Our Oceans Are Getting Healthier

By Roland Piquepaille

A surprising new study from NASA reveals that a new trend about the evolution of phytoplankton in our oceans is emerging. Instead of declining globally by 6 percent between the 1980s and 1990s, phytoplankton levels are now growing, by more than 4 percent between 1998 and 2003. But according to the data gathered by NASA satellites, this evolution is not uniform. The increase is by far larger near the coasts, where the ocean floor is less than 200 meters and where phytoplankton levels grew by more than 10 percent in the last 5 years. At a moment where everyone is concerned by the global warming effect, this is very good news because one of the things phytoplankton does is absorbing carbon dioxide.

Let's start our today's story with more details about the importance of phytoplankton.

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.

Now, what are the results of this new study from NASA?

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.

These images were captured with the help of NASA satellites. The two images show the situation in 2003 and in 1998. "The bottom panel depicts the trend in chlorophyll between 2003 and 1998, shown as a percent difference. Many of the areas showing an increasing trend appear along the coasts, in red, while most of the dark blue areas indicate a decreasing trend. Units for the top two panels are milligrams of chlorophyll per cubic meter." (Credit: NASA, Gregg et al.) A larger version can be seen on this page at NASA.

The above images don't really show it, but ocean colors also have changed.

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 Watson 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."

This evolution is so recent that the researchers are cautious before giving conclusions.

"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 oxygen.

For more technical information, this study has been published on February 8, 2005 by Geophysical Research Letters under the title "Recent trends in global ocean chlorophyll." Here is a link to the abstract.

A 6-year time series of remotely-sensed global ocean chlorophyll was evaluated using linear regression analysis to assess recent trends. Global ocean chlorophyll has increased 4.1% (P < 0.05). Most of the increase has occurred in coastal regions, defined as bottom depth < 200 m, where an increase of 10.4% was observed. The main contributors to the increase were the Patagonian Shelf, Bering Sea, and the eastern Pacific, southwest African, and Somalian coasts. Although the global open ocean exhibited no significant change, 4 of the 5 mid-ocean gyres (Atlantic and Pacific) showed declines in chlorophyll over the 6 years. In all but the North Atlantic gyre, these were associated with significant increases in sea surface temperature in at least one season. These results suggest that changes are occurring in the biology of the global oceans.

Sources: NASA/Goddard Space Flight Center news release, via EurekAlert!, March 3, 2005; and various websites

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