GEOC 29 |
| Caroline A Masiello, dept of Geography, UCSB/CalTech, 3611 Ellison Hall, UC Santa Barbara, Santa Barbara, CA 93106, Jeff A Baldock, Land and Water, CSIRO, PMB 2, Glen Osmond, 5064, Australia, Ronald J Smernik, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, SA, Australia, Oliver A Chadwick, Department of Geography, UC Santa Barbara, Santa Barbara, CA 93106, and Jim T Randerson, Dept of Earth System Science, UC Irvine/CalTech, zot code 3100, Irvine, CA 92697. |
| The oxidative state of organic matter (Cox) in terrestrial and marine ecosystems is a fundamental indicator of organic carbon production and decomposition processes and can be related to the energy stored in an ecosystem and to ecosystem gas exchange. Although Cox of pure organic compounds can be easily calculated from a molecular formula, the use of Cox as a geochemical tracer has been hindered by the difficulty of separating organic matter from mineral matrices for elemental analysis. Specifically, the measurement of %O and %H in organic matter contained in soils, sediments and rocks has not been possible due to interferences from abundant O and H present in minerals and water. Although many organic matter extraction schemes are available, none have the capacity to completely separate the organic from mineral components. We are testing two techniques for measurement of Cox of natural, mineral-bound organics via 13C CP/MAS NMR: first, via direct calculation from dipolar dephasing experiments, and second, via application of a molecular mixing modeling to cross- and direct-polarization spectra. In our molecular modeling approach, we use a technique that represents complex organic matter 13C CP/MAS NMR spectra as a mixture of the spectra of 3-6 classes of biomolecules (carbohydrate, protein, lignin, lipid and char). Inputs to the model include the distribution of NMR signal intensity associated with each component biomolecule and their respective C, H, N, and O molar elemental contents; output is an estimation of the molar proportion of sample C found in each of the 6 component biomolecules. The molar ratios of C to H, O and N can then be derived using the elemental contents of the component biomolecules and a molecular formula of the form CxHyOzNw estimated for the organic material being examined. From this formula, Cox can be calculated as (2z + 3w - y)/x. We will present an update of the accuracy of the dipolar dephasing approach and the modeling approach for estimating Cox, and will discuss climatological and ecological applications of this variable. |
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Multi-Tracer Studies in Geochemistry: When the Sum is Greater Than the Parts
8:10 AM-11:30 AM, Monday, March 29, 2004 Marriott -- Marquis NW, Oral
Division of Geochemistry |