Abstract

A diverse array of records now exists from the dry central Andes and the hyperarid Atacama Desert. Overall, these records indicate that during the late Glacial-early Holocene both areas experienced millennial-scale changes in the frequency and magnitude of precipitations resulting mainly from ENSO-like variability. Throughout the latest Holocene, high-frequency precipitation oscillations have been detected in several Atacama records, but the timing, magnitude and cause of these fluctuations have remained poorly defined. Here, we used a regional climate proxy network to reconstruct precipitation patterns over the last 2 ka, encompassing two climatologically interesting periods: the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). The data set compromises 138 well-dated records of paleoprecipitations proxies such abundance of rodent middens (per 100 yrs bins) and paleowetland deposits collected along the western slope of the Andes (16°-26°S, 810-3800 m of elevation). By 2-1 ka, low abundance of rodent middens suggests that early MCA stage was in general dry. The record of paleowetlands deposits, however, suggests short-lived wet pulses within the interval 1.5-1 ka. Sharp increases in middens abundance and paleowetlands by the late MCA stage (0.95-0.6 ka) indicate a sustained enhance in precipitations, peaking at ∼0.85 ka. Starting at ∼0.55 ka, reduced midden abundances and total lack of paleowetland deposits imply prevailing dryer conditions. This widespread dry interval was interrupted by a brief but prominent rainfall event during LIA as indicated by elevated midden abundance at ∼0.2 ka. Our results point to important precipitation variability on centennial timescales across the Atacama Desert over the past two millennia; marked as a wet MCA and a dry LIA. Several marine records from the eastern Tropical Pacific indicate negative (positive) SST anomalies during MCA (LIA). This implies that positive (negative) precipitation anomalies during the latest Holocene were related to periods of sustained La Niña-like (El Niño-like) conditions. We conclude that mean states in the Pacific SST gradient during the MCA and LIA drove alternation of wetter and arid conditions throughout the Atacama Desert, as the Tropical Pacific responded to external forcing of the Earth’s climate system at centennial timescales