Controls on sediment residence times in an Alpine river catchment inferred from uranium isotopes

Type Article
Date 2023-06
Language English
Author(s) Thollon Maude1, 2, Dosseto AnthonyORCID1, Toucanne SamuelORCID2, Bayon Germain2
Affiliation(s) 1 : Wollongong Isotope Geochronology Laboratory, School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, NSW 2522, Australia
2 : Univ Brest, CNRS, Ifremer, Geo-Ocean, F-29280 Plouzane, France
Source Earth And Planetary Science Letters (0012-821X) (Elsevier BV), 2023-06 , Vol. 611 , P. 118130 (10p.)
DOI 10.1016/j.epsl.2023.118130
Keyword(s) uranium isotopes, Var River, sediment residence time, sediment transport, hillslope

Quantifying the timescale of sedimentary processes in river basins, such as erosion, transport and deposition, and their relationships with geomorphic parameters is important in the context of ongoing climate change. In this study, we combine uranium activity ratios (234U/238U) for fine-grained (<63 μm) fluvial sediments from the Var River basin (Southern French Alps) and inferred sediment residence times, to catchment-scale spatial analysis of geomorphic parameters with the aim to investigate the factors that influence the timescale of hillslope storage and alluvial transport.

Our results show that the U isotope composition of sediments and inferred sediment residence time are mostly controlled by geomorphic parameters such as catchment elevation, slope and curvature, rather than catchment lithology. We show that sediment residence times are shorter in steep, high elevation terranes, but markedly increase wherever catchment-averaged slopes <30°, reflecting the transition from bedrock-dominated to soil-covered landscapes. Independent estimates of sediment residence times using spatial data for soil thickness and 10Be-derived denudation rates show good agreement with those calculated from U isotopes. This observation validates the suitability of U isotopes to quantify sediment residence times in river catchments and for investigating how geomorphic processes control the duration of hillslope storage and fluvial transport. Furthermore, these results show that the application of U isotopes to sedimentary deposits provides robust information on the relationship between climate variability and catchment erosion, allowing us to assess the role of intrinsic vs extrinsic controls on sediment routing at the millennial timescale.

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Publisher's official version 10 1 MB Open access
MMC 1. Supplementary Figure 1. Adsorption (red circles and curve) and desorption (blue squares and curve) isotherms for sample BV-VAR-08. 1 130 KB Open access
MMC 2. Supplementary Figure 2. Sediment residence times calculated using U isotopes as a function of soil residence times estimated using catchment-averaged soil thickness (SoilGrids) and the 10Be... 1 126 KB Open access
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