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    Saltier tropical oceans and fresher ocean waters near the poles further signs of global climate change s impacts Arlington, Va.-Tropical ocean waters have
    Message 1 of 1 , Dec 18, 2003
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      Saltier tropical oceans and fresher ocean waters near the poles further
      signs of global climate change's impacts

      Arlington, Va.-Tropical ocean waters have become dramatically saltier
      over the past 40 years, while oceans closer to Earth's poles have become
      fresher, scientists report in the December 18th issue of the journal
      Nature. These large-scale, relatively rapid oceanic changes suggest that
      recent climate changes, including global warming, may
      be altering the fundamental planetary system that regulates evaporation
      and precipitation and cycles fresh water around the globe.

      The study was conducted by Ruth Curry of the Woods Hole Oceanographic
      Institution (WHOI); Bob Dickson of the Centre for Environment, Fisheries,
      and Aquaculture Science in Lowestoft, U.K.; and Igor Yashayaev of the
      Bedford Institute of Oceanography in Dartmouth, Canada.

      "This study is important because it provides direct evidence that the
      global water cycle is intensifying," said Elise Ralph, associate director
      of the National Science
      Foundation's (NSF) physical oceanography program, which funded the
      research. "This is consistent with global warming hypotheses that
      suggest ocean evaporation will
      increase as Earth's temperature does. These issues are particularly
      important as pressure on freshwater resources has become critical in many
      areas around the world."

      An acceleration of Earth's global water cycle can potentially affect
      global precipitation patterns that govern the distribution, severity and
      frequency of droughts, floods and storms. It would also exacerbate global
      warming by rapidly adding more water vapor-itself a potent, heat-trapping
      greenhouse gas-to the atmosphere. And it could continue to freshen North
      Atlantic Ocean waters to a point that could disrupt ocean circulation and
      trigger further climate changes.

      The oceans and atmosphere continually exchange fresh water. Evaporation
      over warm, tropical and subtropical oceans transfers water vapor to the
      atmosphere, which transports it toward both poles. At higher latitudes,
      that water vapor precipitates as rain or snow and ultimately returns to
      the oceans, which complete the cycle by circulating fresh water back
      toward the equator. The process maintains a balanced distribution of
      water around our planet.

      The oceans contain 96 percent of the Earth's water, experience 86 percent
      of planetary evaporation, and receive 78 percent of planetary
      precipitation, and thus represent a
      key element of the global water cycle for study, the scientists said.
      Because evaporation concentrates salt in the surface ocean, increasing
      evaporation rates cause detectable spikes in surface ocean salinity
      levels. In contrast, salinity decreases generally reflect the addition
      of fresh water to the ocean through precipitation and runoff from the

      Curry, Dickson, and Yashayaev analyzed a wealth of salinity measurements
      collected over recent decades along a key region in the Atlantic Ocean,
      from the tip of Greenland to the tip of South America. Their analysis
      showed the properties of Atlantic water masses have been changing-in some
      cases radically-over the five decades for which
      reliable and systematic records of ocean measurements are available, the
      scientists report.

      They observed that surface waters in tropical and subtropical Atlantic
      Ocean regions became markedly saltier. Simultaneously, much of the water
      column in the high
      latitudes of the North and South Atlantic became fresher.

      This trend appears to have accelerated since 1990-when 10 of the warmest
      years since records began in 1861 have occurred. The scientists estimated
      that net evaporation rates over the tropical Atlantic have increased by
      five percent to ten percent over the past four decades.

      These results indicate that fresh water has been lost from the low
      latitudes and added at high latitudes, at a pace exceeding the ocean
      circulation's ability to compensate, say
      the scientists. Taken together with other recent studies revealing
      parallel salinity changes in the Mediterranean, Pacific, and Indian
      Oceans, a growing body of evidence
      suggests that the global hydrologic cycle has revved up in recent

      Among other possible climate impacts, an accelerated evaporation -
      precipitation cycle would continue to freshen northern North Atlantic
      waters. The North Atlantic is one
      of the few places on Earth where surface waters become dense enough to
      sink to the abyss. The plunge of this great mass of cold, salty water
      helps drive a global ocean circulation system, often called the Ocean
      Conveyor. This Conveyor helps draw warm Gulf Stream waters northward in
      the Atlantic, pumping heat into the northern regions that significantly
      moderates wintertime air temperatures, especially in Europe.

      If the North Atlantic becomes too fresh, its waters would stop sinking
      and the Conveyor could slow down. Analyses of ice cores, deep-sea
      sediment cores, and other geologic
      evidence have clearly demonstrated the Conveyor has abruptly slowed down
      or halted many times in Earth's history. That has caused the North
      Atlantic region to cool significantly and brought long-term drought
      conditions to other areas of the Northern Hemisphere over time spans as
      short as years to decades.

      Melting glaciers and Arctic sea ice, another consequence of global
      warming, are other sources of additional fresh water to the North
      Atlantic. An accelerated water cycle also
      appears to be increasing precipitation in higher latitudes, contributing
      to the freshening of North Atlantic waters and increasing the possibility
      of slowing the Conveyor.

      A cooling of the North Atlantic region would slow the melting process,
      curtail the influx of fresh water to the North Atlantic. The Conveyor
      would again begin to circulate ocean waters. But global warming and an
      accelerated water cycle would continue to bring fresh water to high
      latitudes-possibly enough to maintain a cap on the Conveyor
      even if the Arctic melting ceased. Monitoring Earth's hydrological cycle
      is critical, the scientists said, because of its potential near-term
      impacts on Earth's climate.

      The research was also supported by the Framework V Programme of the
      European Community, the National Oceanic and Atmospheric Administration's
      on the Ocean's Role in Climate, and the Ocean and Climate Change
      Institute at the Woods Hole Oceanographic Institution.

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      >NSF PR03-145
      >Program contact: Elise Ralph, <mailto:eralph@...>eralph@...,
      >(703) 292-8582
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      Fwded from Lance Olsen


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