INVESTIGATING THE LITTLE ICE AGE IN THE SOUTHERN ALPS OF NEW ZEALAND

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. Here the LIA includes an early phase from around AD 1280 to 1390 and a main phase from around AD 1556 to 1860, followed by warming and ice retreat. It has recently been demonstrated from records of North Atlantic ice-rafted debris that the LIA is the latest cooling episode in a pervasive 1500yr cycle of the climate system that may lie at the heart of abrupt climate change. 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 thermohaline circulation). New Zealand is ideally situated to address the problem as it is located on the other side of the planet. Glaciers in the Southern Alps of New Zealand respond to climate change on a decade timescale. The moraines deposited by these glacier oscillations are therefore ideal for determining the character of the LIA signal in the Southern Hemisphere. A detailed chronology of the Hooker and Mueller Holocene moraine systems was constructed using geomorphologic maps, historical records, and the FALL lichenometry technique. This study found that the Holocene moraines fronting the Mueller and Hooker Glaciers were deposited predominantly during the main phase of the LIA. The glacier advances recorded by these moraines are equivalent in age with those deposited in the North Atlantic region. The magnitude and timing of the LIA climate signal is the same in the two regions. The collapse of the Hooker and Mueller Glaciers in the last 140 yrs is also synchronous with that of glaciers in the North Atlantic region. Therefore, the LIA signal is found as far south as New Zealand, on the other side of the planet.