The Reconstruction Potential of a 350 year-long, Mid-Elevation Proxy for PDSI in a Tree-Ring Record from Tropical North Queensland, Australia.

Abstract:

In far northern Queensland (FNQ) there are only sporadic coral and speleothem precipitation proxy records, and only one annually resolved, terrestrial record of rainfall that predates 1850 CE. Black kauri pine, Agathis atropurpurea, is a large conifer present in isolated stands near 1000 masl in the wet tropical dividing range of FNQ. Little is known about its phenology or responses to climate, although its presence near the elevational limit of the dividing range may hinder its ability to respond to increased temperature or decreased precipitation through elevational migration. We hypothesize that in this energy-limited forest, increased (decreased) solar radiation leads to increased (decreased) ring widths, and higher (lower) evapotranspiration rates produce increases (decreases) in the oxygen isotopic composition (^δ18O) of the a-cellulose component of wood. To test this hypothesis, we collected over 60 cores from 21 large (dbh = 56 to 186 cm) A. atropurpurea trees from Spurgeon Peak National Park. The resulting tree-ring chronology extends from 2013 to 1438 CE and shows high average mean sensitivity (0.642) although expressed population signal drops off at 1650 CE as sample depth decreases. Comparison of the most recent 100 years of ring widths and direct climate observations show a significant positive relationship (r² = 0.4, p < 0.01) to PDSI in December through March, coinciding with the austral rainy season associated with onset of the northern Australian Monsoon. Annualized δ¹⁸Oxygen (a-cellulose) maxima for 1983-2013 show strong and significant spatial positive relationships to T_max and Pacific seasurface temperatures. Work to refine the interpretation of the data is onoing, but the resulting dataset may enable extension of the terrestrial climate record of north Queensland two centuries beyond current tree-ring proxies and historical observations.