The Heat Is Online

Australian Scientists Find "Missing Ocean Current Link"

Australia discovers ocean current "missing link"


Reuters News Service, Aug. 15, 2007


SYDNEY (Reuters) - Australian scientists have discovered a giant underwater current that is one of the last missing links of a system that connects the world's oceans and helps govern global climate.


New research shows that a current sweeping past Australia's southern island of Tasmania toward the South Atlantic is a previously undetected part of the world climate system's engine-room, said scientist Ken Ridgway.


The Southern Ocean, which swirls around Antarctica, has been identified in recent years as the main lung of global climate, absorbing a third of all carbon dioxide taken in by the world's oceans.


"We knew that they (deep ocean pathway currents) could move from the Pacific to the Indian Ocean through Indonesia. Now we can see that they move south of Tasmania as well, another important link," Ridgway, of the Commonwealth Scientific and Industrial Research Organization, told Reuters.


In each ocean, water flows around anticlockwise pathways, or gyres, the size of ocean basins.


The newly discovered Tasman Outflow, which sweeps past Tasmania at an average depth of 800-1,000 meters (2,600 to 3,300 feet), is classed as a "supergyre" that links the Indian, Pacific and Atlantic southern hemisphere ocean basins, the government-backed CSIRO said in a statement on Wednesday.


The CSIRO team analyzed thousands of temperature and salinity data samples collected between 1950 and 2002 by research ships, robotic ocean monitors and satellites between 60 degrees south, just north of the Antarctic Circle, and the Equator.


"They identified linkages between these gyres to form a global-scale 'supergyre' that transfers water to all three ocean basins," the CSIRO said.


Ridgway and co-author Jeff Dunn said identification of the supergyre improves the ability of researchers to more accurately explain how the ocean governs global climate.


"Recognizing the scales and patterns of these subsurface water masses means they can be incorporated into the powerful models used by scientists to project how climate may change," Ridgway said in a statement.


The best known of the global ocean currents is the North Atlantic loop of the Great Ocean Conveyer, which brings warm water from the Equator to waters off northern Europe, ensuring relatively mild weather there. Scientists say if the conveyor collapsed, northern Europe would be plunged into an ice age.


Earlier this year, another CSIRO scientist said global warming was already having an impact on the vast Southern Ocean, posing a threat to myriad ocean currents that distribute heat around the world.


Melting ice-sheets and glaciers in Antarctica are releasing fresh water, interfering with the formation of dense "bottom water", which sinks 4-5 kilometers to the ocean floor and helps drive the world's ocean circulation system.


A slowdown in the system known as "overturning circulation" would affect the way the ocean, which absorbs 85 percent of atmospheric heat, carries heat around the globe, Steve Rintoul, a senior scientist at the CSIRO Division of Marine and Atmospheric Research, said in March.


© Reuters 2006. All rights reserved.


Hidden Ocean Current a Climate Clue?, Aug. 21, 2007


Australian climate scientists have located a deep-ocean current in the Tasman Sea that may play a big role in connecting the world's oceans, and therefore regulating Earth's climate.


The newfound Tasman Outflow is part of the "super-gyre" ocean current pathway which helps connect the Indian, South Atlantic and South Pacific oceans and is part of the global heat conveyor belt known as the thermohaline circulation. It's not certain, however, just how big a player the Tasman Outflow is.


"It's another link between the Pacific and Indian Ocean," said Ken Ridgway of the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO). "The other is through Indonesia." Ridgway and his colleagues report on the Tasman Outflow in the August issue of Geophysical Journal Letters.


"What we've been really able to show is the pathway and define the very narrow boundary current," said Ridgway. "It's these boundary flows that connect everything up."


Ridgway describes the Tasman Outflow as a current that runs west from Tasmania at a depth of 2,600 to 3,300 feet (800 to 1,000 meters). He also describes the waters south of Tasmania as a "choke-point" in the connections between southern oceans.


In the broader picture in which each ocean contains giant "gyres" of currents, the Tasman Outflow is a small eddy, or spin off, that carries Pacific water from the Coral Sea down the east coast of Australia and then away to the Indian Ocean. It was identified by crunching a large amount of temperature and salinity data collected by ships, buoys and satellites from 1950 to 2002.


Other experts agree that the Tasman Outflow exists, but are not convinced it plays a very significant role globally, primarily because it doesn't appear to carry that much water or much heat or salinity variation  essential for driving the thermohaline circulation  into the Indian Ocean.


"I think it's there, but it cannot be very large," said Arnold Gordon, associate director of Ocean and Climate Physics division at Lamont-Doherty Earth Observatory at Columbia University.


In terms of flow, the current is weak in comparison to others, Gordon added.


He said the Tasman Outflow could not flow at more than three sverdrups  one sverdrup being a million cubic meters of water per second, or about 264 million gallons per second. The Gulf Stream, by comparison, varies from 30 to 15 sverdrups. All the freshwater streams and rivers on Earth come to about one sverdrup, collectively.


"I do not think that's an important part of the thermohaline circulation," Gordon told Discovery News.


The bigger, far more important connection between the Pacific and Indian oceans is the three to seven sverdrups which navigate through Indonesia, he said. And since the resources for studying these currents are very limited, he suggested that research would be better focused around Indonesia.


"Inter-ocean exchanges are really important to the climate system," said Gordon. "We really do need to quantify them. I don't think the climate modelers are getting it right."