Ocean waters colder than a decade ago

Dramatic changes in temperature and salinity have been discovered in the deep waters of the Southern Ocean by scientists, who warn this could have a major impact on global climate change.

Scientists believed deep ocean waters to be stable, but new evidence reveals they are now colder and less salty than ten years ago, holding serious implications for climate change. Copyright AAD / Dr Des Lugg

Scientists believed deep ocean waters to be stable, but new evidence reveals they are now colder and less salty than ten years ago, holding serious implications for climate change. Copyright AAD / Dr Des Lugg

This alarming research shows that even the ocean's deep waters, previously considered to be stable and largely unaffected by global warming, have become considerably colder and less salty than they were just ten years ago.

Led by Dr Steve Rintoul of the Antarctic Climate and Ecosystems Cooperative Research Centre, the expedition team stopped at various stations to sample water in the deep basin between Antarctica and Australia over an eight-week period, and every single station gave the same result.

"Our measurements suggest that the movement of water between the warm surface layers of the ocean and the cool deep layers is changing," Dr Rintoul explained. "Ocean circulation has a big influence on global climate, so it is critical that we understand why this is happening and why it is happening so quickly."

"We used to think of the deepest layers of the oceans being very stable in their properties and current patterns, but these new observations show that the dense water produced around the periphery of Antarctica is capable of rapid and widespread change."

This discovery comes at the heels of an announcement from a group of American scientists who found the first clear evidence of climate change by studying the world's oceans (see related story).

There are two main sources of the bottom water in the region - a salty variety from the Ross Sea, and a fresher type of water formed near the Mertz glacier in Antarctica. Dr Rintoul told edie that the cooler, fresher water near the sea floor indicated a change in the sources of dense water supplying the basin.

"The influence of Mertz bottom water seems to be more widespread now than it was in the past," he explained. "The challenge now is to use these new observations to explain why the cool, fresh water is currently more dominant than in the past."

He added that the world's network of oceans and their currents strongly influenced the earth's climate, which made it vitally important to find out what had caused the changes.

This would lead to the calculation of the transport of heat and fresh water for the first time, by using the measurements collected by Dr Rintoul's expedition team.

Nineteen free-floating ocean robots, called Argo floats, were also deployed as part of an international ocean monitoring effort, and will measure temperature and salinity at all depths of the ocean every ten days. The results are then sent back to scientists by satellite, providing a continuous analysis of changes to the ocean.

"On ocean voyages like this one, we work hard to obtain about 100 ocean profiles over eight weeks. The Argo floats will add an additional 190 profiles every ten days, and will stay fully functional for around four years," Dr Rintoul continued.

"These automated systems will make a huge contribution to our understanding of remote and hostile regions like the Southern Ocean."

The voyage was partly funded by the Australian Antarctic Division and the Greenhouse Office.

By Jane Kettle


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