Abstract
AbstractErosion at Earth’s surface exposes underlying bedrock to climate-driven chemical and physical weathering, transforming it into a porous, ecosystem-sustaining substrate consisting of weathered bedrock, saprolite, and soil. Weathering in saprolite is typically quantified from bulk geochemistry assuming physical strain is negligible. However, modeling and measurements suggest that strain in saprolite may be common, and therefore anisovolumetric weathering may be widespread. To explore this possibility, we quantified the fraction of porosity produced by physical weathering, FPP, at three sites with differing climates in granitic bedrock of the Sierra Nevada, California, USA. We found that strain produces more porosity than chemical mass loss at each site, indicative of strongly anisovolumetric weathering. To expand the scope of our study, we quantified FPP using available volumetric strain and mass loss data from granitic sites spanning a broader range of climates and erosion rates. FPP in each case is ≥0.12, indicative of widespread anisovolumetric weathering. Multiple regression shows that differences in precipitation and erosion rate explain 94% of the variance in FPP and that >98% of Earth’s land surface has conditions that promote anisovolumetric weathering in granitic saprolite. Our work indicates that anisovolumetric weathering is the norm, rather than the exception, and highlights the importance of climate and erosion as drivers of subsurface physical weathering.
Highlights
In eroding landscapes, chemical and physical weathering transform unaltered protolith into weathered bedrock, saprolite, and soil as it is exhumed by erosion and gradually exposed to climate
Subsurface weathering is commonly studied using the bulk geochemistry of weathered rock and saprolite to quantify chemical mass losses accrued during exhumation of protolith by erosion (Riebe et al, 2017)
Our results indicate that weathering in granitic saprolite is commonly anisovolumetric and that climate and erosion rate strongly regulate the relative importance of subsurface physical and chemical weathering
Summary
Chemical and physical weathering transform unaltered protolith into weathered bedrock, saprolite, and soil as it is exhumed by erosion and gradually exposed to climate. Our results indicate that weathering in granitic saprolite is commonly anisovolumetric and that climate and erosion rate strongly regulate the relative importance of subsurface physical and chemical weathering.
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