Pre-Incan agricultural activity recorded in dust layers in two tropical ice cores

Abstract

In South America, no documentary records survive from before the incursion of the Spaniards in the mid-sixteenth century. Knowledge of pre-Hispanic civilizations in this region comes largely from archaeological excavations, which may now be supplemented by information recorded in two ice cores drilled in the Quelccaya ice cap in southern Peru (Fig. 1)^1,2. A 1,500-year record of particle concentrations and conductivity in these cores shows two major dust episodes, each lasting about 130 years, centred at AD 920 and 600. Here we examine these dust events in the light of oxygen isotope and net accumulation records, and suggest a correlation with pre-Incan agricultural activity. The annual net accumulation record for AD 1915–1984 compares well with annual changes in Lake Titicaca water levels and with annual precipitation at El Alto (LaPaz, Bolivia), suggesting that the 1,500-year net accumulation record from Quelccaya may serve as a proxy for water level changes in Lake Titicaca. The ice-core record suggests that climatic variability, reflected in lake level changes, has strongly influenced fluctuations in agricultural activity in southern Peru.