Stable isotopic analysis and firn air reconstruction of the atmospheric history of methane and delta-carbon-13
- 出版日期：2004.
- 页数：1 v. :
- 第一责任说明：M. E. Trudeau.
- 分类号：a454 ; a275
- ISBN：0542008858(ebk.) :
MARC全文
02h0029532 20120621152245.0 cr un||||||||| 120621s2005 xx ||||f|||d||||||||eng | 3165813 0542008858(ebk.) : CNY371.35 NGL NGL NGL a454 ; a275 Trudeau, M. E. Stable isotopic analysis and firn air reconstruction of the atmospheric history of methane and delta-carbon-13 [electronic resource] / M. E. Trudeau. 2004. 1 v. : digital, PDF file. Adviser: Tans, Pieter P. Thesis (Ph.D.)--University of Colorado at Boulder, 2005. An infrared absorption spectrometer has been constructed to measure the stable isotopic composition of atmospheric methane samples. The spectrometer employs periodically poled lithium niobate PPLN) to generate difference frequency radiation from two near infrared diode lasers, an 811 nm Fabry-Perot diode laser and a 1066 nm alpha-DFB diode laser. This technique yields &sim；15 microwatts of single mode, tunable radiation that probes the nu 3 rotational-vibrational band of methane at 3.3 microns. The radiation is split between a multipass absorption cell for spectral measurements of the sample, and a reference absorption cell containing a standard gas. Methane is extracted from 25 L of air using cryogenic preconcentration procedures to increase the multipass cell partial pressure and enhance the signal, and wavelength modulation is utilized to reduce spectrometer noise. Isotopic composition is expressed as the ratio of singular value decomposition coefficients in conventional "per mil" notation. The 1sigma instrument precision was &sim；12&permil； for both delta13C and deltaD. A firn air diffusion model has been developed to reconstruct histories of atmospheric methane and methane isotopic composition using firn air measurements from expeditions at North GRIP Greenland), South Pole, and Siple Dome Antarctica). Model predictions of gravitational fractionation are verified with 40Ar/36Ar ratios and 15N/14N ratios of N2, isotopomers of inert gases with constant atmospheric mixing ratios. Methane diffusivity in porous snow is calibrated using known histories of SF6 and CO2 mixing ratios, long-lived gases with histories of rapid atmospheric increase. Monte Carlo modeling is used to quantify reconstruction uncertainties. Methane mixing ratio histories derived from South Pole and Siple Dome firn air agree well with direct southern hemisphere measurements and the Law Dome reconstruction of Etheridge et al. [34]. North GRIP measurements have allowed for the first reconstruction of the polar northern hemisphere methane mixing ratio, demonstrating methane growth rates between 1.0--1.1%yr-1 from 1950 to 1990. The polar southern hemisphere methane delta13C reconstruction using carbon isotope measurements from Siple Dome firn also agrees well with two previous studies, however reconstruction uncertainties overwhelm the magnitude of the atmospheric growth rate over the time period of this study, prohibiting definitive statements concerning trends in methane delta13C in the recent past. In the light of the Siple Dome results, it seems likely that the stated uncertainties of these earlier studies have been underestimated due to a combination of uncertainty contributions from sampling procedures/flask storage effects and the inherent convoluted nature of air contained in polar firn. Coalbed methane. ; Isotope geology. Electronic dissertations. aeBook. aCN bNGL http://pqdt.bjzhongke.com.cn/Detail.aspx?pid=4CA6%2b7vQlBY%3d NGL Bs1588 rCNY371.35 ; h1 bs1204