Ancient Murray-Darling Basin streamflows reveal evidence of climate change

Posted 4 April 2017

Murray-Darling BasinSome 90,000-years worth of Murray-Darling Basin streamflows has been mapped for the first time, and the picture that has emerged should serve as a warning, researchers say.

In a study led by the Australian National University, a deep-sea core from near Kangaroo Island (opposite the present mouth of the Murray River) was analysed to identify the geochemical composition of the sediment.

The sample revealed Australia had become increasingly arid over the past few thousand years due to human activities and strong El Niño-Southern Oscillation signals, with alternating wet and dry conditions.

“Our research emphasises the importance of using water from the Murray-Darling Basin with extreme care, because less and less water is going through the system,” said co-lead researcher ANU Emeritus Professor Patrick De Deckker. 

“In recent years, both the Murray and Darling Rivers, and many of their confluents, have been altered by human activities, especially damming, irrigation and vegetation clearance.”

The study, published in Scientific Reports, described the significant climatic changes the Murray-Darling Basin has undergone. This includes when small glaciers adorned the Snowy Mountains, and a very wet period about 50,000 years ago when Lake Mungo was full and humans lived on its shores, De Deckker said.

“We know that when Lake Eyre and adjacent bodies of water are full, rain usually comes from the northern part of Australia. But we didn't know the source of the rain for the Willandra Lakes or the snow that was needed to maintain glaciers near Charlotte Pass about 20,000 years ago,” he said. 

Co-researcher ANU Emeritus Fellow Dr Marc Norman said the team identified sediment origins by analysing two isotopes of neodymium.

“From about 90,000 years ago, the Murray sub-basin contributed to sediments deposited at sea; that progressively changed to a Darling sub-basin influence that prevailed from about 70,000 years ago,” said Norman.

He noted that rainfall in the Murray sub-basin came from the south, generally in winter, while the Darling sub-basin usually received waters from the north via monsoonal rains, mostly in summer.

“Since the deglaciation that began about 18,000 years ago, the sediments transported to sea display a change from a northern influence to a southern influence,” Norman said.