Browsing by Author "Hogg, AG"

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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
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    SHCal13 Southern Hemisphere calibration, 0–50,000 years cal BP
    (University Arizona Department Geosciences, 2016-02-09) Hogg, AG; Hua, Q; Blackwell, PG; Niu, M; Buck, CE; Guilderson, TP; Heaton, TJ; Palmer, JG; Reimer, PJ; Reimer, RW; Turney, CSM; Zimmerman, SRH
    The Southern Hemisphere SHCal04 radiocarbon calibration curve has been updated with the addition of new data sets extending measurements to 2145 cal BP and including the ANSTO Younger Dryas Huon pine data set. Outside the range of measured data, the curve is based upon the ern Hemisphere data sets as presented in IntCal13, with an interhemispheric offset averaging 43 ± 23 yr modeled by an autoregressive process to represent the short-term correlations in the offset. © 2013, by the Arizona Board of Regents on behalf of the University of Arizona.
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    SHCal20 Southern Hemisphere calibration, 0–55,000 years cal BP
    (Cambridge University Press, 2020-08-12) Hogg, AG; Heaton, TJ; Hua, Q; Palmer, JG; Turney, CSM; Southon, J; Bayliss, A; Blackwell, PG; Boswijk, G; Bronk Ramsey, C; Pearson, C; Petchey, F; Reimer, P; Wacker, L
    Early researchers of radiocarbon levels in Southern Hemisphere tree rings identified a variable North-South hemispheric offset, necessitating construction of a separate radiocarbon calibration curve for the South. We present here SHCal20, a revised calibration curve from 0–55,000 cal BP, based upon SHCal13 and fortified by the addition of 14 new tree-ring data sets in the 2140–0, 3520–3453, 3608–3590 and 13,140–11,375 cal BP time intervals. We detail the statistical approaches used for curve construction and present recommendations for the use of the Northern Hemisphere curve (IntCal20), the Southern Hemisphere curve (SHCal20) and suggest where application of an equal mixture of the curves might be more appropriate. Using our Bayesian spline with errors-in-variables methodology, and based upon a comparison of Southern Hemisphere tree-ring data compared with contemporaneous Northern Hemisphere data, we estimate the mean Southern Hemisphere offset to be 36 ± 27 14C yrs older. © 2020 by the Arizona Board of Regents on behalf of the University of Arizona. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.