Pandanus nutshell generates a palaeoprecipitation record for human occupation at Madjedbebe, northern Australia

S Anna Florin,Catherine E Lovelock,Linda A Barry,Djaykuk Djandjomerr,James Shulmeister,Ben Marwick,Quan Hua,Patrick Roberts,Lynley A Wallis,Nicholas R Patton,Chris Clarkson,Richard Fullagar,May Nango,Andrew S Fairbairn

doi:10.1038/s41559-020-01379-8

Abstract

Little is known about the Pleistocene climatic context of northern Australia at the time of early human settlement. Here we generate a palaeoprecipitation proxy using stable carbon isotope analysis of modern and archaeological pandanus nutshell from Madjedbebe, Australia’s oldest known archaeological site. We document fluctuations in precipitation over the last 65,000 years and identify periods of lower precipitation during the penultimate and last glacial stages, Marine Isotope Stages 4 and 2. However, the lowest effective annual precipitation is recorded at the present time. Periods of lower precipitation, including the earliest phase of occupation, correspond with peaks in exotic stone raw materials and artefact discard at the site. This pattern is interpreted as suggesting increased group mobility and intensified use of the region during drier periods.

Highlights

Madjedbebe is a large sandstone rockshelter located on Mirarr country in the Alligator Rivers region, northern Australia, with evidence for human occupation from at least 65 thousand years ago to the present (Fig. 1b)[1]
Pandanus has been found in archaeological sites across the tropics, including as part of Melanesian and Pacific foraging and agricultural systems[14,15,16,17], and P. spiralis was recovered from almost all occupation layers at Madjedbebe (Fig. 2)[2]
We demonstrate that stable carbon isotope analysis of this taxon can provide a reliable palaeoprecipitation proxy, and use it in concert with the analysis of soil stable carbon isotopes, and lithic artefact and exotic raw material discard rates from Madjedbebe, to investigate the relationship between environmental change and human mobility and settlement in the past

Summary

G6-4 G6-2 MD98-2167

Nature Ecology & Evolution | VOL 5 | March 2021 | 295–303 | www.nature.com/natecolevol. The lower WUE evidenced near Katherine is a factor of increased waterlogging during the growing season of P. spiralis drupes While this means that variability in local topography can cause variability in the effects of MAP on δ13C values of P. spiralis drupes at a particular location, the fit of δ13C values from the direct vicinity of Madjedbebe to the linear relationship observed between precipitation and δ13C values along the Stuart Highway transect suggests that Madjedbebe is an ideal site at which to use this proxy (Fig. 3c). This is partially offset by the reduction in available moisture in the atmosphere, but overall a minor increase in monsoon strength is inferred This is supported archaeologically by the peaks in artefact discard at Madjedbebe during dry phases (Fig. 5c), which suggest increased use of the site during these phases, and are consistent with earlier arguments that human occupation intensified in the Alligator Rivers region during the Last Glacial Maximum owing to its relatively wet environment[34]. Peaks in exotic raw materials during dry phases (Fig. 5d) indicate that people were probably more mobile at these times, with decreased abundance of resources requiring them to extend their foraging range and possibly their social networks[35,36]

Discussion

Findings

Methods