Late-glacial re-advance during the Last Glacial-Interglacial Transition; revisiting the Misery moraines in the Southern Alps of New Zealand
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Date
2009-05-15
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GNS Science
Abstract
Locating evidence for or against a glacial readvance commensurate with Northern Hemisphere YD-time (~11-13 ka) in Southern Hemisphere glacial systems is a key aspect in addressing millennial-scale hemispheric climate linkages during the late Quaternary. Paleo-environmental evidence from New Zealand pollen records suggest a minor cooling or hiatus in warming during the period from ~14.5 – 12.0 ka that predates the onset but overlaps with the YD chron, and is more commonly associated with the Antarctic Cold Reversal (ACR). Evidence for a glacial re-advance during the YD chron has been proposed previously (Waiho Loop moraine, Denton and Hendy, 1994) and more recently based on a limited exposure age sample set (n=4, 11.7 ± 0.3 ka) from the Misery moraine sequence at Arthur’s Pass (~950 masl), Southern Alps, NZ (Ivy-Ochs et al 1999). The full group of moraines comprises a set of discontinuous latero-terminal moraines and elevated kame terraces (McGrath moraines) positioned on the eastern flanks of the Pass up to 3 kilometres down valley from the proximal Misery moraines within the Otira Gorge. However, a recalculation of the original data set (Ivy-Ochs et al 1999), based on revised 10-Be production rates, updated production rate scaling schemes and a remeasure of horizon site shielding, shifts the mean age from 11.7 ± 0.3 ka to 14.0-14.5 ka – a result more in line with other deglaciation ages (~14-16 ka) from proximal and cirque moraine sequences in NZ, Tasmania and southern South America. To further investigate this issue, we have determined paired 10-Be and 26-Al exposure ages from 38 greywacke samples taken from all major moraines throughout the Arthur’s Pass area and including repeat sampling from the Otira Gorge (Misery) moraine complex. The new exposure ages show that the Arthur’s Pass moraine system represents a glacial chronology for the last deglaciation spanning a period of 18.8 ka (at distal sites) to 10.4 ka (at proximal sites) (maximum to minimum sample age) with mean moraine ages following in chrono-stratigraphic sequence with ice flow direction. Although our new age for the proximal Misery moraine complex does not revise the conclusion reached by Ivy Ochs et al (1999) (though it does challenge the validity of the measurement) our more comprehensive sampling regime and extensive data set provides a different interpretation. The timing of deglaciation at Arthur’s Pass is similar to that observed at more distal down-valley terminal positions of the Rakaia and Rangitata Valleys and suggests that the scale of any late glacial readvance, as evidenced at the Misery moraine site, was insignificant in comparison to the magnitude of ice volume at the end of the LGM in New Zealand. Details regarding age interpretation, the importance of production-rate corrections necessary to provide a robust and reliable glacial chronology at the required sub-millennial resolution will be presented.
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Keywords
New Zealand, Moraines, Alps, Quaternary period, Climatic change, Glaciers, Ice, Defrosting
Citation
Fink. D., Rother, H., & Schulmeister, J. (2009). Late-glacial re-advance during the last glacial-interglacial transition; revisiting the misery moraines in the southern alps of New Zealand. Presentation to the Annual Antarctic Conference 2009 - "Sustaining the Gains of the International Polar Year", 1st – 3rd July 2009. In Proceedings of the Annual Antarctic Conference 2009, (pp. 81). Auckland, New Zealand: University of Auckland.