65,000 years of vegetation change in central Australia and the Australian summer monsoon

Carbon isotopes in fossil emu (Dromaius novaehollandiae) eggshell from Lake Lyre, South Australia,demonstrate that the relative abundance of C-4 grass es varied substantially during the past 65,000 years. Currently, C-4 grasse s are more abundant in regions that are increasingly affected by warm-seaso n precipitation. Thus, an expansion of C-4 grasses Likely reflects an incre ase in the relative effectiveness of the Australian summer monsoon, which c ontrols summer precipitation over Lake Lyre. The data imply that the Austra lian monsoon was most effective between 45,000 and 65,000 years ago, Least effective during the Last Glacial Maximum, and moderately effective during the Holocene.