Abstract

Multiple paleoclimate reconstructions reveal that the hyperarid Atacama Desert has experienced important hydroclimate variations on centennial and millennial timescales over the past 18,000 years. These past hydroclimate anomalies are known to have affected significantly regional hydrological patterns and distribution of terrestrial biota. The relationship between such paleoclimate events and population dynamic of pre-Hispanic societies that inhabited the driest desert on Earth, however, remains unclear. Here, we tackle this issue by reconstructing the long-term population history for the Atacama Desert (16°-24°S) over the past 3,000 years. Specifically, we evaluate changes in population size by examining the summed probability distribution of 334 calibrated 14C dates from 123 archeological sites across the interior of the Atacama (>900 masl). Our results point to important centennial-scale variations in demographic patterns for agricultural societies from the Atacama throughout the late Holocene. The resulting curve indicates that population started to increase gradually at 3.0 ka and then stabilize at relatively high level between ~2.8 and 2.3 ka. A strong decline in population size is evident between 2.3 and 1.4 ka. Population recovered again by 1.4 ka and peaked at 1.05-0.5 ka. Thereafter, demographic levels decrease sharply. Overall, these demographic changes in the Atacama Desert occurred at the same times as the major late Holocene paleoclimate changes of that region. Actually, increased population levels by 1.05-0.5 ka are coeval with a prominent positive hydroclimate anomaly detected regionally during the so-called Medieval Climate Anomaly (MCA). Conversely, the sustained decline after 0.5 ka coincide with a protracted negative hydroclimate anomaly during the Little Ice Age (LIA). Our findings indicate that preHipanic agrarian populations from the hyperarid Atacama Desert were sensitive to Late Holocene hydroclimate variability. Moreover, the observed relationship between paleoclimate and long-term population trends over the past 3,000 years, suggest that regional hydroclimate was a first-order factor for the past demographic structure of these societies.