Richard F Ott, Sean F Gallen, David Helman

Carbonate rocks are highly reactive and presumably have higher ratios of chemical weathering to total denudation relative to most other rock types. Their high chemical reactivity affects the first-order morphology of carbonate-dominated landscapes and their sensitivity to climate. However, there have been few efforts to quantify the partitioning of denudation into physical erosion and chemical weathering in carbonate landscapes such that their sensitivity to changing climate and tectonic conditions and its effect on topography remains elusive. Here, we compile bedrock and catchment-average cosmogenic calcite-36Cl denudation rates and compare them to weathering rates. Local bedrock lowering and weathering rates are comparable, ~20 – 40 mm/ka, whereas catchment-average rates, which exist only for the Mediterranean, are ~2.7 times higher. This discrepancy is lower than the 15-fold difference in silicate-rich rocks illustrating that elevated weathering rates make denudation more spatially uniform in carbonate-dominated landscapes. Catchment-average denudation rates correlate well with topographic relief and hillslope gradient. Comparing these results with weathering rates shows that mechanical erosion processes contribute ~50% of denudation in southern France and ~70% in Greece and Israel. Our results indicate that the partitioning between largely slope-independent chemical weathering and slope-dependent mechanical erosion varies based on climate and tectonics. In humid, slowly uplifting regions, carbonates are associated with low-lying, flat topography because slope-independent chemical weathering dominates denudation. In contrast, in more arid climates with rapid rock uplift rates, carbonate rocks form steep mountains that facilitate rapid, slope-dependent mechanical erosion required to compensate for inefficient chemical weathering coupled with runoff loss to groundwater systems.