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Ice Age North Atlantic Temperatures, Tropical Oceans Linked

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  • Pat Neuman
    Ice Age North Atlantic Temperatures, Tropical Oceans Linked Satellite image of the Atlantic Ocean. by Staff Writers Davis CA (SPX) Oct 05, 2006 Sudden shifts
    Message 1 of 1 , Oct 6 7:44 AM
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      Ice Age North Atlantic Temperatures, Tropical Oceans Linked

      Satellite image of the Atlantic Ocean.
      by Staff Writers
      Davis CA (SPX) Oct 05, 2006
      Sudden shifts in temperature over Greenland and tropical rainfall
      patterns during the last ice age have been linked for the first time
      to rapid changes in the salinity of the north Atlantic Ocean,
      according to research published Oct. 5 in the journal Nature. The
      results provide further evidence that climate change can have a
      direct and rapid impact on ocean circulation and chemistry.
      "It's a very complicated system," said lead author Matthew Schmidt,
      who carried out the work as a graduate student at the University of
      California, Davis, and is now a visiting NOAA Climate and Global
      Change Postdoctoral Fellow at the Georgia Institute of
      Technology. "But when it responds, it responds big time."

      Schmidt, Maryline Vautravers of Cambridge University in England, and
      Howard Spero, professor of geology at UC Davis, reconstructed a
      45,000-to-60,000-year-old record of ocean temperature and salinity
      from the chemical traces in fossil shells of tiny planktonic animals
      recovered from deep sea sediment cores. They compared their results
      to the record of abrupt climate change recorded in ice cores from

      At that time, much of North America and Europe was a frigid sheet of
      ice. But the ice records show repeated patterns of sudden warming,
      called Dansgaard-Oeschger cycles, when temperatures in Greenland
      rose by five to 10 degrees Celsius over a few decades.

      Those cycles were matched by rapid changes in surface-water salinity
      in the north Atlantic, the researchers found. The Atlantic got
      saltier during cold periods, and fresher during warm intervals. The
      freshening likely reflects shifts in rainfall patterns, mostly in
      the tropics, Spero said.

      "Suddenly, we're looking at a record that links moisture balance in
      the tropics to climate change," he said.

      Close to the tropics, warm, moist air forms a zone of heavy tropical
      rainfall, called the Intertropical Convergence Zone, which dilutes
      the salty ocean with fresh water. Today, the tropical rainfall zone
      reaches into the northern Caribbean, but during the colder periods
      of the ice age it was pushed much farther south, toward Brazil. That
      kept fresh water out of the northern Atlantic, so it became more
      salty, Spero said.

      "The most striking thing is that a measurable transition is
      happening over decades," Spero said.

      The circulation, or gyre, in the north Atlantic moves warm, salty
      water north, keeping Europe relatively temperate. The deep ocean
      circulation is very sensitive to the saltiness of north Atlantic
      surface waters, Spero said. Warming climate, higher rainfall and
      fresher conditions can alter the circulation. During glacial times,
      reduced circulation caused climate to cool.

      The new paper shows that as the climate cooled in Greenland,
      salinity rapidly increased in the North Atlantic subtropical gyre.
      The build-up of salt during these cold intervals when the conveyor
      circulation was reduced would have primed the system to quickly
      restart on transitions into warm intervals, Schmidt said. However,
      the actual trigger that caused Atlantic circulation to restart
      during the ice age is still unknown, he said.

      Once warming began, melting ice sheets would have contributed fresh
      water to the Atlantic, but this would have been partly buffered by
      the elevated saltiness of the Atlantic.

      The research looked at changes during the last ice age, when global
      temperatures were much lower than today. But the results show that
      ocean salinity is very sensitive to climate change, and could change
      rapidly -- over a matter of decades, Spero said.

      "The salinity of the north Atlantic is the canary of the climate
      system," Spero said.

      Related Links
      University of California - Davis
      Beyond the Ice Age
      Learn about Climate Science at TerraDaily.com

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