Climatic and environmental influence on the speleothem growth rates during the last 25.000 years BP in South America

• Ano de defesa: 2025
• Autor(a) principal: Perroud, Vinicius de Almeida Salles
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Carste; Holocene; Holoceno; Karst; Last Glacial Maximum; Paleoclima; Paleoclimate; Stalagmites Growth rate; Taxa de crescimento de estalagmites; Último Máximo Glacial
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/44/44142/tde-27052025-075315/

Stalagmites growth rates (GR) greatly vary through time, as the same sample can sometimes double or triple its GR while active or cease to grow in a relatively short period. The rate of stalagmite formation depends on multiple factors, being temperature, rainfall, soil processes and soil bioactivity the most important on a millenary timescale. The complex interaction between these factors and the host calcareous rock dictates the amount of dissolved carbonate in the percolating solution, and consequently, the stalagmite growth rate. This study proposes the analysis of multiple GRs from stalagmites in South America, comparing the U/Th dating to their oxygen and carbon isotopic profiles to better understand how growth rate varied throughout the last 23 ky and how climatic and environmental variables affected it, specifically temperature, rainfall and soil erosion/formation due to changes in vegetation. Nine different caves were selected: Botuverá (SC, Brazil), Tapagem (SP, Brazil), Jaraguá (MS, Brazil), Lapa Sem Fim (MG, Brazil), Paixão (BA, Brazil), Cueva del Diamante (Peru), Paraíso (PA, Brazil), Carracos (Colombia) and Rainha (RN, Brazil). The spatial distribution of the sites chosen assures that diverse climatic and environmental conditions are compared, facilitating the isolation and comparison between variables influence on GR. As for the time frame selected, the transition from LGM to Holocene is ideal as the temperature differences (up to 5-6 °C on average) between the two periods isolates the most important variable on calcite dissolution and reprecipitation, as the chemical kinetics of the H2O-CaCO3-CO2 system and soil bioactivity are highly dependent on it. The results of this study show firstly a clear temperature influence on GRs throughout South America, as hotter regions presented much higher rates than colder sites during the same climatic periods. Colder regions, as southern Brazil caves (Botuverá and Tapagem) and Cueva del Diamante, situated at the Andes foothill in Peru, have GR ranging from 3-10 mm/ky during the whole-time frame targeted, while sites with higher average temperature like Rainha and Paixão show much higher rates, ranging from 30-120 and 100-300 mm/ky, respectively, during the Holocene-LGM time frame. Moreover, this temperature-related behavior is also seen on the GR when comparing the Holocene and LGM periods, as all stalagmites with exception to Paixão have faster precipitation rates during the last 10 ky despite very low water availability. An interesting pattern of lower rainfall and soil cover stabilization occurs in most cases, as 13C values decrease, 18O values increase and GR increases during the Holocene. Overall, temperature is the main driver of stalagmites GR, as it impacts the chemical kinetics of the H2O-CaCO3-CO2 system, with higher temperatures accelerating the reprecipitation of the dissolved carbonates. Furthermore, increased temperatures also result in higher soil bioproduction of CO2, increasing the dissolution rates of the host rock, which combined with a more stable soil cover can greatly increase GR. In semi-arid regions water availability is the main driver, as even though these sites show the largest GRs, their formation ceases to happen or decreases to rates like southeastern Brazil during the Mid-Holocene.