Jens M. Turowski Matthew Winnick Mathieu Dellinger Patrick Schleppi Kenneth H. Williams Corey Lawrence Katharine Maher Martin West Amanda Hayton Robert Hilton 2021 <div class="article-section__content en main"><p>Oxidative weathering of sedimentary rocks plays an important role in the global carbon cycle. Rhenium (Re) has been proposed as a tracer of rock organic carbon (OC_petro) oxidation. However, the sources of Re and its mobilization by hydrological processes remain poorly constrained. Here we examine dissolved Re as a function of water discharge, using samples collected from three alpine catchments that drain sedimentary rocks in Switzerland (Erlenbach, Vogelbach) and Colorado, USA (East River). The Swiss catchments reveal a higher Re flux in the catchment with higher erosion rates, but have similar [Re]/[Na⁺] and [Re]/[SO₄^2-] ratios, which indicate a dominance of Re from OC_petro. Despite differences in rock type and hydro-climatic setting, the three catchments have a positive correlation between river water [Re]/[Na⁺] and [Re]/[SO₄^2-] and water discharge. We propose that this reflects preferential routing of Re from a near-surface, oxidative weathering zone. The observations support the use of Re as a proxy to trace rock-organic carbon oxidation, and suggest it may be a hydrological tracer of vadose zone processes. We apply the Re proxy, and estimate CO₂<span>&nbsp;</span>release by OC_petro<span>&nbsp;</span>oxidation of 5.7<span>&nbsp;</span>^+6.6/_-2.0<span>&nbsp;</span>tC km^-2<span>&nbsp;</span>yr^-1<span>&nbsp;</span>for the Erlenbach. The overall weathering intensity was ∼40%, meaning that the corresponding export of un-weathered OC_petro<span>&nbsp;</span>in river sediments is large, and the findings call for more measurements of OC_petro<span>&nbsp;</span>oxidation in mountains and rivers as thet cross floodplains.</p></div> application/pdf 10.1029/2021WR029844 en American Geophysical Union Concentration-discharge relationships of dissolved rhenium in Alpine catchments reveal its use as a tracer of oxidative weathering article