Friday, 2 December 2011

Price et al (2010)...avid supporters of the climate change theory

This study is a bit of a more complicated one, so sorry if I don’t explain it very well! This study is carried out by Price et al (2010) based on Late Pleistocene vertebrate fossil remains from the Darling Downs, eastern Australia.

The fossils are stratigraphically intact with abundant megafaunal sequences (remains) allowing for a accurate test of both the climate change and human predation hypotheses. Price et al (2010) use a multi-disciplinary approach to dating the deposits, which consists of more than 40 dates. Accelerator mass spectrometry (AMS) and thermal ionisation mass spectrometry – now I know this probably doesn’t mean much to most people, but I thought I would put it in for those of you who do!
But basically after AMS 14C dating of charcoal remains, dating clustered in the upper chronological limits of the technique, dating 40-48 ka at the youngest possible date. With added dating techniques from taken from the teeth and freshwater molluscs remains at the site, chronological dates of up to 120-83Ka were found. This obviously shows the AMS 14C dating technique was not robust enough to stretch chronologically to such an early age. Thus indicating from the thermal ionisation mass spectrometry dating, the decline in biological diversity was 75,000 years before human colonisation in Australia. 

Figure 1:
Just to spice things up a bit, here is a picture of some of the remains found at the site, specifically from a giant forest wallaby’s skull.
Figure 2:
And also a chart to illustrate the temporal occurrence of the megafaunal taxa at the Darling Downs site in relation to the hypothesised megafaunal extinction window and first human arrival.
The period between species extinction and human arrival was a time of extreme changes in climate including decreasing temperatures during the transition into the glacial age, falling sea levels, increases in aridity and the contraction of wet forest and spread of Sclerophyllus vegetation and grassland. This study gives the work of Hope et al (2004) as a comparison of the extinction patterns with climatic shifts. Hope et al (2004) suggested floral changes to more arid adapted open floras at around 80-70ka and 50-40ka linked to increased aridity. Although the study admits the most recent change in flora at 50-40ka may have been related to human induced burning, arid intervals before human arrival have also been associated with increased burning, for example at New Caledonia. So the increased aridity even if it is found to be linked with increased charcoal remains and hence increased burning need not be related directly to human presence. 

This study uses accurate dating techniques to link faunal macrofossils to the climate change hypothesis. I have already covered studies that emphasize and present evidence for the sharp climate changes towards aridity in Australia, for example Horton (1984), Dodson (1989) and Owen Smith (1987). I have been reading some more articles describing and articulating the shifting climate in the late Pleistocene and will present them in later blog entries to analyse in depth how the climate could have affected the megafaunal species. But all in all I think this study provides ample evidence that climate changes induced the extinctions, especially since the gap between human arrival and species extinction was so long. One thing is for sure is that the ‘Blitzkrieg model’ (see glossary) doesn’t not apply in Australia, humans and species were just living too long together for it to be plausible.

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