A two-million-year record reveals long-term increase in precipitation over western Amazonia and the tropical Andes

Long-term hydroclimate records from the Amazon Basin are scarce, limiting our understanding of how this climatically critical region responded to Pleistocene climate changes. Here we present a 1.93-million-year reconstruction of hydroclimate variability in the western Amazonia and the tropical Andes, derived from titanium-to-calcium and iron-to-potassium ratios of a marine sediment core collected offshore the Amazon River mouth. These geochemical proxies reveal a long-term trend toward wetter conditions through the Pleistocene, particularly after approximately 650,000 years ago. Glacial intervals are characterized by higher proxy variability and more frequent high-amplitude excursions, likely reflecting bundled humid episodes associated with southward shifts of the Intertropical Convergence Zone during North Atlantic cold events, rather than uniformly wetter mean conditions. Temperature-driven processes, including Andean glacial erosion, may also contribute to the geochemical signals. These findings suggest that western Amazonian hydroclimate is sensitive to high-latitude forcing on both millennial and orbital timescales. Western Amazonia and the tropical Andes experienced a long-term trend toward wetter conditions over the past 1.93 million years, with greater variability during glacial periods, as revealed by geochemical proxies from an offshore Amazon sediment core.