The Last Big Change: Holocene Deglaciation and Paleoclimate Reconstruction from High-Altitude Speleothems in the Peruvian Andes

Much of our modern understanding of the last deglaciation is defined by paleoclimate data from Greenland ice cores which show Northern Atlantic climate influences but are an unknown influence on the tropics. We used oxygen isotope (δ18O), carbon isotope (δ13C) and trace metal stalagmite records from Antipayarguna cave in the Peruvian Andes (4050 masl) to reconstruct centennial-resolution changes in South American Summer Monsoon (SASM) intensity and map Holocene climate variability. The data show 20,000-year intervals where Andean climate influence shifts between SASM intensity and North Atlantic cooling. Additionally, concurrent shifts in δ13C and δ18O suggest an overall increase in soil respiration and vegetation cover during periods of increased precipitation. Oxygen isotopes reveal a positively correlated relationship with SASM strength, with higher δ18O values corresponding to stronger monsoon/wetter conditions. Correlated trace metals and δ18O indicate dominant prior calcite precipitation during dry periods and lower SASM intensity. The isotope record shows the first recorded evidence of the 8.2 ka event in a speleothem from South America. Notably, δ13C from 8.3 to 7.6 ka show a trend like the δ13C record from Heinrich event 1 at 16.5 ka, suggesting similar climate forcings. The δ18O record also matches previous data identifying the Holocene Climatic Optimum (HCO), though we constrain the period further to between 10.5 and 8.5 ka, excluding the 8.2 ka event. At 18.2 ka δ18O decreases to -17.2‰ before steadily increasing to -10.1‰ by 10 ka, indicating a period of increased consistent rainfall prior to a reduction in overall monsoon intensity during the HCO. Concurrent shifts in δ13C suggest an overall increase in soil respiration and vegetation cover, with lower values (-6.2‰ to -7‰) during wetter periods. Our composite oxygen isotope record shows evidence matching that of the Greenland ice core - we see the last deglaciation and other Northern hemispheric climate events evidenced in equatorial records, as well as the influence of this deglaciation on seasonal monsoonal patterns in the Andes. Carbon isotopes and trace metal data indicate local effects like altitude and vegetation cover play a significant role in water availability to cave systems. This study underscores the sensitivity of tropical Andean climate to hemispheric forcings and the critical role of speleothem proxies in elucidating past hydroclimatic variability.