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NASA Satellite Sees Ocean Plants Increase, Coasts Greening

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  • Pat Neuman
    NASA Satellite Sees Ocean Plants Increase, Coasts Greening http://www.terradaily.com/news/eo-05y.html Greenbelt MD (SPX) Mar 04, 2005 A few years ago, NASA
    Message 1 of 1 , Mar 4, 2005
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      NASA Satellite Sees Ocean Plants Increase, Coasts Greening


      Greenbelt MD (SPX) Mar 04, 2005
      A few years ago, NASA researcher Watson Gregg published a study
      showing that tiny free-floating ocean plants called phytoplankton had
      declined in abundance globally by 6 percent between the 1980s and
      1990s. A new study by Gregg and his co-authors suggests that trend may
      not be continuing, and new patterns are taking place.
      Why is this important? Well, the tiny ocean plants help regulate our
      atmosphere and the health of our oceans. Phytoplankton produce half of
      the oxygen generated by plants on Earth.

      They also can soften the impacts of climate change by absorbing carbon
      dioxide, a heat-trapping greenhouse gas. In addition, phytoplankton
      serve as the base of the ocean food chain, so their abundance
      determines the overall health of ocean ecosystems.

      Given their importance, it makes sense that scientists would want to
      closely track trends in phytoplankton numbers and in how they are
      distributed around the world.

      Gregg and his colleagues published their new study in a recent issue
      of Geophysical Research Letters. The researchers used NASA satellite
      data from 1998 to 2003 to show that phytoplankton amounts have
      increased globally by more than 4 percent.

      These increases have mainly occurred along the coasts. No significant
      changes were seen in phytoplankton concentrations within the global
      open oceans, but phytoplankton levels declined in areas near the
      center of the oceans, the mid-ocean gyres.

      Mid-ocean gyres are "ocean deserts", which can only support low
      amounts of phytoplankton. When viewed by satellite, these
      phytoplankton-deprived regions look deep-blue, while in aquatic
      regions where plant life thrives, the water appears greener.

      "The ocean deserts are getting bluer and the coasts are getting
      greener," said Gregg, an oceanographer at NASA's Goddard Space Flight
      Center (GSFC), Greenbelt, Md. "The study suggests there may be changes
      occurring in the biology of the oceans, especially in the coast regions."

      Phytoplankton amounts have increased by 10.4 percent along global
      coast regions, where the ocean floor is less than 200 meters (656
      feet) deep. Ocean plant life has greened the most in the Patagonian
      Shelf and the Bering Sea, and along the coasts of the Eastern Pacific
      Ocean, Southwest Africa, and near Somalia.

      Both the Patagonian Shelf and the California/Mexican Shelf showed
      large increases in phytoplankton concentrations of over 60 percent.

      Meanwhile, the researchers observed declines in phytoplankton amounts
      in five mid-ocean gyres over the six-year study period, including the
      North and South Atlantic, and North and South Pacific oceans, and a
      possible new gyre region in the North Central Indian ocean.

      At the same time, for all but the North Atlantic gyre, sea surface
      temperatures increased in at least one season.

      "In the mid-ocean gyres, the downward trends in phytoplankton
      concentrations do appear related to mid-ocean sea surface
      temperatures," said Gregg.

      Phytoplankton growth is largely dependent on amounts of nutrients and
      light available to the plants. Warmer water temperatures can create
      distinct layers in the ocean surface, which allows less of the
      nutrient-rich, colder deeper water to rise up and mix with sunny
      surface layers where phytoplankton live.

      Winds churn and mix the ocean water, carrying nutrient-rich waters to
      the sunny surface layer, so when winds decline mixing declines, and
      phytoplankton can suffer.

      In a number of open ocean regions, increases in phytoplankton levels
      countered the declines found in the gyres and other areas. For
      example, a 72 percent increase in phytoplankton abundance occurred in
      the Barents Sea.

      The researchers observed a smaller 17 percent increase in
      phytoplankton amounts in the Western Central Pacific near Indonesia
      and the Philippines. The waters cooled in the Western Pacific, while
      wind stresses increased by 26 percent over the study period. The
      cooling water and increasing winds are consistent with climate
      conditions that lead to greater mixing of water.

      The six full years of data used in this analysis came from NASA's
      Sea-viewing Wide Field-of-view Sensor (SeaWiFS), which detects ocean

      Chlorophyll is the substance or pigment in plants that appears green
      and captures energy from sunlight. The sunlight, along with carbon
      dioxide and water, are processed by the phytoplankton to form
      carbohydrates for building cells. SeaWiFS measures this greenness.

      While the study refers to the measurement of chlorophyll a
      concentrations in the ocean, researchers use the measures of
      chlorophyll a to estimate amounts of phytoplankton.

      While declines in phytoplankton abundance in mid-ocean gyres appear
      related to warming oceans, a number of factors requiring more study to
      may be contributing to the coastal increases in plant life.

      "We don't know the causes of these coastal increases," said Gregg.
      "The trends could indicate improved health of the ecosystems as a
      whole, or they could be a sign of nutrient stress."

      Causes of nutrient stress include land run-off that deposits
      agricultural fertilizers and other nutrients in the oceans. The
      run-off can promote large algal blooms that can deplete the water of

      Gregg and coauthors caution that the length of time the data cover is
      too short to answer questions about long term trends, but for the time
      being the phytoplankton declines in the global oceans observed between
      the 1980s and 1990s appear to have subsided.

      Co-authors on the study include Nancy Casey of Science Systems
      Applications, who works at NASA GSFC, and Charles McClain, also a
      researcher at NASA GSFC.

      Given their importance, it makes sense that scientists would want to
      closely track trends in phytoplankton numbers as made possible by the
      data shown in this file image obtained from SeaWIFS.

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