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Calcium carbonate hexahydrate (ikaite) is a rare mineral that forms as metastable species in the organic-carbon-rich sediments of the King George Basin, Bransfield Strait, Antarctica, as a consequence of early diagenetic decomposition of organic matter under cold water (−1.4 °C) and high pressure (200 bar) conditions. Large crystals grow in the sediment immediately below the diagenetic transition between microbial sulfate reduction and methanogenesis at ~320 cm below sea floor (bsf). This process is reflected in the dissolved sulfate, total carbon dioxide, and methane concentrations, as well as in the carbon, hydrogen, and oxygen isotope chemistries of the interstitial fluids and dissolved gases of the host sediment. The ikaite crystal faithfully records in its zonal structure the changing carbon isotope ratio of the total dissolved carbon dioxide pool as it gradually diminishes during methanogenesis (δ13Cikaite = −17.5 to −21.4‰). These changes in the crystal’s host environment follow general Rayleigh carbon isotope fractionation. The oxygen isotopes of the ikaite carbonate (δ18Oikaite = 1.46 to 4.45‰) also show a strong zonal distribution, unrelated to temperature of formation, but perhaps controlled by the degree of recrystallization of ikaite to calcite. The crystal water of the ikaite is depleted 11‰ in 2H/1H (VSMOW) relative to the coexisting interstitial water, which is in excellent agreement with the isotope fractionation of other hydrated minerals. In addition to the in situ temperature and pressure, nucleation of the ikaite crystals in the Bransfield Basin sediments may be induced by the high alkalinity, high phosphate concentrations, and dissolved organic compounds. Intense microbial metabolism generates such compounds; of these, aspartic acid and glutamic acid may play an important role, as they do in biological and extracellular carbonate mineral precipitation. All indications are that low temperatures (such as of polar environments), high calcium carbonate supersaturation caused by interstitial methanogenesis, and a sufficiently large supply of dissolved phosphate and amino acids favor metastable ikaite formation. These conditions, modified by recrystallization, may be preserved in calcite glendonites, thinolites, and other calcitic pseudomorphs derived from ikaite and found throughout the ancient sedimentary record.

Methane (CH4), often in substantial quantities, is reported for numerous surface manifestations (seeps, springs) and aquifers in continental serpentinized ultramafic rocks, in ophiolites, peridotite massifs and intrusions. Frequently, this gas is considered to have a dominant abiotic origin, with variable, though generally minor, components of biotic gas (thermogenic or microbial). Abiotic CH4 production through low temperature Fischer-Tropsch Type reactions (FTT) between a carbon (C) compound and H2 is endorsed by most of scholars, but direct derivation from olivine hydration (serpentinization), magmatic sources and fluid inclusions have also been suggested. Here, we review the application of FTT in geology, discussing the appropriateness of several C compounds (CO2, CO, formic acid, formate or elemental C) as CH4 precursors and of aqueous versus gas phase reactions. We examine published gas geochemical and flux data that provide clear constraints on the methane origins. In the analysis we add new isotopic and gas seepage data acquired in surface gas manifestations at Acquasanta, in the Voltri ophiolite (Genova, Italy). Multiple lines of evidence including (a) stable isotope compositions of CH4, CO2 and helium, (b) radiocarbon-free CH4, (c) isotopic disequilibrium between CH4 and H2O, (d) low temperatures of CH4 production based on clumped isotopes and heat flow data, and (e) methane seepage forms and intensities, suggest that CH4 is not formed directly in water or from magmatic sources or fluid inclusions. Rather, all the lines of evidence taken together are compatible with the hypothesis of low temperature (

The Quest Carbon Capture and Storage (CCS) project in Alberta, Canada, is a fully integrated project, as it involves the capture, transport, injection, storage of CO2, and a measurement, monitoring and verification (MMV) program. The MMV program has two key objectives: a) to ensure containment and b) to ensure conformance. Prior to the start of CO2 injection at the end of August 2015, a number of projects were undertaken to gather data from various domains, namely the atmosphere, biosphere, hydrosphere and geosphere, to provide input to the Quest MMV program. The focus of this paper is on monitoring activities undertaken in relation to the atmosphere and biosphere domains. Activities undertaken across the Quest sequestration lease area (SLA) included an eddy covariance system, soil gas probes, soil flux chambers, and walk-over surveys. In conclusion, understanding the spatial and temporal variability of CO2 levels prior to start of CO2 injection represents an important activity of a CCS MMV program. It provides technical input to the development of such a program, but also provides knowledge for communication to and awareness of project stakeholders (e.g. landowners) regarding CO2 levels within the atmosphere and biosphere across a SLA.

This paper investigates the molecular and stable isotope compositions of sediment gases from seven coastal lakes along the southern Baltic coast in Poland. The aim is to extend the knowledge of the genesis and distribution of microbial gases in the zone of mixing of fresh and salt waters with special attention to the effect of salinity, climate-related seasonality, and vertical sediment mixing. We found differences in the compositions of gas between the studied lakes and within each lake. These differences are mainly controlled by lake water depth and the presence of macrophytes. Due to the dissolution of rising bubbles in highly oxygenated water, the concentrations of CH4 and CO2 show up to 67% decline along the water column in favor of N2 and O2. On the other hand, in vegetated parts of the lakes, the CH4 is depleted in favor of CO2, and the residual CH4 and CO2 are enriched in 13C. Despite the fact that the coastal lakes display highly oxidizing conditions in the water column and that the bottom sediments are mixed by wind waves the CH4 reveals rather low oxidation. On the basis of the CH4/N2 ratio we established that there are differences in the intensity of ebullition throughout the lakes. Higher intensities of ebullition were found in shallower parts of the lakes. Salinity has no effect on the stable C and H isotope composition of sediment gas. It seems, however, that salinity affects the molecular composition of hydrocarbons via preferential oxidation of CH4 under higher salinity conditions.

Tracing the flow of nutrients from aquaculture operations to the surrounding biota is important for environmental monitoring and developing integrated aquaculture practices. A novel approach in this context, compound specific stable isotope analysis (CSIA) was used to trace fatty acid (FA) carbon in benthic invertebrates from multiple aquaculture sites in the Broughton Archipelago, British Columbia, Canada, up to 2500 m away from each site. We found that the carbon isotope ratios (δ13C) of certain FA in mussels and limpets were gradually 13C-enriched with increasing distance away from the site, suggesting that the farm contributed to more depleted isotopic signatures among organisms within the vicinity of the site. In mussels, the δ13C of 16:2n-4, 16:3n-4, 20:1n-9, 22:6n-3, saturated FA, the bacterial FA marker, and the overall weighted mean of FA became significantly more 13C-enriched with increasing distance from the farm (r2 > 0.28, p < 0.05). In limpets, the δ13C of 17:0, 18:4n-3, 20:4n-3 and the zooplankton FA marker became more enriched with distance away from the farm (r2 > 0.37, p < 0.05). The δ13C of mussels was also influenced by location of the farm, regardless of distance from the site. Non-indigenous isotopic signatures, as a result of feed inputs, physical properties of the farm location, and other anthropogenic influences, likely contributed to the depleted signature of mussels and limpets within the vicinity of the farm. This study was the first to use CSIA to determine the uptake and movement of organic nutrients from aquaculture outputs to the surrounding ecosystem.

Abiotic methane in serpentinized peridotites (MSP) has implications for energy resource exploration, planetary geology, subsurface microbiology and astrobiology. Once considered a rare occurrence on Earth, reports of MSP are increasing for numerous localities worldwide in low temperature, land-based springs and seeps. We report the discovery of six methane-rich water springs and two ponds with active gas bubbling in the Ronda peridotite massif, in southern Spain. Water is hyperalkaline with typical hydrochemical features of active serpentinization (pH: 10.7 to 11.7, T: 17.1 to 21.5 °C, Ca–OH facies). Dissolved CH4 concentrations range from 0.1 to 3.2 mg/L. The methane stable C and H isotope ratios in the natural spring and bubbling sites (δ13CCH4: −12.3 to −37‰ VPDB; δ2HCH4: −280 to −333‰ VSMOW) indicate a predominant abiotic origin. In contrast, springs with manmade water systems, i.e., pipes or fountains, appear to have mixed biotic-abiotic origin (δ13CCH4: −44 to −69‰; δ2HCH4: −180 to −319‰). Radiocarbon (14C) analyses show that methane C in a natural spring is older than ca. 50,000 y BP, whereas dissolved inorganic carbon (DIC) analysed in all springs has an apparent 14C age ranging from modern to 2334 y BP. Therefore most, if not all, of the CH4 is allochthonous, i.e., not generated from the carbon in the hyperalkaline water. Methane is also released as bubbles in natural ponds and as diffuse seepages (∼101–102 mg CH4 m−2d−1) from the ground up to several tens of metres from the seeps and springs, albeit with no overt visual evidence. These data suggest that the gas follows independent migration pathways, potentially along faults or fracture systems, physically isolated from the hyperalkaline springs. Methane does not seem to be genetically related to the hyperalkaline water, which may only act as a carrier of the gas. Gas-bearing springs, vents and invisible microseepage in land-based peridotites are more common than previously thought. In addition to other geological sources, MSP is potentially a natural source of methane for the troposphere and requires more worldwide flux measurements.

Ponds and lakes are widespread across the rapidly changing permafrost environments. Aquatic systems play an important role in global biogeochemical cycles, especially in greenhouse gas (GHG) exchanges between terrestrial systems and the atmosphere. The source, speciation and emission rate of carbon released from permafrost landscapes are strongly influenced by local conditions, hindering pan-Arctic generalizations. This study reports on GHG ages and emission rates from aquatic systems located on Bylot Island, in the continuous permafrost zone of the Eastern Canadian Arctic. Dissolved and ebullition gas samples were collected during the summer season from different types of water bodies located in a highly dynamic periglacial valley: polygonal ponds, collapsed ice-wedge trough ponds, and larger lakes. The results showed strikingly different ages and fluxes depending on aquatic system types. Polygonal ponds were net sinks of dissolved CO2, but variable sources of dissolved CH4. They presented the highest ebullition fluxes, 1 or 2 orders of magnitude higher than from other ponds and lakes. Trough ponds appeared as substantial GHG sources, especially when their edges were actively eroding. Both types of ponds produced modern to hundreds of years old (< 550 yr BP) GHG, even if trough ponds could contain much older carbon (> 2000 yr BP) derived from freshly eroded peat. Lakes had small dissolved and ebullition fluxes, however they released much older GHG, including millennium-old CH4 (up to 3500 yr BP) from lake central areas. Acetoclastic methanogenesis dominated at all study sites and there was minimal, if any, methane oxidation in gas emitted through ebullition. These findings provide new insights on GHG emissions by permafrost aquatic systems and their potential positive feedback effect on climate.

The stable carbon isotope ratios of coalbed methane (CBM) demonstrate diagnostic changes that systematically vary with production and desorption times. These shifts can provide decisive, predictive information on the behaviour and potential performance of CBM operations. Samples from producing CBM wells show a general depletion in 13C-methane with increasing production times and corresponding shifts in δ13C-CH4 up to 35.8‰. Samples from canister desorption experiments show mostly enrichment in 13C for methane with increasing desorption time and isotope shifts of up to 43.4‰. Also, 13C-depletion was observed in some samples with isotope shifts of up to 32.1‰. Overall, the magnitudes of the observed isotope shifts vary considerably between different sample sets, but also within samples from the same source. The δ13C-CH4 values do not have the anticipated signature of methane generated from coal. This indicates that secondary processes, including desorption and diffusion, can influence the values. It is also challenging to deconvolute these various secondary processes because their molecular and isotope effects can have similar directions and/or magnitudes. In some instances, significant alteration of CBM gases has to be considered as a combination of secondary alteration effects.

Two-dimensional petroleum systems models (PSMs) are calculated for a cross-section through Hecate Strait in order to estimate the timing of hydrocarbon generation, expulsion and migration in the Queen Charlotte Basin, offshore BC, Canada. Our PSMs account for dominant kerogen types in the potential source rocks, and predict timing of generation, expulsion, and migration patterns of petroleum. The PSMs highlight the importance of fault zones for migration and potential loss of petroleum through the seafloor. Rich marine Jurassic source rocks (Ghost Creek Formation, Sandilands Formation) are assumed to underlie Hecate Strait. We predict these source rocks to be overmature with more than 80% kerogen transformation into oil and gas (>27 kg petroleum/t rock), even if significant heating was only restricted to Tertiary rifting. Our PSMs predict that most of the petroleum has been expelled from the source beds, with some potential seepage loss to the surface. Cretaceous source rocks are thicker and more extensive with less structural deformation on Haida Gwaii. They have variable, but generally low total organic carbon (TOC) content. If time equivalent sediments exist under Hecate Strait, they are likely to be terrestrial, Type III kerogen. Basin-wide, these source rocks are not considered to be highly productive, and only where they are buried >4.1 km (an area of approximately 2700 km2) do we calculate a transformation ratio >50%. Only a minor amount of Cretaceous derived petroleum is anticipated to have migrated and accumulated in the overlying Skonun Formation sediments, which comprise the most extensive and suitable reservoir facies. No significant accumulations of hydrocarbon are expected from the terrestrial, Mio-Pliocene Skonun Formation source rocks. The area of the basin, where the anticipated transformation ratio exceeds 50% is less than approximately 1400 km2.

Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) were measured in sediments and benthic invertebrates near submarine municipal outfalls in Victoria and Vancouver, B.C., Canada, two areas with contrasting receiving environments. PBDE concentrations in wastewater exceeded those of the legacy PCBs by eight times at Vancouver and 35 times at Victoria. Total PBDE concentrations in benthic invertebrates were higher near Vancouver than Victoria, despite lower concentrations in sediments, and correlated with organic carbon-normalized concentrations in sediment. Principal Components Analysis indicated uptake of individual PBDE congeners was determined by sediment properties (organic carbon, grain size), while PCB congener uptake was governed by physico-chemical properties (octanol-water partitioning coefficient). Results suggest the utility of sediment quality guidelines for PBDEs and likely PCBs benefit if based on organic carbon-normalized concentrations. Also, where enhanced wastewater treatment increases the PBDEs to particulate organic carbon ratio in effluent, nearfield benthic invertebrates may face increased PBDE accumulation.

The abrupt warming across the Younger Dryas termination (~11 600 yr before present) was marked by a large increase in the global atmospheric methane mixing ratio. The debate over sources responsible for the rise in methane centers on the roles of global wetlands, marine gas hydrates, and thermokarst lakes. We present a new, higher-precision methane stable carbon isotope ratio (δ13CH4) dataset from ice sampled at Påkitsoq, Greenland that shows distinct 13C-enrichment associated with this rise. We investigate the validity of this finding in face of known anomalous methane concentrations that occur at Påkitsoq. Comparison with previously published datasets to determine the robustness of our results indicates a similar trend in ice from both an Antarctic ice core and previously published Påkitsoq data measured using four different extraction and analytical techniques. The δ13CH4 trend suggests that 13C-enriched CH4 sources played an important role in the concentration increase. In a first attempt at quantifying the various contributions from our data, we apply a methane triple mass balance of stable carbon and hydrogen isotope ratios and radiocarbon. The mass balance results suggest biomass burning (42–66% of total methane flux increase) and thermokarst lakes (27–59%) as the dominant contributing sources. Given the high uncertainty and low temporal resolution of the 14CH4 dataset used in the triple mass balance, we also performed a mass balance test using just δ13C and δD. These results further support biomass burning as a dominant source, but do not allow distinguishing of thermokarst lake contributions from boreal wetlands, aerobic plant methane, or termites. Our results in both mass balance tests do not suggest as large a role for tropical wetlands or marine gas hydrates as commonly proposed.

Tisbe furcata, Nitokra lacustris, Calanus finmarchicus and Calanus glacialis were reared for several months in the laboratory prior to feeding selected diets. Copepods were fed Isochrysis galbana, Tetraselmis sp., Dunaliella tertiolecta, Thalassiosira pseudonana, Rhodomonas sp., Rhodomonas lens and Oxyrrhis marina individually or in combination. Oxyrrhis marina itself was fed up to four of the algae species. The lipid class and fatty acid composition of the copepods was determined and compared with each other, the diets and with wild C. finmarchicus, C. glacialis and Pseudocalanus sp. Cultured O. marina, T. furcata and N. lacustris had greater proportions of essential 22:6v3 or 20:5v3 acids than in their diets suggesting nutritional enrichment through synthesis or preferential retention. Lower proportions of 18:3v3 than in their diets fed individually or in combination suggests desaturation and elongation of 18:3v3. Stable isotope analysis of the heterotroph samples and their dietary sources revealed similar values for 18:3v3 in each dietary pair and different ones for 22:6v3 and 20:5v3 supporting derivation from precursors rather than trophic magnification. Principal components analysis of copepods and their diets showed cultured Calanus spp. to have the most similar fatty acid composition to their diet indicating little modification or sequestration of polyunsaturated fatty acids.

Measurement of the concentration and stable isotope ratios of methane from air enclosures in ancient ice can aid in understanding the temporal dynamics of methane sources and sinks. These measurements can reconstruct past atmospheric compositions on scales of tens-to-hundreds of years with adequate precision and accuracy. We present an improved micro-extraction gas-chromatography continuous-flow isotope ratio mass spectrometer (CF-IRMS) method to extract and measure the methane C-13/C-12 ratio (delta(CH4)-C-13) of air occluded in glacial ice. The technique described uses a unique post-combustion trapping of the methane signal to produce a high amplitude sample peak increasing the signal to noise ratio of the sample. The technique requires only ca. 165 pmol of CH4 (ca. 30-150 g of ice depending on methane concentration). The small sample requirement permits very fine temporal sampling resolution and the possibility of routine duplicate measurements from multi-parameter ice core samples. The technique was applied to atmospheric air, artificial ice samples, and samples from the GISP2 ice core. The precision of our technique was evaluated using both atmospheric air and artificial ice samples and is less than +/- 0.3% (1 sigma). Our test measurements of shallow, poorer quality GISP2 ice from 225 +/- 20 yr BP give a delta(CF4)-C-13 value of -47.37 +/- 0.6%. (corrected for gravitational fractionation and referenced to VPDB), which is in excellent agreement with other published data. (C) 2011 Elsevier B.V. All rights reserved.

Methane concentration [CH4] and stable isotope ratio values (δ13C) characterize methanogenic and methanotrophic processes within two contrasting peatland ecosystems of the Fluxnet Canada Research Network: (i) a western Canada peatland fen in northern Alberta (Fen) and (ii) an eastern Canada peatland bog in southeastern Ontario (Bog). We use carbon isotope ratio discrimination of produced methane (δ13CCH4) from the precursor carbon compounds (δ13CpreC) to estimate the relative proportions of archaebacterial acetoclastic methanogenesis (AM) and hydrogenotrophic carbonate reduction methanogenesis (HM) in these terrestrial ecosystems. The [CH4] and δ13CCH4 signatures describe contrasts in the methanogenic and methanotrophic processes between the Fen and the Bog. The differences are substantiated by stable hydrogen isotope ratio (δD) separation between the dissolved δDCH4 and co-existing δDH2O. Methanogenesis at the Fen is dominated by AM, in contrast to the Bog, which is essentially HM. We suggest that this is potentially a result of differences in type/quality of organic substrates. The trajectory of 13C enrichment in δ13CCH4 values with depth at the Bog reflects a closed system, substrate depletion effect. Our Rayleigh distillation model estimates 58–76% depletion in the source dissolved inorganic carbon (DIC).

The oceanographic and tectonic conditions of accretionary margins are well-suited for several potential processes governing methane generation, storage and release. To identify the relevant methane evolution pathways in the northern Cascadia accretionary margin, a four-site transect was drilled during Integrated Ocean Drilling Program Expedition 311. The δ13C values of methane range from a minimum value of − 82.2‰ on an uplifted ridge of accreted sediment near the deformation front (Site U1326, 1829 mbsl, meters below sea level) to a maximum value of − 39.5‰ at the most landward location within an area of steep canyons near the shelf edge (Site U1329, 946 mbsl). An interpretation based solely on methane isotope values might conclude the 13C-enrichment of methane indicates a transition from microbially- to thermogenically-sourced methane. However, the co-existing CO2 exhibits a similar trend of 13C-enrichment along the transect with values ranging from − 22.5‰ to +25.7‰. The magnitude of the carbon isotope separation between methane and CO2 (ec = 63.8 ± 5.8) is consistent with isotope fractionation during microbially mediated carbonate reduction. These results, in conjunction with a transect-wide gaseous hydrocarbon content composed of > 99.8% (by volume) methane and uniform δDCH4 values (− 172‰ ± 8) that are distinct from thermogenic methane at a seep located 60 km from the Expedition 311 transect, suggest microbial CO2 reduction is the predominant methane source at all investigated sites. The magnitude of the intra-site downhole 13C-enrichment of CO2 within the accreted ridge (Site U1326) and a slope basin nearest the deformation front (Site U1325, 2195 mbsl) is ~ 5‰. At the mid-slope site (Site U1327, 1304 mbsl) the downhole 13C-enrichment of the CO2 is ~ 25‰ and increases to ~ 40‰ at the near-shelf edge Site U1329. This isotope fractionation pattern is indicative of more extensive diagenetic alteration at sites with greater 13C-enrichment. The magnitude of the 13C-enrichment of CO2 correlates with decreasing sedimentation rates and a diminishing occurrence of stratigraphic gas hydrate. We suggest the decreasing sedimentation rates increase the exposure time of sedimentary organic matter to aerobic and anaerobic degradation, during burial, thereby reducing the availability of metabolizable organic matter available for methane production. This process is reflected in the occurrence and distribution of gas hydrate within the northern Cascadia margin accretionary prism. Our observations are relevant for evaluating methane production and the occurrence of stratigraphic gas hydrate within other convergent margins.

Lipid classes, fatty acids (FAs), and stable carbon isotopes of FAs were used to investi- gate dietary sources of organic carbon for juvenile Atlantic cod Gadus morhua during settlement into eelgrass Zostera marina. Primary producers, epibenthic prey, zooplankton, and fish were collected from August to November 2002 in shallow ( 80 µm) were associated with fresh organic material, while seston (5-80 µm) had high levels of bacterial FA and non-acyl lipids, typical of sedimentary material. Zooplankton, mysids, and amphipods showed a seasonal decrease in 22:6n-3 with a con- comitant increased in the ubiquitous terrestrial indicators 18:2n-3 and 18:3n-3. Based on essential FA composition of prey, there was a decrease in the quality of food available to juvenile fish from August until November. Earlier (August) pelagic juveniles had higher levels of marine-sourced FA (22:6n-3) than late (November) arrivers. Further, in October and November settled juveniles had higher pro- portions of terrestrial FA biomarkers than pelagic cod, indicating an increased dietary terrestrial input at settlement. Isotopic evidence demonstrated that eelgrass was the most enriched (-14‰) source of organic carbon and supported multivariate FA analysis, confirming that eelgrass was not incorporated into the food web of juvenile cod. Increased terrestrial input of organic carbon coupled with low proportions of dietary essential FAs indicate that the functional significance of this habitat is refuge and not nutrition.

Fossil methane from the large and dynamic marine gas hydrate reservoir has the potential to influence oceanic and atmospheric carbon pools. However, natural radiocarbon ( 14 C) measurements of gas hydrate methane have been extremely limited, and their use as a source and process indicator has not yet been systematically established. In this study, gas hydrate-bound and dissolved methane recovered from six geologically and geographically distinct high-gas-flux cold seeps was found to be 98 to 100% fossil based on its 14 C content. Given this prevalence of fossil methane and the small contribution of gas hydrate (≤ 1%) to the present-day atmospheric methane flux, non-fossil contributions of gas hydrate methane to the atmosphere are not likely to be quantitatively significant. This conclusion is consistent with contemporary atmospheric methane budget calculations. In combination with δ 13 C- and δ D-methane measurements, we also determine the extent to which the low, but detectable, amounts of 14 C (~ 1–2% modern carbon, pMC) in methane from two cold seeps might reflect in situ production from near-seafloor sediment organic carbon (SOC). A 14 C mass balance approach using fossil methane and 14 C-enriched SOC suggests that as much as 8 to 29% of hydrate-associated methane carbon may originate from SOC contained within the upper 6 m of sediment. These findings validate the assumption of a predominantly fossil carbon source for marine gas hydrate, but also indicate that structural gas hydrate from at least certain cold seeps contains a component of methane produced during decomposition of non-fossil organic matter in near-surface sediment.

The decomposition of deep peat deposits controls the long-term carbon balance of peatlands but is poorly understood with respect to rates and controls. To rectify this deficiency, we estimated in situ dissolved inorganic carbon (DIC) and methane (CH4) production rates from a beaver pond to a central bog dome and related them to organic matter properties, Gibbs free energies of respiration, and d13C values of DIC and CH4. DIC and CH4 production decreased from maxima of ,10 nmol cm23 d21 near the water table to values ,0.1 nmol cm23 d21 at depths .1 m, and there was little differentiation among sites. Deeper into the peat, we measured an accumulation of DIC, CH4, and dissolved organic matter (DOM) enriched in aromatic and phenolic moieties, which resulted from the slowness of diffusive vertical pore-water movement. Lack of transport may have slowed decomposition in two ways: (1) Aromatic and phenolic DOM moieties accumulated, while the release of carbohydrate-rich DOM from peat was apparently impeded. (2) The accumulation of DIC and CH4 reduced Gibbs free energy of acetoclastic methanogenesis toward a critical threshold value of 225 to 220 kJ mol 21 CH4. Hydrogenotrophic methanogenesis was energetically more favorable and generally dominated according to an isotopic fractionation between CO2 and CH4 of 1.053 to 1.076, but it was apparently impeded by some other factor. We conclude that lateral homogeneity and slowness of decomposition in geologically sealed deep peat deposits are assisted by a lack of solute transport, which facilitates the formation of deep peat deposits over millennia.

Upon closer inspection, the classical view of the synchronous relationship between tropospheric methane mixing ratio and Greenland temperature observed in ice samples reveals clearly discernable variations in the magnitude of this response during the Late Pleistocene (13 CH 4 and δD-CH 4 of tropospheric methane recorded in ice samples provide a useful constraint on the palaeomethane budget estimations. Anticipated changes in palaeoenvironmental conditions are recorded as changes in the isotope signals of the methane precursors, which are then translated into past global δ 13 CH 4 and δD-CH 4 signatures. We present the first methane budgets for the late glacial period that are constrained by dual stable isotopes. The overall isotope variations indicate that the Younger Dryas (YD) and Preindustrial Holocene have methane that is 13 C- and 2 H-enriched, relative to Modern. The shift is small for δ 13 CH 4 (approx. 1‰) but greater for δD-CH 4 (approx. 9‰). The YD δ 13 CH 4 –δD-CH 4 record shows a remarkable relationship between them from 12.15 to 11.52 kyr BP. The corresponding C- and H-isotope mass balances possibly indicate fluctuating emissions of thermogenic gas. This δ 13 CH 4 –δD-CH 4 relationship breaks down during the YD–Preboreal transition. In both age cases, catastrophic releases of hydrates with Archaeal isotope signatures can be ruled out. Thermogenic clathrate releases are possible during the YD period, but so are conventional natural gas seepages.

Methane concentrations and carbon isotope ratios in ice samples offer an approach to study past budgets of atmospheric methane and to investigate changes in source composition or sink processes. Methane concentrations in ice samples also provide a tool for age correlation between different ice cores. Critical for the use of these parameters are measurements with sufficient accuracy and precision on small samples. To this end we developed a micro-extraction gas chromatography-continuous-flow isotope ratio mass spectrometry (GC-IRMS) technique to extract, focus and measure the methane 13 C/ 12 C ratio ( δ 13 CH 4 ) from extremely small gas occlusions in ice (ca. 300 pmol of methane from 100 to 250 g of ice). This micro-measurement allows the time resolution (sample stratigraphic thickness) necessary in paleo-records to investigate decadal-range changes in the methane cycle coupled to abrupt warming events during the last glacial period. The accuracy (±0.4‰) and precision (1 σ = 0.32‰) of our method was established by in-house ice standards and confirmed with analysis of ice from GISP2 and the Agassiz ice cap. Our δ 13 CH 4 measurements of −49.7‰ between 225 and 330 yr BP agree very well with previously published data. These δ 13 CH 4 ice core results indicate an unexpected 13 C-enrichment of the pre-industrial atmospheric methane, compared to predictions by mass balance models.

Ponds and lakes are widespread across the rapidly changing permafrost environments. Aquatic systems play an important role in global biogeochemical cycles, especially in greenhouse gas (GHG) exchanges between terrestrial systems and the atmosphere. The source, speciation and emission of carbon released from permafrost landscapes are strongly influenced by local specific conditions rather than general environmental setting. This study reports on GHG ages and emission rates from aquatic systems on Bylot Island in the eastern Canadian Arctic. Dissolved and ebullition gas samples were collected during the summer season from different types of water bodies located in a highly dynamic periglacial valley: polygonal ponds, collapsed ice-wedge trough ponds, and larger lakes overlying unfrozen soils (talik). The results showed strikingly different ages and fluxes depending on aquatic system types. Polygonal ponds were net sinks of dissolved CO2, but variable sources of dissolved CH4. They presented the highest ebullition fluxes, one or two orders of magnitude higher than from other ponds and lakes. Trough ponds appeared as substantial GHG sources, especially when their edges were actively eroding. Both types of ponds produced modern to hundreds of years old (2000 yr BP) derived from freshly eroded peat. Lakes had small dissolved and ebullition fluxes, however they released much older GHG, including millennium-old CH4 (up to 3500 yr BP) sampled from lake central areas. Acetoclastic methanogenesis dominated at all study sites and there was minimal, if any, methane oxidation in gas emitted through ebullition. These findings provide new insights on the variable role of permafrost aquatic systems as a positive feedback mechanism on climate.

We report atmospheric methane carbon isotope ratios (δ 13 CH 4 ) from the Western Greenland ice margin spanning the Younger Dryas–to–Preboreal (YD-PB) transition. Over the recorded ∼800 years, δ 13 CH 4 was around –46 per mil (‰); that is, ∼1‰ higher than in the modern atmosphere and ∼5.5‰ higher than would be expected from budgets without 13 C-rich anthropogenic emissions. This requires higher natural 13 C-rich emissions or stronger sink fractionation than conventionally assumed. Constant δ 13 CH 4 during the rise in methane concentration at the YD-PB transition is consistent with additional emissions from tropical wetlands, or aerobic plant CH 4 production, or with a multisource scenario. A marine clathrate source is unlikely.

The isotopic (δ13C and δD) and hydrocarbon compositions of hydrate-bound and vent gas collected from the seafloor of Barkley Canyon (northern Cascadia Margin, offshore Vancouver Island, Canada) were evaluated to characterize the gas and infer the type and maturity of the source rock kerogen. The hydrate gas contained methane having δ13C values from −43.4‰ to −42.6‰, δD values from −143‰ to −138‰ and a large percentage (14.9% to 31.9%) of C2 to C5+ hydrocarbons. These data are consistent with a thermogenic gas source. The data from Barkley Canyon are interpreted within the context of similar data from the Gulf of Mexico and Caspian Sea thermogenic hydrates, which occur in regions where the petroleum systems supporting gas and oil generation are better understood. A stable carbon isotope-based natural gas plot model and D/H data from the hydrate gas indicate that the source rock for the Barkley Canyon hydrate and vent gas had primarily Type III kerogen mixed with a small fraction of Type II kerogen. Oil from a seep having a pristane/phytane ratio of 3.2 was identified as a gas condensate, which supports the conclusions drawn from the gas data. A mechanism for explaining how fluids are conducted from the deep petroleum reservoir to the seafloor of Barkley Canyon is proposed.

A suite of 27 oils from predominantly Nisku reservoirs of the Western Canada Sedimentary Basin (WCSB), in central and southern Alberta, can be classified into six groups or families based on stable carbon isotope ratios of individual gasoline range (C5-C10) compounds. A novel analytical technique combining Solid Phase MicroExtraction (SPME) and Continuous Flow Isotope Ratio Mass Spectrometry (CF-IRMS) is employed to measure the 13C/12C ratios. The majority of oils show characteristics of generation from a common source rock, the Upper Devonian Duvernay Formation. Systematic isotope distributions in straight chain and branched alkanes can help to delineate a common source rock along with the influence of secondary alteration processes such as biodegradation, evaporation, and thermochemical sulfate reduction. A 1-2‰ enrichment in 13C between groups can distinguish different levels of thermal maturity during oil genesis. Numerous analytical challenges are inherent in obtaining accurate 13C measurements for gasoline range analytes, but when utilized in conjunction with biomarkers and other compound specific geochemical techniques, the isotopic composition of these compounds exhibits good potential as a correlation tool. End_Page 99

High organic loading (4–5 wt%) and sedimentation rates (1.4 mm yr −1 ) in Eckernforde Bay sediments lead to anaerobic conditions within the uppermost 15 cm. Intense bacterial sulphate reduction (0.011–0.15 mM SO 4 red 2− yr −1 ) exhausts dissolved sulphate around 150 cm sediment depth, resulting in methanogenesis at greater sediment depth by carbonate reduction (1.8–8.5 μM CH 4 yr −1 ). Extensive regions of Eckernforde Bay are characterized by acoustically turbid sediments (>300 cm sediment depth), resulting from deeper sediments supersaturated in methane, forming free gas accumulation zones. Methane migrating upward into the sulphate reduction zone is effectively consumed by sulphate reducing bacteria at rates 3–10 times greater than methanogenesis, i.e. 46–95 μM CH 4 ox yr −1 . The pathways of methane formation and anaerobic oxidation are confirmed by stable carbon and hydrogen isotope evidence. Pockmarks, i.e. shallow surface depressions in some Eckernforde Bay sediments, are not associated with gas ebullition; rather, these physical features result from the expulsion of freshwater. These episodic springs or seepages of groundwater from the underlying, Holocene glacial lags and sands into the basin at pockmark sites have characteristic low chloride and methane concentrations. The geochemical evidence indicates that the commercial accumulation of petroleum in the lower Cretaceous, Dogger–Beta–Hauptsandstein Schwedeneck field in Eckernforde Bay (1500 mbsf) has no surface manifestation and does not influence either the occurrence of acoustic turbidity or pockmarks.

Saanich Inlet has been a highly productive fjord since the last glaciation. During ODP Leg 169S, nearly 70 m of Holocene sediments were recovered from Hole 1034 at the center of the inlet. The younger sediments are laminated, anaerobic, and rich in organic material (1–2.5 wt.% Corg), whereas the older sediments below 70 mbsf are non-laminated, aerobic, with glacio-marine characteristics and have a significantly lower organic matter content. This difference is also reflected in the changes of interstitial fluids, and in biomarker compositions and their carbon isotope signals. The bacterially-derived hopanoid 17α(H),21β(H)-hop-22(29)-ene (diploptene) occurs in Saanich Inlet sediments throughout the Holocene but is not present in Pleistocene glacio-marine sediments. Its concentration increases after ∼6000 years BP up to present time to about 70 μg/g Corg, whereas terrigenous biomarkers such as the n-alkane C31 are low throughout the Holocene (

Changes in palaeoproduction in Saanich Inlet, British Columbia, were examined from sediments using total organic carbon contents and stable carbon isotope ratios. Sediments were obtained from Holes 1033B and 1034B of Ocean Drilling Program Leg 169S. These cores contain two distinct zones: (1) carbon poor (%Corg

Sites 1033 and 1034 of ODP Leg 169S in Saanich Inlet have an unusual diagenetic system, that has the appearance of being depth reversed, i.e. a bacterial methane accumulation zone underlain by a sulphate reduction zone. During the late Pleistocene grey, undifferentiated, glacio-marine clays were deposited with low Corg contents (

Cold seeps in the Aleutian deep-sea trench support prolific benthic communities and generate carbonate precipitates which are dependent on carbon dioxide delivered from anaerobic methane oxidation. This process is active in the anaerobic sediments at the sulfate reduction-methane production boundary and is probably performed by archaea working in syntrophic co-operation with sulfate-reducing bacteria. Diagnostic lipid biomarkers of archaeal origin include irregular isoprenoids such as 2,6,11,15-tetramethylhexadecane (crocetane) and 2,6,10,15,19-pentamethylicosane (PMI) as well as the glycerol ether lipid archaeol (2,3-di-O-phytanyl-sn-glycerol). These biomarkers are prominent lipid constituents in the anaerobic sediments as well as in the carbonate precipitates. Carbon isotopic compositions of the biomarkers are strongly depleted in 13C with values of δ13C as low as −130.3‰ PDB. The process of anaerobic methane oxidation is also reflected in the carbon isotope composition of organic matter with δ13C-values of −39.2 and −41.8‰ and of the carbonate precipitates with values of −45.4 and −48.7‰. This suggests that methane-oxidizing archaea have accumulated within the microbial community, which is active at the cold seep sites. The dominance of crocetane in sediments at one station indicates that, probably due to decreased methane venting, archaea might no longer be growing, whereas high amounts of crocetenes found at other more active stations may indicate recent fluid venting and active archaea. Comparison with other biomarker studies suggests that various archaeal assemblages might be involved in the anaerobic consumption of methane. The assemblages are apparently dependent on specific conditions found at each cold seep environment. Selective conditions probably include water depth, temperature, degree of anoxia, and supply of free methane.

Isotope effects by Prymnesiophyte algae were determined on samples of marine particulate organic material collected by MULVFS pumps during three C-JGOFS cruises along Line P in the northeast Pacific. Carbon isotope fractionation associated with photosynthetic carbon uptake was calculated from 13 C / 12 C ratios of dissolved carbon dioxide and the C37:2 alkenone, a biomarker originating from Prymnesiophyte algae. In the presence of nitrate (N) the magnitude of the carbon isotope fractionation (ep) is dependent on dissolved phosphate concentration (PO4) normalized to the concentration of dissolved carbon dioxide (Ce), i.e. ep∝PO4/Ce for N≠0. In nitrate-depleted waters, the magnitude of carbon isotope fractionation is lower than expected from the ep vs PO4/Ce relationship. These results suggest that growth conditions approaching nitrogen starvation can severely affect carbon isotope fractionation in these paleo-climatically important algae.

Tree ring-width chronologies from the west coast of North America were obtained from on-line data archives, maintained by the National Oceanic and Atmospheric Administration (NOAA). Data covered the period 1650–1983, for trees sampled at 43 sites between Dawson Creek, British Columbia (55°N) and Yosemite Park, CA (37°N). These time series were analyzed using Fourier transformation methods. Spyglass Transform software allowed the resulting power spectra to be stacked and compared, based on characteristics such as topography and continentality, latitude and species ecological niche. Results suggested that several regular or quasi-regular cycles are occurring over various time periods. There are some similarities, though not an exact match, with El Nino periodicities noted by earlier authors. These patterns appear to be widespread, affecting trees at various elevations and distances from the coast, and from different species. A separate analysis of the oldest trees revealed sub-century cycles. In particular, the longer fluctuations at 50–65 years are consistent with recent findings on north Pacific climate by other authors. A Euclidean cluster analysis of individual years identified unusual year groupings between 1924–1946, a period associated with positive temperature anomalies and generally higher precipitation. These findings appear to be consistent with other basin-scale climate cycles, like the Southern Oscillation, and the recently-proposed Pacific Interdecadal Oscillation (PDO).

Forty-two oils/condensates from the Western Canada Sedimentary Basin (WCSB) ranging in reservoir age from Devonian to Cretaceous are compared using the stable carbon isotopic ratio of individual hydrocarbons in the gasoline-range fraction (C 5 –C 8 ) of these oils. Continuous Flow-Isotope Ratio Mass Spectrometry (CF-IRMS), using a modified solid dilution, purge and trap inletting system can provide reproducible isotopic ratios for the ca. 26 dominant n -, iso -, and cyclo -alkanes and aromatics in the gasoline range. The resulting isotopic signatures, or gasoline “isotopograms”, for oils/condensates provide a diagnostic geochemical technique for oil–oil and oil–source correlations. In many instances, the non-straight-chained hydrocarbons are more diagnostic than n -alkanes. Hierarchical cluster analysis provides a non-subjective approach to the treatment of individual isotopic information. This study confirms that oils from similar or the same sources produce isotopic signatures that are highly correlated. Clear carbon isotopic relationships between individual hydrocarbon compounds in the oils suggest a steady-state kinetic relationship for the generation of oil and gas, as opposed to a thermodynamic equilibrium relationship. This mechanism explains the consistent shift in isotopic ratios between similar compounds, such as the methylalkanes and dimethylalkanes.

The diagenetic cycling of carbon within recent unconsolidated sediments and soils generally can be followed more effectively by discerning changes in the dissolved constituents of the interstitial fluids, rather than by monitoring changes in the bulk or solid organic components. The major dissolved carbon species in diagenetic settings are represented by the two carbon redox end-members CH4 and CO2. Bacterial uptake by methanogens of either CO2 or “preformed” reduced carbon substrates such as acetate, methanol or methylated amines can be tracked with the aid of carbon ( 13 C / 12 C ) and hydrogen ( D/H≡ 2 H/ 1 H ) isotopes. The bacterial reduction of CO2 to CH4 is associated with a kinetic isotope effect (KIE) for carbon which discriminates against 13 C . This leads to carbon isotope separation between CO2 and CH4 (eC) exceeding 95 and gives rise to δ 13 C CH 4 values as negative as −110‰ vs. PDB. The carbon KIE associated with fermentation of methylated substrates is lower (eC is ca. 40 to 60, with δ 13 C CH 4 values of −50‰ to −60‰). Hydrogen isotope effects during methanogenesis of methylated substrates can lead to deuterium depletions as large as δ D CH 4 =−531‰ vs. SMOW, whereas, bacterial D/H discrimination for the CO2-reduction pathway is significantly less (δDCH4 ca. −170‰ to −250‰). These field observations have been confirmed by culture experiments with labeled isotopes, although hydrogen isotope exchange and other factors may influence the hydrogen distributions. Bacterial consumption of CH4, both aerobic and anaerobic, is also associated with KIEs for C and H isotopes that enrich the residual CH4 in the heavier isotopes. Carbon fractionation factors related to CH4 oxidation are generally less than eC=10, although values >20 are known. The KIE for hydrogen (eH) during aerobic and anaerobic CH4 oxidation is between 95 and 285. The differences in C and H isotope ratios of CH4, in combination with the isotope ratios of the coexisting H2O and CO2 pairs, differentiate the various bacterial CH4 generation and consumption pathways, and elucidate the cycling of labile sedimentary carbon.

An improved method for molecular and stable isotope analysis of gasoline range hydrocarbons (C 5 –C 10 ) in oils uses Solid Phase Microextraction. Analytes are sampled from the headspace above oil droplets and analyzed by gas chromatography and continuous-flow isotope-ratio mass spectrometry. Analytical considerations with this sampling technique include equilibration times, vapor pressure/temperature effects, and the presence of a complex matrix. Instrumentation factors such as column/split flows are also considered. The results are compared with an alternative purge and trap method. Molecular analyses prove reproducible between the two methods, however, stable carbon isotope ratios exhibit a non-systematic depletion and enrichment of 0.2–2.0‰ for 16 pre-selected compounds.

a b s t r a c t We evaluated the utility of vitamin A and E profiles as biomarkers of contaminant exposure in beluga whales (Delphinapterus leucas; n = 66) harvested by the Inuvialuit in the Beaufort Sea. Blubber was an important repository for these vitamins, accounting for 76.8 ± 2.6% of the total body store of vitamin A, and 98.5 ± 0.4% of total vitamin E. While the free alcohol form of vitamin A (retinol) appeared highly regulated, the vitamin A esters were influenced by several biological factors including age, body con- dition and length. Vitamin E concentrations in liver and blubber were related to age, condition, length and feeding ecology, as described 15N and 13C. Despite the influence of these factors, collective results from univariate statistics, best fit multiple regressions, and principal component analysis (PCA) identified polychlorinated biphenyls (PCBs) as important determinants of vitamin concentrations and profiles in beluga tissues. Blubber PCB concentrations best explained variation of the first principal component in a PCA of hepatic vitamins (r 2 = 0.13, p = 0.014), and regression models found that vitamin A concentrations were negatively correlated with PCB levels in liver (esters: r2 = 0.19, p = 0.001), but positively in plasma (retinol: r 2 = 0.20, p = 0.06) and blubber (retinol: r 2 = 0.22, p = 0.001, esters: r 2 = 0.43, p < 0.001). Our anal- yses provide a basis to propose an integrated toxicity reference value for disruption of vitamin A and E profiles in beluga of 1.6 mg/kg lw PCBs. This disruption of vitamin profiles by moderate levels of PCBs in an arctic cetacean highlights the global reach and impact of these legacy chemicals decades after their peak use.

The crest of Hydrate Ridge harbors a variety of gas hydrates in near-surface sediments. Hydrate formation and destruction continuously shape the ridge topography. Interstitial Cl-anomaly patterns in conjunction with video-guided sampling have established that the uppermost sediment column contains several distinct layers of gas hydrate which are exposed at the sea floor. A methane-oxidizing bacterial consortium populates the exposures of hydrate; colonies of vent macro-fauna are abundant as well. Discharge of methane from destabilized hydrate at the seafloor stimulates high rates of benthic oxygen consumption. These rates, however, vary by many orders of magnitude spatially and temporally, highlighting the need for implementing seafloor observatories at gas hydrate sites. Two types of hydrate fabrics were observed: A highly porous fabric with an estimated pore space of approx. 60 vol.-% and a massive type, with no visible pore space. Both types contain varying amounts of chloride, which need to be taken into account when estimating hydrate volumes from Cl-depletion of pore waters. The porous hydrate has low bulk density, which may cause periodic release of large chunks of hydrate from the sea floor. They float to the surface and leave behind a chaotic topography of mounds and depressions. These pieces of floating hydrates constitute an important transport mechanism for methane from the seafloor directly to the atmosphere.

The microbial community inhabiting anaerobic sediments of Hydrate Ridge, an area characterized by extensive methane-venting and gas hydrate occurrence on the Cascadia accretionary prism, is dominated by a complex consortium of archaea and bacteria which performs anaerobic methane oxidation (AMO). The process is indicated by the dominance of archaeal-derived biomarkers such as crocetane, pentamethylicosane, and archaeol in anaerobic sediments and authigenic carbonates. The biomarkers are highly depleted in 13 C relative to their methane carbon source, which results in carbon isotopic compositions as low as -128%o PDB. The essentially limitless reservoir of methane available to the archaea in this gas hydrate environment allows the kinetic carbon isotope effect (e CH4-biomarker ) associated with AMO to be fully developed (e max = 72%o). No substrate depletion effects were detected. Varying isotope effects and concentrations of the biomarkers on and off Hydrate Ridge indicate that the abundance of these compounds is essentially dependent on the supply of methane from this special environmental setting.

The diagenetic cycling of carbon within recent unconsolidated sediments can be followed by discerning changes in the dissolved constituents of the interstitial fluids. The major dissolved carbon sp...

Polychlorinated biphenyl (PCB) biomagnification was characterized in a harbor seal food web in the Strait of Georgia, British Columbia, Canada. Trophic magnification factors (TMFs) for PCBs averaged 3.6, with a range of 0.7 to 9.4. The TMFs for individual congeners correlated with log KOW (r2 = 0.56, p

The fate of contaminants entering the marine environment through wastewater outfalls depends on the contaminant's persistence and affinity for particles. However, the physical characteristics of the receiving environment, for example, current velocity and sedimentary processes, may be even more important. Because of the complexity of natural settings and the lack of appropriate comparative settings, this is not frequently evaluated quantitatively. The authors investigated the near-field accumulation of particle-reactive polybrominated diphenyl ethers (PBDEs) entering coastal waters by way of two municipal outfalls: one discharging into a high-energy, low-sedimentation environment near Victoria, BC, Canada; the other into a low-energy, high-sedimentation environment, near Vancouver, BC. The authors used 210Pb profiles in box cores together with an advection-diffusion model to determine surface mixing and sedimentation rates, and to model the depositional history of PBDEs at these sites. Surprisingly, 88 to 99% of PBDEs were dispersed beyond the near-field at both sites, but a greater proportion of PBDEs was captured in the sediment near the Vancouver outfall where rapid burial was facilitated by inorganic sediment supplied from the nearby Fraser River. Although the discharge of PBDEs was much lower from the Victoria outfall than from Vancouver, some sediment PBDE concentrations were higher near Victoria. Environ. Toxicol. Chem. 2012;31:566–573. © 2011 SETAC

Methane production by anaerobic digestion of biomass has recently become more attractive because of its potential for renewable energy production. Analytical tools are needed to study and optimize the ongoing processes in biogas reactors. It is considered that optical methods providing continuous measurements at high temporal resolution of carbon isotope ratios of methane (delta(13)C(CH4)) might be of great help for this purpose. In this study we have tested near-infrared laser optical spectrometry and compared it with conventional continuous-flow isotope ratio mass spectrometry (CF-IRMS) using several methane carbon isotope standards and a large number of biogas samples from batch anaerobic reactors. Results from measurements on these samples were used to determine and compare the precision of the two techniques and to quantify for systematic offsets. With pure standards analytical precision of measurements for delta(13)C(CH4) was found to be in the range of 0.33 and 0.48 per thousand, and 0.09 and 0.27 per thousand for the optical method and CF-IRMS, respectively. Biogas samples showed an average mean deviation of delta(13)C(CH4) of 0.38 per thousand and 0.08 per thousand for the optical method and CF-IRMS, respectively. Although the tested laser optical spectrometer showed a dependence of delta(13)C(CH4) on CH(4) mixing ratio in the range of 500 to 8000 ppm this could be easily corrected. After correction, the delta(13)C(CH4) values usually varied within 0.7 per thousand from those measured by conventional CF-IRMS and thus results from both methods agreed within the given analytical uncertainties. Although the precision of the conventional CF-IRMS is higher than the tested optical system, both instruments were well within the acceptable delta(13)C(CH4) precision required for biogas methane measurements. The advantages of the optical system are its simplicity of operation, speed of analysis, good precision, reduced costs in comparison to IRMS, and the potential for field applications.

We measured persistent organic pollutant (POP) concentrations in chinook salmon (Oncorhynchus tshawytscha) in order to characterize dietary exposure in the highly contaminated, salmon-eating northeastern Pacific resident killer whales. We estimate that 97 to 99% of polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), dichlorodiphenyltrichloroethane (DDT), and hexachlorocyclohexane (HCH) in returning adult chinook were acquired during their time at sea. Highest POP concentrations (including PCBs, PCDDs, PCDFs, and DDT) and lowest lipids were observed in the more southerly chinook sampled. While feeding by salmon as they enter some more POP-contaminated near-shore environments inevitably contribute to their contamination, relationships observed between POP patterns and both lipid content and delta13C also suggest a migration-related metabolism and loss of the less-chlorinated PCB congeners. This has implications for killer whales, with the more PCB-contaminated salmon stocks in the south partly explaining the 4.0 to 6.6 times higher estimated daily intake for sigmaPCBs in southern resident killer whales compared to northern residents. We hypothesize that the lower lipid content of southerly chinook stocks may cause southern resident killer whales to increase their salmon consumption by as much as 50%, which would further increase their exposure to POPs.