G.J. Denoux

Sediment contaminants in Casco Bay, Maine. Inventories, sources, and potential for biological impact

An inventory-based approach to environmental assessment that determines concentrations of sedimentary contaminants, defines their origins, and assesses the potential for biological impact is illustrated in Casco Bay, ME. The most widespread contaminants in Casco Bay are petroleum and petroleum byproducts. The highest concentrations of contaminants are associated with population centers, effluent outfalls, and spills. The majority of PAH in sediments are the product of high-temperature combustion processes. PAH concentrations at sites in close proximity to Portland exceed values believed to produce toxic responses in marine benthic organisms. In contrast, PCB, DDTs, and chlordane concentrations in the sediments are below concentrations thought to produce toxic effects in marine organisms. Metal concentrations in sediments are also below those that elicit biological responses. The geographic distribution of contaminants is initially controlled by the proximity to sources, and the regional differences in concentrations are the result of sediment accumulation patterns. Detrital (terrestrial), autochthonous marine, pyrogenic, and petroleum sources for PAH, alkanes, and trace metals are defined. 21 refs., 10 figs., 6 tabs.

Leakage of deep, reservoired petroleum to the near surface on the gulf of Mexico Continental slope

Reservoired oils, shallow sediment cores (2m), sea slicks and tar balls were collected in the Green Canyon Lease area of the northern Gulf of Mexico continental slope. The gaseous and liquid hydrocarbons associated with near surface sediments and water have migrated from deep (2000–3000 m) subsurface reservoirs and/or source rocks. This conclusion is based on molecular (GC/FID, GC/FPD, GC/MS) and carbon isotopic evidence. Visual observations at two locations on the continental slope confirm the presence of massive amounts of active liquid as well as gas seepage. Hydrate gas recovered in sediment cores originates from deep, oil-associated gas. This gas has migrated to shallow sediments with little or no isotopic fractionation. In contrast, near surface hydrocarbon liquids (shallow bitumens and sea slicks) are depleted in aliphatics, 4-ring or larger aromatics, naphthalene, C1-naphthalenes and C2-naphthalenes as compared to the reservoired fluids. These near-surface fluids are extensively altered by the concurrent processes of migration, dissolution and microbial degradation. However, the distributions of highly alkylated (> C2) naphthalenes, phenanthrenes and dibenzothiophenes, triterpanes, steranes and triaromatized steranes are similar to the precursor reservoired oil. This study documents, for the first time, a direct link between natural seepage in a deep water marine setting and sea slick and tar ball formation. This and other studies suggest that the natural seepage of oil and gas can be a significant process in the deep ocean.

Hydrocarbon contamination on the Antarctic Peninsula: I. Arthur harbor—Subtidal sediments☆

Abstract Near-field contamination in Arthur Harbor can be traced to spills, ship and boating activities, and run-off. Soil samples from Palmer Station and Old Palmer Station contain hydrocarbons derived from diesel fuel, lubrication oil, and hydraulic fluid. The majority of contamination in subtidal sediments around Palmer Station is due to diesel fuel spills. Subtidal sediments below an abandoned open incineration site also contain combustion-derived polynuclear aromatic hydrocarbons (PAH). Soils collected at Old Palmer Station were also contaminated with diesel fuel residues and combustion-derived PAH. High concentrations of these contaminants were detected in nearby subtidal sediments. Small amounts of diesel fuel contamination are detectable throughout Arthur Harbor. Despite being abandoned for years, soils in the vicinity of Old Palmer Station and Base N represent the most concentrated source of contaminants in Arthur Harbor. Environmentally sound practices at Palmer Station have helped to minimize localized contamination.

Stable isotope partitioning in seep and vent organisms: chemical and ecological significance

Abstract Several hundred stable isotopic ratios (C, N and S) acquired over seven years of investigations at both seep and vent locations are compiled and interpreted. The stable isotopic compositions of tissues derived from the chemosynthetic fixation of carbon reflect a complex interaction between chemical and biological processes. The stable isotopic composition of bivalves that utilize reduced sulfur suggests that seawater-and/or vent water-dissolved inorganic carbon (DIC) is their primary source of carbon during chemosynthesis. All thiotrophic bivalves studied appear to possess a similar sulfide oxidation metabolism. The δ13C-values of tissues from methanotrophic mussels are close to the δ13C of the methane utilized. Apparently, little of the kinetic isotope fractionation associated with methanotrophy is expressed in the hosts tissue. Vestimentiferan carbon isotopic composition reflects both carbon limitation and the isotopic composition of the substrate utilized. The δ13C-values of vent vestimentiferans tend to be affected by carbon limitation, whereas those of seep vestimentiferans reflect the variable isotopic composition of pore-water DIC. Stable nitrogen isotopic compositions are consistent with nitrogen (N2) fixation, but the presence of the enzyme responsible for nitrogen fixation, nitrogenase, has not been conclusively demonstrated. A variety of nitrogen sources [N2, NH4+, PON (particulate organic nitrogen), DON (dissolved organic nitrogen) and NO4−] may be utilized by vent and seep organisms. However, the δ15N data suggest that the mechanism of nitrogen metabolism is not a function of the species or the symbiont type. Sulfur is a key element in vent and seep environments and thiotrophy is the major chemosynthetic activity. The sources of sulfur are highly variable in quantity and isotopic composition but are almost always linked to bacterial activity,l either free-living and/or symbiont. Nitrogen and sulfur nutritional requirements appear to be derived from a wide variety of sources. The relative importance of nutrition derived from heterotrophy and chemoautotrophy depends on the chemical environment and animal physiology. Stable isotope compositions provide insight into these diverse metabolic strategies; however, a complete inventory of the concentration and isotopic composition of inorganic and organic substrates, as well as supporting biochemical, enzymatic and observational studies, are needed to resolve fundamental ecological questions.

Gulf of Mexico hydrocarbon seep communities—I. Regional distribution of hydrocarbon seepage and associated fauna

Abstract A series of otter trawls demonstrate that communities based on chemosynthesis are broadly distributed across the northwestern Gulf of Mexico continental slope in hydrocarbon seep areas. Thirty-nine trawls were taken at 33 locations reported to exhibit transparent or chaotic seismic “wipe-out” zones. The sites, in water depths from 180 to 900 m, span an area from offshore the Mississippi River delta to the upper Texas continental slope. Endosymbiont-containing organisms or their remains (either tube worms, mussels and/or clams) were recovered at 21 sites on the northern Gulf of Mexico slope. Tube worms, clams and mussels known to be associated with symbionts were retreived at 18, 12 and 5 sites, respectively. Carbon isotope analysis of selected animal tissues confirmed the chemosynthetic association. Animals containing isotopically light chemosynthetic carbon were collected at 21 sites. Piston cores at each site were used to determine the presence of mature hydrocarbons. Nine of 30 piston cores were visibly oil-stained. Trawl collections at locations where visibly oil-stained cores were recovered contained at least one species of chemosynthetic-associated organism and generally represented the most abundant catches of endosymbiont-containing animals. The chemical environment (oil and gas seepage) necessary to support chemosynthetic-based ecosystems is widespread on the northern Gulf of Mexico continental slope.

Polynuclear aromatic hydrocarbons (PAH) as indicators of the source and maturity of marine crude oils

Whole oil GC-MS was used to characterize selected polynuclear aromatic hydrocarbons (PAH) in a suite of marine crude oils derived from source rocks deposited under different conditions. The selected PAH consist primarily of 2- and 3-ring aromatic hydrocarbons, including naphthalenes (to C 4 ), fluorenes (to C 3 ), phenanthrenes (to C 4 ) and dibenzothiophenes (to C 3 ), as well as several 4- and 5-ring compounds. Concentrations of the selected PAH range from 2294 to 129,170 ppm and typically comprise between 1% and 20% of the total C 12+ aromatic fraction. PAH compositions in all source types are dominated by naphthalenes. These compounds comprise between 41.9% and 88.9% of the total PAH measured. The greatest difference between oils lies in the relative abundance of dibenzothiophenes. Their abundance rivals that of naphthalenes in the carbonate oils (up to 41.7% of total PAH) but is exceedingly low in the paralic oils ( < 2.1% of total PAH). These differences, which reflect differences in clastic content, Eh-pH, and availability of reduced sulfur in the source rock depositional environment, are captured in the ratio DBT/P, calculated as the sum of all dibenzothiophenes relative to phenanthrenes. DBT/P is greater than 1.0 in most carbonate-sourced oils but ranges between 0.08 and 0.18 in the paralic-sourced oils. Siliciclastic-sourced oils are intermediate, with values ranging from 0.14 to 0.87 (average 0.40). All oils show a predominance of alkylated PAH homologues over the unsubstituted parent, however, the maximum degree of alkylation (the most abundant alkylated homologues within any given PAH series) varies. Carbonate-sourced oils show a high degree of alkylation, often maximizing at C 3 or C 4 , while paralic-sourced oils generally exhibit a lower degree of alkylation in which the C 1 or C 2 isomers predominate. Siliciclastic-sourced oils are intermediate. with alkylation maximizing between the C 2 and C3 isomers. We propose that these alkylation trends reflect differences in the PAH precursor moieties in source kerogens and/or variations in the thermal history of the source types, i.e., milder thermal history for the carbonate oils relative to paralic and siliciclastic oils.

The origins of petroleum in the northern Gulf of Mexico

Abstract The distribution and chemistry of oils in the northern Gulf of Mexico and the adjacent onshore can be explained by multiple sources, fades variations, maturation, and post-generation alteration. Genetic families include Jurassic Smackover, Flexure Trend, Upper Cretaceous, and Paleogene oils. Smackover oils have high sulfur contents, pristane/phytane ratios C 35 C 34 hopane ratios ≥1.0, and C 30 C 29 hopane ratios usuall ≤ 1.0. Flexure Trend oils are similar and contain abundant extended hopanes, high sulfur contents, and V (Ni + V) > 0.5 ; these oils are inferred to be sourced in Upper Jurassic/Lower Cretaceous strata. Upper Cretaceous oils contain a distinctive suite of tricyclic and nonhopanoid triterpanes; oleanane is low or absent. Paleogene oils can be recognized by the presence of 18α(H) oleanane and a lack of extended hopanes. These oils occur from south Texas to southern and offshore Louisiana. Two subfamilies can be recognized based on the relative abundance of triterpanes and steranes. These oils have a presumed Paleogene source. Mixing of oil types is quite prevalent at the geographic boundaries of oil types. The initial control on the distribution of oil and gas in the northern Gulf of Mexico is provided by the areal extent of source rocks. Secondary control is due to Cenozoic deposition, which provides the thermal stress to generate, as well as destroy, oil. Salt tectonics provide conduits for migrating fluids to escape the zone of thermal destruction. Mesozoic source strata again become important in the deep Gulf of Mexico, where Cenozoic sediments thin.

Temporal and spatial patterns of anthropogenic disturbance at McMurdo Station, Antarctica

Human visitations to Antarctica have increased in recent decades, raising concerns about preserving the continents environmental quality. To understand the spatial and temporal patterns of anthropogenic disturbances at the largest scientific station in Antarctica, McMurdo Station, a long-term monitoring program has been implemented. Results from the first nine years (1999?2007) of monitoring are reported. Most physical disturbance of land surfaces occurred prior to 1970 during initial establishment of the station. Hydrocarbons from fuel and anthropogenic metals occur in patches of tens to hundreds of square meters in areas of fuel usage and storage. Most soil contaminant concentrations are not expected to elicit biological responses. Past disposal practices have contaminated marine sediments with polychlorinated biphenyls (PCBs), petroleum hydrocarbons, and metals in close proximity to the station that often exceed concentrations expected to elicit biological responses. Chemical contamination and organic enrichment reduced marine benthic ecological integrity within a few hundred meters offshore of the station. Contaminants were detected in marine benthic organisms confirming bioavailability and uptake. PCBs in sediments are similar to suspected source materials, indicating minimal microbial degradation decades after release. Anthropogenic disturbance of the marine environment is likely to persist for decades. A number of monitoring design elements, indicators and methodologies used in temperate climates were effective and provide guidance for monitoring programs elsewhere in Antarctica.

Hydrocarbon contamination on the Antarctic Peninsula: II. Arthur harbor—Inter- and subtidal limpets (Nacella concinna)

Abstract Accidental and operational releases of hydrocarbons during activities in support of scientific bases in the Antarctic can contaminate organisms in close proximity to these locations. Intertidal and subtidal limpets in Arthur Harbor were found to contain elevated levels of polynuclear aromatic hydrocarbons near Plamer and Old Palmer Stations. Contamination was highest in the intertidal and decreased with increasing water depth in the subtidal. The highest concentrations of tissue contamination were found in intertidal areas associated with high levels of onshore soil contamination. Limpets (Nacella concinna) preferentially incorporated the more water soluble aromatic compounds suggesting exposure to dissolved contaminants in run-off rather than particulates or slicks. This was in contrast to subtidal sediments that were primarily contaminated with freshly spilled diesel fuel. While contamination was present near stations, the concentrations observed are 1–2 orders of magnitude lower than the initial contamination caused by the Bahia Paraiso diesel fuel spill in 1989.

Applications of total scanning fluorescence to exploration geochemistry

A total scanning fluorescence technique is described for correlation (oil/oil and oil/source rock) and surface geochemical prospecting studies. The fluorescence system acquires a total fluorescence spectrum of emission, excitation and intensity for wavelengths between 200 and 800 nm using a computer controlled UV-Spectrofluorometer (Perkin-Elmer 650-40). The resulting matrix of intensity values, obtained at specific emission/excitation wavelengths, can be viewed in a three-dimensional or contour presentation. Similarity indices are calculated to compare spectra for correlation studies. The method can also be used as a regional evaluation tool for surface geochemical prospecting. Shallow surficial (>2 meters) sediments collected over oil, condensate, and gas provinces exhibit distinct fluorescence signatures.