Browsing by Author "Thomas, ZA"

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    Changes in El Niño - Southern Oscillation (ENSO) conditions during the Greenland Stadial 1 (GS-1) chronozone revealed by New Zealand tree-rings
    (Elsevier, 2016-12-01) Palmer, JG; Turney, CSM; Cook, ER; Fenwick, P; Thomas, ZA; Helle, G; Jones, RT; Clement, A; Hogg, AG; Southon, J; Bronk Ramsey, C; Staff, R; Muscheler, R; Corrège, T; Hua, Q
    The warming trend at the end of the last glacial was disrupted by rapid cooling clearly identified in Greenland (Greenland Stadial 1 or GS-1) and Europe (Younger Dryas Stadial or YD). This reversal to glacial-like conditions is one of the best known examples of abrupt change but the exact timing and global spatial extent remain uncertain. Whilst the wider Atlantic region has a network of high-resolution proxy records spanning GS-1, the Pacific Ocean suffers from a scarcity of sub-decadally resolved sequences. Here we report the results from an investigation into a tree-ring chronology from northern New Zealand aimed at addressing the paucity of data. The conifer tree species kauri (Agathis australis) is known from contemporary studies to be sensitive to regional climate changes. An analysis of a ‘historic’ 452-year kauri chronology confirms a tropical-Pacific teleconnection via the El Niño – Southern Oscillation (ENSO). We then focus our study on a 1010-year sub-fossil kauri chronology that has been precisely dated by comprehensive radiocarbon dating and contains a striking ring-width downturn between ∼12,500 and 12,380 cal BP within GS-1. Wavelet analysis shows a marked increase in ENSO-like periodicities occurring after the downturn event. Comparison to low- and mid-latitude Pacific records suggests a coherency with ENSO and Southern Hemisphere atmospheric circulation change during this period. The driver(s) for this climate event remain unclear but may be related to solar changes that subsequently led to establishment and/or increased expression of ENSO across the mid-latitudes of the Pacific, seemingly independent of the Atlantic and polar regions. © 2016, Elsevier Ltd.
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    Radiocarbon protocols and first intercomparison results from the Chronos 14Carbon-Cycle Facility, University of New South Wales, Sydney, Australia
    (Cambridge University Press, 2021-05-11) Turney, CSM; Becerra-Valdivia, L; Sookdeo, A; Thomas, ZA; Palmer, JG; Haines, HA; Cadd, H; Wacker, L; Baker, AA; Andersen, MS; Jacobsen, GE; Meredith, KT; Chinu, K; Bollhalder, S; Marjo, CE
    The Chronos 14Carbon-Cycle Facility is a new radiocarbon laboratory at the University of New South Wales, Australia. Built around an Ionplus 200 kV MIni-CArbon DAting System (MICADAS) Accelerator Mass Spectrometer (AMS) installed in October 2019, the facility was established to address major challenges in the Earth, Environmental and Archaeological sciences. Here we report an overview of the Chronos facility, the pretreatment methods currently employed (bones, carbonates, peat, pollen, charcoal, and wood) and results of radiocarbon and stable isotope measurements undertaken on a wide range of sample types. Measurements on international standards, known-age and blank samples demonstrate the facility is capable of measuring 14C samples from the Anthropocene back to nearly 50,000 years ago. Future work will focus on improving our understanding of the Earth system and managing resources in a future warmer world. © The Author(s) 2021. Published by Cambridge University Press for the Arizona Board of Regents on behalf of the University of Arizona.