Abstract

The stable hyperarid core of the Atacama Desert (18-26°S) along the coast of southern South America is one of the world’s driest deserts, hosts some of the oldest preserved land surfaces on earth, and is often used as an analog of Mars. Yet, very little is known how this coastal desert is affected by major climate change, such as those that occurred during and after the Last Glacial - Interglacial Transition (LGIT). Here, we analyzed plant macrofossils and pollen from 21 radiocarbon dated rodent middens collected from the central and southern portions of the hyperarid core of Atacama Desert in northern Chile (24-26°S). Our unique 34,000 yr record spans the lower desert (1200 m, to within 50 km of the modern coastline) up to the Andean Precordillera (2700 m). A prominent increase in plant macrofossil richness (a proxy for moisture), along with the appearance of Andean extralocals (Phacelia pinnatifida, Stipa frigida and Junellia sp.) and wetland indicators such as Cyperaceae occurs in two Precordillera middens dated to 34 and 19 ka. Six younger middens dated from 6.12-0.11 ka are similar in composition to the modern local vegetation. In the hyperarid desert, (~1500 m) plant macrofossils from middens dated to 19.32, 1.13, 1.0, 0.85, 0.52 ka and a modern sample, have very low richness and are dominated by the same plants that occur today (Nolana sp. and Cistanthe sp.). The presence of Andean extralocal species such as Adesmia atacamensis and Cryptantha diffusa together with elevated richness indicate wet events at 28, 21, 16.98, 3.67 and 0.45 ka. Diverse pollen assemblages also characterize these middens perhaps as the result of increased vegetation cover. Togther, these results indicate that even the hyperarid core of the Atacama experiments major hydrological change during the late Quaternary. The presence of Andean species in these coastal middens indicates that a recurrent riparian corridor connected the Andean Precordillera with the coastal range. Thus, in addition to the presence of ephemeral and/or perennial streamflow caused by elevated groundwater tables, our records imply increased rainfall of mixed origin (summer vs winter rainfall) in the Precordillera during these events. Finally, these results present new prospects for understanding the evolution and diversity of the Atacama Desert flora.