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Ocean 'deserts' expanding

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updated 1:02 p.m. ET, Wed., March. 5, 2008

Warming sea surface waters are causing the oceans' deserts — the least biologically productive areas — to expand much faster than predicted, researchers reported Wednesday.

Federal government and University of Hawaii scientists said that this change could be tied to global warming and stands to negatively impact the populations of many fish species.

"The fact that we are seeing an expansion of the ocean’s least productive areas ... is consistent with our understanding of the impact of global warming," co-author Jeffrey Polovina, an oceanographer with the National Oceanic and Atmospheric Administration, said in a statement.

But he cautioned that since the study covered just nine years, it is also possible that the change is due to a shorter, natural cycle.

Reporting in the peer-reviewed Geophysical Research Letters, the researchers found that between 1998 and 2007 these Pacific and Atlantic ocean deserts, essentially expanses of saltwater with low surface plant life, grew by 15 percent.

That coincided with sea surface temperatures warming about one percent a year, the researchers said.



Red areas show the expansion of the least productive waters. Gray areas remained unproductive through the nine-year study. Blue areas gained in productivity.

"The warming increases stratification of the ocean waters, preventing deep ocean nutrients from rising to the surface and creating plantlife," NOAA said in a statement announcing the study. "These barren areas are found in roughly 20 percent of the world’s oceans and are within subtropical gyres — the swirling expanses of water on either side of the equator."

The research showed that:

  • In the Pacific, the areas of low productivity are expanding from the center toward Hawaii.
  • In the Atlantic, the least productive areas of the subtropical gyre are expanding at an even more rapid rate eastward across the Caribbean toward Africa.
  • In the Indian Ocean, the least productive area "shows the same trend, but there has been too much variability for it to be statistically significant," NOAA stated.

The researchers used satellite data to map ocean productivity. A sensor monitored "reflective color to measure the density of chlorophyll in phytoplankton, the microscopic plants that are the base of the marine food web," NOAA said.


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