Date of Award

8-2014

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor

George Denton

Second Committee Member

Brenda Hall

Third Committee Member

Karl Kreutz

Abstract

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 Northem-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.

Share