『Abstract
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, 1.0mm 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.
Keywords: denudation; climate; climate change; cosmogenic radionuclides』
1. Introduction
2. Methods: Predicting climate driven changes in denudation rates
2.1. Generation of a climate driven input denudation history
2.2. Calculation of a cosmogenic radionuclide-derived denudation
rate
2.3. Evaluation of results
3. Results for theoretical considerations
3.1. Influence of sinusoidal changes in climate
3.1.1. Influence of mean input denudation
3.1.2. Influence of increasing amplitude
3.1.3. Influence of periodicity
3.2. Influence of climate change derived from δ18O
on denudation rates
4. Discussion
4.1. Post-depositional modification of cosmogenic radionuclide
concentrations
4.2. Optimal conditions for quantifying climate driven changes
in denudation rates
4.3. Quantifying climate driven changes in Quaternary denudation
rates
4.3.1. Glacial/interglacial periodicity
4.3.2. 41 to 100 kyr periodicity
4.3.3. General cooling trend
4.4. Application to reported paleo-denudation rates
5. Conclusions
Acknowledgments
Appendix A. Supplementary data
References