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Reconstructing natural rainfall variability for southwest Australia using stalagmites

I am currently reconstructing rainfall for the southwest corner of Western Australia for the past 1000 years. Rainfall decreased almost 20% across this region from about 1970 onwards. It's not yet clear why this happened although the Indian Ocean Climate Initiative (IOCI) have been trying to find out why. IOCI reports suggest that both natural rainfall variability and increased atmospheric greenhouse gases are responsible for the rainfall decrease (to find out more about IOCI and read their reports, visit www.ioci.org.au).

We have no way of knowing how much of this rainfall decrease could be due to natural rainfall variability as our instrumental climate records are too short to define multi-decadal trends. I am thus  reconstructing rainfall for the past 1000 years using stalagmites. Phosphorus, magnesium and oxygen isotopes contained in the speleothem calcite all respond to the 1970s rainfall decrease indicating that these geochemical variables could function as rainfall proxies further back in time.