THE NATURE AND TIMING OF GLACIATION IN AUSTRALASIA BETWEEN C.130 AND 10 KA

Quaternary glaciation in Australasia is confined to the higher mountain ranges in New Zealand particularly on South Island, the highest parts of the South-East Highlands in Australia, and upland areas of Tasmania. During the last glacial cycle, glaciation was extremely limited in Australia with little more than cirque advances in Tasmania and the SE Highlands. In contrast, a piedmont ice cap covered the Southern Alps and valley glaciers were widespread in splay ranges and on the volcanic plateau of North Island. Glaciers also covered many sub-Antarctic islands but their glacial histories are poorly known.

Major glacial advances occurred in the Southern Alps of New Zealand at c. 70 ka, between 34 and 28 ka, around 23-21 ka and at about 19ka. There is some evidence for advances at c. 47 ka and at about 13 ka. A notable feature of the New Zealand record is that the 70 ka and 34-28 ka advances are larger than the LGM advance at 23-21 ka. The 19 ka advance is smaller. In lower elevation areas full scale retreat was under way by the time of the 19 ka advance. The 47 ka advance is secured from only one location, while the c.13 ka advance is only recorded from higher elevation systems in the main range of the Southern Alps.

In South-Eastern Australia LGM ice advances are recorded both on the mainland and Tasmania. Possible earlier advances are recorded at about 60 ka and 32 ka on the mainland. In Tasmania, ice may have advanced between about 46-38 ka.

The nature of glaciation in the region is rather variable. In New Zealand, only modest thermal declines (4-5°C) have been traditionally invoked to explain glaciation. Recent work has challenged even these modest values and glaciation may be triggered by temperature declines of only 2-3°C under hyper-humid conditions. Much of the glacial signal in New Zealand could be explained by synoptic changes rather than large scale global temperature forcing. In contrast, the LGM is seen as arid and cold in Australia with thermal declines of up to 11°C invoked.

A major feature of the record in Australasia is the observation that glaciation seems to be diminishing, with evidence for substantially greater glaciation prior to the last ice age.