Orbitally Paced Hydroclimate Changes in Western Amazonia Wetlands During the Middle Miocene

Abstract Carbon cycling in tropical wetlands may have significantly influenced climate variability during past phases of global warmth, such as during hyperthermal events. However, poorly resolved age models for terrestrial sections hamper correlations with global events. During the warm Middle Miocene, the megalake phase of the Pebas wetland system was active in western Amazonia. Here, we present a cyclostratigraphic analysis of hydroclimate proxies recorded by a Middle Miocene sedimentary archive retrieved from western Amazonia, spanning the intervals 14.4–14.1 Ma (Langhian) and 12.6–12.4 Ma (Serravalian). We identified orbital cycles with periods of ∼87–133, ∼17–19, and 11–13 kyr within the Langhian, and ∼19–23 and 10–11 kyr within the Serravallian. This change of eccentricity‐precession‐semiprecession to precessional‐only forcing suggests a shift toward modern‐like hydroclimate variability over western Amazonia after East Antarctic Ice Sheet expansion during the Middle Miocene Climate Transition.