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Abstract

In this thesis, hydroclimatic and environmental changes in the northeastern Yucatán Peninsula (YP), Mexico, over the past 1,400 years were reconstructed using multi-proxy analyses of stalagmites from Áaktun Kóopo Cave. This region is crucial for understanding interactions between climate and Maya civilization, though detailed records linking changes in hydroclimate and vegetation to major societal transitions have thus far been lacking. The high uranium contents in these stalagmites enabled precise 230Th/U dating, and some stalagmite chronologies could be further improved by analyzing seasonal variations in certain trace element ratios through LA-ICP-MS analyses. The main findings are that multiple elements and isotopes together can trace major transitions in soil and vegetation conditions. Following a growth hiatus, stalagmite E0-C reveals a persistent shift in soil-sensitive proxies (δ13C, dead carbon fraction (DCF), U/Ca) around the onset of the Medieval Warm Period (MWP). This shift can be understood as reflecting major changes in soil CO2 levels, openness of the system, and vegetation (C3/C4 plants). Although there is no direct evidence of past agriculture above the cave, the proxies suggest that human activities such as deforestation and cultivation may have impacted the soil environment before and after the Terminal Classic Period (TCP). At the same time, the YP experiences a shift toward wetter conditions at the beginning of the MWP, suggesting atmospheric reorganization that was likely linked to tropical Atlantic sea surface temperature (SST) and trade wind patterns. Finally, a composite δ18O record from Áaktun Kóopo Cave provides a qualitative high-resolution rainfall history for the northeastern YP over the last 1,400 years, capturing prominent centennial-scale hydroclimate fluctuations. These variations align with other stalagmite records from the YP and beyond, indicating common forcings such as tropical SSTs in the Atlantic (and Pacific) and displacements in the mean path of the Intertropical Convergence Zone (ITCZ). Preliminary spectral analyses show periodicities consistent with ENSO variability and solar cycles, indicating that solar forcing may influence regional hydroclimate, though this relationship varies over time. These findings underscore the importance of further research in speleothem archives to better understand Mesoamerican climate dynamics on both local and regional scales.