IMPACT OF THE LAST GLACIAL-INTERGLACIAL ON DENUDATION IN THE ALPS

Study Area

Methods used

Project Summary


Reconstruction of denudation rates through time is an important task to quantify and understand the impact of climate on landscape evolution. For this study, we analyzed the in situ 10Be cosmogenic concentration in sediments of two long-piston cores that were collected offshore the Var River (Western Mediterranean Sea), precisely along the Var sedimentary ridge. These sedimentary archives have been well dated at a high resolution and analyzed for sediment provenance (Bonneau et al., 2017) thus providing a unique record to reconstruct the denudation history of the Var catchment in the Southern French Alps over the last 70 ka. 

This period covers the majority of the last glacial period and the associated Dansgaard-Oeschger events, the last glacial maximum (LGM, 26-19 ka) and the subsequent deglaciation (19-11 ka), and the Holocene, with all these events being precisely defined in the studied cores. Therefore, this setting offers the rare opportunity to study the impact of rapid climate fluctuations on denudation rates in a mountainous glaciated catchment over a time scale that is not impacted by tectonics.

 

We present 21 10Be paleo concentrations ranging from 1.24±0.51 x 104 atoms/gquartz to 5.99±1.90 x 104 atoms/gquartz. The 10Be paleo concentrations overall are very similar to present day 10Be concentrations (average of 4.20±0.67 x 104 atoms/gquartz at the watershed's outlet in 2016, or a denudation rate of 0.20 ±0.03 mm/year). This suggests similar paleo denudation rates between today, the 0-17 ka period and the 27-70 ka period.

 

Only the LGM shows a clear change in 10Be concentrations with much lower concentrations (average of 1.68±0.48 x 104 atoms/gquartz) suggesting high denudation rates during this period of maximum glacial extent in the French Alps.

These results suggest that climatic settings have a limited impact on overall denudation rates and that glaciers in the Mediterranean Alps either weren't strong agents of erosion during the MIS 3 (70-25 ka) or were smaller than previously thought. These results also suggest that only strong climatic fluctuations (such as the LGM) can induce meaningful changes in denudation rates.


Scientific Results

First results from this project were presented at the 4th Nordic Workshop on Cosmogenic Nuclides in 2018 and at EGU 2019 in Vienna.

The full study was published in 2021 in Nature Geoscience.