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Laminated travertine forms in and around an active hot spring on the west coast of Tamiahua Lagoon, north of the state of Veracruz, Mexico. Fluid chemistry is characterized by discharging slightly acidic pH hot water and gas at a constant flow rate. Moreover, finely interbedded mineralogical products from discharging waters at 70 °C host scattered hydrocarbons. The mineralogy and geochemistry of the travertine formations were characterized to determine their origin. Rock samples were collected and further studied by transmitted light petrography, X-ray diffraction, and EDS-coupled scanning electron microprobe. Identified mineralogy from outcrop samples includes aragonite, gypsum, anhydrite, and elemental sulfur as essential minerals, with calcite, celestine, barite, jarosite, opal, and fluorite as accessory minerals. Isotopic analyses for C and O were determined in carbonates, S isotope ratios on both elemental sulfur and sulfates, whereas measurements for trace elements and lanthanides were performed on carbonates. A suit of brines and condensates from gas samples was collected for H and O isotopic analyses and concentration determinations of the main ions and major and trace elements. Isotopic values of δ13C and δ18O of aragonite are in the range of +1.75‰ to +2.37‰ and −1.70‰ to −0.78‰, respectively. The δ34S isotopic values of native sulfur and sulfates ranged from −4.0‰ to +1.2‰. The isotopic values of δ2H (−5.50‰) and δ18O (+7.77‰) of hot water samples collected in terraces where aragonite precipitates suggest a mixture between meteoric water and the Gulf of Mexico oil-field related waters. It was concluded that the aragonitic formations near Tamiahua Lagoon are hypogenic and were generated by CO2 and H2S emanations of deep origin and by oxidation-reduction reactions that can be linked to surficial bacterial activity. [ABSTRACT FROM AUTHOR]

Oil spills threaten the structure and function of ecological communities. The Deepwater Horizon spill was predicted to have catastrophic consequences for nearshore fishes, but field studies indicate resilience in populations and communities. Previous research indicates many marsh fishes exhibit avoidance of oil contaminated areas, representing one potential mechanism for this resilience. Here, we test whether prior oil exposure of Gulf killifish Fundulus grandis alters this avoidance response. Using choice tests between unoiled and oiled sediments at one of three randomized concentrations (low: 0.1 L oil m-2, medium: 0.5 L oil m-2, or high: 3.0 L oil m-2), we found that, even at low prior exposure levels, killifish lose recognition of oiled sediments compared to control, unexposed fish. Preference for unoiled sediments was absent across all oil concentrations after oil exposure, and some evidence for preference of oiled sediments at high exposure was demonstrated. These results highlight the lack of response to toxic environments in exposed individuals, indicating altered behavior despite organism survival. Future research should document additional sublethal consequences that affect ecosystem and food web functioning. [ABSTRACT FROM AUTHOR]

The 2010 Deepwater Horizon disaster introduced an unprecedented discharge of oil into the deep Gulf of Mexico. Considerable uncertainty has persisted regarding the oil's fate and effects in the deep ocean. In this work we assess the compound-specific rates of biodegradation for 125 aliphatic, aromatic, and biomarker petroleum hydrocarbons that settled to the deep ocean floor following release from the damaged Macondo Well. Based on a dataset comprising measurements of up to 168 distinct hydrocarbon analytes in 2,980 sediment samples collected within 4 y of the spill, we develop a Macondo oil "fingerprint" and conservatively identify a subset of 312 surficial samples consistent with contamination by Macondo oil. Three trends emerge from analysis of the biodegradation rates of 125 individual hydrocarbons in these samples. First, molecular structure served to modulate biodegradation in a predictable fashion, with the simplest structures subject to fastest loss, indicating that biodegradation in the deep ocean progresses similarly to other environments. Second, for many alkanes and polycyclic aromatic hydrocarbons biodegradation occurred in two distinct phases, consistent with rapid loss while oil particles remained suspended followed by slow loss after deposition to the seafloor. Third, the extent of biodegradation for any given sample was influenced by the hydrocarbon content, leading to substantially greater hydrocarbon persistence among the more highly contaminated samples. In addition, under some conditions we find strong evidence for extensive degradation of numerous petroleum biomarkers, notably including the native internal standard 17α(H),21β(H)- hopane, commonly used to calculate the extent of oil weathering. [ABSTRACT FROM AUTHOR]

To investigate the long-term weathering of oil from the Deepwater Horizon (DWH) incident, oil-soaked sand patties were collected from Gulf of Mexico beaches from Florida to Alabama over a three-year period from 2012 to 2014. Analysis of oil residues by gas chromatography with flame ionization detection (GC-FID), thin-layer chromatography with flame ionization detection (TLC-FID), and Fourier transform infrared spectroscopy (FT-IR) indicated uniformity in their chemical composition. Some variability within and between samples was observed, arising from differences in exposure to light and water, which increase the amount of weathering. Oxygenated hydrocarbons (OxHC) produced by weathering processes dominate the majority of oil residues. These OxHC have continued recalcitrance in the environment, and increase in relative abundance over time. Analyses of the bulk characteristics of oil residues via TLC-FID and FT-IR should be continued as these techniques provide important insight into the weathering state of oil residues. [ABSTRACT FROM AUTHOR]

A literature review demonstrates that crude oil spills can affect phytoplankton, favoring the growth of some while inhibiting the growth of others. Subsequently, the phytoplankton assemblage can change as a result of exposure to crude oil. Studies of phytoplankton responses to the Macondo (Deepwater Horizon) oil spill indicate that the phytoplankton may have been stimulated by the oil spill, although the presence of low-salinity water in the region makes it difficult to discount the importance of riverine-borne nutrients as a factor. A few studies suggest that the oil spill was toxic to some phytoplankton species, whereas others indicate that the degree of tolerance to the oil or to dispersants differs among species. These results generally comply with findings of previous studies, but a lack of published field data analyses prevents further assessment of the impacts of the Deepwater Horizon oil spill on phytoplankton population dynamics in the northern Gulf of Mexico. [ABSTRACT FROM PUBLISHER]

Abstract: The fluorescence EEM technique, PARAFAC modeling, and hydrocarbon composition were used to characterize oil components and to examine the chemical evolution and degradation pathways of Macondo crude oil under controlled laboratory conditions. Three major fluorescent oil components were identified, with Ex/Em maxima at 226/328, 262/315, and 244/366nm, respectively. An average degradation half-life of ∼20d was determined for the oil components based on fluorescence EEM and hydrocarbon composition measurements, showing a dynamic chemical evolution and transformation of the oil during degradation. Dispersants appeared to change the chemical characteristics of oil, to shift the fluorescence EEM spectra, and to enhance the degradation of low-molecular-weight hydrocarbons. Photochemical degradation played a dominant role in the transformation of oil components, likely an effective degradation pathway of oil in the water column. Results from laboratory experiments should facilitate the interpretation of field-data and provide insights for understanding the fate and transport of oil components in the Gulf of Mexico. [Copyright &y& Elsevier]

High quality gas compositional data are an important factor in interpreting the genetic source of natural gas hosted in hydrate-bearing sediments and other subsurface systems. In order to accurately characterize the composition of gas samples degassed from hydrate-bearing pressure cores, one must use a reproducible sampling technique that minimizes artifacts of the sampling process. Herein, we review sediment core degassing techniques and compare data obtained from a commonly used degassing approach, which we term the standard quantitative degassing (SQD) technique, to our newly developed modified quantitative degassing (MQD) method designed to minimize atmospheric contamination and gas-water interactions. The SQD method allows sample gas to interact with water in a bubbling chamber, which we hypothesize could alter the gas composition following mixing with water or dissolved gases in the bubbling chamber. Whereas, the MQD method allows for the collection of sample gas prior to the bubbling chamber. To compare the SQD and MQD methods, we performed a side-by-side comparison of noble (He, Ne, Ar, Kr, and Xe), major (H 2 , N 2 , O 2 , and CO 2), and hydrocarbon (CH 4 , C 2 H 6 , C 3 H 8 , i-C 4 H 10 , C 4 H 10 , i-C 5 H 12 , C 5 H 12) gas concentrations and select isotopic compositions obtained using both sample collection techniques. Gas samples were collected from hydrate-bearing pressure cores recovered and maintained under hydrate stable conditions from the northern Gulf of Mexico during the UT-GOM2-1 Expedition. The MQD method displayed significantly lower concentrations of atmospheric gases, higher proportions of hydrocarbon gases, lower ratios of C 1 /C 2 +, and heavier stable carbon and hydrogen isotopes of methane than the SQD method. These results demonstrate that the MQD method reduced air contamination and minimized alteration of the hydrocarbon gases. Therefore, we conclude this method may be important for future work that seeks to determine the composition of natural gas from pressure cores using quantitative degassing experiments, especially those seeking to measure major (e.g., N 2) and noble gases. • Standard quantitative degassing (SQD) methods display atmospheric contamination. • SQD air contamination levels preclude noble gas analyses and alters other tracers. • A side-by-side investigation compared SQD and newly developed modified QD methods. • The MQD method showed less atmospheric contamination, enabling noble gas analyses. • The MQD method mitigated alteration of hydrocarbon molecular ratios. [ABSTRACT FROM AUTHOR]