HOLOCENE-SCALE TRENDS IN ANDEAN SOUTH AMERICAN SUMMER MONSOON VARIABILITY INFERRED FROM A COUPLED LAKE SYSTEM IN THE CENTRAL PERUVIAN ANDES

The South American summer monsoon (SASM) is a major feature of the global climate system that provides fresh water to more than 350 million people in tropical South America. As the number of paleoclimate records from tropical South America has increased, our understanding of long-term SASM variability on human timescales during the Holocene has improved. Many of these studies infer changes in the SASM based on variations in the oxygen isotopic composition of precipitation (d¹⁸O_precip) as archived in ice cores, lake sediments and speleothems from the tropical Andes. Observational and modeling studies show that Andean d¹⁸O_precip records are dominated by synoptic-scale changes SASM variability, leaving the local expression of Andean SASM variability poorly represented. Separating local from synoptic-scale variability is critical for a clearer understanding of how future climate trends will impact Andean water resources, which is essential for those in the Andes living at subsistence levels and for urban and agricultural centers located along the hyper-arid Pacific coast. Here, we investigate synoptic-scale and local changes in the SASM using two well-dated oxygen isotope records from Laguna Pumacocha and Laguna Pucpush, a coupled lake system in the central Peruvian Andes. Previous work on L. Pumacocha shows that evaporation exerts a negligible influence on the lake’s modern isotopic mass balance and that this has likely been the case for the Holocene. In contrast, L. Pucpush’s isotopic mass balance is influenced by evaporation, as well as variations in d¹⁸O_precip. In order to explore local changes in humidity, we differenced the L. Pumacocha and L. Pucpush records to produce a Dd¹⁸O_{Pucpush-Pumacocha} time series. With this record, we explore local changes humidity during climatically important time periods including the early Holocene, the middle Holocene Neoglacial transition at ~5ka, and the SASM maximum during the late Holocene.