Freshening of deep Antarctic waters worries experts
Reuters News Service, April 21, 2008
The scientists returned to the southern Australian city of
Voyage leader Steve Rintoul said his team found that salty, dense water that sinks near the edge of Antarctica to the bottom of the ocean about 5 km (3 miles) down was becoming fresher and more buoyant.
So-called Antarctic bottom water helps power the great ocean conveyor belt, a system of currents spanning the Southern, Pacific, Indian and
"The main reason we're paying attention to this is because it is one of the switches in the climate system and we need to know if we are about to flip that switch or not," said Rintoul of Australia's government-backed research arm the CSIRO.
"If that freshening trend continues for long enough, eventually the water near
Cold, salty water also sinks to the depths in the far north Atlantic Ocean near Greenland and, together with the vast amount of water that sinks off
This system brings warm water into the far north Atlantic, making Europe warmer than it would otherwise be, and also drives the large flow of upper ocean water from the tropical Pacific to the
If these currents were to slow or stop, the world's climate would eventually be thrown into chaos.
"We don't see any evidence yet that the amount of bottom water that's sinking has declined. But by becoming fresher and less dense it's moving in the direction of an ultimate shutdown."
Rintoul said results of the bottom water samples in the
"We didn't know that before we left but it's now clear that both of those regions are becoming fresher for some reason."
GLOBAL WARMING TO BLAME?
During the voyage, scientists from
Rintoul said his team are studying if faster melting of icesheets or sea ice is the source of the fresher water but he said it was too early to tell if global warming was to blame.
Over the coming months, his team will study oxygen isotopes collected from water samples.
"Oxygen isotopes act as a tracer of ice melt and that information should help pin down exactly what the cause of the freshening is in the deep ocean," said Rintoul, of the Antarctic Climate and Ecosystems Cooperative Research Centre.
"The leading hypothesis at the moment for why it's freshening is that the floating ice around
He pointed to studies showing winds around
"The most likely scenario is that those changes in winds have changed the circulation of the ocean, in particular caused more upwelling of relatively warm water from below and that could have caused the increased melting of ice around
"The next challenge over the coming months and year will be to see just how well we can this pin down."
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