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 1.4ka, 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.
Bibliographical noteFunding Information:
This work is supported by NSF grants ATM-1003466 to S.J.B., 0502535 and 1103403 to R.L.E. and H.C., NSFC 41230524 and 2013CB955902 to H.C., and AGS-1003690 to M.V. We thank C. Morales-Bermudez for his invaluable assistance in the field. Comments from two anonymous reviewers significantly helped to improve the manuscript. The data in this paper are archived online at ftp://ftp.ncdc.noaa.gov/pub/data/paleo .
- El Niño-Southern Oscillation
- Oxygen isotopes
- Peruvian Andes
- South American summer monsoon