The Fate of Carbon in Sediments of the Xingu and Tapajós Clearwater Rivers, Eastern Amazon

摘要: The Xingu and Tapajos rivers in the eastern Amazon are largest clearwater systems of basin. Both have “fluvial rias” (i.e., lake-like channels) their downstream reaches as they naturally impounded by mainstem. Fluvial rias widespread landscape most sedimentary load from major blackwater is deposited these channels. So far, little known about role a trap reactor for organic sediments. In this study, we used inorganic geochemistry, magnetic susceptibility, diatom, pollen analyses sediments (suspended, riverbed, downcore) to investigate effects hydrologic variations on carbon budget over Holocene. Ages sediment deposition (~100 5,500 years) were constrained optically stimulated luminescence radiocarbon. Major elements geochemistry concentration total (TOC) indicate that seasonal exert strong influence riverine productivity input preservation matter Stable isotope data (δ13C -31.04 -27.49‰) analysis buried derived forests. River, diatom bottom revealed 65 infrageneric taxa mostly well-adapted slack oligotrophic acidic waters. TOC values cores similar measured riverbed suitable conditions at least since mid-Holocene, with burial rates varying 84 g m-2 yr-1 169 yr-1. However, redox-sensitive core alternation between anoxic/dysoxic oxic water-sediment interface may be linked abrupt changes precipitation. variation controls mineralization methanogenesis. Thus, such promoted hydrological significantly affect capacity act either sources or sinks carbon.