Late Holocene climate variability and associated paleoenvironmental changes in northern South America, Colombia

Sediment records have been widely used to reconstruct Holocene environmental and climate conditions around the world. Despite the climatic sensitivity of northern South America, paleoenvironmental studies remain limited, particularly regarding ecosystem responses to Late Holocene climate fluctuations. Here we present a multiproxy reconstruction based on a radiocarbon-dated sediment core retrieved from the Nechí wetland, located in the Lower Cauca region of the Antioquia Department (LCA), Colombia, documenting environmental changes over the past ~2,500 years. We combined sedimentological, XRF, and palynological analyses to reconstruct the vegetation changes and their response to climate events. The results indicate that the region experienced a general wetter trend and massive floods over the last 2,500 years, with a pronounced climate anomaly dominated by droughts and a reduction in flood pulses occurring between 1,000 and 1,300 CE. A peak of ecological change took place ca. 1,100 CE, characterized by a clear turnover in pollen assemblages toward herbaceous (e.g., Asteraceae) and disturbance taxa (e.g., Cecropia), indicating a change in climate conditions and instability of forest cover over an interval of ~250 years, spanning roughly from ca. 950 to 1,200 CE. After ca. 1,300 CE, an increase of Symmeria and pollen taxa associated with flooded areas suggests the return of wetter conditions and a reduced ecological change. We suggest that this transition was strongly influenced by the Late Holocene Climate Anomaly, a period of increased climate instability documented across tropical South America. Vegetation trends over the last 500 years demonstrate substantial losses of forest cover associated with human activities in the region and an increase in open areas and disturbance-associated vegetation. This study highlights the sensitivity of lowland wetland ecosystems in the LCA region to Late Holocene climate variability. It provides new insights into the interaction and timing between climate, hydrology, and vegetation in northern South America.