Browsing by Author "Fenwick, P"

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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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    Reconstructing late pleistocene atmospheric radiocarbon using subfossil New Zealand Kauri (Agathis australis)
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) O'Brien, PP; Turney, CSM; Palmer, JG; Fenwick, P; Hogg, AG; Lorrey, AM; Hua, Q
    Subfossil New Zealand kauri (Agathis australis) buried in bogs across Northland, New Zealand, provide considerable potential for a continuous high-precision radiocarbon calibration curve that extends across the full range of radiocarbon dating. Kauri currently is a significant contributor to our understanding of calibration in this Southern region. The preserved samples also offer a unique opportunity to reconstruct climate events on multi-millennial timescales with annual resolution and carbon concentration. Here we investigate a key site called Waipu, where 40 subfossil trees have been crossdated to form 5 floating chronologies. These series cover collectively 6000 years and preliminary radiocarbon dating suggests a range of ages from 22,000 to 49,000 years BP. Further radiocarbon dating and crossdating of other kauri tree-ring series using the new RingdateR package and visual inspection has identified other trees that may cross-date. This suggests it may be possible to link the floating Waipu series, forming a continuous chronology.If successful this would form the one of the longest subfossil kauri chronologies, with the help of radiocarbon dating. The Waipu chronology would form a world-class palaeo-archive for the Southern Hemisphere and provide a valuable contribution to future iterations of the international calibration curves. © The Authors