Spatiotemporal Variations of Riverine Discharge Within the Amazon Basin During the Late Holocene Coincide With Extratropical Temperature Anomalies

Late Holocene hydroclimate variations have been extensively recognized in Amazonia, but the effects of such changes on riverine discharge within the Amazon lowlands are still poorly understood. We investigated a sediment core covering circa 4,000 to 300 cal yr BP collected in the lower valley of the Xingu River (Xingu Ria) in an area under the influence of the Amazon River. Our results indicate a decrease in precipitation in the Amazon lowlands throughout the studied period and reduced input of coarser and potassium-rich Amazon River sediments to the confluence from about 2,600 to 1,400 cal yr BP. We suggest that lower temperatures in the extratropical Southern Hemisphere weakened the South American Summer Monsoon and led to a decrease in the water discharge of the Amazon River during this period. Plain Language Summary The variability of the Amazon River water discharge over the last millennia is still poorly understood. Sediments deposited in the lower valley of the Xingu River, a major eastern tributary of the Amazon River, allowed for the identification of a decrease in rainfall over the Amazon lowlands throughout the last 4,000 years. Changes in the relative input of Amazon and Xingu sediments in an area affected by both rivers indicate that the water discharge of the Amazon River decreased from about 2,600 to 1,400 years ago. We suggest that anomalously low temperatures in the Southern Hemisphere led to drier conditions in Amazonia during this period. (AU)