Frequency-Dependent Covariance of Warm- and Cool-Season Temperature Reconstructions for Southern Australia over the Last Five Centuries.

Abstract:

Very few long and annually-resolved temperature proxy records exist in the Southern Hemisphere and those that do typically reflect warm-season climate. However, trees in Tasmania, Australia, provide the opportunity to produce reconstructions of both warm-season (December to February) and cool-season temperatures (July to October). High quality warm-season reconstructions based largely on Huon pine cover the last millennium (979-2008 CE) and explain up to ~60% of the variance in instrumental observations. Here, we describe the continued development and temporal extension of a cool-season temperature reconstruction continuously spanning the period from 1550 to 2007 CE that explains ~40% of instrumental variance. Prior to the 16th century, tree-ring material for this reconstruction becomes sparse and between ~1370 and 1550 CE and then prior to ~450 CE there are significant reductions in sample depth related to extensive landscape-scale disturbances. A comparison of the warm- and cool-season temperature reconstructions shows that the persistent warming in both seasons in the instrumental record since ~1950 CE is unprecedented. While the low-frequency variability of the two seasonal reconstructions are generally coherent, high-frequency variability is not, illustrating the need for seasonally based reconstructions to help improve understanding of variability in intra-annual dynamics given their importance for ecological and hydrological processes. A significant extension of this cool season record for the entire Common Era using material from far southern Tasmania would greatly enhance our understanding of inter-seasonal dynamics and long-term climate variability.