Late Holocene rainfall dynamics in southeastern Brazil linked to monsoon variability: Terrigenous inputs and vegetation shifts influenced by the South Atlantic Convergence Zone activity

Abstract

A sediment core high-resolution multiproxy analysis (Grain size, bulk-δ¹³C, and n-alkanes) from Mamanguá Ria, southeastern Brazil, reveals centennial-scale hydroclimatic variability over the past ~2628 years. Located within the core of the South Atlantic Convergence Zone (SACZ), this ria environment offers a sensitive archive of monsoon-driven environmental change. Our proxies registered a transition at ~1400 cal BP, indicating a shift toward increased humidity, observed through continental runoff and vegetation shift. This change suggests enhanced fluvial input and SACZ intensification, possibly linked to broader South American Monsoon System (SAMS) dynamics. Based on the core’s age model, the period between ~1000 and ~700 cal BP (Medieval Climate Anomaly, MCA) was relatively drier compared to the preceding period, while the interval from ~550 and ~250 cal BP (Little Ice Age, LIA) is characterized by wetter conditions. These results indicate significant multidecadal to centennial-scale variability during the transition from MCA to LIA. The changes in the SACZ and South American Low Level Jet (SALLJ) during the LIA and MCA suggest a possible influence between SAMS dynamics and remote climate anomalies. This aspect suggests that a substantial portion of the reconstructed precipitation variability in southeastern South America was affected by climatic phenomena linked to large-scale North Atlantic climate variability. This study offers new insights into timing, magnitude, and regional centennial-scale climate variability in southeastern South America, especially the interplay between tropical rainfall regimes and vegetation dynamics during the Late-Holocene.