Hydroclimate and Extreme Rainfall Variability over the Past 7500 years in Southeastern and Southern Brazil
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Abstract
Southern and Southeastern Brazil are strongly affected by extreme rainfall events (ERE), which frequently trigger landslides and flash floods, causing severe socioeconomic impacts that is proportionately affect vulnerable populations. Current climate projections indicate that the frequency and magnitude of ERE are likely to increase due to enhanced atmospheric moisture and evaporative demand under global warming. In addition, El Niño–Southern Oscillation (ENSO) events are projected to intensify and occur more frequently, further amplifying ENSO-related extremes through Pacific–South American teleconnections. Despite these projections, the lack of reliable ERE records extending beyond the period of anthropogenic climate change constrains our understanding of the natural variability and forcing mechanisms behind such events, particularly over longer time-scales. In this context, speleothems collected from caves subjected to flood in response to ERE offer a valuable archive for reconstructing past ERE occurrences. The integration of cave hydrological monitoring with paleoclimate reconstructions provides a robust framework for investigating the natural variability of ERE. Precise 230Th–U dating combined with detailed microstratigraphic analyses provide a robust framework for the reconstruction of ERE time series and allows us to assess how their frequency have changed through time. Furthermore, speleothems offer the potential for multi-proxy analyses, allowing the reconstruction of hydroclimate and environmental conditions across multiple temporal scales along with the ERE. By combining ERE reconstructions with a multi-proxy approach, we can generate a comprehensive record of past ERE variability and hydroclimatic changes, allowing us to evaluate the how forcings and changes in the hydroclimate impact the ERE occurrence. In this study, we use multiple speleothems from Malfazido Cave to reconstruct extreme rainfall variability over the past 7,500 years. A multi-year cave monitoring program has evidenced Malfazido Cave response to extreme rainfall events. Stable isotope (δ18O and δ13C) and trace element records reveal persistent interannual periodicities consistent with ENSO variability, as well as multi-centennial cycles evidencing a pattern of shifting wet/dry phases over Southeastern Brazil. The wet anomalies are synchronous with events of North Atlantic cooling, such as the Little Ice Age and Bond events, and are associated with a weakening of the Atlantic Meridional Overturning Circulation (AMOC) and large-scale atmospheric reorganization related to shifts in the Intertropical Convergence Zone (ITCZ). Our results also evidenced a multi-centennial rainfall dipole pattern between Southern (SB) and Southeastern Brazil (SEBRA), resembling the intraseasonal South American Dipole. Finally, comparisons with Antarctic, Pacific, and North Atlantic records highlight the influence of both tropical and extratropical teleconnections on the modulation of the hydroclimate and ERE of SEBRA and SB.