Dual biomarker δ2H and δ13C records allow deconvolution of precipitation and evaporation signals in Lake Junin sediments since the last glacial maximum

The current understanding of millennial-scale changes in the intensity of the South American Summer Monsoon was developed using stable isotopes from lake sediments, cave deposits, and mountain glaciers. While these studies suggest a close link between insolation and monsoon intensity, the resultant water balance remains poorly understood. Sediment-based monsoon records are either affected by evaporation, lack a proxy that is independent of evaporation, or are derived from multiple lakes with different hydrologic states and independent age models. The well-studied Lake Junín sediment record provides a means to document both the precipitation signal, from the n C 29 alkanes (terrestrial), and the evaporation signal, from the n C 23 alkanes (aquatic), to document changes in precipitation-evaporation (P-E) balance. The use of a dual isotope approach (δ 2 H wax and δ 13 C wax ) isolates precipitation and evaporation signals using independent isotope systems, while also identifying changes in organic matter source. Additionally, brGDGTs were used to constrain the relationship between temperature and drought. The water balance reconstruction indicates the central Andes are extremely sensitive to changes in monsoon intensity, driven by changes in both large-scale circulation (P) and local environmental conditions (E). Furthermore, we identify significant variations in evaporative enrichment of lake water throughout the past ∼22,000 years, with reduced P-E balance and local water stress particularly evident in the middle Holocene. The dual isotope approach provides a means to isolate the local evaporation and temperature signal from paleorecords while capturing the evolution of the precipitation signal across the Amazon rainforest.