Nonlinear forcing of climate on mountain denudation during glaciations

摘要

Denudation is one of the main processes that shapes landscapes. Because temperature, precipitation and glacial extents are key factors involved in denudation, climatic fluctuations are thought to exert a strong control on this parameter over geological timescales. However, the direct impacts of climatic variations on denudation remain controversial, particularly those involving the Quaternary glacial cycles in mountain environments. Here we measure in situ cosmogenic Be-10 concentration in quartz in marine turbidites of two high-resolution cores collected in the Mediterranean Sea, providing a near-continuous (temporal resolution of similar to 1-2 kyr) reconstruction of denudation in the Southern Alps since 75 kyr ago (ka). This high-resolution palaeo-denudation record can be compared with well-constrained climatic variations over the last glacial cycle. Our results indicate that total denudation rates were approximately two times higher than present during the Last Glacial Maximum (26.5-19 ka), the glacial component of the denudation rates being 1.5(-1.0)(+0.9) mm yr(-1). However, during moderately glaciated times (74-29 ka), denudation rates were similar to those today (0.24 +/- 0.04 mm yr(-1)). This suggests a nonlinear forcing of climate on denudation, mainly controlled by the interplay between glacier velocity and basin topography. Hence, the onset of Quaternary glaciations, 2.6 million years ago, did not necessarily induce a synchronous global denudation pulse.