| Summary: | Detailed records of past climate variations can help to reveal the causes of ice-age climate cycles and place the global warming of recent decades in a broader context. My goal is to determine the timing of deglacial and Holocene climate changes in the Southern Hemisphere mid-latitudes. My approach is to develop novel moraine chronologies based on beryllium-10 surface-exposure dating, together with glaciological model simulations to determine past temperature. I measured the ages of two sequences of glacial landforms: one in the Rakaia River valley that records glacier-length changes during the past 15,000 years, and a second in front of the Classen Glacier that shows ice-margin fluctuations during the past 5200 years. Moraines in New Zealand's Rakaia River valley record rapid recession of the Rakaia glacier at the end of the last ice age between ~18,000 and ~15,000 years ago in response to an inferred temperature rise of 4°C. Deglaciation was interrupted by two glacier still stands at 13,950 ± 130 and 13,170 ± 260 years ago. The Rakaia glacier then receded after ~13,200 years ago, with brief pauses at 12,150 ± 200 and 11,610 ± 160 years ago. Net glacier thinning of ~250 m between 13,200 and 11,600 years ago occurred in response to a temperature rise of ~1°C. Additional thinning by 8000 years ago implies warming of ~ 0.5°C, which separated the Lyell Glacier at the valley head from tributaries in the lower Rakaia River valley. Culminations of late-Holocene advances of Lyell Glacier occurred at 574 ± 30, 315 ± 8, 273 ± 28, and 141 ± 13 years before 2011 C.E. Moraines of the Classen Glacier document greater ice extent at 5260 ± 130 years ago than at any later interval. Successively less extensive advances culminated at 5160 ± 77, 462 ± 25, 334 ± 35, 287 ± 30, and 220 ± 13 years before 2011 C.E., respectively. I conclude that New Zealand glacier retreat coincided with Northern-Hemisphere cooling on millennial to decadal time scales between 18,000 and 100 years ago, a pattern that differs from worldwide glacier recession during the past century.
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