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The quantitative estimation of paleoaltitude has become an increasing focus of Earth scientists because surface elevation provides constraints on the geodynamic mechanisms operating in mountain belts, as well as the influence of mountain belt growth on regional and global climate. The general observation of decreasing δ18O and δ2H values in rainfall as elevation increases has been used in both empirical and theoretical approaches to estimate paleoelevation. These studies rely on the preservation of ancient surface water compositions in authigenic minerals to reconstruct the elevation at the time the minerals were forming. In this review we provide a theory behind the application of stable isotope-based approaches to paleoaltimetry. We apply this theory to test cases using modern precipitation and surface water isotopic compositions to demonstrate that it generally accords well with observations. Examples of the application of paleoaltimetry techniques to Himalaya-Tibet and the Andes are discussed with implications for processes that cause surface uplift.
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Download Supplemental Figures 1-4 as a PDF, or see below.
Supplemental Figure 1 Trajectory of the isotopic composition of vapor-derived condensate (black) and weighted mean δ18Op derived from 1000 m (light gray), 1500 m (dark gray), and 2000 m (medium gray) above the ground surface sampled within a layer 1000 m thick. The vapor-derived condensate trajectory is based on a RH of 80% at low elevations and starting T of 287 K. The box with dashes represents the sampling interval, with the stars gray-scale coordinated with the curves to represent the mean heights from which precipitation would be derived for each of the three curves for the station corresponding to Grimsel. Weighted mean annual isotopic compositions and reported 1σ standard deviations of IAEA stations (dots with error bars) (IAEA 1992) plotted at each station's elevation compared with model-derived weighted mean precipitation for the Alps. The best-fit curve used in all of the modeling is for precipitation to result from sampling the condensation weighted mean isotopic composition of the condensation 1500 m above the surface in a 1000-m-thick parcel. Inset map: Locations of IAEA stations and their heights and weighted mean δ18Op as reported. Abbreviations: Ko, Konstanz; Be, Bern; Me, Meiringen; Ga, Garmisch-Pertenkirch; Gu, Guttannen; Gr, Garmisch. Note that Meiringen and Guttannen are located deep within the Alps in the Aare Valley and hence precipitation falling there is likely more fractionated than typical of their station elevations.
Supplemental Figure 2 Probability density function of T and RH extracted from entirely oceanic areas of the low-latitude (<35°) part of Earth from the 40-year NCEP-CDAS reanalysis output (Kalnay et al. 1996). Sampling of T and RH from within this distribution provides an estimate of the variance of resulting isotopic compositions as a function of elevation.
Supplemental Figure 3 Data from a transect of precipitation as a function of elevation from Trinidad (200 m) to El Alto (4080 m) (Gonfiantini et al. 2001). Weighted mean data are normalized relative to the amount weighted mean isotopic composition of Trinidad (−5.17‰), and unweighted mean data are normalized relative to the unweighted mean isotopic composition of Trinidad (−3.84‰) where means are calculated from data in table 6 and not the summary information in table 5 from Gonfiantini et al. (2001). Points are plotted at the station elevation where the precipitation was collected. Curves of the global mean isotopic composition as a function of elevation and ± 1σ and ± 2σ variations from Rowley et al. (2001) are included.
Supplemental Figure 4 Plot of the δ18OSMOW value of water in equilibrium with soil carbonate nodules versus growth temperatures of soil carbonate nodules (from Ghosh et al. 2006b). Small symbols are individual samples and large symbols are averages for the 11.4–10.3 Ma, 7.6–7.3 Ma, and 6.7–5.8 Ma age groups. See Ghosh et al. (2006b) for discussion of error bars. Gray curves show the mean annual trend (solid curve) and trend of Jan/Feb extremes (dashed curve) for the modern relationships between surface temperature and δ18OSMOW value of meteoric water, with contours showing altitude in kilometers. Green curves plot the expected location of the mean annual and Jan/Feb extremes in the mid-Miocene based on inferred changes in the latitude of Bolivia, low-latitude climate, and the δ18OSMOW value of sea water. Fine dashed lines connecting the mid-Miocene mean annual curve and Jan/Feb extreme curve show the slopes of seasonal variations in T and δ18OSMOW value of water at a fixed altitude (inferred to be the same in the Miocene as today). Paleoaltitudes of age-group averages were estimated by their intersections with this set of altitude contours, as indicated by the red, yellow, and blue dashed lines.