Limits to quantifying climate driven changes in denudation rates with cosmogenic radionuclides

The hypothesis that climate change significantly modifies the denudation history of an orogen can be tested by reconstructing catchment-wide denudation histories. Cosmogenic radionuclides measured in sediment deposits of known age (e.g. a sequence of fluvial terraces) offer one approach for quantifying catchment-wide paleo-denudation rates. We present a numerical model, and two case studies, that evaluate the utility of this technique for reconstructing different denudation histories. The concentration of cosmogenic beryllium-10 (10Be) is calculated for a sequence of sediments produced from climate driven variations in the mean denudation rate of a drainage basin at sea level and high latitude. The model accounts for the nucleonic and muonic production, and decay of 10Be as sediment is eroded and stored in deposits of different ages. Two scenarios for different climate driven denudation histories are considered: (1) A sinusoidal variation in the input denudation rate with free parameters of periodicity (23, 41, 100 kyr), amplitude (0.1, 0.5, 1.0), and mean denudation rate (0.01, 0.1, 1.0 mm yr− 1). (2) A climate driven denudation history based on oscillations of a global benthic foraminiferal oxygen isotope (δ18O) record over the last 2 Myr. Results from both scenarios suggest cosmogenic radionuclides measured in a system with high denudation rates (> ∼ 0.5 mm yr− 1), longer periodicity (100 kyr), and low amplitude have the highest potential for reconstructing climate driven paleo-denudation rates. Unfortunately, the high denudation rates preferred in the theoretical consideration are not suitable for paleo-denudation rate determination due to overprinting of nuclides accumulated during denudation by post-depositional decay and irradiation. Hence, a compromise between the capability to determine changes in paleo-denudation rates and the determination of true denudation rates has to be accepted. Application of the model to previous data sets from northwest Europe and southwest North America produce a good agreement, but highlight the need for future work to consider how geomorphic processes (e.g. landsliding) respond to climate change and influence catchment-wide denudation rates. In addition, other climate proxies than the benthic foraminiferal δ18O record should be used for specific sample locations.