INFERENCE OF PAST ATMOSPHERIC DELTA CARBON-13 AND ATMOSPHERIC CARBON-DIOXIDE FROM CARBON-13/CARBON-12 MEASUREMENTS IN TREE RINGS.
AuthorLEAVITT, STEVEN WARREN.
KeywordsDendrochronology -- Arizona.
Atmospheric carbon dioxide -- Arizona.
Carbon cycle (Biogeochemistry) -- Arizona.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractCarbon dioxide release from fossil-fuel burning is significant enough that we may soon experience perceptible changes in climate with important human consequences. Man's activities involving deforestation and agriculture have undoubtedly also affected atmospheric CO₂, although quantitative, and even qualitative, net effects of these processes are incompletely understood relative to fossil-fuel production. An accurate reconstruction of past ¹³C/¹²C ratios of atmospheric CO₂ may provide key constraints on the historical activity of the biosphere as CO₂ source or sink. Tree rings appear to be a repository of this information but there is much noise in the collection of previous reconstructions, presumably associated with site selection, radial variability, choice of representative wood chemical constituent, and subtle effects of climate on fractionation. This study attempts to avoid these pitfalls and develop a 50-yr δ¹³C(ATM) record from juniper trees (genus Juniperus), in fact, by taking advantage of the influence of climate on fractionation. Trees were harvested from suitable sites in close proximity to weather stations with monthly records of temperature and precipitation. Ring material was then separated from each of the sections in 5-yr intervals from 1930 to 1979 around their full circumference, and cellulose was extracted from the wood. After measuring δ¹³C of the cellulose by standard mass-spectrometric techniques, a variety of δ¹³C vs. climate functions were examined for each interval. The most useful relationships for at most 7 of the 10 sites were δ¹³C with December temperature or precipitation, because the coefficients were nearly constant from one interval to the next (averaging -0.27%₀ °C⁻¹ for temperature and -0.04%₀ mm⁻¹ for precipitation) and the intercepts differed. Local pollution effects are believed responsible for the three anomalous sites. The separation of these regression lines of different intervals is interpreted as the response of the trees to the changing δ¹³C of atmospheric CO₂ so that δ¹³C(ATM) curves are constructed from this spacing. The shape of the best-fit reconstruction suggests the biosphere has acted as CO₂ source to about 1965 and may now be a net sink. Although these conclusions are limited by certain assumptions and statistical restrictions, evidence from the recent scientific literature tends to support the increasing role of the biosphere as an important carbon sink.
Degree GrantorUniversity of Arizona
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THE EFFECTS OF THE CHEMICAL AND PHYSICAL CHARACTERISTICS OF IRON OXIDES ON THE KINETICS OF THE CATALYZED REACTION, 2CARBON-MONOXIDE ---> CARBON + CARBON-DIOXIDE, IN SIMULATED BLAST FURNACE ATMOSPHERESLowry, Michael Lee (The University of Arizona., 1980)Seven iron ore pellets, two sinters, and one lump ore were studied in CO-CO₂-H₂-N₂ atmospheres from 350°C to 750°C, simulating the upper stack of the ironmaking blast furnace. Experiments were performed in a flowing gas reactor on single specimens of each type of substrate. Two different measurements were made: (1) the carbon deposition and concurrent iron oxide reduction rate at 550°C in 30%CO, 10%CO₂, 2%H₂, and 58%N₂; and (2) the amount of carbon deposited during a programmed increase in temperature and change in CO-CO₂ ratio simulating the descent of an ore specimen in the blast furnace stack. The rates of the concurrent reaction were determined from mass balances based on gas chromatographic analyses of the CO, CO₂H₂, and N₂ in both the inlet and outlet gases and the continuously recorded mass of the specimen. The materials were examined as to chemical composition, internal structure, porosity, and surface area. Elemental analyses of single iron oxide grains were made by electron microprobe. Slag materials and composition, and crystallinity were determined by microprobe and X-ray diffraction. The results of the experiments show that carbon deposition occurs only in the presence of metallic iron which is produced from the concurrent reduction of Fe₃O₄. The degree of reduction is controlled largely by the structure of the substrate, but the carbon deposition is controlled only by the chemical composition of the substrate--specifically, silicon in the iron and the CaO to MgO ratio. In the blast furnace simulation, the carbon deposition increases for pellets fluxed with dolomite to a maximum with lime-fluxed pellets. The effects of H₂ and CO₂ on the reactions were investigated in the isothermal experiments using an Empire pellet. The CO₂ controlled only the reduction, and this by diffusion of the CO₂. The hydrogen in very small amounts enhanced the deposition of carbon, probably by eliminating the presence of the inactive iron carbides. Under blast furnace conditions, the changes in the operation when the chemistry of the ore feed is changed to fluxed pellets will be due more to the shifts in the available heat within the stack from carbon deposition than to the low temperature reduction of the ores, which does not change with the addition of the flux materials.
Elevated Atmospheric CO2 Impacts Carbon Dynamics in a C4-Sorghum-Soil Agroecosystem---An Application of Stable Carbon Isotopes (d13C) in Tracing the Fate of Carbon in the Atmosphere-Plant-Soil EcosystemCheng, Li (The University of Arizona., 2005)Although a strong inter-dependence exists between atmospheric carbon dioxide (CO2) and the terrestrial carbon (C) cycle, the response of plant-soil ecosystems to the rapid increase in atmospheric CO2 is not well understood. My dissertation research focused on the impacts of elevated CO2 on the carbon dynamics of plant-soil ecosystems, which were a major part of the overall C4-sorghum Free-Air CO2 Enrichment (FACE) experiment conducted by the University of Arizona and USDA at the Maricopa Agriculture Center, Arizona, USA, in 1998 and 1999. In the experiment, sorghum (Sorghum bicolor (L) Mőench) crop was exposed to elevated CO2 ("FACE": ca. 560 mmol mol-1) and ambient CO2 ("Control": ca. 360 mmol mol-1) interacting with well-watered and water-stressed treatments. The results from my study showed that the seasonal mean soil respiration rate measured in elevated CO2 plots over two growing seasons was 3.3 mmol m-2 s-1, i.e., 12.7% higher than the 2.9 mmol m-2 s-1 in ambient CO2 plots. The increased respiration mainly resulted from the stimulated root respiration under elevated CO2, which increased 36.1% compared to that under ambient CO2. Measured changes in sorghum residue biochemistry caused by CO2 were detected, with decrease of amino acids and hemicellulose carbohydrates by 7% and 8%, respectively, and increase of cellulose carbohydrates and lignin by 49% and 5%, respectively. Phenolics were only significantly higher in FACE roots. The C:N ratio of sorghum tissues was not affected by elevated CO2, but was substantially lower under water stress. The laboratory incubation showed that an average of 7.3% significantly less respired CO2 was released from the FACE-tissue-amended soil than the Control-tissues-amended soil over the full 79-d incubation period. Non-lignin phenolics (r2 = 0.93, p = 0.002), and lignin (r2 = 0.89, p = 0.004) were found to be the most important factors related to the sorghum tissue decomposition. Highly stable residues of FACE sorghum input to the soil resulted in the increase of the recalcitrant C pool and the decrease of the labile C pool. As a result, mean residence time of SOC in FACE field plot increased compared to that in Control plot, suggesting that the SOC under elevated CO2 was more stable against decomposition.