Geochemical data and luminescence ages from riverbed, downcore, and suspended sediment samples from the Xingu, Tapajós and Amazon Rivers

In this study, we analyzed the organic and inorganic geochemistry and magnetic susceptibility of sediments (suspended, riverbed, and downcore) from the Amazon, Xingu, and Tapajós Rivers to investigate the effects of hydrologic variations on the carbon budget of amazonian clearwater rivers over the Holocene. Ages of sediment deposition (∼100 to 5,500 years) were constrained by optically stimulated luminescence. Major elements concentrations were measured using an inductively coupled plasma-optical emission spectrometer (ICP-OES) for suspended sediments and an energy dispersive x-ray fluorescence (XRF) spectrometer for riverbed and downcore sediment samples. TOC values in sediment cores are similar to values measured in riverbed sediments and indicate suitable conditions for organic matter preservation in sediments of the Xingu and Tapajós rias at least since the mid-Holocene, with carbon burial rates varying from about 84g m−2 yr−1 to 169 g m−2 yr−1. Redox-sensitive elements in the sediment core indicate alternation between anoxic/dysoxic and oxic conditions in the water-sediment interface that may be linked to abrupt changes in precipitation. Changes promoted by hydrological variations significantly affect the capacity of amazonian rias to act either as sources or sinks of carbon.