The anatomy of Last Glacial Maximum climate variations in south Westland, New Zealand, derived from pollen records

• Published in: Quaternary science reviews 2013-08, Vol.74, p.215-229
• Main Authors: Vandergoes, Marcus J., Newnham, Rewi M., Denton, George H., Blaauw, Maarten, Barrell, David J.A.
• Format: Article
• Language: English
• Subjects: 14C dating; Chronostratigraphy; Climate events; Kawakawa/Oruanui tephra; Last Glacial Maximum (LGM); Marine; New Zealand; Paleoclimate; Pollen records; Southwest Pacific
• ISSN: 0277-3791; 1873-457X
• DOI: 10.1016/j.quascirev.2013.04.015

We present pollen records from three sites in south Westland, New Zealand, that document past vegetation and inferred climate change between approximately 30,000 and 15,000 cal. yr BP. Detailed radiocarbon dating of the enclosing sediments at one of those sites, Galway tarn, provides a more robust chronology for the structure and timing of climate-induced vegetation change than has previously been possible in this region. The Kawakawa/Oruanui tephra, a key isochronous marker, affords a precise stratigraphic link across all three pollen records, while other tie points are provided by key pollen-stratigraphic changes which appear to be synchronous across all three sites. Collectively, the records show three episodes in which grassland, interpreted as indicating mostly cold subalpine to alpine conditions, was prevalent in lowland south Westland, separated by phases dominated by subalpine shrubs and montane-lowland trees, indicating milder interstadial conditions. Dating, expressed as a Bayesian-estimated single ‘best’ age followed in parentheses by younger/older bounds of the 95% confidence modelled age range, indicates that a cold stadial episode, whose onset was marked by replacement of woodland by grassland, occurred between 28,730 (29,390–28,500) and 25,470 (26,090–25,270) cal. yr BP (years before AD, 1950), prior to the deposition of the Kawakawa/Oruanui tephra. Milder interstadial conditions prevailed between 25,470 (26,090–25,270) and 24,400 (24,840–24,120) cal. yr BP and between 22,630 (22,930–22,340) and 21,980 (22,210–21,580) cal. yr BP, separated by a return to cold stadial conditions between 24,400 and 22,630 cal. yr BP. A final episode of grass-dominated vegetation, indicating cold stadial conditions, occurred from 21,980 (22,210–21,580) to 18,490 (18,670–17,950) cal. yr BP. The decline in grass pollen, indicating progressive climate amelioration, was well advanced by 17,370 (17,730–17,110) cal. yr BP, indicating that the onset of the termination in south Westland occurred sometime between ca 18,490 and ca 17,370 cal. yr BP. A similar general pattern of stadials and interstadials is seen, to varying degrees of resolution but generally with lesser chronological control, in many other paleoclimate proxy records from the New Zealand region. This highly resolved chronology of vegetation changes from southwestern New Zealand contributes to the examination of past climate variations in the southwest Pacific region. The stadial and interstadial episodes