High-resolution variability of the South American summer monsoon over the last seven millennia: insights from a speleothem record from the central Peruvian Andes

Stable oxygen isotope (δ18O) measurements of two speleothems, collected from Huagapo Cave in the central Peruvian Andes and with overlapping age from 1.1 to 1.4 ka, characterize tropical South American climate variability over the last 7150 years. In the study region, precipitation δ18O (δ18Op) is inversely correlated to rainfall amount upstream in the Amazon Basin and the intensity of convection associated with the South American summer monsoon (SASM). Speleothem long-axis profiles yield an average age resolution of five years and permit investigation of climate over orbital to decadal timescales. Variations in the isotopic composition of Huagapo Cave calcite (δ18Oc) are in good agreement with several precipitation proxy records from ice cores, speleothems, and lake sediments from the central Peruvian Andes. From the mid-Holocene to today, δ18Oc, a proxy for δ18Op, tracks changes in local insolation and exhibits a ∼2‰ decrease. In the Late Holocene, Huagapo Cave δ18Oc is characterized by two periods of significant decline in SASM intensity (up to 1.5‰ increase in δ18Oc) even when insolation is reaching a local maximum and the SASM would be expected to intensify. These millennial-scale reductions in SASM intensity could in part be influenced by a reduction in the zonal SST gradient of the Pacific Ocean, favoring El Niño-like development.