HR: 08:15h
AN: T31E-02    [Abstracts]
TI: Testing Thermodynamic-Based Model Predictions of Stable Isotope-Based Paleo-Altimetry Using Modern Surface Waters
AU: * Rowley, D B
EM: drowley@uchicago.edu
AF: The University of Chicago, Department of the Geophysical Sciences 5734 S. Ellis Avenue, Chicago, IL 60637 United States
AB: Rowley et al. (2001, EPSL, 188, 253-268) present an atmospheric thermodynamic based calculation of the expected relationship between the oxygen and hydrogen isotopic composition of precipitation and elevation in low-latitude orographic settings. The isotopic lapse rate thus derived normalizes the absolute isotopic composition by differencing isotopic compositions of high elevation samples and low elevation starting composition and expressed as Δ(δ¹⁸O). This theoretical approach contrasts with empirical approaches of applying observed isotopic lapse rates to paleo-elevation estimates as it quantifies the major controlling factors (primarily starting low elevation temperature (T) and relative humidity (RH) on the lapse rate and allows them to be assessed at times in the past. Theoretically, the isotopic composition of surface waters should represent the precipitation-weighted, hypsometric mean elevation of the drainage basin above the sampling elevations. Because hypsometry and precipitation are not simple linear functions Δ(δ¹⁸O) measured in surface water systems should not increase in a simple linear fashion with increasing elevation, in accord with observation. Comparison of isotopic and hydrographic data from numerous collections of surface waters from the Indo-Gangetic plain, frontal and high Himalaya, and southern Tibet with model predictions suggests that predictions are typically within about plus/minus 500m of reality directly testing the reliability of the model. Data-model comparisons reveal an asymmetry such that predicted elevations more often underestimate real elevations rather than overestimate them. Finally orographic precipitation is typically concentrated at relatively low elevations at orographic fronts resulting in relatively little contribution of high altitude run-off in low land rivers potentially negating the possibility of assessing elevations from isotopic records of foreland basin river systems.
DE: 1051 Sedimentary geochemistry
DE: 4914 Continental climate records
DE: 9320 Asia
DE: 9604 Cenozoic
DE: 9810 New fields (not classifiable under other headings)
SC: Tectonophysics [T]
MN: Fall Meeting 2005