Late-Holocene environmental change on the Nullarbor Plain, southwest Australia, based on speleothem pollen records

Abstract

Fossil pollen from two stalagmites is examined to reconstruct a c. 2400-year history of vegetation change on the Nullarbor Plain. Environmental changes are reflected by variation in chenopod species abundance, and by a peak in woody taxa between 1000 and 800 years ago which is interpreted as evidence of increased moisture conditions associated with a positive phase of the Southern Annular Mode. While no strong palynological signal is observed at the time of European colonization of Australia, a significant change occurs in the past 40 years, which is interpreted as a vegetation response to a recorded fire event. As speleothems (secondary cave carbonates including stalagmites, stalactites and flowstones) rarely contain enough fossil pollen for analysis, the taphonomic biases of speleothem archives remain poorly understood. This study, as well as being a high-resolution record of environmental change, presents an opportunity to examine these taphonomic filters. The record is shown to be sensitive to episodic deposition of presumably insect-borne pollen, but overall appears to provide a faithful representation of local and regional vegetation change. There is a need for greater research into taphonomic processes, if speleothem palynology is to be developed as a viable alternative to lacustrine sediments in the investigation of past environmental change.