Martins G. S. auteur aut IRD Cordeiro R. C. auteur aut IRD Turcq Bruno auteur aut IRD Meyers P. A. auteur aut IRD Mendez-Millan Mercedes auteur aut IRD Moreira L. S. auteur aut IRD Fontes D. auteur aut IRD Rodrigues R. A. auteur aut IRD Sifeddine Abdelfettah auteur aut IRD Behling H. auteur aut IRD Bouloubassi I. D. auteur aut IRD text journalArticle eng text/pdf born digital access The molecular distributions and isotopic ratios (delta C-13 and 8D) of n-alkanes in sediments deposited during the last 35 cal kyr BP in Saci Lake, southeastern Amazonia, have been measured and interpreted for their paleoclimate information. A terrestrial origin for the odd carbon-numbered long-chain (> C27) n-alkanes has been inferred from molecular distributions. A shift in the n-alkane delta C-13 values across the Pleistocene-Holocene boundary coincides with a climate-induced floral change previously deduced from palynological analyses. Dry conditions during the late Pleistocene and mid-Holocene were confirmed by several n-alkane indices used to estimate the availability of moisture and by larger 8D values. High ACL values indicate relatively dry conditions from 29 to 18.2 cal kyr BP and again from 8.0 and 5.0 cal kyr BP with a decrease in precipitation and an increase of grasses. Changes in the n-alkane C-29 isotopic compositions (delta D and delta C-13) were observed during the PleistoceneHolocene transition, coinciding with a floristic change induced by climatic conditions that is also observed in palynological results from the same lake. The n-alkane C-29 delta C-13 values remain between -33.2%o and - 35.7%o, which is representative for n-alkanes derived from C-3 vegetation. These lines of evidence suggest a continuous gallery forest cover in the Saci Lake catchment for the last ~35 cal kyr BP in contrasted with the observed palynological changes which represent the dynamics of the vegetation on the upland areas. The n-alkane C-29 delta D values are less negative in the Pleistocene and more negative during the Holocene in the lake record. These characteristics suggest more humid conditions during the Holocene than in the Pleistocene, probably associated with the South American Monsoon System (SAMS). However, an increase of approximately 10%o occurs during the late Holocene, which coincides with the forest expansion around 5 cal kyr BP that is recorded in palynological data of Saci Lake and other records of the Amazon Forest. This change suggests that the D/H ratio is also influenced by the increase of the plant biomass, which would provide an enrichment of D in the isotopic signal as a function of regional moisture recycling caused by evapotranspiration. specialized Southeastern Amazon basin Vegetation Paleoclimate, n-Alkane Compound specific isotope composition BRESIL PARA ETAT AMAZONE BASSIN SACI LAC 076 064 021 213 103833 [15 p.] 2022 0921-8181 https://www.documentation.ird.fr/hor/fdi:010085191 10.1016/j.gloplacha.2022.103833 0921-8181 [F B010085191] https://www.documentation.ird.fr/hor/fdi:010085191 https://www.documentation.ird.fr/intranet/publi/2022-07/010085191.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2022-07-01 2025-02-24 fdi:010085191 fre