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

Ricardo Villalba,Ana M. Srur,Mukund Palat Rao,Mathias Vuille,Valérie Daux,Rosanne D’Arrigo,Milagros Rodriguez‐Caton,Rose Oelkers,Mariano S. Morales,Duncan A. Christie,Françoise Vimeux,Laia Andreu‐Hayles,Arianna M. Varuolo‐Clarke

doi:10.1029/2021gl095883

Abstract

AbstractHydroclimate 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 tarapacana in 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 δ18OTR values were found at the southern sites likely due to the increasing aridity toward the southwest of the Altiplano. The climate signal of P. tarapacana δ18OTR is 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.

Highlights

Droughts in the South American Altiplano, a semi-arid high-elevation plateau located in the Central Andes, affect millions of people and produce large economic losses across the Andes and the adjacent arid lowlands (Canedo-Rosso et al, 2021)
The build-up of the Bolivian High, an anticyclonic system situated over Bolivia, during the austral summer is a key atmospheric feature associated with the South American Summer Monsoon (SASM)
Precipitation 18O and proxy records in the Altiplano and surrounding areas GNIP observations and ice-core proxy data show more negative 18O values as elevation increases (Fig. 1a). This altitude effect likely reflects the first order isotopic Rayleigh distillation with decreasing temperature (Fig. 1c) and orographic precipitation (Fig. 1d) as air masses approach the Andes and are lifted along the eastern slopes. This depletion in heavy isotopes as air masses move from the lowlands in the Amazon basin toward the higher altitude environments in the Altiplano is consistent with the distribution of precipitation 18O seen in IsoGSM (Fig. 1b)

Summary

Introduction

Droughts in the South American Altiplano, a semi-arid high-elevation plateau located in the Central Andes, affect millions of people and produce large economic losses across the Andes and the adjacent arid lowlands (Canedo-Rosso et al, 2021). Previous studies have shown that the degree of moisture recycling and rainout upstream over the Amazon Basin largely control 18O in precipitation over the tropical and Central Andes and the Bolivian lowlands (Hoffmann et al, 2003; Vuille and Werner, 2005; Vimeux et al, 2005; Vimeux et al, 2011; Vuille et al, 2012; Kanner et al, 2013; Baker et al, 2015) These studies were based on models and natural archives mostly located north of 19o S, less is known about the driest and most distal part of the SASM domain located at the southwestern margin of the Altiplano adjacent to the Atacama Desert (Galewsky and Samuels-Crow, 2015). Since 18OTR carries a strong signal of the water used by the trees, we hypothesize that our 18OTR records reflect hydroclimate and register the SASM and ENSO variability in this region

Data and Methods

Results

Discussion and Conclusions

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