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...tion (CDF), decrease with increasing erosion rates and decreasing soil thickness, reflecting the decreasing influence of the supply of fresh minerals from soil production and increasing influence of shortened mineral residence times in a thinning weathering zone. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) 41J.L. Dixon et al. / Earth and Planetary Science Letters 323-324 (2012) 40–49the highest global riverine solute fluxes (Gaillardet et al., 1999; Waldbauer and Chamberlain, 2005) and soil weathering rates (Riebe et al., 2001), suggesting that tectonic uplift stimulates chemical weathering rates by increasing the supply of freshminerals. Conversely, rapid upliftmay also limit chemicalweathering rates as erosion rates increase, soil residence times decrease, and weatherable minerals do not have sufficient time to weather completely (Riebe et al., 2004; Stallard and Edmond, 1983; West et al., 2005). In such a case, mineral weathering extent (the relative amount lost to dissolution) and rates (how rapidly mineral mass is lost) are limited by the kinetics of chemical reactions. Recent modeling studies (Ferrier and Kirc...

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...rns in both chemical erosion rates and the degree of soil chemical alteration differ markedly between studies, and this clouds interpretations about how climate should affect chemical erosion rates and soil development elsewhere. In this contribution, we document chemical and physical erosion rates along two altitudinal (and hence climatic) transects in the canyon of the South Fork of the Salmon River in central Idaho (Figure 1). We measured these rates using a solid-phase mass balance technique that yields co-located estimates of long-term chemical and physical erosion rates [Stallard, 1985; Riebe et al., 2001], which permits us to directly account for the potentially confounding effects of physical erosion rates and dust on chemical erosion rates. Before discussing the study sites, we first present the conceptual framework we use to estimate long-term chemical and physical erosion rates. 2. Measuring Chemical and Physical Erosion Rates With Cosmogenic Nuclides and Elemental Abundances in Regolith, Rock, and Dust [8] An increasingly popular method for estimating chemical erosion rates in eroding terrain is the solid-phase mass balance method, which combines regolith production rates with rockto-reg...

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... the HTP is not a major sink for atmospheric CO2. We note that other studies have concluded the opposite, namely that uplift-induced changes inweathering do regulate long-term atmospheric CO2 levels (=-=Riebe et al., 2001-=-;Hilley et al., 2010;Misra and Froelich, 2012). We reconcile this apparent discrepancy with three observations. The first is that many studies have neglected the significant contribution of trace calc...

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...can quantify with direct measurements. These measurements include in situ produced cosmogenic radionuclides (CRNs) (10Be and 26Al) in saprolites and river sands to quantify soil production and catchment-averaged erosion rates, and major (Si, Al, Fe, Ca, Na, K, and Ti oxides) and trace (Zr, Th and Ce) element analyses of the parent material and soils to quantify their weathered condition and weathering rates. Coupling these methods across diverse upland landscapes is an effective way to quantify the role of climatic (Porder et al., 2007; Dixon et al., 2009a; Ferrier et al., 2012) and tectonic (Riebe et al., 2001b; West et al., 2005; Dixon et al., 2012) forcing on landscape evolution, given the assumption of spatially homogenous 76 A.M. Heimsath, B.C. Burke / Geomorphology 200 (2013) 75–88initial conditions for the elements in the parent material. All studies applying these methods recognize the potential for local variability, and important work highlights the complexity introduced by local variability of measured parameters (Riebe et al., 2001a; Riggins et al., 2011; Ferrier et al., 2012). To evaluate how local variation of the major element oxides and trace element concentrations can indeed impact ...

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... in Eq. (17), predicted weathering rind advance rates will be faster than measured advance rates (Fig. 6). Physical erosion rates can also influence weathering advance rates (Gaillardet et al., 1999; =-=Riebe et al., 2001-=-, 2003). For the data compiled here, the only systems where physical erosion is occurring are those measured at the watershed scale; therefore, variations in weathering advance rates due to erosion ar...

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...n syntaxis and high CWRSil due to high precipitation. These data support weathering models that show that rapid rates of chemical weathering are generated in areas of rapid surface uplift or erosion (=-=Riebe et al., 2001-=-; Riebe et al., 2004; Chamberlain et al., 2005; Waldbauer and Chamberlain, 2005). Rapid chemical denudation in the eastern syntaxis generates markedly higher rates of CO2 consumption by silicate weath...