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TitleCarbon-13 fractionation in carbon dioxide emitting diurnally from soils and vegetation at ten sites on the North American continent
Publication TypeThesis
Year of Publication1990
AuthorsLancaster, J.
IssuePh. D.
Pagination197
Place PublishedUniversity of California, San Diego
Publication Languageen
Abstract

A series of field experiments explore the characteristic fractionation of the $\sp{13}$C isotope by land plants on the North American continent, as seen in CO$\sb2$ emitting from plants and soils to the canopy layer during a diurnal cycle. CO$\sb2$ concentrations are reported for 495 discrete air samples taken within forests and over tundra at ten, rural sites ranging from 9$\sp\circ$N to 69$\sp\circ$N (Barro Colorado, Panama; Chamela, Mexico; Cuyamaca, CA; Yosemite, CA; Scotia Ridge, PA; Barnard, VT; Hamilton, MT; Rock Lake, Alberta; Bethel, AL; and Toolik, AL).

$\delta\sp{13}$C, $\delta\sp{18}$O and N$\sb2$O concentration are reported for 236 samples of CO$\sb2$ extracted cryogenically from the air samples. The results show the intercepts, $\delta\sp{13}$C$\sb{\rm I}$, of least-squares fits to the isotopic and reciprocal concentration at each site to range progressively from $-$28% near the equator to $-$23% near the Artic Circle. The latitudinal trend toward greater fractionation within the closed, tropical canopy is consistent with previous hypotheses regarding cyclic enrichment and water-use-efficiency relations, but is inconsistent with the hypothesis that $\sp{13}$C enrichment simply follows greater insolation. The mean value found for $\delta\sp{13}$C$\sb{\rm I}$, $-$25% ($\pm$1.6%), is in close agreement with nominal values used in global computer modelling of the biosphere-atmosphere CO$\sb2$ flux. Variability in samples from soil enclosure experiments and between years at some sites suggests that multiple factors may cause spatial and temporal heterogeneity in the $\sp{13}$C fractionation of as much as 2% to 3%.

Anomalous N$\sb2$O or $\delta\sp{18}$O values identify 90% of the $\delta\sp{13}$C data departing significantly ($>$2 sigma) from the least-squares fit for each site. N$\sb2$O concentrations range from 267 ppb to 3,882 ppb, while N$\sb2$O corrections to $\delta\sp{13}$C range from +0.06% to +1.95%. 20% of all samples require N$\sb2$O-based correction to the $\delta\sp{13}$C data that depart from the nominal +0.23% correction by more than 1%, suggesting that applying a constant correction for N$\sb2$O, or no correction at all may expose such assessments of characteristic isotopic composition in biospheric-atmosphere CO$\sb2$ exchange to an additional uncertainty exceeding 1%.

URLhttp://search.proquest.com/docview/303894067
Topics

Biology

Locational Keywords

Rock Lake

Active Link

http://www.worldcat.org/oclc/21343508

Group

Science

Citation Key37359

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