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Ocean Plant Life Slows Down
Plant life in the world's oceans has become less productive during the past two decades, another possible signal of a climate change. NASA scientists have recently found evidence showing increased temperatures and other factors may be responsible for the decline of tiny ocean plants, called phytoplankton, which transfer carbon dioxide from the environment into plant cells by photosynthesis. Carbon dioxide is a primary heat-trapping gas in the atmosphere. Watson Gregg and other NASA researchers found that the oceans' net primary productivity (NPP) has fallen considerably over the last two decades. NPP is the rate at which plant cells take in carbon dioxide during photosynthesis from sunlight, using carbon for growth.

Distributions of Ocean Net Primary Productivity (1997

Above: Distributions of Ocean Net Primary Productivity (1997-2002). Microscopic marine plants contain chlorophyll, a green pigment they use during photosynthesis. Using satellite sensors, we can measure chlorophyll concentrations in oceans, lakes and seas to indicate the distribution and abundance of phytoplankton. Click image above to see animation of phytoplankton growth around the world (Data from SeaWiFS Project). More information.Credit: NASA

As marine plants decline in numbers, they may disrupt the Earth's carbon cycle. A reduction in transcontinental dust clouds that carry iron has lessened the amount of iron falling into certain parts of the oceans. Iron is an essential nutrient for phytoplankton to grow, and without it, their numbers are limited.

March 4, 2003 : Aqua/MODIS and Terra/MODIS both take images of the west african dust storm as it carries dust across the Atlantic Ocean

Above: A 48 hour dust storm on March 1 and 2, 2003 is responsible for a very large dust transport over the Atlantic on March 2 through March 6, 2003. This animation starts with a global view of the world, zooms into the storm area, and dissolves between each day

The Eyes Above

NASA scientists used data from two satellites to study the level of chlorophyll, or green pigment in plants. When combined with other information provided by NOAA research vessels and buoys they found that about 70 percent of the observed drop in marine plant life productivity occurred in high latitudes. In these areas, phytoplankton bloom rapidly in high concentrations in spring, leading to shorter, more intense lifecycles. And, when the plankton die, they sink and create a potential pathway of carbon from the atmosphere into the ocean floor.

Phytoplankton bloom, Galapogos Islands

Above: Satellite image showing phytoplankton concentrations around the Galapagos Islands in May 1998. Reds represent high concentration of phytoplankton, followed by orange, yellow, green, and blue. Credit: NASA

Other Observed Changes

The decline in ocean productivity corresponds with a marked increase in global sea surface temperatures in some areas during the past 20 years. Warming waters create more distinct ocean layers and limits the mixing of deeper nutrient-rich cooler water with warmer surface water. The lack of rising nutrients reduces the growth of phytoplankton at the surface.

The amount of iron deposited from desert dust clouds into the global oceans has also decreased by 25 percent since the early 1980's. These clouds blow across the oceans and some reductions in marine plant productivity are directly correlated with a decline in atmospheric iron deposition.

An Unsteady Future

Many scientists agree that more changes are on the way. Our oceans can't be considered a separate entity from the remainder of our surrounding environment--they are truly key players in the future of global climate. Study co-author, Margarita Conkright, a scientist at National Oceanic and Atmospheric Administration's National Oceanographic Data Center says "these results illustrate the complexities of climate change, since there may be one or more processes, such as changes in temperature and the intensity of the winds, influencing how much carbon dioxide is taken up by photosynthesis in the oceans."

Other recent NASA findings have shown land cover on Earth has actually been greening. For more information on this topic and other, please visit:

Earth's Becoming A Greener Greenhouse
Ocean Sponging Up Some Warmth Over Next 50 Years
NASA's Earth Observatory
Mike Bettwy
NASA Goddard Space Flight Center