Denudation systematics inferred from in situ cosmogenic Be-10 concentrations in fine (50-100 mu m) and medium (100-250 mu m) sediments of the Var River basin, southern French Alps

Type Article
Date 2019-12
Language English
Author(s) Mariotti ApollineORCID1, Blard Pierre-Henri1, Charreau Julien1, Petit Carole2, Molliex Stephane1, 3, Aumaitre Georges4, Bourles Didier L.4, Keddadouche Karim4
Affiliation(s) 1 : Univ Lorraine, CNRS, CRPG, UMR 7358, F-54500 Vandoeuvre Les Nancy, France.
2 : Univ Nice, Geoazur, F-06905 Sophia Antipolis, France.
3 : Inst Univ Europeen Mer, Lab Geosci Ocean, F-29280 Plouzane, France.
4 : Aix Marseille Univ, CNRS, Technopole Environm Arbois Meditetranee, INRA,Coll France,UM 34 CEREGE,IRD, BP80, F-13545 Aix En Provence, France.
Source Earth Surface Dynamics (2196-6311) (Copernicus Gesellschaft Mbh), 2019-12 , Vol. 7 , N. 4 , P. 1059-1074
DOI 10.5194/esurf-7-1059-2019
WOS© Times Cited 4
Abstract

Marine sedimentary archives are well dated and often span several glacial cycles; cosmogenic Be-10 concentrations in their detrital quartz grains could thus offer the opportunity to reconstruct a wealth of past denudation rates. However, these archives often comprise sediments much finer (< 250 mu m) than typically analyzed in Be-10 studies, and few studies have measured Be-10 concentrations in quartz grains smaller than 100 mu m or assessed the impacts of mixing, grain size, and interannual variability on the Be-10 concentrations of such fine-grained sediments. Here, we analyzed the in situ cosmogenic Be-10 concentrations of quartz grains in the 50-100 and 100-250 mu m size fractions of sediments from the Var basin (southern French Alps) to test the reliability of denudation rates derived from Be-10 analyses of fine sands. The Var basin has a short transfer zone and highly variable morphology, climate, and geology, and we test the impact of these parameters on the observed Be-10 concentrations. Both analyzed size fractions returned similar Be-10 concentrations in downstream locations, notably at the Var's outlet, where concentrations ranged from (4.02 +/- 0.78) x 10(4) to (4.40 +/- 0.64) x 10(4) atoms g(-1) of quartz. By comparing expected and observed Be-10 concentrations at three major river junctions, we interpret that sediment mixing is efficient throughout the Var basin. We resampled four key locations 1 year later, and despite variable climatic parameters during that period, interannual Be-10 concentrations were in agreement within uncertainties, except for one upper subbasin. The Be-10-derived denudation rates of Var subbasins range from 0.10 +/- 0.01 to 0.57 +/- 0.09 mm yr(-1), and spatial variations are primarily controlled by the average subbasin slope. The integrated denudation rate of the entire Var basin is 0.24 +/- 0.04 mm yr(-1), in agreement with other methods. Our results demonstrate that fine-grained sediments (50-250 mu m) may return accurate denudation rates and are thus potentially suitable targets for future Be-10 applications, such as studies of paleo-denudation rates using offshore sediments.

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Mariotti Apolline, Blard Pierre-Henri, Charreau Julien, Petit Carole, Molliex Stephane, Aumaitre Georges, Bourles Didier L., Keddadouche Karim (2019). Denudation systematics inferred from in situ cosmogenic Be-10 concentrations in fine (50-100 mu m) and medium (100-250 mu m) sediments of the Var River basin, southern French Alps. Earth Surface Dynamics, 7(4), 1059-1074. Publisher's official version : https://doi.org/10.5194/esurf-7-1059-2019 , Open Access version : https://archimer.ifremer.fr/doc/00637/74894/