Ocean Desert Areas are Growing
Study: Ocean's Least Productive Waters Are Expanding
Global warming is linked to growth of low productivity ocean deserts that have reached 51 million square kilometers in size worldwide.
Researchers with the National Marine Fisheries Service (NMFS) and University of Hawaii have documented the expansion of barren areas within subtropical gyre currents found near the equator. These biologically nonproductive areas are growing at a rate greater than anticipated.
In a press release announcing these findings, NMFS Oceanographer Jeffrey J. Polovina says, "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. But with a nine-year time series, it is difficult to rule out decadal variation."
Introduction to the Research - Polovina with co-authors Evan Howell and Melanie Abecassis published their research report, Ocean's Least Productive Waters Are Expanding, in the journal Geophyical Research Letters sponsored by the American Geophysical Union. Data was collected using a unique resource, the NASA SeaStar spacecraft borne sea-viewing wide field of view sensor (SeaWiFS).
Sea-Viewing Wide Field-of-View Sensor - SeaWiFS measures the colored light reflected from chlorophyll found in phytoplankton to measure the biological productivity of the ocean. Phytoplankton are microscopic plants key to the marine food chain. Institutions like Oregon State University use SeaWiFS data to produce color maps that show world ocean productivity.
Subtropical Gyres - There are large ocean circulation patterns near the equator that account for about 20% of the barren areas found in the world's oceans. This study measured their expansion towards Hawaii in the Pacific and across the Caribbean in the Atlantic Ocean.
Research Outcomes - The project looked at changes in the Pacific and Atlantic Oceans over a nine-year period from 1998 to 2007. Some conclusions were:
- The unproductive regions or ocean deserts grew by 15 percent or 6.6 million square kilometers
- Sea surface temperatures have grown an average of one percent or about 0.03 degrees Celsius a year
- Increased ocean surface warming stratifies water into layers and reduces the flow of nutrients to the surface
- The low productivity ocean deserts now cover 51 million square kilometers worldwide
- In the three ocean regions studied, the rate of growth for these desert zones was greater in the winter
- The gyre found in the Atlantic Ocean is smallest of those observed, but growing the fastest
- The ocean desert zone of the Indian Ocean showed trends similar to other regions, but the changes were not statistically significant
This research supports global warming theories predicting increased stratification of ocean waters and reduced plant productivity. Rates of expansion shown in the project are much greater than anticipated in many climate models.
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