QUANTIFYING CLIMATE DRIVEN TRANSIENT DENUDATION RATES WITH COSMOGENIC NUCLIDES

Quantifying present and past denudation rates is important for understanding landscape evolution. Unfortunately the interaction between climate, tectonics and landscape evolution is complex and difficult to constrain. Cosmogenic nuclides measured in sediment deposits of known age (e.g. a sequence of river terraces) offer the possibility to determine transient denudation rates. In this study we determine the utility of this approach for quantifying climate driven denudation histories. A numerical model was used for the production and decay of ¹⁰Be during denudation of a drainage basin providing sediment to river terraces of different ages. The model quantifies the sensitivity of cosmogenic-derived denudation rates to climatic change by comparing true input denudation rates to what the measured cosmogenic denudation rate would be at the time of sediment deposition. Two scenarios for different climate driven input denudation rates are considered: (1) A sinusoidal variation in the true denudation rate with free parameters of cyclicity (23kyr, 41kyr, 100kyr), amplitude (0.1, 0.5, 1.0), and mean denudation rate (0.01, 0.1, 1.0 mm yr^-1). (2) A climate-derived denudation history based on oscillations of the δ18O record over the last 3 Myr. Variations in the amplitude and mean denudation rates of the record are considered.

Results are as follows: (a) Lower mean denudation rates (0.01-0.5 mm yr^-1) have a large misfit between the true and cosmogenic-derived denudation rates: (b) The difference between true and measured denudation rates decreases with decreasing amplitude: (c) a larger cyclicity in climate change results in a better fit of the cosmogenic and true denudation rates. Taken together, these results suggest cosmogenic nuclides measured in a system with high denudation rates (> ~0.5 mm yr^-1), larger cyclicity (100 kyr), and low amplitude have the highest potential for reconstructing climate driven paleodenudation rates. Unfortunately, the sediment recording the denudation rates is not accessible at the time of deposition and the nuclide concentration signal of climate change is overprinted by postdepositional nuclide production and decay. Therefore, the successful application of cosmogenic nuclides for paleodenudation rates also depends on the age of the sediment deposit, and the burial depth.