Tropical environments are, however, often defined by pronounced and relatively regular variations in moisture, which can be indirectly observed in the oxygen isotopic composition of the -cellulose component of tropical wood. As a result, annually resolved tree rings may provide long, replicated records in the extratropics, but they are rarely reported in the tropical and sub-tropical regions that are directly influenced by ENSO dynamics. ![]() The presence of false and missing growth increments undermines our ability to date materials accurately and precisely – a necessary precursor for paleoclimatic reconstructions from tropical trees. Furthermore, persistently poor growing conditions over long time periods may result in missing annual growth increments ("missing rings"). Short-duration, transient climatic conditions may lead to opportunistic growth and dormancy cycles, which may masquerade as annual growth increments (so-called "false rings") –. Tropical and sub-tropical tree species and environments present a challenge for paleoclimatology because they often fail to generate the regular annual patterns of cambial activity and dormancy that produce anatomical features reliably identified as annual growth increments ("tree rings"). Trees are a widely distributed terrestrial archive and may provide highly replicated paleodata, but in ENSO-affected tropical regions, may not reliably produce annually resolved tree rings. ![]() Corals and speleothem archives are sparsely distributed and hence the paleodata acquired from them often have limited replication. However, the most widely used high resolution tropical paleoclimatic archives – corals, speleothems, and tree rings – have significant limitations. The relationship between ENSO and regional climate variability requires a longer historical context, and paleoclimatic reconstructions provide a means of achieving this goal. A more complete understanding of longer-term, intrinsic variability in ENSO is limited, however, by the absence of direct observations of surface climate before the second half of the 20th century this is particularly true in the southwest Pacific – and across the West Pacific Warm Pool. The El Niño-Southern Oscillation (ENSO) is one of the leading sources of regional- and global-scale climate variability. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.įunding: This research was supported through US National Science Foundation grants AGS0902794 and EAR0929983 to MNE and Australian Research Council grant DP0878744 to PJB. Received: FebruAccepted: JPublished: July 25, 2014Ĭopyright: © 2014 Boysen et al. PLoS ONE 9(7):Įditor: Peter Wilf, Penn State University, United States of America 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.Ĭitation: Boysen BMM, Evans MN, Baker PJ (2014) δ 18O in the Tropical Conifer Agathis robusta Records ENSO-Related Precipitation Variations. The O 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 results are consistent with process-based forward modeling of the oxygen isotopic composition of -cellulose. However, in a detailed examination of the most recent 15 years of growth (1995–2010), we found significant correlation between O and local precipitation, the latter associated with ENSO activity. ![]() Standard ring-width chronologies yielded low internal consistency due to the frequent presence of false ring-like anatomical features. ![]() We measured tree-ring width and oxygen isotopic composition ( O) of -cellulose from Agathis robusta (Queensland Kauri) samples collected in the Atherton Tablelands, Queensland, Australia. U.S.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. Note: "Regional Climate Centers" are joint programs among university, state, and/or Federal Goverment agencies. NOAA locations that provide climatic data & historical data records Press enter or select the go button to submit request
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