GEOC 5 |
| The advent of compound-specific hydrogen and carbon isotopic analysis has extended the range of paleoclimatic information entrained within leaf wax lipids. The primary objective of this research was to evaluate empirically the environmental controls on δD and δ13C values of higher plant n-alkanes, since these compounds are refractory and readily preserved in the geologic record. Our approach was to extensively sample leaves and stems of seven species of trees that span the Eastern US. One hundred and thirty-three trees from forty sites were collected along with topsoils and surface waters from each locality in order to assess leaf wax input to soils and establish a water δD baseline for the transect. Red maple and Eastern redcedar n-alkanes δ13C have been analyzed and range from -38.0 to -30.2‰ and -34.7 to -29.1‰, respectively, and demonstrate no relationship with latitude, elevation, aspect, canopy cover, tree height, or leaf height. In addition, the gymnosperms are on average 1.9‰ more enriched in 13C than the angiosperms. This isotopic offset likely stems from physiological differences that led to greater water-use efficiency in the gymnosperms, however, future δD measurements will shed more light on these issues. In addition, soil-extracted n-alkane δ13C range between -36.2 to -30.7‰ and correlate positively with latitude (R2=0.40). Furthermore, soil n-alkane distributions demonstrate a wider range of n-alkanes than either present in the red maple or redcedar, indicative of other leaf wax inputs to the soils. Notably, redcedar-specific waxes make up minor measurable component of the n-alkanes extracted from topsoils and therefore contribute very little to the wax input in the soils. Finally, surface water δD and δ18O were highly correlated and similar to the meteoric water line with a relationship of δD = 7.4453 δ18O + 4.3016, laying the groundwork for detailed leaf wax and stem water δD analysis. |
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Modern Calibrations and Terrestrial Applications of Stable Isotope Paleo Proxies
9:00 AM-12:10 PM, Sunday, August 19, 2007 Boston Park Plaza -- St. James Rm, Oral
Division of Geochemistry |