Abstract
AbstractOxidative 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 (OCpetro) 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 and Vogelbach) and Colorado, USA (East River). The Swiss catchments reveal a higher dissolved Re flux in the catchment with higher erosion rates, but have similar [Re]/[Na+] and [Re]/[SO42−] ratios, which indicate a dominance of Re from OCpetro. Despite differences in rock type and hydro‐climatic setting, the three catchments have a positive correlation between river water [Re]/[Na+] and [Re]/[SO42−] 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 release by OCpetro oxidation of 5.7 +6.6/−2.0 tC km−2 yr−1 for the Erlenbach. The overall weathering intensity was ∼40%, meaning that the corresponding export of unweathered OCpetro in river sediments is large, and the findings call for more measurements of OCpetro oxidation in mountains and rivers as they cross floodplains.
Highlights
When sedimentary rocks are exposed to oxygen in the atmosphere and hydrosphere, organic matter contained within the rocks can be oxidized (Petsch et al, 2000) and release carbon dioxide (CO2) during “geo-respiration” (Keller & Bacon, 1998)
Based on our ideas of how water moves through the landscape, our results suggest that rhenium is moved from a near-surface zone in all three catchments, where oxygen and rock organic carbon react
We explore the mobility of Re and oxidative weathering in three alpine catchments underlain by sedimentary rocks
Summary
When sedimentary rocks are exposed to oxygen in the atmosphere and hydrosphere, organic matter contained within the rocks can be oxidized (Petsch et al, 2000) and release carbon dioxide (CO2) during “geo-respiration” (Keller & Bacon, 1998). Katharine Maher Writing – original draft: Robert G. Katharine Maher megatons of carbon per year, MtC yr−1 (Petsch, 2013). The process plays a central role in the geological carbon cycle (Derry & France-Lanord, 1996; Hayes et al, 1999; Hilton & West, 2020), and in part, governs oxygen concentrations in the atmosphere (Berner & Canfield, 1989)
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