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I use time-constrained sediment volumes delivered by glaciers calving into Marinelli Fjord (55°S), an outlet glacier of the Cordillera Darwin Ice Cap, Southern Patagonia, to determine erosion rates across different timescales. These results indicate that modern sediment yields and erosion rates from temperate tidewater glaciers can exceed long-term values over the time of deglaciation after the LGM (centennial and millennial time scales) by up to two orders of magnitude. In northern Patagonia (Gualas glacier area, 46.5°S), an overall increase in sediment production in the late Holocene is interpreted as result of a sharp increase in centennial timescale precipitation (intensified westerly winds). Erosion rates values span two orders of magnitude from 0.03 mm/yr for Lapeyrere Bay at Anver Island (~64.5°S), up to 1.09 mm/yr for San Rafael glacier at northern Patagonia (~46.5°S). Rates from the Antarctic Peninsula glaciers are in general lower than the temperate Patagonian glaciers. A good correlation of erosion rates and modern (estimated sea level annual 1970 temperature) sea level annual temperature was found. Latitudinal decrease of millenial is interpreted as result of decreasing annual temperature although decreasing in annual precipitation is suggested. The pattern of thermochronology ages from other studies (Thompson et al., 2010; Guenthner et al., 2010), along with the values of 10 3 and 10 6 years timescales erosion rates from this study, indicate that long-term glacial erosion decreases significantly its efficiency with latitude, implying that long-term glacial cover acts as a protective blanket, hindering erosion and allowing mountain growth. We conclude that the pattern of erosion rate decrease with timescale reflects the sensitivity of glaciers to climate variability. Temperate glaciers have higher sensitivity and greater response amplitude to climatic stress than subpolar or polar glaciers. This results in a decrease in erosion rates (sediment production) with latitude, and also in a decrease of erosion rate gradients with timescale.

L’érosion et la redistribution des particules détachées représentent un enjeu environnemental, sociétal et économique majeur. Afin de mettre en place des mesures de protection, il est nécessaire d’identifier et quantifier les sources et puits de sédiments ainsi que leur dynamique spatiale et temporelle. L’objectif de cette thèse est donc de dresser le bilan sédimentaire d’un large bassin versant (Loire Bretagne, 155 000 km2) aux paysages contrastés. Sur les versants, les particules détachées issues des différentes sources (érosion diffuse, concentrée, mouvements de masse) représentent un apport de 1.5 * 107 t.an−1 (contribution respective au stock : 82.4%, 12.9%, 4.7%). La prise en compte de la distribution spatiale des processus mis en jeu dans le transfert particulaire et des caractéristiques du site d’étude (ruissellement par saturation en zone de plaine et présence de haies) dans un indice qualitatif permet d’évaluer la connectivité des versants. L’érosion de berge contribue également au stock sédimentaire à hauteur de 6.9 * 105 t.an−1. Au final, seuls 5% des particules détachées, toutes sources confondues, sont transportées jusqu’à l’exutoire du bassin versant et témoignent du fort taux de dépôt au sein du bassin. En parallèle, une valorisation de la base de données des éléments dissous permet de montrer l’importance des flux sédimentaires exportés sous forme dissoute (~ 90% des exports totaux). La représentation de l’ensemble de ces résultats à différentes résolutions spatiales permet de développer une approche qualitative du transfert particulaire et d'identifier les zones à risque. / Erosion and particles redistribution represent major environmental, societal and economic issues. To adopt protection measures, it is essential to identify and quantify sources and sinks of sediment and their spatial and temporal dynamic. The aim of this work is thus to establish a sediment budget for a large river basin (Loire and Brittany river basin 155,000 km2) with contrasted landscapes. On hillslopes, detached particles from the miscellaneous form of erosion (sheet and rill erosion, gullies and mass movements) represent a supply of 1.5 * 107 t.yr−1 (contribution to the stock of 82.4%, 12.9%, and 4.7% respectively). The consideration of the spatial distribution of processes involved in sediment transport and the characteristics of the study site (soil saturation and presence of hedgerows) in a qualitative landscape-based index allows us to assess the hillslope connectivity. Bank erosion also participates in the sediment budget with 6.9 * 105 t.yr−1 of material provided to the river network. In the end, only 5% of detached particles, from all sources of sediment, reach the basin outlet indicating a substantial deposition on the way from source to outlet. In parallel, the use of the database of dissolved elements allows us to highlight the importance of the dissolved sediment fluxes ( 90% of the total exports of the Loire river). The presentation of all results at different spatial scales permits to provide a qualitative approach of sediment source-to-sink transfers and to identify hotspots of erosion and transfers.