RECONSTRUCTING DROUGHT IN PERU DURING THE MEDIEVAL CLIMATE ANOMALY: IMPLICATIONS FOR SOCIETIES PAST AND PRESENT

On the altiplano of Peru, rainfall is dominated by the South American Summer Monsoon, where the majority of the 600 mm of annual precipitation (60%) falls during the months of December, January, and February. Precipitation regimes in this region are strongly correlated with the location of the Intertropical Convergence Zone (ITCZ), and by extension, Atlantic sea surface temperatures. In the past, higher sea surface temperatures in the Northern Atlantic displaced the ITCZ to the north of its current mean position. This displacement had a cascading impact on precipitation patterns in South America. Here, we report on a centennial-scale drought in Peru associated with higher sea surface temperatures during the Medieval Climate Anomaly (ca. 900-1200 CE). We reconstructed the drought using hydrogen and oxygen isotope ratios from leaf wax lipids and authigenic carbonates extracted from a well-date lacustrine sediment core. The remarkable correspondence between these two proxies demonstrates that the South American Summer Monsoon weakened during the Medieval Climate Anomaly, causing lake levels to drop considerably. This drought is implicated with the collapse of the Tiwanaku civilization in Peru at ca. 1000 CE, and may serve as an important ancient analogue to climate outcomes of the current warm period.