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Ocean Phytoplankton Reveals Major Global Changes

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    NHNE News List Current Members: 674 Subscribe/unsubscribe/archive info at the bottom of this message. ... Thanks to Jim Torson. ... PHYTOPLANKTON IN NORTHERN
    Message 1 of 1 , Aug 11, 2002
      NHNE News List
      Current Members: 674
      Subscribe/unsubscribe/archive info at the bottom of this message.


      Thanks to Jim Torson.


      Goddard Space Flight Center
      August 08, 2002


      Since the early 1980s, ocean phytoplankton concentrations that drive the
      marine food chain have declined substantially in many areas of open water in
      Northern oceans, according to a comparison of two datasets taken from
      satellites. At the same time, phytoplankton levels in open water areas near
      the equator have increased significantly. Since phytoplankton are especially
      concentrated in the North, the study found an overall annual decrease in
      phytoplankton globally.

      The authors of the study, Watson Gregg, of NASA's Goddard Space Flight
      Center, Greenbelt, Md., and Margarita Conkright, a scientist at the National
      Oceanic and Atmospheric Administration's (NOAA) National Oceanographic Data
      Center, Silver Spring, Md., also discovered what appears to be an
      association between more recent regional climate changes, such as higher sea
      surface temperatures and reductions in surface winds, and areas where
      phytoplankton levels have dropped.

      Phytoplankton consist of many diverse species of microscopic free-floating
      marine plants that serve as food to other ocean-living forms of life. "The
      whole marine food chain depends on the health and productivity of the
      phytoplankton," Gregg said.

      The researchers compared two sets of satellite data -- one from 1979 to 1986
      and the other from 1997 to 2000 -- that measured global ocean chlorophyll,
      the green pigment in plants that absorbs the Sun's rays for energy during
      photosynthesis. The earlier dataset came from the Coastal Zone Color Scanner
      (CZCS) aboard NASA's Nimbus-7 satellite, while the latter dataset was from
      the Sea-Viewing Wide Field of View Sensor (SeaWiFS) on the OrbView-2

      The researchers re-analyzed the CZCS data with the same processing methods
      used for the SeaWiFS data, and then blended both satellite measurements with
      surface observations of chlorophyll from ocean buoys and research vessels
      over corresponding time periods. By doing so, the researchers reduced errors
      and made the two records compatible.

      Results indicated that phytoplankton in the North Pacific Ocean dropped by
      over 30 percent during summer from the mid- 80s to the present.
      Phytoplankton fell by 14 percent in the North Atlantic Ocean over the same
      time period.

      Also, summer plankton concentrations rose by over 50 percent in both the
      Northern Indian and the Equatorial Atlantic Oceans since the mid-80s. Large
      areas of the Indian Ocean showed substantial increases during all four

      "This is the first time that we are really talking about the ocean
      chlorophyll and showing that the ocean's biology is changing, possibly as a
      result of climate change," said Conkright. The researchers add that it
      remains unclear whether the changes are due to a longer-term climate change
      or a shorter-term ocean cycle.

      Phytoplankton thrive when sunlight is optimal and nutrients from lower
      layers of the ocean get mixed up to the surface. Higher sea surface
      temperatures can reduce the availability of nutrients by creating a warmer
      surface layer of water. A warmer ocean surface layer reduces mixing with
      cooler, deeper nutrient-rich waters. Throughout the year, winds can stir up
      surface waters, and create upwelling of nutrients from below, which also add
      to blooms. A reduction in winds can also limit the availability of

      For example, in the North Pacific, summer sea surface temperatures were .4
      degrees Celsius (.7 Fahrenheit) warmer from the early 1980s to 2000, and
      average spring wind stresses on the ocean decreased by about 8 percent,
      which may have caused the declines in summer plankton levels in that region.

      Phytoplankton currently account for half the transfer of carbon dioxide from
      the atmosphere back into the biosphere by photosynthesis, a process in which
      plants absorb carbon dioxide (CO2) from the air for growth. Since carbon
      dioxide acts as a heat-trapping gas in the atmosphere, the role
      phytoplankton play in removing carbon dioxide from the atmosphere helps
      reduce the rate at which CO2 accumulates in the atmosphere, and may help
      mitigate global warming.

      The paper appears in the current issue of Geophysical Research Letters.


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