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Glacial-interglacial transitions and abrupt millennial-scale events are the most prominent features in many paleoclimate records. Understanding these oscillations requires high-resolution time series from multiple locations to constrain the latitudinal response to forcings. Few high-resolution records exist from the Southern Hemisphere tropics that predate the last two glaciations. We present a high-resolution speleothem oxygen and carbon isotope record from Huagapo Cave in the Central Peruvian Andes covering Marine Isotope Stage (MIS) 8 glacial and MIS 9 interglacial (339 to 249 ka). Uranium-series dates on three stalagmites (n=18) with small age uncertainty ±1% allows us to resolve abrupt climate events similar in structure and duration to Dansgaard-Oescchger and Heinrich events. The South American Summer Monsoon (SASM) controls modern hydroclimate variability in the Andes, and previous records from Huagapo Cave have provided records of past SASM variability. Termination three (T-III) in our record has a steep increase in δ18O values of 5‰, punctuated by two stadial event decreases of ~3‰ (S8.1 and S8.2). This pattern is mirrored in the δ13C record, indicating that these millennial-scale events record hydroclimate and vegetation productivity changes. The same structure as our T-III record is found in other records globally, where they are noted to be Heinrich-like events. Frequency analysis indicates that the occurrence of these abrupt events changes between glacial cycles. Precession is weakly expressed in the δ18O record during MIS 8; similar to speleothem records from the region dating to the Last Glacial Maximum (LGM). Global ice cover and sea levels were similar in the LGM and MIS 8, but the Milankovitch insolation forcing differed. This change in SASM behavior is not observed in the East Asian monsoon, where the precession signal is dominant throughout. Interglacial precessional control is apparent during the latter half of MIS 9 and during Huagapo Cave intervals dating to MIS 6 and 7. These data indicate that the response to high-latitude forcing in the Southern Hemisphere tropics fluctuates through time, and potential explanations for low-latitude sensitivity to forcing factors are further explored. 

Recent studies have improved our understanding of how karst hydrology impacts variability in modern cave drip water δ18O values and the resultant calcite δ18O values of speleothem paleoclimate records. Monitoring of cave drip water isotope values reveals that flow path controls the differences in drip site values in many caves worldwide. We present a case study of three caves from the central Peruvian Andes where isotopic differences between sites are informed by monitoring data. Relative humidity at Huagapo and Pacupahuain caves is 100% year-round with no fluctuations, so any isotopic fractionation of waters must occur in the vadose zone or epikarst. Precipitation isotope data from the 2022-2023 year show differences with elevation, where annual mean precipitation at 3600 masl (meters above sea level) is, on average, 2‰ greater than precipitation at 4100 masl. Cave drip water was sampled four times (April, June, and November 2022, and June 2023). Average drip water δ18O values were lowest at the high elevation (4004 masl) cave of Antipayargunan -14.7 ± 2.5‰; similar values were found at the lowest elevation (3600 masl) cave of Huagapo -14.5 ± 1.2‰. Pacupahuain cave had the highest values with an average of -13.9 ± 1.7‰. The higher values at Pacupahuain Cave (3800 masl) may be attributed to higher evaporation due to vadose zone residence time, a lower average recharge elevation for this catchment and/or potential contribution from a sinkhole lake (Lago Gallerina) above the cave. Huagapo Cave is large, and sampling sites over 1 km in distance show that the δ18O value of drip water increases by 0.5‰ with increasing distance from the cave entrance. Drip counting sensor data and a continuous SYP autosampler at Pacupahuain Cave provide a time series showing that drip rate peaks during the monsoon season. More specifically, the data show a maximum of 2 ‰ difference in drip water at the autosampler site between the end of the wet season in May and the middle of the dry season in August – at which point drips cease for six months. Seasonal recharge dominates most drip water sites, while drip counters show evidence for fracture and diffuse flow-dominated drip sites. These data suggest that, similar to other cave sites, flow path is important for intra-cave differences in drip water isotope values. However, we find that karst hydrology plays a more dominant role between caves.