Australasian Science: Australia's authority on science since 1938

How Australia Dried Out

Image of ancient lake

Sediments of the ancient Lake Bungunnia near Rufus River in western NSW. The white horizon is the dust layer marking the start of arid climatic regimes. Photo: Richard Stanaway

By Sandra McLaren & Malcolm Wallace

Lake Bungunnia, a megalake that existed 1–2 million years ago in today’s Murray–Darling Basin, reveals the story and timing of the onset of arid climatic conditions in south-eastern Australia.

Dr Sandra McLaren and Dr Malcolm Wallace are from the School of Earth Sciences at the University of Melbourne. This article is based on their research published recently in the journal Global and Planetary Change.

The full text of this article can be purchased from Informit.

The modern challenge of climate change demands a sound scientific understanding of the Earth’s climatic history. Historic temperature and rainfall records are very important, but so is the geological evidence of climate recorded in sedimentary rocks that are formed on the surface of the Earth.

The late Neogene, a period of the Earth’s history beginning around 5 million years ago, was characterised by particularly dramatic climatic change around the globe. In Australia this was the time of change from a warm and wet climate, where lush rainforest covered much of southern Australia, to the arid climate we know today, where one-third of the continent receives rainfall of less than 250 mm per year.

However, despite considerable research, exactly when this change occurred and the reasons why it occurred remain poorly understood. Since the early 1980s geo­scientists have thought that the big “drying out” occurred around 700–800,000 years ago, and that it was related to the build-up of ice in Antarctica and the associated changes in Southern Ocean circulation. Additional data collected since that time has added to our understanding but has not further refined the age or the origin of the change.

What we do know about climatic changes in the Neogene is revealed mainly from sediments preserved in deep sea environments. However, sediments on the continents...

The full text of this article can be purchased from Informit.