Modern pollen-vegetation-climate data set based on surface and rodent midden samples from the Atacama Desert (Chile) and its potential application to Late Quaternary reconstructions

Abstract

Although the Atacama is the oldest and most continuous dry desert on Earth, organic matter (OM) is ubiquitous in its surface sediments. Today, vegetation growth is restricted to the Coastal Cordillera and the Andean foothills, which are predominantly supplied by fog or rainfall. The sources of OM in topsoils of hyperarid regions and deep sediments remain an open question; therefore, we hypothesized that desert plants exhibit specific n-alkane compositions that can be traced in adjacent topsoils and assessed possible OM sources and formation processes in hyperarid regions and soil depths of desert. We determined the n-alkane signatures of plants (n = 28), of soil OM in their vicinity, of hyperarid surface sediments (n = 82), and of four depth profiles (up to 200 cm).We found that n-alkane distributions in fog-fed plants were dominated in order by nC31, nC29, nC33, and nC27 alkanes, while rain-fed plants were dominated by nC29 and nC31 alkanes. When the ratio of nC27+nC33/nC29+nC31 was applied as a “fog-to-rain n-alkane ratio”, the data in surface soils and sediments below 1200 m a.s.l. (in the west of the desert) indicated fog-influenced formation of organics, while all soils and sediments formed higher than 1200 m a.s.l. (in the center and east of the desert) archived n-alkanes from plants fed by rain. Surprisingly, 75–98% of the desert’s OM was found in deep sediments, even under recent vegetation cover. Hence, our findings indicate that currently vegetation-free hyperarid regions of the Atacama Desert once varied in size depending on climate change.