THE TIMING AND NATURE OF THE LAST GLACIAL CYCLE IN NEW ZEALAND

This talk reviews the progress on understanding the nature, timing and climatic implications of glacial advances in the Southern Alps of New Zealand since the seminal work by Stephen Porter on ELAs in the mid-1970s. This progress includes the development of one of the largest inventories of cosmogenic ages for any glaciated region, detailed stratigraphic and sedimentological studies, high resolution climate and glacier modelling and classical geomorphological work.

There is an emerging pattern that the maximum ice extent in the last (Otiran) glaciation occurred during the early part of the glaciation (at c. 65 ka) in the regions of the Southern Alps south of the 44°S. In contrast, the largest advance of the last glacial cycle in the northern half of the South Island appears to have occurred during a time window between 36 and 28 ka.

Everywhere in New Zealand glaciers were extended to near maximum positions between c. 36 and 28 ka and gradually retreated after c. 28 ka. The global LGM (25-19 ka) is reflected in New Zealand by a recessional ice stillstand or minor glacial re-advance before deglaciation continued after c. 18 ka. There is some dispute about the scale of retreat during the early part of termination I, but there is general agreement about the existence of a stadial in NZ during the time of the Antarctic Cold Reversal (ACR). The scale of the ACR re-advance (or stillstand) remains unclear.

Long established ideas of an early Holocene glacial minimum and neo-glaciation in the last 5000 years have recently been challenged. A separate but cognate debate relates to the role of tectonics in modifying the climatic signature of glacial advances. These debates are important both for the use of New Zealand as a testing ground for global climate teleconnections but also for understanding the sensitivity of New Zealand glaciers to anthropogenic warming.