Impact of paleo-rainfall events in the South Atlantic Convergence Zone (SACZ) and human pressures since ~ 1950 in southeastern Brazil: Paraty and Saco de Mamanguá

Protected coastal areas, such as bays, estuaries, and coastal lagoons, are generally highly populated and impacted by anthropogenic activities. These regions are also vulnerable to the effects of climate change and sea level fluctuations. This work aims to study the records of temporal changes induced by shifts in rainfall and human factors in the western region of Ilha Grande Bay (BIG; Rio de Janeiro State, SE Brazil). The study compares textural, mineralogical, and geochemical data in two cores, BIG01 and BIG02, collected in Paraty Harbor and Saco de Mamanguá, respectively. The two cores have recorded sedimentary changes since 1950, as indicated by ²¹⁰Pb and ¹³⁷Cs dating. The statistically integrated results indicate higher moisture levels before ~ 2000 in this region and a general trend toward reduced rainfall since then, accompanied by an increase in the sediment accumulation rate since the 1980s, likely due to the progressive expansion of urbanization, deforestation, agriculture, and dredging activities in BIG. The Paraty region (BIG01) was most affected by recurrent landslides during concentrated rainfall in SACZ events and by anthropic impact, especially since ~ 1970. This impact has resulted in silting, eutrophication, and moderate pollution by potentially toxic elements, especially Cu, Pb, Sn, Zn, and As. The records of cores BIG01 and BIG02 highlight the influence of climate change, namely SACZ and human activities, on sedimentation and sediment quality. The recurrence of mega-events, such as SACZ paleo-events, and their impact on landslides in slope zones require further study, particularly in densely populated areas.