Hydroclimate and ENSO Variability Recorded by Oxygen Isotopes From Tree Rings in the South American Altiplano

Hydroclimate variability in tropical South America is strongly regulated by the South American Summer Monsoon (SASM). However, past precipitation changes are poorly constrained due to limited observations and high‐resolution paleoproxies. We found that summer precipitation and the El Niño‐Southern Oscillation (ENSO) variability are well registered in tree‐ring stable oxygen isotopes (δ18OTR) of Polylepis tarapacanain the Chilean and Bolivian Altiplano in the Central Andes (18–22°S, ∼4,500 m a.s.l.) with the northern forests having the strongest climate signal. More enriched δ18OTRvalues were found at the southern sites likely due to the increasing aridity toward the southwest of the Altiplano. The climate signal of P. tarapacana δ18OTRis the combined result of moisture transported from the Amazon Basin, modulated by the SASM, ENSO, and local evaporation, and emerges as a novel tree‐ring climate proxy for the southern tropical Andes. Understanding past climatic changes in the Central Andes in tropical South America is of great importance to contextualize current hydroclimatic conditions. Here, we present the first P. tarapacanatree‐ring stable oxygen isotope (δ18OTR) chronologies and analyze their value as environmental records for this region. Locally known as queñoa, P. tarapacanagrows in the South American Altiplano from 16°S to 23°S at very high elevations (up to 5,100 m a.s.l), making it the highest elevation tree species worldwide. We analyze P. tarapacana δ18OTRfrom 1950 to present and find that it registers precipitation changes in the Altiplano and the El Niño ‐ Southern Oscillation (ENSO). We suggest that δ18OTRis likely affected by soil evaporation and leaf transpiration due to the high solar radiation and aridity in the Altiplano, leading to an enrichment in δ18OTRvalues with a more pronounced effect at the more arid sites. P. tarapacana δ18OTRreflects the atmospheric processes transporting moisture to the Altiplano and the influence of local evaporation. Our findings are relevant for generating robust hydroclimate reconstructions in the Central Andes to improve circulation models and provide better management of water resources in tropical South America. Tree‐ring stable oxygen isotopes of Polylepis tarapacanarecord austral summer precipitation variability in the South American AltiplanoEl Niño‐Southern Oscillation is imprinted in the tree‐ring oxygen isotopes with a stronger signal toward the north of the studied area Tree‐ring stable oxygen isotopes of Polylepis tarapacanarecord austral summer precipitation variability in the South American Altiplano El Niño‐Southern Oscillation is imprinted in the tree‐ring oxygen isotopes with a stronger signal toward the north of the studied area