Fossil Carbon Sources Research Articles

Origins of lipid biomarkers in Santa Monica Basin surface sediment: a case study using compound-specific Δ14C analysis

Compound-specific Δ14C values are reported for 31 different lipid biomarker molecules obtained from Santa Monica Basin and Santa Barbara Basin surface sediments. These organic compounds represent phytoplanktonic, zooplanktonic, bacterial, archaeal, terrestrial higher plant, and fossil carbon sources. The lipid classes include the following: long-chain n-alkanes, fatty acids (as methyl esters; FAMEs), n-alcohols, C30 midchain ketols and diols, sterols, hopanols, and C40 isoprenoid side chains from the ether-linked glycerols of Archaea. The data show that the carbon source for the majority of the biomarkers is marine euphotic zone primary production or subsequent heterotrophic consumption of this biomass. A small amount of benthic incorporation of 14C-depleted dissolved inorganic carbon was identified for the bacterial hopanols and C15 linear and branched-chain fatty acids. However, there is no apparent uptake of 14C-depleted dissolved inorganic carbon in Santa Monica Basin by the bacteria, including filamentous Beggiatoa spp., that produce C18:1ω7 fatty acid. Two of the lipid classes did not reflect carbon originally fixed by marine photoautotrophs. These were the n-alkanes, for which the Δ14C data are consistent with mixed fossil carbon and contemporary terrestrial higher plant sources, and the archaeal isoprenoids, for which the Δ14C data are consistent with chemoautotrophic growth below the euphotic zone.

Direct Quantification of PM2.5 Fossil and Biomass Carbon within the Northern Front Range Air Quality Study's Domain

Radiocarbon (14C) analyses of PM2.5 (particulate matter with an aerodynamic diameter of 2.5 μm or less) of both ambient and source samples from the Northern Front Range Air Quality Study (NFRAQS) in Colorado were performed. The 14C analyses were undertaken to provide direct fossil vs modern (biomass) carbon source discrimination data for a subset of summer and winter 1996−1997 samples collected within the Denver metropolitan area. Samples were prepared for 14C accelerator mass spectrometry measure ments using techniques specially developed for small samples, i.e., <100 μg C. For the days and sampling periods analyzed the median and interquartile range of the winter blank corrected fraction of modern carbon was 23% (16−34%) at Welby and 27% (25−37%) at Brighton. The summer samples exhibited a more mixed signature with a median and interquartile range of 47% (9−70%). Source samples yielded 14C signatures consistent with expectation. We conclude fossil-derived sources contribute substantially in both seasons...

Identification of Age Anomalous Components of Food Commodities by Radiocarbon (14C) Analyses

“Post-maximum-bomb” 14C activities (1964 to the present) provide a natural isotopic signature to obtain information on biomass source age in contemporary food preparations. An analysis of the 14C content in frozen orange juice-containing products purchased in 1996 suggested, in one case, an inferred growth period between 1992 and 1994 for oranges used in the preparation of this commodity. In another case, the 14C analysis indicated an inferred average growth period of 1988−90 for the organics in a “frozen concentrated enriched citrus beverage”. The presence of significant amounts of chemical additives obtained or synthesized from fossil carbon sources can also be documented by measuring 14C content. Keywords: Radiocarbon; carbon isotopes; orange juice; component age

Origin and structures of groundwater humic substances from three Danish aquifers

Structural, chemical, and isotopic parameters were used to identify the origins of groundwater humic substances from three Danish aquifers. A variety of analytical techniques (visible light absorption, molecular weight distribution, 13C-NMR spectroscopy, elemental composition with major elements and halogens, hydrolyzable amino acids and carbohydrates, carbon isotopes) applied to aquatic humic and fulvic acids led to consistent structural interpretations for each of the three aquifers studied. For humic substances in two aquifers, the analyses suggested source rocks in agreement with geological and hydrogeochemical information. In a third aquifer, source rock identification was inconclusive, and multiple fossil and recent organic carbon sources are suggested.

A global warming forum: scientific, economic, and legal overview

Role of Geophysical and Geoengineering Methods to Solve Problems Related to Global Climatic Change: Radiative, Hydrological and Dynamic Interaction in the Air Space System (D. Yang and W. Yang). The Measurements of Atmospheric Aerosols and Condensation Nuclei and the Potential Role of These Particles in Cloud Formation and Transfer of Radiative Energy (J. Podzimek). What do Data Analyses Tell Us about the Variability of Global Temperature? (A.A. Tsonis and J.B. Elsner) Space-Based Geoengineering Options for Dealing with Global Change (L.M. Jenkins). Results of Analyses of a Lunar-Based Power System to Supply Earth with 30,000 GW of Electric Power (D.R. Criswell and R.D. Waldron). Role of Oceanographic and Geochemical Methods to Provide Evidence for Global Climatic Change: Climate and the Marine Record: Scientific Results of the Ocean Drilling Program (P.D. Rabinowitz and J.G. Baldauf). The Climate Continuum: An Overview of Global Warming and Cooling Throughout the History of Planet Earth (A.D. Socci). Anthropogenic Fossil Carbon Sources of Atmospheric Methane (T.R. Barber and W.M. Sackett). Elevated Sea Surface Temperatures Correlate with Caribbean Coral Reef Bleaching (T.J. Goreau, R.L. Hayes, J.W. Clark, D.J. Basta, and C.N. Robertson). Geochemical Methods to Evaluate Methane Concentrations in Soils and Sediments (R.C. Pflaum). Possible Reduction of Atmospheric CO2 by Iron Fertilization in the Antarctic Ocean (T.-H. Peng). Land-Water Interactions and Climate Change (P. Firth). Global Assessment of Greenhouse Gas Production Including Need for Additional Information: Climate History During the Recent Greenhouse Enhancement (P.J. Michaels and R.C. Balling, Jr.). Environmental and Economic Benefits of Natural Gas Use for Pollution Control (P.R. Dey, E.E. Berkau, and K.B. Schnelle). Methane Emissions to the Global Atmosphere from Coal Mining (R.C. Harriss, T. Bensel, and D. Blaha). What to Do About Greenhouse Warming: Look Before You Leap (S.F. Singer, R. Revelle,and C. Starr). Atmospheric Trace Gases: Sources, Sinks, and Role in Global Change (M.A.K. Khalil). Natural Resource Management needed to Provide Long Term Global Energy and Agricultural Uses: Some Considerations in Applying GIS Technology to the Global Warming Problem (L.K. Smith). Global Warming and Agriculture: A Survey of Economic Anlyses and Preliminary Assessments (H. Onal). Greenhouse Gases and Agriculture (R.B. Jackson, IV). Global Warming and the Water Resources of Sahel (Lake Chad) Region (S.A. Isiorho). Satellite Monitoring of Desert Expansion (H.E. Dregne and C.J. Tucker). The Use of Biofuels to Mitigate Global Warming (M.D. Ackerson, E.C. Clausen, and J.L. Gaddy). Prospects of Agriculture in a Carbon Dioxide Enriched Environment (N.C. Bhattacharya). Legal, Policy, and Education Considerations Required to Properly Evaluate Global Warming Proposals: Beyond Vienna and Montreal-A Global Framework Convention on Greenhouse Gases (D.A. Wirth and D.A. Lashof). The Developing Law of the Atmosphere: Toward a 1992 Rio de Janeiro Convention on Global Environmental Change (J. Lancaster). Global Warming: The Energy Policy Challenge (C. Flavin and N. Lenssen). Japan and the Global Environment (A.S. Miller and C. Moore). Regulatory Aspects of Acid Rain (P.R. Dey, E.E. Berkau, and K.B. Schnelle). A Strategy for Global Environmental Education at the University (S.T. Hussain and R.L. Hayes).

Shifts in 14C Patterns of Soil Profiles Due to Bomb Carbon, Including Effects of Morphogenetic and Turbation Processes

Principles contributing to changes and the final balance of rejuvenation in 14C dates of soil profiles are identified. The annual addition to the atmosphere of ca 5.5·1012kg of dead carbon from fossil carbon sources and 1.5·1012kg of older carbon from forest clearing make soil appear older. Bomb carbon and annual recycling of most of the 115·1012kg of terrestrial organic carbon, equivalent to the annual photosynthetic turnover of carbon, rejuvenates soil dates. This also applies to root growth, animal transport, and in acid or alkaline soils, to humus percolation. All available 14C dates of soil profiles were evaluated for the impact of bomb carbon. We also studied the effects of morphogenetic soil-forming processes, such as turbations, on soil rejuvenation. Bioturbation, as a general principle of soil dynamics, requires more differential treatment due to modern and bomb carbon that constitutes body carbon of earthworms as well as steadily increasing 14C age with depth in all Mollisols.

Fossil carbon sources of atmospheric methane

Fossil carbon sources of atmospheric methane

Radiocarbon determination of atmospheric methane at Baring Head, New Zealand

Although methane in the atmosphere is clearly increasing, its sources are still poorly defined. Measurement of carbon isotope ratios allows constraints to be placed on relative source strengths of atmospheric methane because different potential sources have different isotope ratios. Unfortunately, interpreting 13C/12C ratios of atmospheric methane is subject to uncertainty because a correction for isotope fractionation in the oxidation of methane is not well determined. Interpreting 14C/12C ratios is also complicated by the need to correct for release of 14CH4 from nuclear power plants using rough estimates. Simultaneous use of both carbon isotope ratios, however, improves the confidence of interpretation. Here we show that measurements of the 14C/12C ratio, using accelerator mass spectrometry, and 13C/12C ratio of methane from clean Southern Hemisphere air are consistent with current estimates of both types of correction and imply that about 32% of atmospheric methane is derived from fossil carbon sources.

On the identification of carbonaceous aerosols via 14C accelerator mass spectrometry, and laser muprobe mass spectrometry

Carbon isotopic measurements ( 12C, 14C), derived from chemical measurements of total carbon plus AMS measurements of 14C/ 12C have become an accepted means for estimating fossil and contemporary carbon source contributions to atmospheric carbon. Because of the limited sensitivity of these techniques, however, such measurements are restricted to “bulk” samples comprising at least 10–100 μg of carbon. Laser microprobe mass spectrometry (LMMS) offers an important complementary opportunity to investigate the chemical nature of individual particles as small as 0.1 μm in diameter. Although there is little hope to measure 14C/ 12C in such small samples, the compositional and structural information available with the laser microprobe is of interest for possible source discrimination. Also, the analysis of individual particles, which may reflect individual sources, yields significant potential increases in spatial, temporal and source resolution, in comparison to bulk sample analysis. Results of our exploratory investigation of known sources of carbonaceous particles, using LMMS, are presented. By applying multivariate techniques to laser mass spectra of soot from the combustion of heptane and wood, we found striking differences in the alkali metals (notably potassium) in the positive ion mass spectra. For ambient particles, 14C has proved to be a crucial adjunct for the development and validation of the LMMS approach to single particle source assignment via carbon cluster pattern recognition. The combined techniques offer great promise for objective modeling (number and types of carbon sources) and for extension of the dichotomous carbon apportionment (fossil, contemporary) to subclasses such as soot from wood and agricultural burning, and that from coal and petroleum combustion.

On the Origin of Carbonaceous Particles in American Cities: Results of Radiocarbon “Dating” and Chemical Characterization

During the past three years radiocarbon assay has emerged as a primary tool in the quantitative assignment of sources of urban and rural particulate pollution. Its use in several major field studies has come about because of its excellent (fossil/biogenic) discriminating power, because of advances in 14C measurements of small samples, and because of the increased significance of carbonaceous particles in the atmosphere. The problem is especially important in the cities, where increased concentrations of fine particles lead to pollution episodes characterized by poor visibility and changes in the radiation balance (absorption, scattering), and immediate and possibly long-term health effects. Efforts in source apportionment in such affected areas have been based on emissions inventories, dispersion modeling, and receptor modeling – ie, chemical and physical (and statistical) characterization of particles collected at designated receptor sites. It is in the last category that 14C has become quite effective in helping to resolve particle sources. Results are presented for studies carried out in Los Angeles, Denver, and Houston which incorporated 14C measurements, inorganic and organic chemical characterization, and receptor modeling. The 14C data indicated wide ranging contributions of biogenic and fossil carbon sources – eg, &lt;10% to 60% contemporary (biogenic) in Houston – depending on meteorological, biological, and anthropological activity. The combined (chemical, isotopic, statistical) data point to sources such as vehicles, wood combustion, power plants, and vegetation.

Anthropogenic Changes in Organic Carbon and Trace Metal Input to Lake Washington

An example of how man's contaminants are introduced, deposited, and retained in sediments giving a chronological record of events has been developed for Lake Washington, Seattle. Significant amounts of both inorganic and organic compounds in the environment originate from fossil fuel sources, such as power plants and motor vehicles. Many organic compounds are introduced also from contemporary biogenic materials. Through the combined carbon isotope analysis technique (CCIA), we can distinguish between fossil and contemporary carbon sources classes (using14C), as well as sources within each class (using13C). To establish the chronology of the organic carbon pollutant input to the lake sediment, the ages of the layers were determined using210pb dating techniques. Sediment profiles of trace metals and a fallout radionuclide plutonium were also obtained and compared with the carbon isotope profiles. The results show that the total organic carbon (TOC) concentration correspond to 93% modern carbon before 1905. This14C concentration in TOC decreased to ∼60% modern in the 1930's and now is between 95 and 80% modern. The lipid fraction is ca 30% modern and the total aromatic hydrocarbon fraction reached a minimum of 5% modern in 1954. The large decrease in14C of TOC around 1930 is believed to be due to coal dust or fly ash. The trace metal concentration also increased substantially at this time. The pattern observed in the sediment thus reflects the change in the local energy consumption pattern from a predominately coal to an oil-based economy. From the plutonium profile we infer that mixing occurs for 3 or 4 years before the sediment layers are compacted.

Radiocarbon Measurements of Particulates in Smog

In recent years in California, smog aerosols have been observed in metropolitan and rural areas. We wondered what the relative contribution is from sources such as fossil fuel combustion (eg, cars, factories) and emissions from trees and other plants. Pollution produced by fossil fuel combustion can be distinguished from biological sources using radioactive carbon. Carbon in fossil organic materials is radioactively dead whereas carbon in living plants contains 14C. Smog particles were collected on clean glass or quartz fiber paper and analyzed in a small volume CO2 proportional counter for 14C content. Results are given for sampling locations at UCLA, El Monte, Riverside, and Lake Tahoe showing the relative contributions of fossil and modern carbon sources ranging from 0 to 74% and 26 to 100% respectively.