Interpreting past climate using southwest Australian speleothems

Abstract

There is an identified need to extend our baseline climate information beyond the relatively short duration of instrumental records in Australia. An improved knowledge of natural rainfall variability would assist in our understanding of climate change. SW Australia (SWWA) is one region that has been identified as having a changing climate since the 1970s. Speleothems (cave stalagmites) are an effective archive of past climate variability and caves from the coastal region of SWWA are being studied for paleoclimate records. The modern speleothem record from this region has been assessed and shown to record the post-1970s rainfall decrease (Treble et al., 2003; 2005; Fischer and Treble, 2008). The extension of the speleothem record is currently underway, however, a long-term cave monitoring program was also deemed necessary to separate the climatic from non-climatic signals i.e. to reduce uncertainty when interpreting these records. This presentation outlines what we have learnt about the possible hydrological modification of the climate signal in speleothems. In particular, we present results from a five-year long monitoring study of rainfall and cave drip water O isotopes (!18O) from Golgotha Cave, SWWA. From this study, we have been able to characterize the probable flow paths feeding stalagmites in our monitored cave. These flow paths range from slow diffuse flow of isotopically-averaged rainfall to preferential routing of high-magnitude, 18O-depleted, events along fast flow routes into the cave. Hence, we offer a possible explanation for why paleoclimate records from coeval speleothems in our cave may differ. Our study suggests that this disagreement may simply be due to different flow paths resulting in a bias towards the preservation of high or low magnitude rainfall events.