Rock erosion and sediment transport under climate and anthropogenic influences: Records in Ilha Grande Bay (Southeast Brazil)

Coastal environments are vulnerable to climate conditions and human activities, recording changes in sedimentary input and depositional conditions over time. This study intends to analyze evidence of soil erosion and sediment transfer under climate and anthropogenic impacts in Saco de Mamanguá, Ilha Grande Bay (Rio de Janeiro, Southeast Brazil). It is based on a multiproxy analysis applied to samples of the sediment core BIG03, integrating textural, mineralogical, and geochemical data. It is supported by an age model based on ²¹⁰Pb and ¹³⁷Cs. The BIG03 core is a muddy sequence composed of poorly to very poorly sorted sediments, indicating deposition under calm hydrodynamic conditions, with settling predominating. Its mineralogical composition is mainly siliciclastic, comprising phyllosilicates, quartz, and feldspars, related to continental rock weathering. The sediments of the study area have remained eutrophic and anoxic since ≈1925, becoming sulfidic, except in the upper part of the core. Variations in textural, mineralogical, and geochemical data indicate changes over the last ≈100 years in: terrigenous input and weathering, sediment sources, fluvial discharge, and marine influence. The results show a sedimentological dialogue between the erosion of the Rio Negro Complex, which is crossed by the Paraty-Mirim River and composes the Algodão and Cocos islands located in the external sector of the Saco de Mamanguá, and the erosion of the Paraty and Paraty Mirim granites, crossed by the Meros and the Paraty-Mirim rivers. The greatest expression of the contributions of the Rio Negro Complex is associated with a greater marine influence in the area (lesser continental influence) between 1925 and 1956. On the other hand, the highest erosion rates in the Paraty and Paraty Mirim granites were recorded between 2004 and 2022 (except in 2011), associated with anomalies of intense rainfall events, mass landslides and increased anthropogenic fingerprints in the region. The BIG03 core results document the influence of climate variability associated with the South Atlantic Convergence Zone (SACZ) and anthropogenic impacts on soil erosion and coastal sedimentary dynamics.