Abstract. Modern precipitation anomalies in the Altiplano, South America, are closely
linked to the strength of the South American summer monsoon (SASM), which is
influenced by large-scale climate features sourced in the tropics such as
the Intertropical Convergence Zone (ITCZ) and El Niño–Southern
Oscillation (ENSO). However, the timing, direction, and spatial extent of
precipitation changes prior to the instrumental period are still largely
unknown, preventing a better understanding of the long-term drivers of the
SASM and their effects over the Altiplano. Here we present a detailed pollen
reconstruction from a sedimentary sequence covering the period between
4500 and 1000 cal yr BP in Lago Chungará (18∘ S; 4570 m a.s.l.), a
high-elevation lake on the southwestern margin of the Altiplano where
precipitation is delivered almost exclusively during the mature phase of the
SASM over the austral summer. We distinguish three well-defined
centennial-scale anomalies, with dry conditions between 4100–3300 and
1600–1000 cal yr BP and a conspicuous humid interval between 2400 and 1600 cal yr BP, which resulted from the weakening and strengthening of the SASM,
respectively. Comparisons with other climate reconstructions from the
Altiplano, the Atacama Desert, the tropical Andes, and the southwestern
Atlantic coast reveal that – unlike modern climatological controls – past
precipitation anomalies at Lago Chungará were largely decoupled from
north–south shifts in the ITCZ and ENSO. A regionally coherent pattern of
centennial-scale SASM variations and a significant latitudinal gradient in
precipitation responses suggest the contribution of an extratropical
moisture source for the SASM, with significant effects on precipitation
variability in the southern Altiplano.
Delayed onset of the South American Summer Monsoon during the Last Glacial Maximum