Erosion and weathering in carbonate regions reveal climatic and tectonic drivers of carbonate landscape evolution

Abstract

Carbonate rocks are highly reactive and can have higher ratios of chemical weathering to total denudation relative to most other rock types. Their chemical reactivity affects the first-order morphology of carbonate-dominated landscapes and their climate sensitivity to weathering. However, there have been few efforts to quantify the partitioning of denudation into mechanical erosion and chemical weathering in carbonate landscapes such that their sensitivity to changing climatic and tectonic conditions remains elusive. Here, we compile bedrock and catchment-averaged cosmogenic calcite–36Cl denudation rates and compare them to weathering rates derived from stream water chemistry from the same regions. Local bedrock denudation and weathering rates are comparable, ∼20–40 mm ka−1, whereas catchment-averaged denudation rates are ∼2.7 times higher. The discrepancy between bedrock and catchment-averaged denudation is 5 times lower compared to silicate-rich rocks, illustrating that elevated weathering rates make denudation more spatially uniform in carbonate-dominated landscapes. Catchment-averaged denudation rates correlate well with topographic relief and hillslope gradients, and moderate correlations with runoff can be explained by concurrent increases in weathering rates. Comparing denudation rates 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 and impacts the landscape morphology. This leads us to propose a conceptual model whereby in humid, slowly uplifting regions, carbonates are associated with low-lying, flat topography because slope-independent chemical weathering dominates denudation. In contrast, in 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 and runoff loss to groundwater systems. This result suggests that carbonates represent an end member for interactions between climate, tectonics, and lithology.