Patterns and rates of 10³-10⁵ yr denudation in carbonate terrains under subhumid to subalpine climatic gradient, Mount Hermon, Israel

Despite the worldwide ubiquity of carbonate terrains, quantification and understanding of rates and patterns of carbonate erosion are still lacking. Carbonate landscapes are prone to chemical weathering (dissolution) and should therefore be strongly influenced by climatic variables such as precipitation. However, isolating the impact of these variables is difficult, as denudation rates are also influenced by tectonic processes and lithology. This study focused on deciphering 10³-10⁵ yr denudation patterns across Mount Hermon, Israel, exploiting its climatic gradient (1500-600 mm/yr) and homogeneous lithology (Jurassic limestone). The concentrations of in situ cosmogenic ³⁶Cl in bedrock and sediment samples were utilized to characterize the spatial distribution of denudation and examine its potential drivers. Our results indicate differential denudation rates of Mount Hermon hilltops. The subalpine region (1700-2200 m, ~1300-1500 mm yr^-1, mean annual temperature of 7 °C) yielded an average hilltop denudation rate of 19 ± 5 mm k.y.^-1 (n = 5), while hilltops at intermediate altitudes (1000-1600 m, ~900-1200 mm yr^-1) seem to erode faster at 42 ± 8 mm k.y.^-1 (n = 7). In addition, soil cover seems to enhance denudation rates relative to bare bedrock conditions. This highlights a major difference between carbonates and silicates, where numerous silicates data sets suggest an exponential decrease in bedrock weathering and soil production as the soil thickness increases. Our new ³⁶Cl results, in conjunction with previously measured average hilltop lowering rates within the subhumid Mediterranean climate across the Judean mountain range (500-600 mm yr^-1, 19 ± 7 mm k.y.^-1), suggest that optimum conditions for carbonate denudation and chemical weathering occur below the tree line, where soil is abundant, pCO2 is higher, and snow cover is scarce. This observation has intriguing implications in terms of long-term landscape evolution-an increase in the elevation of a mountain range above the tree line may provide negative feedback, which will decrease its hilltop erosion rate.