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Fwd: [CAD] Freshening of deep Antarctic waters worries experts

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  • pat neuman
    ... From: Tim Jones Date: Apr 18, 2008 11:39 AM Subject: [CAD] Freshening of deep Antarctic waters worries experts To:
    Message 1 of 1 , Apr 18, 2008

      ---------- Forwarded message ----------
      From: Tim Jones <deforest@...>
      Date: Apr 18, 2008 11:39 AM
      Subject: [CAD] Freshening of deep Antarctic waters worries experts
      To: ClimateArchiveDiscussion@yahoogroups.com, Paleontology_and_Climate@yahoogroups.com

      Freshening of deep Antarctic waters worries experts
      Published April 18, 2008 09:09 AM

      SINGAPORE (Reuters) - Scientists studying the icy depths of the sea
      around Antarctica have detected changes in salinity that could have
      profound effects on the world's climate and ocean currents.

      The scientists returned to the southern Australian city of Hobart on
      Thursday after a one-month voyage studying the Southern Ocean to see
      how it is changing and what those changes might mean for global
      climate patterns.

      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
      Atlantic Oceans that shifts heat around the globe.

      "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 Antarctica would be too light, too buoyant to sink and
      that limb of the global-scale circulation would shut down," he said
      on Friday.

      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 Antarctica, this drives the ocean conveyor belt.

      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 Indian
      Ocean through the Indonesia Archipelago.

      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 Ross Sea
      directly south of New Zealand and off Antarctica's Adelie Land
      further to the west, were a crucial finding.

      "We didn't know that before we left but it's now clear that both of
      those regions are becoming fresher for some reason."


      During the voyage, scientists from Australia, Britain, France and the
      United States measured salinity, carbon dioxide and iron
      concentrations as well as currents between Antarctica and Australia.

      Rintoul said his team are studying if faster melting of ice sheets 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 Antarctica is melting more rapidly than in
      the past."

      He pointed to studies showing winds around Antarctica changing
      because of global warming and the ozone hole.

      "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 Antarctica," he said.

      "The next challenge over the coming months and year will be to see
      just how well we can this pin down."

      (Editing by Jeremy Laurence)

      For documentation please go to: http://picasaweb.google.com/npatnew or email me at: npatnew@...
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