Environmental Changes over the Last 35,000 Years in the Southern Amazon Basin (Lago do Saci)

Abstract:

Variable climatic and environmental conditions in southern Amazonia were reconstructed using sedimentological, geochemical and pollen data in a sediment core from Lago do Saci that span back 35,000 years. Between 35,000 and 18,300 cal yr BP, the climate was cold and dry reaching maximum dryness between 22,000 to 21,000 cal yr BP, as reflected by low TOC and chlorophyll derivatives. The increase of δ¹³C organic matter and Poaceae pollen indicating open vegetation and high BC:OC content, suggesting the occurrence of fires. A lack of sediment between 18,200 and 9,200 cal yr BP could be linked to dryness during the late glacial. The transition from the Pleistocene to the Holocene was marked by an increase in the lake level indicated by increasing TOC and chlorophyll derivatives. Wetter and warmer climatic conditions are also evidenced by an increase in arboreal pollen indicating forest expansion during 9,200–7,500 cal yr BP. A drier mid-Holocene between 7,500–5,000 cal yr BP is suggested by a decrease in TOC and high concentrations of BC:OC, accompanied by an increase in C4 plants. Higher TOC, chlorophyll derivatives and arboreal pollen between 5,000 cal yr BP until the present indicate the highest lake level and the establishment of forest ecosystems.