Date of Award

8-2001

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Quaternary and Climate Studies

Advisor

George H. Denton

Second Committee Member

Thomas V. Lowell

Third Committee Member

Kirk A Maasch

Abstract

The Little Ice Age (LIA) was a late Holocene interval of climate cooling registered in the North Atlantic region by expansion of alpine glaciers and sea ice (Grove, 1988). Here the LIA includes an early phase from about AD 1280 to AD 1390, along with a main phase from about AD 1556 to AD 1860, followed by warming and ice retreat (Holzhauser and Zumbiihl, 1999a). It has recently been demonstrated from records of North Atlantic ice-rafted debris that the LIA is the latest cooling episode in a pervasive 1500-year cycle of the climate system that may lie at the heart of abrupt climate change (Bond et al., 1999). This raises the question of whether the LIA climate signal is globally synchronous (implying atmospheric transfer of the climate signal) or out of phase between the polar hemispheres (implying ocean transfer of the climate signal by a bipolar seesaw of thennohaline circulation) (Broecker, 1998). New Zealand is ideally situated to address this problem as it is located on the opposite side of the planet from the North Atlantic region where the classic LIA signal is registered so clearly. Due to high precipitation and ablative activity gradients, glaciers in the Southern Alps of New Zealand respond to climate change on a decadal timescale (Chinn, 1996). Therefore, moraine sequences deposited during oscillations of these glaciers are ideal for determining the character of the LIA signal in this portion of the Southern Hemisphere. The chronology of the late Holocene moraine sequences fronting Hooker and Mueller Glaciers in the Southern Alps is controversial. Initial dating of these moraines from historical records, as well as from lichenometric and tree-ring analyses (Lawrence and Lawrence, 1965; Burrows, 1973), pointed to deposition in the LIA, indicating a global near-synchronous climate signal. In contrast, a subsequent chronology based on weathering rinds of surface clasts suggested that most of the late Holocene moraines antedate the LIA (Gellatly, 1984), implying lack of a classic LIA climate signal in this portion of the Southern Hemisphere. To resolve this dilemma, a new and detailed chronology of the Hooker and Mueller Holocene moraine systems was constructed in this study by using geomorphologic maps, historical records, and the FALL lichenometry technique. A major result of this study is that most of the Holocene moraines fronting Mueller and Hooker Glaciers were Deposited during the main phase of the LIA as defined in the North Atlantic region. The glacier advances recorded by these moraines are about equivalent in age with those in the North Atlantic region. The magnitude and timing of the ILA climate signal is nearly the same in the two regions. The collapse of Hooker and Mueller Glaciers in the last 140 years is also approximately synchronous with retreat of glaciers in the North Atlantic region. Therefore, the LIA climate signal occurs in the atmosphere as far south as New Zealand, on the other side of the planet from the North Atlantic region.

Comments

As of 2002, Degree of Master of Science (MS) Quaternary and Climate Studies published under the auspices of the Climate Change Institute.

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