Nelson Robert K.

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Nelson

First Name

Robert K.

ORCID

0000-0003-0534-5801

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Air-sea gas transfer : its dependence on wind stress, small-scale roughness, and surface films

(American Geophysical Union, 2004-08-21) Frew, Nelson M. ; Bock, Erik J. ; Schimpf, Uwe ; Hara, Tetsu ; Haußecker, Horst ; Edson, James B. ; McGillis, Wade R. ; Nelson, Robert K. ; McKenna, Sean P. ; Uz, B. Mete ; Jahne, B.

The influence of wind stress, small-scale waves, and surface films on air-sea gas exchange at low to moderate wind speeds (<10 m s−1) is examined. Coincident observations of wind stress, heat transfer velocity, surface wave slope, and surface film enrichments were made in coastal and offshore waters south of Cape Cod, New England, in July 1997 as part of the NSF-CoOP Coastal Air-Sea Chemical Fluxes study. Gas transfer velocities have been extrapolated from aqueous heat transfer velocities derived from infrared imagery and direct covariance and bulk heat flux estimates. Gas transfer velocity is found to follow a quadratic relationship with wind speed, which accounts for ~75–77% of the variance but which overpredicts transfer velocity in the presence of surface films. The dependence on wind stress as represented by the friction velocity is also nonlinear, reflecting a wave field-dependent transition between limiting transport regimes. In contrast, the dependence on mean square slope computed for the wave number range of 40–800 rad m−1 is found to be linear and in agreement with results from previous laboratory wind wave studies. The slope spectrum of the small-scale waves and the gas transfer velocity are attenuated in the presence of surface films. Observations over large-scale gradients of biological productivity and dissolved organic matter show that the reduction in slope and transfer velocity are more clearly correlated with surface film enrichments than with bulk organic matter concentrations. The mean square slope parameterization explains ~89–95% of the observed variance in the data and does not overpredict transfer velocities where films are present. While the specific relationships between gas transfer velocity and wind speed or mean square slope vary slightly with the choice of Schmidt number exponent used to scale the heat transfer velocities to gas transfer velocities, the correlation of heat or gas transfer velocity with mean square slope is consistently better than with wind speed.
Floating oil-covered debris from Deepwater Horizon : identification and application

(IOP Publishing, 2012-01-18) Carmichael, Catherine A. ; Arey, J. Samuel ; Graham, William M. ; Linn, Laura J. ; Lemkau, Karin L. ; Nelson, Robert K. ; Reddy, Christopher M.

The discovery of oiled and non-oiled honeycomb material in the Gulf of Mexico surface waters and along coastal beaches shortly after the explosion of Deepwater Horizon sparked debate about its origin and the oil covering it. We show that the unknown pieces of oiled and non-oiled honeycomb material collected in the Gulf of Mexico were pieces of the riser pipe buoyancy module of Deepwater Horizon. Biomarker ratios confirmed that the oil had originated from the Macondo oil well and had undergone significant weathering. Using the National Oceanic and Atmospheric Administration's records of the oil spill trajectory at the sea surface, we show that the honeycomb material preceded the front edge of the uncertainty of the oil slick trajectory by several kilometers. We conclude that the observation of debris fields deriving from damaged marine materials may be incorporated into emergency response efforts and forecasting of coastal impacts during future offshore oil spills, and ground truthing predicative models.
Reference material for radionuclides in sediment IAEA-384 (Fangataufa Lagoon sediment)

( 2006-07-11) Povinec, Pavel P. ; Pham, Mai Khanh ; Sanchez-Cabeza, J. A. ; Barci-Funel, G. ; Bojanowski, R. ; Boshkova, T. ; Burnett, William C. ; Carvalho, Fernando ; Chapeyron, B. ; Cunha, I. L. ; Dahlgaard, H. ; Galabov, N. ; Fifield, L. K. ; Gastaud, J. ; Geering, J. -J. ; Gomez, I. F. ; Green, N. ; Hamilton, T. ; Ibanez, F. L. ; Ibn Majah, M. ; John, M. ; Kanisch, G. ; Kenna, Timothy C. ; Kloster, M. ; Korun, M. ; Liong Wee Kwong, L. ; La Rosa, J. ; Lee, S.-H. ; Levy-Palomo, I. ; Malatova, M. ; Maruo, Y. ; Mitchell, P. ; Murciano, I. V. ; Nelson, Robert K. ; Nouredine, A. ; Oh, J.-S. ; Oregioni, B. ; Le Petit, G. ; Pettersson, H. B. L. ; Reineking, A. ; Smedley, P. A. ; Suckow, A. ; van der Struijs, T. D. B. ; Voors, P. I. ; Yoshimizu, K. ; Wyse, E.

A reference material designed for the determination of anthropogenic and natural radionuclides in sediment, IAEA-384 (Fangataufa Lagoon sediment), is described and the results of certification are presented. The material has been certified for 8 radionuclides (40K, 60Co, 155Eu, 230Th, 238U, 238Pu, 239+240Pu and 241Am). Information values are given for 12 radionuclides (90Sr, 137Cs, 210Pb (210Po), 226Ra, 228Ra, 232Th, 234U, 235U, 239Pu, 240Pu and 241Pu). Less reported radionuclides include 228Th, 236U, 239Np and 242Pu. The reference material may be used for quality management of radioanalytical laboratories engaged in the analysis of radionuclides in the environment, as well as for the development and validation of analytical methods and for training purposes. The material is available from IAEA in 100 g units.
Combining biomarker and bulk compositional gradient analysis to assess reservoir connectivity

( 2010-04-10) Pomerantz, Andrew E. ; Ventura, Gregory T. ; McKenna, Amy M. ; Canas, Jesus A. ; Auman, John ; Koerner, Kyle ; Curry, David ; Nelson, Robert K. ; Reddy, Christopher M. ; Rodgers, Ryan P. ; Marshall, Alan G. ; Peters, Kenneth E. ; Mullins, Oliver C.

Hydraulic connectivity of petroleum reservoirs represents one of the biggest uncertainties for both oil production and petroleum system studies. Here, a geochemical analysis involving bulk and detailed measures of crude oil composition is shown to constrain connectivity more tightly than is possible with conventional methods. Three crude oils collected from different depths in a single well exhibit large gradients in viscosity, density, and asphaltene content. Crude oil samples are collected with a wireline sampling tool providing samples from well‐defined locations and relatively free of contamination by drilling fluids; the known provenance of these samples minimizes uncertainties in the subsequent analysis. The detailed chemical composition of almost the entire crude oil is determined by use of comprehensive two‐dimensional gas chromatography (GC×GC) to interrogate the nonpolar fraction and negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT‐ICR MS) to interrogate the polar fraction. The simultaneous presence of 25‐ norhopanes and mildly altered normal and isoprenoid alkanes is detected, suggesting that the reservoir has experienced multiple charges and contains a mixture of oils biodegraded to different extents. The gradient in asphaltene concentration is explained by an equilibrium model considering only gravitational segregation of asphaltene nanoaggregates; this grading can be responsible for the observed variation in viscosity. Combining these analyses yields a consistent picture of a connected reservoir in which the observed viscosity variation originates from gravitational segregation of asphaltene nanoaggregates in a crude oil with high asphaltene concentration resulting from multiple charges, including one charge that suffered severe biodegradation. Observation of these gradients having appropriate magnitudes suggests good reservoir connectivity with greater confidence than is possible with traditional techniques alone.
MV Wakashio grounding incident in Mauritius 2020: the world’s first major spillage of very low sulfur fuel oil

(Elsevier, 2021-09-03) Scarlett, Alan G. ; Nelson, Robert K. ; Gagnon, Marthe Monique ; Holman, Alex I. ; Reddy, Christopher M. ; Sutton, Paul A. ; Grice, Kliti

Very Low Sulfur Fuel Oils (VSLFO, <0.5% S) are a new class of marine fuel oils, introduced to meet recent International Maritime Organization regulations. The MV Wakashio was reported to have released 1000 t of VLSFO when it grounded on a reef in Mauritius on 25th July 2020. A field sample of oily residue contaminating the Mauritian coast was collected on 16th August 2020 and compared with the Wakashio fuel oil. Both oils were analyzed for organic and elemental content, and stable isotope ratios δ13C and δ2H measured. Comprehensive two-dimensional gas chromatography with high-resolution mass spectrometry was used to identify and compare biomarkers resistant to weathering. The aromatic content in the VLSFO was relatively low suggesting that the potential for ecosystem harm arising from exposure to toxic components may be less than with traditional fuel oil spills. The Wakashio oil spill is, to our knowledge, the first documented spill involving VLSFO.
Molecular evidence of Late Archean archaea and the presence of a subsurface hydrothermal biosphere

( 2006-12-13) Ventura, Gregory T. ; Kenig, Fabien ; Reddy, Christopher M. ; Schieber, Juergen ; Frysinger, Glenn S. ; Nelson, Robert K. ; Dinel, Etienne ; Gaines, Richard B. ; Schaeffer, Philippe

Highly cracked and isomerized archaeal lipids and bacterial lipids, structurally changed by thermal stress, are present in solvent extracts of 2,707-2,685 million year old (Ma) metasedimentary rocks from Timmins, Ontario, Canada. These lipids appear in conventional gas chromatograms as unresolved complex mixtures (UCMs) and include cyclic and acyclic biphytanes, C36-C39 derivatives of the biphytanes, and C31-C35 extended hopanes. Biphytane and extended hopanes are also found in high pressure catalytic hydrogenation (HPCH) products released from solvent-extracted sediments,indicating that archaea and bacteria were present in Late Archean sedimentary environments. Post-depositional, hydrothermal gold mineralization and graphite precipitation occurred prior to metamorphism (~2,665 Ma). Late Archean metamorphism significantly reduced the kerogen’s adsorptive capacity and severely restricted sediment porosity, limiting the potential for post-Archean additions of organic matter to the samples. Argillites exposed to hydrothermal gold mineralization have disproportionately high concentrations of extractable archaeal and bacterial lipids relative to what is releasable from their respective HPCH product and what is observed for argillites deposited away from these hydrothermal settings. The addition of these lipids to the sediments likely results from a Late Archean subsurface hydrothermal biosphere of archaea and bacteria.
Fish fingerprinting: identifying crude oil pollutants using bicyclic sesquiterpanes (bicyclanes) in the tissues of exposed fish

(Wiley, 2022-09-27) Spilsbury, Francis D. ; Scarlett, Alan G. ; Rowland, Steven J. ; Nelson, Robert K. ; Spaak, Gemma ; Grice, Kliti ; Gagnon, Marthe Monique

In the present study, we investigated the possibility of identifying the source oils of exposed fish using ratios of bicyclic sesquiterpane (bicyclane) chemical biomarkers. In the event of an oil spill, identification of source oil(s) for assessment, or for litigation purposes, typically uses diagnostic ratios of chemical biomarkers to produce characteristic oil “fingerprints.” Although this has been applied in identifying oil residues in sediments, water, and sessile filtering organisms, so far as we are aware this has never been successfully demonstrated for oil‐exposed fish. In a 35‐day laboratory trial, juvenile Lates calcarifer (barramundi or Asian seabass) were exposed, via the diet (1% w/w), to either a heavy fuel oil or to Montara, an Australian medium crude oil. Two‐dimensional gas chromatography with high‐resolution mass spectrometry and gas chromatography–mass spectrometry were then used to measure selected ratios of the bicyclanes to examine whether the ratios were statistically reproducibly conserved in the fish tissues. Six diagnostic bicyclane ratios showed high correlation (r2 > 0.98) with those of each of the two source oils. A linear discriminatory analysis model showed that nine different petroleum products could be reproducibly discriminated using these bicyclane ratios. The model was then used to correctly identify the bicyclane profiles of each of the two exposure oils in the adipose tissue extracts of each of the 18 fish fed oil‐enriched diets. From our initial study, bicyclane biomarkers appear to show good potential for providing reliable forensic fingerprints of the sources of oil contamination of exposed fish. Further research is needed to investigate the minimum exposure times required for bicyclane bioaccumulation to achieve detectable concentrations in fish adipose tissues and to determine bicyclane depuration rates once exposure to oil has ceased. Environ Toxicol Chem 2023;42:7–18. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Production of two highly abundant 2-methyl-branched fatty acids by blooms of the globally significant marine cyanobacteria Trichodesmium erythraeum

(American Chemical Society, 2021-08-26) Gosselin, Kelsey M. ; Nelson, Robert K. ; Spivak, Amanda C. ; Sylva, Sean P. ; Van Mooy, Benjamin A. S. ; Aeppli, Christoph ; Sharpless, Charles M. ; O’Neil, Gregory W. ; Arrington, Eleanor C. ; Reddy, Christopher M. ; Valentine, David L.

The bloom-forming cyanobacteria Trichodesmium contribute up to 30% to the total fixed nitrogen in the global oceans and thereby drive substantial productivity. On an expedition in the Gulf of Mexico, we observed and sampled surface slicks, some of which included dense blooms of Trichodesmium erythraeum. These bloom samples contained abundant and atypical free fatty acids, identified here as 2-methyldecanoic acid and 2-methyldodecanoic acid. The high abundance and unusual branching pattern of these compounds suggest that they may play a specific role in this globally important organism.
Sterane and hopane biomarkers capture microbial transformations of complex hydrocarbons in young hydrothermal Guaymas Basin sediments

(Nature Research, 2022-10-28) Mara, Paraskevi ; Nelson, Robert K. ; Reddy, Christopher M. ; Teske, Andreas ; Edgcomb, Virginia P.

In Guaymas Basin, organic-rich hydrothermal sediments produce complex hydrocarbon mixtures including saturated, aromatic and alkylated aromatic compounds. We examined sediments from push cores from Guyamas sites with distinct temperature and geochemistry profiles to gain a better understanding on abiotic and biological hydrocarbon alteration. Here we provide evidence for biodegradation of hopanoids, producing saturated hydrocarbons like drimane and homodrimane as intermediate products. These sesquiterpene by-products are present throughout cooler sediments, but their relative abundance is drastically reduced within hotter hydrothermal sediments, likely due to hydrothermal mobilization. Within the sterane pool we detect a trend toward aromatization of steroidal compounds within hotter sediments. The changes in hopane and sterane biomarker composition at different sites reflect temperature-related differences in geochemical and microbial hydrocarbon alterations. In contrast to traditionally observed microbial biodegradation patterns that may extend over hundreds of meters in subsurface oil reservoirs, Guaymas Basin shows highly compressed changes in surficial sediments.
Simulating gas–liquid−water partitioning and fluid properties of petroleum under pressure : implications for deep-sea blowouts

(American Chemical Society, 2016-04-27) Gros, Jonas ; Reddy, Christopher M. ; Nelson, Robert K. ; Socolofsky, Scott ; Arey, J. Samuel

With the expansion of offshore petroleum extraction, validated models are needed to simulate the behaviors of petroleum compounds released in deep (>100 m) waters. We present a thermodynamic model of the densities, viscosities, and gas–liquid−water partitioning of petroleum mixtures with varying pressure, temperature, and composition based on the Peng–Robinson equation-of-state and the modified Henry’s law (Krychevsky−Kasarnovsky equation). The model is applied to Macondo reservoir fluid released during the Deepwater Horizon disaster, represented with 279–280 pseudocomponents, including 131–132 individual compounds. We define >n-C8 pseudocomponents based on comprehensive two-dimensional gas chromatography (GC × GC) measurements, which enable the modeling of aqueous partitioning for n-C8 to n-C26 fractions not quantified individually. Thermodynamic model predictions are tested against available laboratory data on petroleum liquid densities, gas/liquid volume fractions, and liquid viscosities. We find that the emitted petroleum mixture was ∼29–44% gas and ∼56–71% liquid, after cooling to local conditions near the broken Macondo riser stub (∼153 atm and 4.3 °C). High pressure conditions dramatically favor the aqueous dissolution of C1−C4 hydrocarbons and also influence the buoyancies of bubbles and droplets. Additionally, the simulated densities of emitted petroleum fluids affect previous estimates of the volumetric flow rate of dead oil from the emission source.
Interpreting comprehensive two-dimensional gas chromatography using peak topography maps with application to petroleum forensics

(BioMed Central, 2016-11-28) Ghasemi Damavandi, Hamidreza ; Sen Gupta, Ananya ; Nelson, Robert K. ; Reddy, Christopher M.

Comprehensive two-dimensional gas chromatography (GC×GC) provides high-resolution separations across hundreds of compounds in a complex mixture, thus unlocking unprecedented information for intricate quantitative interpretation. We exploit this compound diversity across the (GC×GC) topography to provide quantitative compound-cognizant interpretation beyond target compound analysis with petroleum forensics as a practical application. We focus on the (GC×GC) topography of biomarker hydrocarbons, hopanes and steranes, as they are generally recalcitrant to weathering. We introduce peak topography maps (PTM) and topography partitioning techniques that consider a notably broader and more diverse range of target and non-target biomarker compounds compared to traditional approaches that consider approximately 20 biomarker ratios. Specifically, we consider a range of 33–154 target and non-target biomarkers with highest-to-lowest peak ratio within an injection ranging from 4.86 to 19.6 (precise numbers depend on biomarker diversity of individual injections). We also provide a robust quantitative measure for directly determining “match” between samples, without necessitating training data sets. We validate our methods across 34 (GC×GC) injections from a diverse portfolio of petroleum sources, and provide quantitative comparison of performance against established statistical methods such as principal components analysis (PCA). Our data set includes a wide range of samples collected following the 2010 Deepwater Horizon disaster that released approximately 160 million gallons of crude oil from the Macondo well (MW). Samples that were clearly collected following this disaster exhibit statistically significant match (99.23±1.66)% using PTM-based interpretation against other closely related sources. PTM-based interpretation also provides higher differentiation between closely correlated but distinct sources than obtained using PCA-based statistical comparisons. In addition to results based on this experimental field data, we also provide extentive perturbation analysis of the PTM method over numerical simulations that introduce random variability of peak locations over the (GC×GC) biomarker ROI image of the MW pre-spill sample (sample #1 in Additional file 4: Table S1). We compare the robustness of the cross-PTM score against peak location variability in both dimensions and compare the results against PCA analysis over the same set of simulated images. Detailed description of the simulation experiment and discussion of results are provided in Additional file 1: Section S8. We provide a peak-cognizant informational framework for quantitative interpretation of (GC×GC) topography. Proposed topographic analysis enables (GC×GC) forensic interpretation across target petroleum biomarkers, while including the nuances of lesser-known non-target biomarkers clustered around the target peaks. This allows potential discovery of hitherto unknown connections between target and non-target biomarkers.
Accessing monomers, surfactants, and the queen bee substance by acrylate cross-metathesis of long-chain alkenones

( 2017-05) O’Neil, Gregory W. ; Williams, John R. ; Craig, Alexander M. ; Nelson, Robert K. ; Gosselin, Kelsey M. ; Reddy, Christopher M.

Polyunsaturated long-chain alkenones are a unique class of lipids biosynthesized in significant quantities (up to 20% of cell carbon) by several algae including the industrially grown marine microalgae Isochrysis. Alkenone structures are characterized by a long linear carbon-chain (35-40 carbons) with one to four trans-double bonds and terminating in a methyl or ethyl ketone. Alkenones were extracted and isolated from commercially obtained Isochrysis biomass and then subjected to cross-metathesis (CM) with methyl acrylate or acrylic acid using the Hoveyda-Grubbs metathesis initiator. Within 1 h at room temperature alkenones were consumed, however complete fragmentation (i.e. conversion to the smallest subunits by double bond cleavage) required up to 16 h. Analysis of the reaction mixture by gas chromatography and comprehensive two-dimensional gas chromatography revealed a predictable product mixture consisting primarily of long-chain (mostly C17) acids (or methyl esters from CM with methyl acrylate) and diacids (or diesters), along with smaller amounts (~5%) of the honey bee “queen substance” (E)-9-oxo-decenoic acid. Together, these compounds comprise a diverse mixture of valuable chemicals that includes surfactants, monomers, and an agriculturally relevant bee pheromone.
Hydroxyapatite catalyzed hydrothermal liquefaction transforms food waste from an environmental liability to renewable fuel

(Cell Press, 2022-09-16) LeClerc, Heather O. ; Tompsett, Geoffrey A. ; Paulsen, Alex D. ; McKenna, Amy M. ; Niles, Sydney F. ; Reddy, Christopher M. ; Nelson, Robert K. ; Cheng, Feng ; Teixeira, Andrew R. ; Timko, Michael T.

Food waste is an abundant and inexpensive resource for the production of renewable fuels. Biocrude yields obtained from hydrothermal liquefaction (HTL) of food waste can be boosted using hydroxyapatite (HAP) as an inexpensive and abundant catalyst. Combining HAP with an inexpensive homogeneous base increased biocrude yield from 14 ± 1 to 37 ± 3%, resulting in the recovery of 49 ± 2% of the energy contained in the food waste feed. Detailed product analysis revealed the importance of fatty-acid oligomerization during biocrude formation, highlighting the role of acid-base catalysts in promoting condensation reactions. Economic and environmental analysis found that the new technology has the potential to reduce US greenhouse gas emissions by 2.6% while producing renewable diesel with a minimum fuel selling price of $1.06/GGE. HAP can play a role in transforming food waste from a liability to a renewable fuel.
Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean sediments by comprehensive two-dimensional gas chromatography (GC×GC)

( 2008-03) Ventura, Gregory T. ; Kenig, Fabien ; Reddy, Christopher M. ; Frysinger, Glenn S. ; Nelson, Robert K. ; Van Mooy, Benjamin A. S. ; Gaines, Richard B.

Hydrocarbon mixtures too complex to resolve by traditional capillary gas chromatrography display gas chromatograms with dramatically rising baselines or “humps” of coeluting compounds that are termed unresolved complex mixtures (UCMs). Because the constituents of UCMs are not ordinarily identified, a large amount of geochemical information is never explored. Gas chromatograms of saturated/unsaturated hydrocarbons extracted from Late Archean argillites and greywackes of the southern Abitibi Province of Ontario, Canada contain UCMs with different appearances or “topologies” relating to the intensity and retention time of the compounds comprising the UCMs. These topologies appear to have some level of stratigraphic organization, such that samples collected at any stratigraphic formation collectively are dominated by UCMs that either elute early- (within a window of C15-C20 of n-alkanes), early- to mid- (C15-C30 of n-alkanes), or have a broad UCM that extends through the entire retention time of the sample (from C15-C42 of n-alkanes). Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-MS) was used to resolve the constituents forming these various UCMs. Early- to mid- eluting UCMs are dominated by configurational isomers of alkyl-substituted and non substituted polycyclic compounds that contain up to six rings. Late eluting UCMs are composed of C36-C40 mono-, bi-, and tricyclic archaeal isoprenoid diastereomers. Broad UCMs spanning the retention time of compound elution contain nearly the same compounds observed in the early-, mid-, and late retention time UCMs. Although the origin of the polycyclic compounds is unclear, the variations in the UCM topology appear to depend on the concentration of initial compound classes that have the potential to become isomerized. Isomerization of these constituents may have resulted from hydrothermal alteration of organic matter.
Ocean Dumping of Containerized DDT Waste Was a Sloppy Process

(American Chemical Society, 2019-03-04) Kivenson, Veronika ; Lemkau, Karin L. ; Pizarro, Oscar ; Yoerger, Dana R. ; Kaiser, Carl ; Nelson, Robert K. ; Carmichael, Catherine A. ; Paul, Blair G. ; Reddy, Christopher M. ; Valentine, David L.

Industrial-scale dumping of organic waste to the deep ocean was once common practice, leaving a legacy of chemical pollution for which a paucity of information exists. Using a nested approach with autonomous and remotely operated underwater vehicles, a dumpsite offshore California was surveyed and sampled. Discarded waste containers littered the site and structured the suboxic benthic environment. Dichlorodiphenyltrichloroethane (DDT) was reportedly dumped in the area, and sediment analysis revealed substantial variability in concentrations of p,p-DDT and its analogs, with a peak concentration of 257 μg g–1, ∼40 times greater than the highest level of surface sediment contamination at the nearby DDT Superfund site. The occurrence of a conspicuous hydrocarbon mixture suggests that multiple petroleum distillates, potentially used in DDT manufacture, contributed to the waste stream. Application of a two end-member mixing model with DDTs and polychlorinated biphenyls enabled source differentiation between shelf discharge versus containerized waste. Ocean dumping was found to be the major source of DDT to more than 3000 km2 of the region’s deep seafloor. These results reveal that ocean dumping of containerized DDT waste was inherently sloppy, with the contents readily breaching containment and leading to regional scale contamination of the deep benthos.
Climatically driven emissions of hydrocarbons from marine sediments during deglaciation

( 2006-07-31) Hill, T. M. ; Kennett, J. P. ; Valentine, David L. ; Yang, Z. ; Reddy, Christopher M. ; Nelson, Robert K. ; Behl, R. J. ; Robert, C. ; Beaufort, L.

Marine hydrocarbon seepage emits oil and gas, including methane (~30 Tg CH4/year), to the ocean and atmosphere. Sediments from the California margin contain preserved tar, primarily formed via hydrocarbon weathering at the sea surface. We present a record of variation in the abundance of tar in sediments for the past 32ky, providing evidence for increases in hydrocarbon emissions prior to and during Termination IA (16-14 ka) and again over Termination IB (11-10 ka). Our study provides the first direct evidence for increased hydrocarbon seepage associated with deglacial warming via tar abundance in marine sediments, independent of previous geochemical proxies. Climate-sensitive gas hydrates may modulate thermogenic hydrocarbon seepage during deglaciation.
Integrating comprehensive two-dimensional gas chromatography and downhole fluid analysis to validate a spill-fill sequence of reservoirs with variations of biodegradation, water washing and thermal maturity

( 2016-09) Forsythe, Jerimiah C. ; Martin, Robin ; De Santo, Ilaria ; Tyndall, Richard ; Arman, Kate ; Pye, Jonathan ; De Nicolais, Nelly ; Nelson, Robert K. ; Pomerantz, Andrew E. ; Kenyon-Roberts, Stephen ; Zuo, Julian Y. ; Betancourt, Soraya S. ; Reddy, Christopher M. ; Peters, Kenneth E. ; Mullins, Oliver C.

Optimization of crude oil production depends heavily on crude oil composition and its variation within individual reservoirs and across multiple reservoirs. In particular, asphaltene content has an enormous impact on crude oil viscosity and even the economic value of the fluids in the reservoir. Thus, it is highly desirable to understand the primary controls on crude oil composition and asphaltene distributions in reservoirs. Here, a complex oilfield in the North Sea containing six separate reservoirs is addressed. The crude oil is believed to have spilled out of deeper reservoirs into shallower reservoirs during the overall reservoir charging process. Asphaltene content is measured in-situ through downhole fluid analysis and is generally consistent with a spill-fill sequence in reservoir charging. Detailed compositional analysis of crude oil samples by comprehensive two-dimensional gas chromatography (GC×GC) is used to determine the extent and variation among the reservoirs of water washing, biodegradation and thermal maturity. Increased biodegradation and water washing in the shallower reservoirs is consistent with a spill-fill sequence. The water washing is evidently assisted by biodegradation. Moreover, analyses of four thermal maturity biomarkers show that shallower reservoirs contain less mature oil, again consistent with a spill-fill sequence. The combination of DFA for bulk compositional analysis and GC×GC for detailed compositional analysis with geochemical interpretation is an effective tool for unraveling complex oilfield scenarios.
Elevated levels of diesel range organic compounds in groundwater near Marcellus gas operations are derived from surface activities

( 2015-08) Drollette, Brian D. ; Hoelzer, Kathrin ; Warner, Nathaniel R. ; Darrah, Thomas H. ; Karatum, Osman ; O’Connor, Megan P. ; Nelson, Robert K. ; Fernandez, Loretta A. ; Reddy, Christopher M. ; Vengosh, Avner ; Jackson, Robert B. ; Elsner, Martin ; Plata, Desiree L.

Hundreds of organic chemicals are utilized during natural gas extraction via high volume hydraulic fracturing (HVHF). However, it is unclear if these chemicals, injected into deep shale horizons, reach shallow groundwater aquifers and impact local water quality, either from deep underground injection sites or from the surface or shallow subsurface. Here, we report detectable levels of organic compounds in shallow groundwater samples from private residential wells overlying the Marcellus Shale in northeastern Pennsylvania. Analyses of purgeable and extractable organic compounds from 64 groundwater samples revealed trace levels of volatile organic compounds, well below the Environmental Protection Agency’s maximum contaminant levels, and low levels of both gasoline range (GRO; 0-8 ppb) and diesel range organic compounds (DRO; 0-157 ppb). A compound-specific analysis revealed the presence of bis(2-ethylhexyl)phthalate, which is a disclosed HVHF additive, that was notably absent in a representative geogenic water sample and field blanks. Pairing these analyses with 1) inorganic chemical fingerprinting of deep saline groundwater, 2) characteristic noble gas isotopes, and 3) spatial relationships between active shale gas extraction wells and wells with disclosed environmental health and safety (EHS) violations, we differentiate between a chemical signature associated with naturally occurring saline groundwater and a one associated with alternative anthropogenic routes from the surface (e.g., accidental spills or leaks). The data support a transport mechanism of DRO to groundwater via accidental release of fracturing fluid chemicals derived from the surface rather than subsurface flow of these fluids from the underlying shale formation.
Characterizations and comparison of low sulfur fuel oils compliant with 2020 global sulfur cap regulation for international shipping

(Elsevier, 2022-06-01) Nelson, Robert K. ; Scarlett, Alan G. ; Gagnon, Marthe Monique ; Holman, Alex I. ; Reddy, Christopher M. ; Sutton, Paul A. ; Grice, Kliti

The International Marine Organization 2020 Global Sulfur Cap requires ships to burn fuels with <0.50% S and some countries require <0.10% S in certain Sulfur Emission Control Areas but little is known about these new types of fuels. Using both traditional GC–MS and more advanced chromatographic and mass spectrometry techniques, plus stable isotopic, δ13C and δ2H, analyses of pristane, phytane and n-alkanes, the organic components of a suite of three 0.50% S and three 0.10% S compliant fuels were characterized. Two oils were found to be near identical but all of the remaining oils could be forensically distinguished by comparison of their molecular biomarkers and by the profiles of the heterocyclic parent and alkylated homologues. Oils could also be differentiated by their δ13C and δ2H of n-alkanes and isoprenoids. This study provides important forensic data that may prove invaluable in the event of future oil spills.
Fire and oil led to complex mixtures of PAHs on burnt and unburnt plastic during the M/V X‑Press Pearl Disaster.

(American Chemical Society, 2023-07-12) James, Bryan D. ; Reddy, Christopher M. ; Hahn, Mark E. ; Nelson, Robert K. ; de Vos, Asha ; Aluwihare, Lihini I. ; Wade, Terry L. ; Knap, Anthony H. ; Bera, Gopal

In May 2021, the M/V X-Press Pearl container ship burned for 2 weeks, leading to the largest maritime spill of resin pellets (nurdles). The disaster was exacerbated by the leakage of other cargo and the ship’s underway fuel. This disaster affords the unique opportunity to study a time-stamped, geolocated release of plastic under real-world conditions. Field samples collected from beaches in Sri Lanka nearest to the ship comprised nurdles exposed to heat and combustion, burnt plastic pieces (pyroplastic), and oil-plastic agglomerates (petroplastic). An unresolved question is whether the 1600+ tons of spilled and recovered plastic should be considered hazardous waste. Due to the known formation and toxicity of combustion-derived polycyclic aromatic hydrocarbons (PAHs), we measured 20 parent and 21 alkylated PAHs associated with several types of spilled plastic. The maximum PAH content of the sampled pyroplastic had the greatest amount of PAHs recorded for marine plastic debris (199,000 ng/g). In contrast, the sampled unburnt white nurdles had two orders of magnitude less PAH content. The PAH composition varied between the types of spilled plastic and presented features typical of and conflicting with petrogenic and pyrogenic sources. Nevertheless, specific markers and compositional changes for burning plastics were identified, revealing that the fire was the main source of PAHs. Eight months after the spill, the PAH contents of sampled stray nurdles and pyroplastic were reduced by more than 50%. Due to their PAH content exceeding levels allowable for plastic consumer goods, classifying burnt plastic as hazardous waste may be warranted. Following a largely successful cleanup, we recommend that the Sri Lankans re-evaluate the identification, handling, and disposal of the plastic debris collected from beaches and the potential exposure of responders and the public to PAHs from handling it. The maritime disaster underscores pyroplastic as a type of plastic pollution that has yet to be fully explored, despite the pervasiveness of intentional and unintentional burning of plastic globally.

Nelson Robert K.

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