Stable isotope constraints on the transport of water to the Andes between 22° and 26°S during the last glacial cycle

Abstract

The modern climate over much of the Andes between 22° and 26°S is very dry. Dated sediment cores from desiccated lake beds contain saline deposits (salars) that have halite fabrics that indicate during previous, less arid climates saline lakes existed at Salar de Hombre Muerto (northwest Argentina, Andean plateau) and Salar de Atacama (northern Chile, west flank of Andes). Paleoclimate conditions are reconstructed from the stable isotope composition of paleo-saline lake waters trapped in fluid inclusions in lacustrine halite. Models of isotopic steady state are applied to estimate the isotopic composition of inflow (meteoric) water to the paleo-lake and paleo-atmospheric water vapor. The two salars' climate records differ. The timing of Atacama saline lakes is similar to lake level highstands on the Altiplano to the northeast with the deepest lake occurring between 24 and 19.8 ka. The modern meteoric water source for Atacama and the Central Andes is currently the tropical Atlantic, via the Amazon Basin, and stable isotopic evidence indicates the same source of water for the paleo-lakes in the Atacama. In contrast, to the southeast, at Hombre Muerto, the lakes that intermittently occupied the salar became progressively smaller since 45 ka. Water isotope composition today reflects atmospheric recycling by evaporation-condensation, as it did between 24 and 20 ka, whereas water transported to the earlier lakes does not indicate significant isotopic recycling. Using knowledge of modern-day atmosphere/oceanic circulation and forcing mechanisms, we hypothesize that the shifts in moisture transport to these Andean sites are directly tied to equatorial and South Atlantic atmospheric and oceanic surface circulation.