Thomas J. Boyd

We compare sediment vertical methane flux off the Mahia Peninsula, on the Hikurangi Margin, east of New Zealand’s North Island, with a combination of geochemical, multichannel seismic and sub-bottom profiler data. Stable carbon isotope data provided an overview of methane contributions to shallow sediment carbon pools. Methane varied considerably in concentration and vertical flux across stations in close proximities. At two Mahia transects, methane profiles correlated well with integrated seismic and TOPAS data for predicting vertical methane migration rates from deep to shallow sediment. However, at our “control site”, where no seismic blanking or indications of vertical gas migration were observed, geochemical data were similar to the two Mahia transect lines. This apparent mismatch between seismic and geochemistry data suggests a potential to underestimate gas hydrate volumes based on standard seismic data interpretations. To accurately assess global gas hydrate deposits, multiple approaches for initial assessment, e.g., seismic data interpretation, heatflow profiling and controlled-source electromagnetics, should be compared to geochemical sediment and porewater profiles. A more thorough data matrix will provide better accuracy in gas hydrate volume for modeling climate change and potential available energy content.

In September 2009, a series of sediment cores were collected across the Alaskan Beaufort Sea shelf-slope. Sediment and porewater organic carbon (OC) concentrations and stable carbon isotope ratios (δ¹³C) were measured to investigate spatial variations in sediment organic matter (OM) sources and distribution of these materials across the shelf. Cores were collected along three main nearshore (shelf) to offshore (slope) sampling lines (transects) from east-to-west along the North Slope of Alaska: Hammerhead (near Camden Bay), Thetis Island (near Prudhoe Bay), and Cape Halkett (towards Point Barrow). Measured sediment organic carbon (TOC) and porewater dissolved organic carbon (DOC) concentrations and their respective δ¹³C values were used to investigate the relative contribution of different OM sources to sediment OC pool cycled at each location. Sources of OM considered included: water column-sourced phytodetritus, deep sediment methane (CH₄), and terrestrial, tundra/river-sourced OM. Results of these measurements, when coupled with results from previous research and additional analyses of sediment and porewater composition, show a pattern of spatial variation in sediment OC concentrations, OM source contributions, and OM cycled along the Alaskan Beaufort Sea shelf. In general, measured sediment total organic carbon (TOC) concentrations, δ¹³C_TOC values, porewater DOC concentrations, and δ¹³C_DOC values are consistent with an east-to-west transport of modern Holocene sediments with higher OC concentrations primarily sourced from relatively labile terrestrial, tundra OM sources and phytodetritus along the Alaskan Beaufort shelf. Sediment transport along the shelf results in the medium-to-long term accumulation and burial of sediment OM focused to the west which in turn results in higher biogenic CH₄ production rates and higher upward CH₄ diffusion through the sediments resulting in CH₄⁻AMO-sourced contribution to sediment OC westward along the shelf. Understanding current OM sources and distributions along the Alaskan Beaufort shelf is important for enhancing models of carbon cycling in Arctic coastal shelf systems. This will help support the prediction of the climate response of the Arctic created in the face of future warming scenarios.

Measuring Carbon-based Contaminant Mineralization Using Combined Co2 Flux And Radiocarbon Analyses. JoVE publishes peer-reviewed scientific video protocols to accelerate biological, medical, chemical and physical research. Watch our scientific video articles. JoVE is the world-leading producer and provider of science videos with the mission to improve scientific research, scientific journals, and education. Millions of scientists, educators and students at thousands of universities, colleges, hospitals and biopharmaceutical companies worldwide use JoVE for their research, teaching and learning.

Chlorinated hydrocarbon turnover (mineralization) estimated by CO₂ radiocarbon content and respiration rate coupled to ZOI models.

The Naval Research Laboratory contributed to an international research expedition to determine the association of methane (CH4) hydrate dissociation with pockmark formation on the Chatham Rise (New Zealand) during previous climate cycles. Piston coring and multi-coring was conducted at four locations with different seismic, multibeam, and physical profiles. Prior to SO226, seismic and multibeam data were obtained by the University of Auckland and IFM-Geomar which helped to identify broad study areas. Seismic and multibeam data collected on Leg 1 (SO226-1) helped to identify specific coring locations. These target areas were determined based on the seafloor morphology and seismic data interpretation of shallow sediments. More specifically, coring locations were selected where seismic profiles suggested high vertical CH4 fluxes to the shallow sediment and at sites that were predicted to have low or nonexistent vertical CH4 fluxes. Sediment cores were also collected in the same locations for paleogeochemical analyses which will be completed by Helen Neil at National Institute of Water and Atmospheric Research, Ltd. (NIWA) in Wellington, NZ. The final assessment of these sediments will require integration of geophysical, geological, and geochemical data.

Dissolved CO₂ radiocarbon and stable carbon isotope ratios were measured in groundwater from a fuel contaminated site at the North Island Naval Air Station in San Diego, CA (USA). A background groundwater sampling well and 16 wells in the underground fuel contamination zone were evaluated. For each sample, a two end-member isotopic mixing model was used to determine the fraction of CO₂ derived from fossil fuel. The CO₂ fraction from fossil sources ranged from 8 to 93% at the fuel contaminated site, while stable carbon isotope values ranged from −14 to +5‰_VPDB. Wells associated with highest historical and contemporary fuel contamination showed the highest fraction of CO₂ derived from petroleum (fossil) sources. Stable carbon isotope ratios indicated sub-regions on-site with recycled CO₂ (δ¹³CO₂ as high as +5‰_VPDB) – most likely resulting from methanogenesis. Ancillary measurements (pH and cations) were used to determine that no fossil CaCO₃, for instance limestone, biased the analytical conclusions. Radiocarbon analysis is verified as a viable and definitive technique for confirming fossil hydrocarbon conversion to CO₂ (complete oxidation) at hydrocarbon-contaminated groundwater sites. The technique should also be very useful for assessing the efficacy of engineered remediation efforts and by using CO₂ production rates, contaminant mass conversion over time and per unit volume.

Ultrafiltered and low molecular weight dissolved organic matter (UDOM and LMW‐DOM, respectively) fluorescence was studied under simulated estuarine mixing using samples collected from Delaware, Chesapeake, and San Francisco Bays (USA) transects. UDOM was concentrated by tangential flow ultrafiltration (TFF) from the marine (>33 PSU), mid‐estuarine (∼16 PSU), and freshwater (<1 PSU) members. TFF permeates (<1 kDa) from the three members were used to create artificial salinity transects ranging from ∼0 to ∼36, with 4 PSU increments. UDOM from the end‐ or mid‐members was added in equal amounts to each salinity‐mix. Three‐dimensional fluorescence excitation‐emission matrix (EEMs) spectra were generated for each end‐member permeate and UDOM through the full estuarine mixing transect. Fluorescence components such as proteinaceous, terrigenous, and marine derived humic peaks, and certain fluorescent ratios were noticeably altered by simulated estuarine mixing, suggesting that LMW DOM and UDOM undergo physicochemical alteration as they move to or from the freshwater, mid‐estuarine, or coastal ocean members. LMW fluorescence components fit a decreasing linear mixing model from mid salinities to the ocean end‐member, but were more highly fluorescent than mixing alone would predict in lower salinities (<8). Significant shifts were also seen in UDOM peak emission wavelengths with blue‐shifting toward the ocean end‐member. Humic‐type components in UDOM generally showed lower fluorescent intensities at low salinities, higher at mid‐salinities, and lower again toward the ocean end‐member. T (believed to be proteinaceous) and N (labile organic matter) peaks behaved similarly to each other, but not to B peak fluorescence, which showed virtually no variation in permeate or UDOM mixes with salinity. PCA and PARAFAC models showed similar results suggesting trends could be modeled for DOM end‐ and mid‐member sources. Changes in fluorescence properties due to estuarine mixing may be important when using CDOM as a proxy for DOM cycling in coastal systems.

Compound Specific Isotope Analysis (CSIA) has been shown to be a useful tool for assessing biodegradation, volatilization, and hydrocarbon degradation. One major advantage of this technique is that it does not rely on determining absolute or relative abundances of individual components of a hydrocarbon mixture which may change considerably during weathering processes. However, attempts to use isotopic values for linking sources to spilled or otherwise unknown hydrocarbons have been hampered by the lack of a robust and rigorous statistical method for testing the hypothesis that two samples are or are not the same. Univariate tests are prone to Type I and Type II error, and current means of correcting error make hypothesis testing of CSIA source-apportionment data problematic. Multivariate statistical tests are more appropriate for use in CSIA data. However, many multivariate statistical tests require high numbers of replicate measurements. Due to the high precision of IRMS instruments and the high cost of CSIA analysis, it is impractical, and often unnecessary, to perform many replicate analyses. In this paper, a method is presented whereby triplicate CSIA information can be projected in a simplified data-space, enabling multivariate analysis of variance (MANOVA) and highly precise testing of hypotheses between unknowns and putative sources. The method relies on performing pairwise principal components analysis (PCA), then performing a MANOVA upon the principal component variables (for instance, three, using triplicate analyses) which capture most of the variability in the original data set. A probability value is obtained allowing the investigator to state whether there is a statistical difference between two individual samples. A protocol is also presented whereby results of the coupled pairwise PCA−MANOVA analysis are used to down-select putative sources for other analysis of variance methods (i.e., PCA on a subset of the original data) and hierarchical clustering to look for relationships among samples which are not significantly different. A Monte Carlo simulation of a 10 variable data set; tanks used to store, distribute, and offload fuels from Navy vessels; and a series of spilled oil samples and local tug boats from Norfolk, VA (U.S.A.) were subjected to CSIA and the statistical analyses described in this manuscript, and the results are presented. The analysis techniques described herein combined with traditional forensic analyses provide a collection of tools suitable for source-apportionment of hydrocarbons and any organic compound amenable to GC-combustion-IRMS.

The IRMS Data Processing software package is designed to allow easy stable isotope data entry and multivariate data analysis. When comparing two of more hydrocarbon samples using compound-specific isotope ratio mass spectrometry, an analyst obtains multiple data variables for each sample. Multivariate statistics allows rigorous comparison(s) to determine if the samples are in fact different and if so, how closely related they are. This software uses three main types of data analyses: Multiple Analysis of Variance (MAN0VA), Principal Components Analysis (PCA), and Cluster Analysis. The layout is a standard Windows interface which should be usable to anyone familiar with modem operating system software.

The program for International Collaboration on CO{sub 2} Ocean Sequestration was initiated December 1997. Preliminary steps involved surveying a suite of biogeochemical parameters off the coast of Kona on the Big Island of Hawaii. The preliminary survey was conducted twice, in 1999 and 2000, to obtain a thorough data set including measurements of pH, current profiles, CO{sub 2} concentrations, microbial activities, and water and sediment chemistries. These data were collected in order to interpret a planned CO{sub 2} injection experiment. After these preliminary surveys were completed, local environment regulation forced moving the project to the coast north east of Bergen, Norway. The preliminary survey along the Norwegian Coast was conducted during 2002. However, Norwegian government revoked a permit, approved by the Norwegian State Pollution Control Authority, for policy reasons regarding the CO{sub 2} injection experiment. As a result the research team decided to monitor the natural CO{sub 2} flow off the southern coast of the Big Island. From December 3rd-13th 2002 scientists from four countries representing the Technical Committee of the International Carbon Dioxide Sequestration Experiment examined the hydrothermal venting at Loihi Seamount (Hawaiian Islands, USA). Work focused on tracing the venting gases, the impacts of the vent fluids onmore » marine organisms, and CO{sub 2} influence on biogeochemical cycles. The cruise on the R/V Ka'imikai-O-Kanaloa (KOK) included 8 dives by the PISCES V submarine, 6 at Loihi and 2 at a nearby site in the lee of the Big Island. Data for this final report is from the last 2 dives on Loihi. « less