A stable oxygen, but not carbon, isotope chronology of Callitris columellaris reflects recent climate change in north-western Australia

Abstract

We investigated the dendroclimatic potential of stable carbon (δ 13 C) and oxygen (δ 18 O) abundances in tree rings of Callitris columellaris F. Muell. Tree-ring chronologies were constructed from the central Pilbara, north-western Australia and span 1919-1999. Variation in δ 18 O was more strongly related to climate than δ 13 C; ecological and physiological factors may have dampened the climate signal in the δ 13 C chronology. Tree-ring δ 18 O was most strongly correlated with relative humidity (RH) and rainfall (r=−0.36 and −0.39) of the wettest months of the summer period, January and February. The correlation with RH reflects its effect on evaporative enrichment of leaf water. However, tree-ring δ 18 O may also partly reflect the variability in 18 O signatures of rainfall, which are influenced by the amount of rainfall and atmospheric humidity. From the δ 18 O chronology, we inferred that from 1919 to 1955 summers were relatively dry and warm, but since 1955, summers in the Pilbara region have become increasingly cooler and more humid. Since 1980, conditions have been the wettest and coolest of the last 80 years. These inferred changes in climate correspond to a measured increase in rainfall since 1980 in north-western Australia associated with a greater intensity of tropical cyclones. We conclude that δ 18 O abundances in tree rings of C. columellaris have significant potential for reconstructing the climate of semi-arid Australia, a region for which observational climate records are sparse.

The role of soil processes in δ18O terrestrial climate proxies

“…A depleted δ 18 O xw signal may be misinterpreted as reflecting more isotopically depleted precipitation or enhanced rainfall due to an inferred “amount effect.” Thus, in regions where these soil moisture transport processes are dominant, there is a positive correlation between δ 18 O xw and relative humidity, even though a decrease in relative humidity would be expected to enrich surface water δ 18 O. This mechanism and interpretation of isotopically low values may represent anomalously low precipitation and should be considered for some years in δ 18 O c studies conducted in places such as the southwest U.S. [ Kanner et al ., ] and subtropical Australia [ Cullen and Grierson , ].…”

Stable isotope and hydrochemical evolution of groundwater in the semi-arid Hamersley Basin of subtropical northwest Australia

“…This is particularly true of the Hamersley Basin, in the semi-arid Pilbara region of northwest of Australia, where water resources are currently subject to increasing pressure from altered hydrology associated with mining activities as well as water abstraction for regional development (Department of Water, 2010). In contrast to much of Australia, rainfall in the northwest has also been increasing since the 1950s, mainly from December to February (e.g., Cullen and Grierson, 2007;Taschetto and England, 2009). Given the highly dynamic nature of rainfall and recharge across the Pilbara, there is now an urgent need to understand the significance of variable rainfall events in the evolution of surface water and groundwater.…”

Variation in stem radial growth of the Australian conifer, Callitris columellaris, across the world’s driest and least fertile vegetated continent

“…Cullen and Grierson 2007;Cullen and Grierson 2009;Sgherza et al 2010), the absolute age of trees for all sites in our study is uncertain as C. columellaris rings are not reliably annual except in the mesic tropical regions . However, while we cannot be sure of relative ring ages among cores, we do know the relative ages of rings within cores because outer rings are more recent than inner rings.…”