Degree Name

Doctor of Philosophy


School of Earth, Atmospheric and Life Sciences


Studying how catchment erosion has responded to past climate change can help us to better understand not only how landscape evolution and source-to-sink processes operate, but also to predict the consequences of future climate change on soil resource availability and sediment discharge to the ocean. In this context, the aim of this PhD project was to investigate the variability of past sediment residence times in watersheds and to assess their relationships with erosion and climate change. The sediment residence times were calculated using uranium isotope activity ratios (234U/238U). First, U isotopic ratios were determined in a large number of world river sediments to improve our understanding of the environmental controls on sedimentary (234U/238U). Our results indicate that a multi-parameter approach can adequately predict the distribution of (234U/238U) in sediments, demonstrating the potential of using (234U/238U) to investigate past environments. Then, the spatial variability of sediment residence times was studied within a mountainous catchment (Var, France). Long residence times were determined in sediments from weathering-limited sub-catchments, while comparatively lower residence times were obtained in sub-catchments characterized by transport-limited weathering conditions. Finally, the temporal variability of sediment residence times in the Var Basin over the last 75,000 years was investigated, via the analysis of marine sediment cores. It revealed significant fluctuations of sediment residence times over glacial - interglacial timescales, which can be explained by the presence of LGM glaciers in the Alps, associated with enhanced erosion. A second-order cyclicity of sediment residence times was also identified during the last glacial period over the short-lived millennial events of the Bond cycle. These variations were tentatively attributed to the rapid evolution of the vegetation cover during the Dansgaard-Oeschger climatic variability.



Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.