Increased precipitation during the Little Ice Age promoted human settling in eastern South America

In the instrumental record, eastern South America (ESA) is marked by severe droughts that triggered substantial human displacements, making it a hotspot for climate-society interactions. It is not clear, however, if past centennial-scale changes in climate like the Little Ice Age (LIA) also controlled human occupation. Here we present a precipitation reconstruction for ESA covering the last two millennia, based on the thermoluminescence sensitivity of the 110°C peak of quartz (TL sensitivity) from a marine sediment core collected off ESA. TL sensitivity serves as a proxy for sediment provenance in the region, which is controlled by rainfall patterns. Our data show that centennial-scale changes in precipitation in semi-arid northern ESA varied according to shifts in the Intertropical Convergence Zone (ITCZ). During the LIA, when the ITCZ moved southward, our core shows lower TL sensitivity values, suggesting wetter conditions over northern ESA. Importantly, these wetter intervals align with peaks in ages of archaeological remains found in the region. Concurrently, hydroclimate and archaeological records point to a drier and less populated southern ESA. Our data indicate a temporal correspondence between changes in hydroclimate and human migration from the southern to the nowadays semi-arid northern ESA. We suggest that improved environmental conditions facilitated settlement in otherwise semi-arid landscapes. By integrating marine sediment proxies and archaeological evidence, this study provides support for a climatic influence on human occupation patterns in ESA, particularly during the LIA. It also highlights the utility of luminescence-based techniques in paleoclimate reconstructions from fluvially influenced marine archives.