Massive
Southern Ocean current discovered
Tuesday, April 27, 2010
A deep ocean current with a volume equivalent to 40 Amazon
Rivers has been discovered by Japanese and Australian scientists
near the Kerguelen plateau, in the Indian Ocean sector of the
Southern Ocean, 4200 kilometres south-west of Perth.
In a paper published today in Nature Geoscience, the
researchers described the current –more than three kilometres below
the Ocean's surface – as an important pathway in a global network
of ocean currents that influence climate patterns.
"The current carries dense, oxygen-rich water that sinks near
Antarctica to the deep ocean basins further north," says co-author
Dr Steve Rintoul from the Antarctic Climate and Ecosystems CRC and
CSIRO's Wealth from Oceans Flagship.
"Without this supply of Antarctic water, the deepest levels of the
ocean would have little oxygen.
While earlier expeditions had detected evidence of the current
system, they were not able to determine how much water the current
carried. The joint Japanese-Australian experiment deployed
current-meter moorings anchored to the sea floor at depths of up to
4500m. Each mooring reached from the sea floor to a depth of 1000m
and measured current speed, temperature and salinity for a two-year
period.
"The continuous measurements provided by the moorings allow us, for
the first time, to determine how much water the deep current
carries to the north," Dr Rintoul said. The current was found to
carry more than 12 million cubic metres per second of Antarctic
water colder than 0 °C (because of the salt dissolved in sea water,
the ocean does not freeze until the temperature gets close to -2
°C).
"It was a real surprise to see how strong the flow was at this
location. With two-year average speeds of more than 20cm per
second, these are the strongest mean currents ever measured at
depths three kilometres below the sea surface.
"Mapping the deep current systems is an important step in
understanding the global network of ocean currents that influence
climate, now and in the future. Our results show that the deep
currents near the Kerguelen Plateau make a large contribution to
this global ocean circulation," Dr Rintoul said.
Antarctic waters carried northward by the deep currents eventually
fill the deep layers of eastern Indian and Pacific
Oceans.
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CSIRO Australia
Thanks to CSIRO Australia for this article.