BEIJING, March 6 (Xinhuanet) -- The oceans'
"deserts," where it is difficult for marine organisms to survive, are expanding
faster than predicted and have been linked to warming ocean waters, a new study
shows.
These barren areas are found in roughly 20 percent of
the world's oceans and are within what are called subtropical gyres, or the
permanent swirling expanses of water in the middle of the ocean on either side
of the equator.
"The fact that we are seeing an expansion of the
ocean's least productive areas as the subtropical gyres warm is consistent with
our understanding of the impact of global warming," said study co-author Jeffrey
J. Polovina, an oceanographer with the U.S. National Marine Fisheries Service in
Honolulu. "But with a nine-year time series, it is difficult to rule out decadal
variation."
But between 1998 and 2007, these expanses of
saltwater with low surface plant life in the Pacific and Atlantic oceans grew by
15 percent, or 2.5 million square miles (6.6 million square kilometers),
according to the new study, detailed in a recent issue of the journal
Geophysical Research Letters.
The expansion is occurring at the same time that sea
surface temperatures are warming about 1 percent or 0.02 to 0.04 degrees Celsius
a year. The warming imposes tougher barriers between different layers of the
ocean waters, preventing deep ocean nutrients from rising to the surface and
feeding plant life.
Polovina and his colleagues used data from NASA's
SeaStar satellite, which maps ocean biological productivity (or the amount of
chlorophyll produced by phytoplankton, the microscopic plants that form the base
of the ocean food chain) around the world.
These maps showed areas of low productivity in the
Pacific Ocean expanding outward from the center toward Hawaii. In the Atlantic
Ocean, these low-productivity areas are expanding even faster eastward from the
Caribbean toward Africa. These areas now cover roughly 20 million square miles
(51 million square kilometers) in the two major oceans.
(Agencies)
