Resuspension, Redistribution, and Deposition of the Deepwater Horizon Recalcitrant Hydrocarbons to Offshore Depocenters – REDIRECT

Multicore deployment for collecting sediment samples at depths >1000m

Natural heterogeneity of bottom topography and circulation processes are key drivers transporting materials to deeper areas in the GoM by erosion and deposition of contaminated sediments beyond the surface extent of the once existing oil slick or the subsurface plumes(s).

The proposed research will transform our understanding of the sinks, distribution, and transport processes of sedimentary hydrocarbons by investigating the connectivity of geomorphological features (erosional channels, lee depocenters, and isolated valleys), and the sedimentological and physical oceanographic processes (resuspension, advection and re-sedimentation) affecting oil-derived hydrocarbon distribution and deposition within the BNL in the deep sea. 

Petrocarbon content (14C) and organic geochemical analyses (aliphatics, aromatics, hopanes, and steranes) will be used to quantify the concentration and degree of weathering of hydrocarbon residues. Laboratory flume analyses will test the behavior of the surface layer to determine threshold current velocities necessary to re-suspend size specific particles and subsequently the behavior during transport of the resuspended material, which can be utilized in sediment transport models. This study will develop a spatial and temporal perspective of the MOS deposited on the seafloor to compare with the MOS projected to have formed in the water column.

A time-series analysis of polycyclic aromatic hydrocarbons in Gulf of Mexico mesopelagic fauna 

Argyropelecus aculeatus, Image No3, DP02-16AUG15-MOC19-B080N-026-N3, LRM
Argyropelecus  aculeatus  (Photo credit: Dante Fenolio)

The Gulf of Mexico (GoM) contains abundant sources of toxic organic compounds including polycyclic aromatic hydrocarbons (PAHs). Due in part to the increases in the exploration of deep-marine resources in the last decade, it is likely that major PAH contamination events will occur. An example was the Deepwater Horizon Oil Spill (DWH) which was primarily a deep-pelagic event. The deep pelagic zone is by far the largest habitat in the GoM that was affected by the DWH spill. The DWH spill highlighted the large data gap for the deep-ocean in the GoM.

Results from a collaborative effort between DEEPEND and C-IMAGE II Consortia indicate that the mesopelagic fauna incorporated DWH oil resulting in diet shifts after the spill and exposure to PAHs.  A 10-fold increase in PAH concentrations during 2010-2011 relative to pre-spill values (2007) and a decline in 2015-2016 was observed. The presence and composition of elevated PAHs confirmed post-spill contamination of deep- pelagic fishes.  PAH data will be integrated with those from population dynamics and stable isotope analysis to provide evidence for effects of oil exposure to deep-pelagic communities. Analyses were conducted at the Paleoceanographic Laboratory – University of South Florida.

Related Publication (more to come soon):

  • Romero I.C., Tracey Sutton, Brigid Carr, Ester Quintana-Rizzo, Steve W. Ross, David J. Hollander, Joseph J. Torres.. 2018. A decadal assessment of polycyclic aromatic hydrocarbons in mesopelagic fishes from the Gulf of Mexico reveals exposure to oil-derived sources. Environmental Science & Technology. DOI: 10.1021/acs.est.8b02243
  • Quintana-Rizzo et al. 2015. Changes in δ13C and δ15N in deep-living fishes and shrimps after the Deepwater Horizon oil spill, Gulf of Mexico. Marine Pollution Bulletin, 94(1-2), 241–250,


The distribution, fate, and transport of hydrocarbons deposited in northern and southern regions of the Gulf of Mexico

Exclusion zone (Southern Gulf of Mexico)

The main objective of this study was to investigate the deposition of hydrocarbons from different sources (e.g., terrestrial, oil exploration) at a more regional scale in the Gulf of Mexico (GoM). Specifically, we focused on the spatial and temporal evolution of petroleum constituents deposited on sediments from the Deepwater Horizon spill (DWH) in 2010, and from the IXTOC-I oil spill in 1979. The IXTOC-I incident that took place over three decades ago provides an important historical analog for predicting future impacts to benthic ecosystems in the northern GoM.

Results indicate that ~19,000 metric tons of weathered DWH-derived hydrocarbons (>C9 saturated and aromatic fractions) were deposited in 56% of the studied area (194,000 km2) containing 21± 10% (up to 47%) of the total amount of oil discharged and not recovered from the DWH spill. Several impacts to the environment and its recovery have been identified, but changes in the productivity of stocks at the population level may take several to many years to recover, depending to the specific life histories of target animals. This study was supported by C-IMAGE II Consortium – Dr. Steve Murawski and Dr. Dave Hollander (PIs). 

Related Publications:

  • Romero et al. 2017. Large-scale deposition and redistribution of hydrocarbons following a deepwater oil spill. Environmental Pollution, 228: 179-189, doi:org/10.1016/j.envpol.2017.05.019
  • Murawski et al. 2016. How Did the Deepwater Horizon Oil Spill Affect Coastal and Continental Shelf Ecosystems? Oceanography 29 (3): 161-173, doi:org/10.5670/oceanog.2016.80


Sediment biota and toxic Polycyclic Aromatic Hydrocarbons interactions

Retrieved sediment core (Northern Gulf of Mexico)

Several collaborative studies with different biology fields showed the potential influence of polycyclic aromatic hydrocarbons (PAHs) on the abundance and diversity of ciliates, foraminifera, and bacteria under natural and experimental conditions. The results obtained in these studies explain the complexity of interactions between toxic compounds and biology, with some species having the potential to enhance the toxicity of crude oil, while others are affected by it, or not affected at all. Indicator studies of complex microbial/benthic communities are encouraged for specific biological groups avoiding generalizations on impact responses among taxa. Chemical analysis of PAHs was conducted at the Paleoceanographic Laboratory – University of South Florida.


Related Publications:

  • Schwing et al. 2017. Characterizing the variability of benthic foraminifera in the northeastern Gulf of Mexico following the Deepwater Horizon event (2010-2012). Environ. Sci. Pollut. Res, doi:org/10.1007/s11356-016-7996-z
  • Moss et al. 2016. Molecular characterization of benthic foraminifera communities from the Northeastern Gulf of Mexico shelf and slope following the Deepwater Horizon event. Deep-Sea Research Part I 115: 1-9., doi:org/10.1016/j.dsr.2016.04.010
  • Moss et al. 2016. Ciliate protists from the sediment-water interface in the Northeastern Gulf of Mexico. Deep-Sea Research Part I 106: 85-96., doi:org/10.1016/j.dsr.2015.10.001
  • Overholta et al. 2016. Hydrocarbon Degrading Bacteria Exhibit a Species Specific Response to Dispersed Oil while Moderating Ecotoxicity. Applied and Environmental Microbiology, DOI:10.1128/AEM.02379-15.


Sedimentary biogeochemical indicators of ecosystem change in the Northern Gulf of Mexico after 2010

Sediment sampling (multicore retrieving, R/V Weatherbird II)

The primary objective of this study was to investigate the impacts of the Deepwater Horizon (DWH) oil spill at the seafloor as recorded in bottom sediments of the DeSoto Canyon region in the northeastern Gulf of Mexico. Sediment cores were analyzed at high-resolution (at 2 mm and 5 mm intervals) to evaluate the concentration, composition, and input of hydrocarbons to the seafloor through a coupling of sedimentological, geochemical, and biological approaches.

Results showed that the upper ~1 cm depth sedimentary interval (corresponding to 2010-2011) is distinct with higher hydrocarbon concentrations and signatures compared to previous years.  This study demonstrates for the first time, the sink to the seafloor of oil-derived hydrocarbons from a submerged oil spill. Our findings underline the complexity of the depositional event observed in the aftermath of the DWH event regarding multiple sources, variable concentrations, and spatial (depth-related) variability. Also, we were able to test our sampling and geochemical approaches after a marine gas well blowout (Hercules 265), indicating the importance of ocean observing systems to coordinate rapid-response efforts to effectively assess environmental impacts resulting from accidental releases of oil contaminants. Analyses were conducted in Dr. Dave Hollander and Dr. Gregg Brook labs (PI’s), under C-IMAGE I and DEEP-C Consortia. 

Selected Publications:


The Importance of Molybdenum Speciation to Nitrogen Fixation and Assimilation in Lakes

Matt Tiahlo
Matt Tiahlo collecting water, Tahoe 2011

The objective of this study was to determine major nutrient controls on N2 fixation and NO3  uptake in three western U.S. lakes with varying trophic status (oligotrophic Lake Tahoe; mesotrophic Walker Lake; and eutrophic Clear Lake). We also studied nutrient controls on bacterial growth, phytoplankton biomass, and total CO2 fixation.

While previous studies have shown the important role of Fe and P in the N cycle of lakes, the dynamics of these nutrients cannot always explain observed rates of N2 fixation. Therefore, we also investigated trace metal co-limitation, including the potentially most bioavailable form of Mo, Mo(V). The results obtained in this study provide a new perspective on nutrient co-limitation in the N cycle of lakes. Analyses were conducted in Dr. Douglas Capone and Dr. Sergio Sanudo-Wilhelmy labs, PIs. 

Related PublicationRomero I.C., Klein N.J., Sañudo-Wilhelmy S.A., Capone D.G. 2013. Potential trace metal co-limitation controls on N2 fixation and NO-3 uptake in lakes with varying trophic status. Frontiers in Aquatic Microbiology, doi:10.3389/fmicb.2013.00054

Biomarker isotopic signals of ecological responses to environmental change in a Salt Marsh Ecosystem


Carpinteria Salt Marsh Reserve (University of California Natural Reserve System)

The main goal of this study was to characterize the lipid and isotopic composition of leaf waxes in living salt marsh plants, to better understand how hydrogen isotope signatures in plants are affected by biological and environmental factors (e.g., climate change). 

This study explained the importance of directly measuring plant water isotopic composition and highlights the role of transpiration in driving isotopic signals in subtropical ecosystems. Results from this study constrained the hydrogen isotopic composition of salt marsh organic matter, and further indicate the potential for plant leaf waxes to resolve paleoenvironmental change, including sea level change, in sediment cores from salt marshes. Analyses were conducted in Dr. Feakins lab (PI) and in the Laboratory of Stable Isotope Ecology of Tropical Ecosystems (L7) at the University of Miami.

Related Publication: Romero I. C. and Feakins S. J. 2011. Spatial gradients in plant leaf wax D/H cross a coastal salt marsh in Southern California. Organic Geochemistry 42: 618-629,


Biocomplexity of Mangroves under different Nutrient Conditions


Mangrove forest (Twin Cays, Belize)

Mangrove forests are among the most productive ecosystems playing a significant role in nutrient sequestration in coastal zones. The primary purpose of this study was to better understand the functional relationship among microorganisms, trees, and sediments. A combination of molecular, chemical and statistical techniques was used for the identification of key biological and environmental factors directly controlling the community structure of microorganisms in mangrove sediments subjected to a long-term fertilization experiment with nitrogen and phosphorus (Twin Cays, Belize).

Results indicated significant disturbance not only on ecological patterns and processes of bacteria and microbial functional groups but as well as on plant-microbial interactions. This research further explored the ecology of marine microorganisms over different temporal and spatial scales, a necessary step to better understand the link between microbial communities and sediment geochemistry in coastal environments under disturbance. Analyses were conducted in Dr. Capone, Dr. Marilyn Fogel, Dr. Susan Ziegler, and Dr. Jed Fuhrman labs.

Selected Publications:

  • Romero et al. 2015. Phylogenetic Diversity of Diazotrophs along an Experimental Nutrient Gradient in Mangrove Sediments. J. Mar. Sci. Eng. 2015, 3, 699-719; DOI:10.3390/jmse3030699.
  • Schaller et al. 2015. Variable nutrient stoichiometry (C:N:P) across trophic levels determines community and ecosystem properties in an oligotrophic mangrove system. Oecologia, doi:10.1007/s00442-015-3379-2.
  • Romero et al. 2011. Long-term nitrogen and phosphorus fertilization effects on N2 fixation rates and nifH gene community patterns in mangrove sediments. Marine Ecology: 1-11. doi:10.1111/j.1439-0485.2011.00465.x.
  • Fogel et al. 2008. Unusually negative nitrogen isotopic compositions (δ15N) of mangroves and lichens in an oligotrophic, microbially-influenced ecosystem. Biogeosciences 5: 1704-2008.