Linking Process and Form in Carbonate Rock Through Cosmogenic 36-Chlorine Erosion Rates, Regolith Mass Balance, and Fluvial and Hillslope Topography

Carbonate minerals are susceptible to dissolution, so any signal from enhanced chemical erosion controlled by climate might be magnified in landscapes underlain by carbonate rocks. The reduction of sediment flux magnitude (an important factor in shaping landscapes) by chemical erosion could be one mechanism by which climate modifies landscape. This study aims to test landscape evolution models on carbonate terrain, and uses recently-developed cosmogenic 36-Chlorine techniques to measure long-term erosion rates combined with a compilation of previously published erosion rates from carbonate rocks. The stream power model of fluvial erosion describes erosion rate in terms of channel steepness and the erosional efficiency coefficient, which incorporates factors such as runoff variability, sediment flux, and bedrock erodibility. The compilation of 32 catchment-averaged erosion rates, including 4 new basin erosion rates, channel steepness, and mean annual precipitation (MAP), show slight sensitivity of erosion rates to MAP when channel steepness is accounted for. Carbonate river basins are not strongly sensitive to MAP in a singular, monotonic manner. The linear sediment transport law predicts that erosion is linearly related to hilltop curvature by a hillslope sediment transport coefficient, D. Previous work finds that vegetation and climate influence D. Since carbonate rocks may be more susceptible to climate, I test whether the topography and erosion rates indicate enhanced chemical erosion or D along a MAP gradient. I recalculate erosion rates, extract hilltop curvature, and calculate D for 50 carbonate hillslopes. Carbonate D values are uncorrelated with MAP, but peak in the 600-900 mm/yr range, a more complex pattern than simply enhanced chemical erosion or D with MAP. Arid regions can accumulate significant amounts of dust over millennia, which could overprint sediment loss due to chemical erosion. Using a mass balance framework, I quantify the chemical erosion and dust accumulation for two carbonate hilltop sites in central Arizona (site MT1; MAP = 450 mm/yr) and SE Spain (NQ; MAP 550 mm/yr) with cosmogenic 36-Chlorine and meteoric 10-Beryllium. More dust accumulated at MT1, the arid site, augmenting bedrock mass flux by 25%. Chemical erosion was greater at NQ, but accounted for >50% of mass loss at both sites. The effect of climate on carbonate rocks appears to be nuanced; future work should expand data coverage and investigate specific mechanisms of chemical erosion across climate gradients.