This two year project will demonstrate whether measuring cosmogenic isotope abundances in sediment provides a useful and efficient way to determine basin-scale denudation rates and sediment fluxes. It has three specific goals: 1) evaluate the simple model we have developed for interpreting the abundance of in-situ-produced cosmogenic nuclides in sediments; 2) use isotope abundance to characterize the variability in sediment production and routing in mesoscale (1000km2) drainage basins in the Oregon Coast Range; 3) measure isotope concentrations in sediments carried by some of the world's largest rivers and compare "cosmogenic" denudation rates with those calculated by other means. At the conclusion, we will have determined the applicability of our interpretive model and we will understand better the dynamics of sediment production and transport in the Coast Range. The study will begin with collection of quartz-rich sediment samples from hillslopes and stream channels in the western Oregon Coast Range. We will sample along the drainages, beginning in first-order tributaries and continuing to the trunk streams. Quartz will be separated from these samples and the abundance of in situ-produced cosmogenic isotopes (26Al and 14C) will be measured. Isotope abundances will be interpreted using the mathematical model that we have developed and will be compared to the rates of sediment production, transport, and storage which we and others have quantified through prior field studies in the Coast Range. In addition to Coast Range samples, we plan to analyze sediment collected by us and by others from rivers draining a variety of geomorphic and hydrologic provinces. These sample sites will be selected to represent areas which have significantly different denudation rates. They will include sites in the Amazon Basin, where we are currently studying sediment transport by more traditional means, as well as sites on other large rivers where we have experience or contacts resulting from the Amazon work
