Oscillations in Mid‐to Late Holocene Environments of the Lower Negro River, Central Amazonia, Recorded in Pollen and Diatom Assemblages From Lake Pacú Sediments

The mid‐to late Holocene transition in the lower Negro River reveals significant insights into the ecological succession and climatic history of central Amazonia. Analyzing sedimentary, pollen, and diatom data, this study presents an uninterrupted regional view of the ecological and environmental variations from the largest lake in the lower Negro River. Microfossil findings indicated dominance of igapó forests throughout the analyzed timespan. The sedimentary record suggests that at ca. 5,020 cal yr BP, there was a transition from a high‐energy “open‐fluvial” environment characterized by sand deposition to a low‐energy setting, allowing the sedimentation of fine‐grained sediments. From ca. 5,020 to 1,600 cal yr BP, the area witnessed multiple alternations between pioneer (periphytic diatoms and herbaceous plants) and climax species (planktonic diatoms and floodplain forests). The synchronized fluctuations in the terrestrial and aquatic ecosystems suggest significant hydrological variations in central Amazonia during the mid‐to late Holocene. After 1,600 cal yr BP, the record is marked by the dominance of floodplain forests and planktonic diatoms, resembling a modern igapó forest climax state. These transitions underscore the role of long‐term precipitation patterns and fluvial dynamics, particularly the influence of the Solimões–Negro confluence, in shaping floodplain ecological succession. Overall, this study highlights a dynamic scenario in the lower Negro River, with water level fluctuations exerting a major control on ecological succession.