Climatic and vegetation control on sediment dynamics during the last glacial cycle

As climate is changing rapidly, there is an increasing need to understand how water and soil resources respond to climate change. Soil and sediment dynamics are sensitive to several external factors such as climate, vegetation type and distribution, human activity, and tectonic activity. However, the relationship between erosion and changes in these factors is difficult to constrain with current available approaches. Here we show that uranium isotopes in sediments from river paleochannels can be used to reconstruct variations in the residence time of sediments in a catchment over the past 100 k.y. We find that sediment residence times increase by an order of magnitude during interglacials compared to glacial periods. This is interpreted as a change in sediment stores in the landscape that are tapped by catchment erosion: young, upland soils during glacial periods, reworking of old alluvial sediments during interglacials. A direct correlation is found between the sediment residence time and climatic parameters (sea-surface temperature, atmospheric carbon dioxide content, and paleorainfall estimates), suggesting that during a glacial cycle, sediment dynamics closely follow variations in climate. However, this relationship is not simple because there is no correlation between sediment residence time and paleodischarge estimates. Because sediment residence time variations correlate with changes in vegetation inferred from pollen data, it is hypothesized that the influence of climate on erosion over a glacial cycle may be indirect, and operates via the influence of climate on the type of plant ecosystems within a catchment. If verified elsewhere, this conclusion would emphasize the important role of biology in the physical evolution of Earth's surface, here observed over a 100 k.y. time scale.