Tracing sediment sources and export dynamics in the Congo River Basin using radiogenic isotopes

The Congo Basin is the second-largest river basin in the world. It is characterized by extensive tropical forests, wetlands, and floodplains that together form one of the largest terrestrial carbon reservoirs on Earth, including the world’s largest tropical peat complex beneath the swamp forests of the Cuvette Centrale. The low-relief morphology and extensive floodplain systems of the basin strongly influence the storage, transformation, and transfer of water, sediment, and organic matter. Consequently, export dynamics from different parts of the Congo Basin remain incompletely understood, including the sourcing and export of clastic sediment and associated particulate organic carbon. Here, we use radiogenic isotope ratios of strontium, neodymium, and lead together with bulk organic carbon (stable and radiocarbon isotopes) and nitrogen isotope data, to constrain the export of clastic and organic particulates from contrasting geomorphic and ecological settings through the Congo River's fluvial network. We analyzed a transect of tributaries spanning peat-dominated swamp forests, evergreen forests, and mixed forest-savanna catchments. Underlying source lithologies range from Archean cratonic rocks to Cretaceous units and Quaternary sediments within the swamp regions of the Cuvette Centrale. We then compare the modern river data with a downcore marine record from Congo Fan deposits to assess how Holocene climate change affected sediment routing dynamics and the preservation of provenance signals from the Congo Basin in the stratigraphic archive. This study provides new insights into the sediment and organic carbon routing systems within the Congo Basin and its connection to the marine sedimentary record.