Low-latitude glacial cooling in the southern hemisphere from amino-acid racemization in emu eggshells

The record of natural climate variability over glacial-interglacial timescales provides a framework from which a better mechanistic understanding of the climate system may be derived. But this approach is limited by the number and distribution of well-dated and reliable palaeoenvironmental archives. Particularly vexing is the conflicting evidence for low-latitude cooling during the Last Glacial Maximum, and the apparent synchrony in glacial activity between the hemispheres despite out-of-phase insolation forcing. Here we utilize the temperature-dependent amino acid racemization reaction in radiocarbon-dated emu eggshell fragments from the continental interior of Australia to reconstruct low-altitude subtropical temperatures for the past 45 kyr. Racemization rate changes indicate that millennial- scale average air temperatures were at least 9°C lower between 45 and 16 kyr BP than since 16 kyr BP. A temperature change of this magnitude, coupled with other low-latitude palaeotemperature records that indicate substantial cooling, must reflect global processes, which, we speculate, involved glacial-age reduction in atmospheric water vapour content.