Late-glacial re-advance during the Last Glacial-Interglacial transition; revisiting the Misery moraines in the Southern Alps of New Zealand.

• Main Authors: Fink, D, Shulmeister, J
• Format: Other/Unknown Material
• Language: English
• Published: 2010
• Subjects: New Zealand; Moraines; Alps; Quaternary Period; Climatic Change; Isotope Dating; Antarctic; The Antarctic; Antarc*
• Online Access: http://apo.ansto.gov.au/dspace/handle/10238/2882

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. Paleoenvironmental evidence from New Zealand pollen records suggest a minor cooling or hiatus in warming during the period from ~14.5 – 12.0 ka that pre-dates 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 m a.s.l.), Southern Alps, NZ (Ivy-Ochs et al 1999). To further investigate this issue, we have determined paired 10Be and 26Al 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 provide 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 and the importance of production-rate corrections necessary to provide a robust and reliable glacial chronology at the required sub-millennial resolution will be presented. Centro de Estudios Científicos (CECS)