Near Steady Late Pleistocene Tropical Denudation Rates in SW Madagascar

Abstract

Denudation is a key parameter controlling the evolution of the Earth's surface, the production of soils, the stability of relief, or the long-term evolution of climate. Climate fluctuations conversely have a strong impact on denudation, but these complex feedback mechanisms are still under-constrained. To better predict future changes that will affect our habitat and understand the links between climate and denudation, precise quantification of paleo-denudation rates is required. In this work, we measure cosmogenic radionuclides (¹⁰Be) in turbidites of a well-dated marine sedimentary core recovered in the Mozambique Channel to provide a 900-ka long near-continuous record of paleo-denudation rates over the 100-ka climatic cycles. Neodymium isotopes and heavy mineral analysis were used to provide constraints on the provenance of terrigenous sediments exported from Madagascar to the studied site and show that temporal variations in sediment provenance are limited and decoupled from climatic cyclicity. Our ¹⁰Be-based paleo-denudation rates are in the same order as modern rates, ranging from 17.4 ± 5.8 mm/ka to 73.9 ± 29.4 mm/ka (1 standard deviation), and do not show major variations through the Middle and Late Pleistocene. Importantly, we did not identify a systematic significant impact of glacial/interglacial cyclicity on denudation rates. Denudation of this subtropical island may instead have been controlled by variability of monsoon intensity associated with shifts in the Inter Tropical Convergence Zone, but this interpretation remains speculative at this stage as it cannot be recorded within the resolution of cosmogenic-derived denudation rates.