title: δ18O in the tropical conifer Agathis robusta records ENSO-related precipitation variations.
abstract: Long-lived trees from tropical Australasia are a potential source of information about internal variability of the El Niño-Southern Oscillation (ENSO), because they occur in a region where precipitation variability is closely associated with ENSO activity. We measured tree-ring width and oxygen isotopic composition (δ18O) of α-cellulose from Agathis robusta (Queensland Kauri) samples collected in the Atherton Tablelands, Queensland, Australia. Standard ring-width chronologies yielded low internal consistency due to the frequent presence of false ring-like anatomical features. However, in a detailed examination of the most recent 15 years of growth (1995-2010), we found significant correlation between δ18O and local precipitation, the latter associated with ENSO activity. The results are consistent with process-based forward modeling of the oxygen isotopic composition of α-cellulose. The δ18O record also enabled us to confirm the presence of a false growth ring in one of the three samples in the composite record, and to determine that it occurred as a consequence of anomalously low rainfall in the middle of the 2004/5 rainy season. The combination of incremental growth and isotopic measures may be a powerful approach to development of long-term (150+ year) ENSO reconstructions from the terrestrial tropics of Australasia.
authors: Department of Environmental and Primary Resources, State of Victoria, East Melbourne, Victoria, Australia.
authors: Bjorn M M
authors: BM
authors: Boysen
authors: Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, United States of America.
authors: Michael N
authors: MN
authors: Evans
authors: Department of Forest and Ecosystem Science, Melbourne School of Land and Environment, University of Melbourne, Victoria, Australia.
authors: Patrick J
authors: PJ
authors: Baker
mesh_terms: D001315:Australia; D002482:Cellulose / Q000302:isolation & purification*; D002910:Chronology as Topic; D059000:El Nino-Southern Oscillation; D010103:Oxygen Isotopes / Q000737:chemistry / Q000302:isolation & purification*; D011891:Rain; D012621:Seasons; D013696:Temperature; D014197:Trees / Q000201:enzymology* / Q000254:growth & development; D014329:Tropical Climate
chemical_list: D010103:Oxygen Isotopes; D002482:Cellulose