Climate–Floodplain Interactions in the Amazon Basin Revealed by Organic Geochemical Proxies

Changes in Amazonian hydrology and vegetation strongly influence global geochemical and hydrological cycles. In particular, the vast Amazon floodplains are a major source of atmospheric methane (CH₄), so variations in their extent can substantially impact the global methane budget. Understanding how these floodplains responded to past climate change, especially during periods prior to dominant anthropogenic influence, is therefore critical for constraining natural methane–climate feedbacks and their role in global climate dynamics.

Here, we investigate past vegetation and hydroclimate changes in lowland Amazonia using organic geochemical proxies from a marine sediment core offshore the Amazon River. The δD and δ¹³C signatures of long-chain n-alkanes provide information on past rainfall and vegetation dynamics, while bacteriohopanepolyol (BHP) biomarkers are used to reconstruct variations in the extent of terrestrial wetlands. We assess how climatic and environmental differences between the Holocene and earlier interglacials, particularly the Last Interglacial, influenced the expansion and contraction of Amazonian floodplains. In particular, we aim to test the hypothesis that differences in orbital-scale insolation between these periods contributed to divergent Glacial–Interglacial methane emission patterns. Funding provided by FAPESP (22/06440-1, 23/15362-7, and 25/09149-4).

Keywords: organic geochemistry, paleoclimatology, Amazon