A Peruvian Speleothem Deposit from 25,000 to 64,000 years BP: Insight into South American Summer Monsoon Variability

The South American Summer Monsoon (SASM) system governs the annual hydrologic cycle in the Amazon Basin and central Andes. It varies strongly on an annual cycle, but recent paleoclimatic records indicate that it may vary on centennial to multimillennial cycles. Speleothem deposits record isotopic variation over both short and long timescales, and have proven to track Dansgaard-Oeschger (D/O) events, which are defined as abrupt warming periods in the Northern Hemisphere. D/O events are represented in Southern Hemisphere proxies, as they impact SASM strength in the Southern Hemisphere tropics. Huagapo Cave is located in Palcamayo, Peru (11.27ËšS; 75.79ËšW; 3,850 meters above sea level) and is 2800 meters in length. Twelve speleothem deposits were collected in May of 2019. Samples were dated using the Uranium-Thorium disequilibrium dating technique, and results indicate the time range covered spans from 2,000 years BP to 440,000 years BP. Time frames not covered in the composite record from all speleothems collected include 2,500-25,000 years BP, 227,000-312,000 years BP, and 320,000-370,000 years BP. One sample, spanning from 25,021 (±53) to 63,799 (±119) years BP, was analyzed for stable oxygen (δ18O) and carbon (δ13C) isotopes with the purpose of better constraining climatic variability in the region and confirm the reproducibility of speleothem records with well-constrained D/O events within South America. Preliminary data suggest that the δ18O and δ13C results follow the amount effect variations, with strong SASM conditions indicated by decreased δ18O and decreased δ13C that reflect rainfall isotopic concentrations and the respiration of organic matter in surface soil horizons. Published speleothem data from a nearby cave was correlated with data from this study, as well as Greenland ice core data (NGRIP) and a 700,000-year sediment core from Lake Junín, showing the D/O events in the Southern Hemisphere tropics region aligning with increased temperatures well-constrained in NGRIP. Data from previously published work confirms that the anti-phase relationship between the Northern Hemisphere and Southern Hemisphere climate fluctuations is caused by meridional shifts in the mean position of the Intertropical Convergence Zone (ITCZ), which changes location based on warming in different hemispheres. The increased warming in the Northern Hemisphere during D/O events caused a likely northward shift of the ITCZ, and a corresponding decrease in strength of the SASM in South America.