City but also from open-sky mining (Castellanos mining complex) and port dredging operations (Mariel). Nematode assemblages were dominated by the deep-sea genera: Acantholaimus, Metadasynemella, Desmodorella, Cervonema, Daptonema, Halalaimus, and Pselionema. α-diversity was about 20–50 genera and γ-diversity of about 100 genera. The β-diversity was substantial likely because small-scale patchiness of resources and heavy metals stress that increased assemblage variability. Individual weight decreased with depth indicating food-supply limitation in the deep sea; also, heavy metals were negatively correlated with weight suggesting deleterious effects on the growing. Our findings indicate that heavy metal pollution has reached deep-sea sediments and corroborate the long-range effects of anthropogenic activities on deep sea. Taxonomic diversity and biological traits (life strategy and trophic composition) constituted a powerful bioindicator of benthic health and benchmark for future potential disturbances in the region. Northwestern Cuba slope is still an understudied portion of the GoM and more research is needed to fully understand its biodiversity and biogeochemical patterns.

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 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.

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.

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.

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.

Gulf of Mexico (GOM) ecosystems are interconnected by numerous physical and biological processes. After the Deepwater Horizon (DWH) disaster, these ecological processes facilitated dispersal of oil-spill toxicants or were damaged and broken. A considerable portion of post-DWH research focused on higher levels of biological organization (i.e., populations, communities, and ecosystems) spanning at least four environments (onshore, coastal, open ocean, and deep benthos). Damage wrought by the oil spill and mitigation efforts varied considerably across ecosystems. Whereas all systems show prolonged impacts because of cascading effects that impacted functional connections within and between communities, deep-sea and mesopelagic environments were particularly hard hit and have shown less resilience than shallow environments. In some environments, such as marshes or the deep-sea benthos, products from the spill are still biologically accessible. Some shallow ecosystems show signs of recovery, and populations of some species show resilience; however, a return to a “pre-spill” state is questionable. Importantly, habitats in which large amounts of energy flow through the ecosystem (marshes, coastal regions) recovered more quickly than low energy habitats (deep-sea benthos). Functional interactions between Gulf of Mexico systems are more complex and widespread than generally recognized. Moreover, ecosystems in the Gulf are subject to multiple stressors that can combine to impart greater, and less predictable, impacts. To help mitigate the effects of future insults, we identified four salient areas of research that should be addressed for each of the major environments within the GOM: establishing monitoring systems; quantifying coupling between GOM ecosystems; developing criteria for assessing the “vulnerability” and “resilience” of species, communities, and ecosystems; and developing holistic predictive modeling.

The focus of this study was to determine the long-term fate of oil-residues from the 2010 Deepwater Horizon (DwH) oil spill due to remobilization, transport, and re-distribution of oil residue contaminated sediments to down-slope depocenters following initial deposition on the seafloor. We characterized hydrocarbon residues, bulk sediment organic matter, ease of resuspension, sedimentology, and accumulation rates to define distribution patterns in a 14,300 km2 area southeast of the DwH wellhead (1,500 to 2,600 m water depth). Oil-residues from the DwH were detected at low concentrations in 62% of the studied sites at specific sediment layers, denoting episodic deposition of oil-residues during 2010–2014 and 2015–2018 periods. DwH oil residues exhibited a spatial distribution pattern that did not correspond with the distribution of the surface oil slick, subsurface plume or original seafloor spatial expression. Three different regions were apparent in the overall study area and distinguished by the episodic nature of sediment accumulation, the ease of sediment resuspension, the timing of oil-residue deposition, carbon content and isotopic composition and foram fracturing extent. These data indicate that resuspension and down-slope redistribution of oil-residues occurred in the years following the DwH event and must be considered in determining the fate of the spilled oil deposited on the seafloor.

It is imperative to understand the carbon (C) and nitrogen (N) pools in tropical mangrove systems considering the diminished C storage potential and increasing nutrient loading in a global context due to rising anthropogenic disturbances. Here, we report that the Mangalavanam Coastal Wetland (MCW), a tropical mangrove stand, is a C-rich environment, with high sediment total organic carbon (70.35 +/- 23.84 mg/g) and the delta C-13 (-26.56 +/- 0.65 parts per thousand) signatures indicate that the major source of carbon in the study area is from mangrove litter. The total nitrogen concentration in the sediment (3.78 +/- 0.18 mg/g) was high despite the low N environment of mangrove ecosystems where the mangrove leaf litter was a major contributor to C. The sediment delta(15) N (7.70 +/- 0.23 parts per thousand) signatures indicated that the influence of anthropogenic N discharges and the contribution of marine algae were the primary cause of N enrichment. The mean delta C-13 and delta N-15 signatures of the mature mangrove leaves of the MCW were -28.66 +/- 1.04 parts per thousand and 5.93 +/- 0.65 parts per thousand, respectively. The mangrove dweller crab Parasesarma plicatum was observed to have enriched delta C-13 (-23.78 +/- 0.33 parts per thousand) and delta N-15 (6.54 +/- 0.35 parts per thousand) signatures, indicative of a mixed dietary source. This study provides the impetus for ongoing conservation efforts to limit the loss of carbon storage and protect against the impact of anthropogenic nitrogen loadings on lowering the carbon and nitrogen emission potential for this system, which can have implications for other tropical mangrove systems as well.

The 2010 Deepwater Horizon (DWH) oil spill released 4.0 million barrels of petroleum into the Northern Gulf of Mexico (NGoM), causing a substantial Marine Oil Snow, Sedimentation and Flocculent Accumulation (MOSSFA) event. Benthic foraminifera have successfully been used as bioindicators of the event with an 80-93% decline in density coinciding with the oil spill, followed by a recovery period to a steady state within three to five years. Here we present the results of a size and morphological study of four species of benthic foraminifera which remained abundant through the DWH oil spill (Uvigerina peregrina, Brizalina subaenariensis var. mexicana, Bulimina marginata and Cassidulina teretis) to understand how different species were impacted and why such a loss in density occurred. Short-lived radioisotope dating distinguished the pre-DWH and post-DWH depth intervals from 2010 to 2015. The species exhibit shape changes in response to the oil and MOSSFA processes and the pre-DWH length/width ratios of Uvigerina peregrina and Brizalina subaenariensis var. mexicana are significantly different than post-DWH length/width ratios within the cores. Reduced oxygen levels were likely a long-term (3-5 years) driver of this shape change and enhanced organic carbon concentrations were a short-term (1-2 years) driver. This study demonstrated the importance of the benthic foraminiferal morphological response to the DWH oil spill and furthers our understanding of the strategies of taxa that occurred abundantly throughout the record.

Tropical mangrove environments have high carbon sequestration potential and this ecosystem service is currently used in mitigating climate change. However, these environments are declining rapidly in developing countries, diminishing their carbon sequestration potential and may ultimately transforming them as carbon dioxide sources. This study investigated the carbon sequestration potential through sediment burial at three mangrove habitats of Cochin, South-West coast of India. High burial estimates were recorded at two mangrove stations (2.95 +/- 0.79-10.41 +/- 2.50 t C ha(-1) yr(-1)), but consistent with other tropical mangrove areas. Lower burial rates were estimated at one station (0.57 +/- 0.24 t C ha(-1) yr(-1)). Eighty percent of the mangrove net primary productivity through litterfall (NPPL) was stored in the sediment at the station with the highest burial rate, which is demonstrative of a robust carbon sink. However, at a different site, which is subject to aquaculture, only 7.23 % of NPPL was buried in the sediment. A major portion of the fixed carbon at this site is presumably emitted back to the atmosphere or exported to adjacent water bodies. The median total regional mangrove carbon burial rate in this study was 2.95 t C ha(-1 )yr(-1) and the organic carbon burial rate was 1.93 +/- 0.75 t C ha(-1) yr(-1). Biological factors such as mangrove biomass, litterfall and crab density have played a major role in controlling the sediment carbon burial rate. Sediment texture and bulk sediment accumulation acted as secondary controlling factors. The carbon source characterisation in the sediment profile using stable isotope techniques revealed the organic carbon origin as mangrove litter. Gaining a better understanding of carbon sources, burial rates and their controlling factors in mangrove habitats aids in regional climate mitigation efforts and global efforts to increase the carbon sequestration potential of tropical mangrove systems.

Following the Deepwater Horizon oil spill (DWHOS), the formation of an unexpected and extended sedimentation event of oil-associated marine snow (MOSSFA: Marine Oil Snow Sedimentation and Flocculent Accumulation) demonstrated the importance of biology on the fate of contaminants in the oceans. We used a wide range of compound-specific data (aliphatics, hopanes, steranes, triaromatic steroids, polycyclic aromatics) to chemically characterize the MOSSFA event containing abundant and multiple hydrocarbon sources (e.g., oil residues and phytoplankton). Sediment samples were collected in 2010–2011 (ERMA-NRDA programs: Environmental Response Management Application – Natural Resource Damage Assessment) and 2018 (REDIRECT project: Resuspension, Redistribution and Deposition of Deepwater Horizon recalcitrant hydrocarbons to offshore depocenter) in the northern Gulf of Mexico to assess the role of biogenic and chemical processes on the fate of oil residues in sediments. The chemical data revealed the deposition of the different hydrocarbon mixtures observed in the water column during the DWHOS (e.g., oil slicks, submerged-plumes), defining the chemical signature of MOSSFA relative to where it originated in the water column and its fate in deep-sea sediments. MOSSFA from surface waters covered 90% of the deep-sea area studied and deposited 32% of the total oil residues observed in deep-sea areas after the DWHOS while MOSSFA originated at depth from the submerged plumes covered only 9% of the deep-sea area studied and was responsible for 15% of the total deposition of oil residues. In contrast, MOSSFA originated at depth from the water column covered only 1% of the deep-sea area studied (mostly in close proximity of the DWH wellhead) but was responsible for 53% of the total deposition of oil residues observed after the spill in this area. This study describes, for the first time, a multi-chemical method for the identification of biogenic and oil-derived inputs to deep-sea sediments, critical for improving our understanding of carbon inputs and storage at depth in open ocean systems.