Browsing by Author "Lorrey, AM"

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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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    Timing, magnitude and effects of late Holocene sea level drawdown on island habitability, Aitutaki, Cook Islands
    (Oceania Publications, 2016-07-06) Allen, MS; Morrison, AE; Lorrey, AM; Zhao, JX; Jacobsen, GE
    Geologist Bill Dickinson argued that prior to late Holocene sea level fall, in many Pacific island settings low-lying islands were awash, shallow nearshore environments were restricted and human settlement was constrained or sometimes impossible. Stable coastlines and islets of modern configuration only developed after the “cross-over date”, when declining high-tide levels fell below mid-Holocene low-tide levels, a regionally variable process. We evaluate evidence from the almost-atoll of Aitutaki, Cook Islands against this model, providing: (1) a local late Holocene sea level reconstruction including nine U/Th-dated microatolls; (2) 22 new AMS dates on human activities, many from small, low-lying offshore islets; and (3) elevation data for 14C-dated cultural deposits on three islets. Our results include an early first millennium sea level position 0.74–0.97 m (± 0.126) above modern height-of-living-corals, an eighth to eleventh century AD minimum relative to the long-term trend, and a sea level rise peaking in the mid-fourteenth to sixteenth centuries. This reconstruction, combined with twelfth century AD Cocos nucifera charcoal, informs on the timing and distribution of human activities across Aitutaki's evolving land and seascapes and sea level impacts. While our findings do not contradict Dickinson's model of sea level constrained island settlement, other explanations cannot be excluded. © 2016, Oceania Publications.