The potential to reconstruct broadscale climate indices associated with southeast Australian droughts from Athrotaxis species, Tasmania

Abstract

Occurrence of drought and dry periods in southeastern Australia has been linked to broad scale climate phenomena including the Southern Oscillation, Interdecadal Pacific Oscillation (IPO), Indian Ocean Dipole (IOD), Southern Annular Mode (SAM) and persistence of blocking high pressure in the Tasman Sea. We examine relationships between Athrotaxis tree ring chronologies from southern Australia extending over much of the past millennia and these broad scale indices. We also examine relationships between the chronologies, temperature, precipitation and a standardised precipitation and evapotranspiration index. Timing of significant correlations with maximum temperature varies between species. The responses of the species with broadscale indices vary with location: northern Athrotaxis cupressoides (Pencil Pine) are more strongly related to the Interdecadal Pacific Oscillation (IPO) and Southern Oscillation Index (SOI) than southern sites. As an exception to this, a site in the far south had significant correlations with both the SOI and IPO, opposite in sign to those observed for the northern sites. Significant spectral power at frequencies consistent with the SOI and IPO occur in all chronologies. Western and southern sites are more strongly related to a seasonalised index of SAM. These three systems have played important roles in determining moisture conditions in southeastern Australia over the past millennium. Results suggest that reconstructions of the SOI, IPO or SAM are unlikely based solely on this Athrotaxis network. The Athrotaxis network of tree ring sites, is however, likely to be an important input to multi-proxy models reconstructing the SOI, IPO or SAM in the Australian sector. The Athrotaxis network of sites is also an important extension of the existing network of Australian tree ring sites that could be used to reconstruct historical drought in southeastern Australia.