Ocean 'Deserts' Becoming More Lifeless

Aug. 27, 2009 -- Ocean "deserts" -- where tiny amounts of life subsist on a scant trickle of nutrients -- have gotten more extreme in the last 10 years, according to a new study.

Despite widespread uncertainty among scientists, these vast stretches of barren sea could affect the marine food chain, and ultimately impact global fish stocks.

There are five ocean deserts on Earth, one each in the North and South Pacific, North and South Atlantic, and the Indian Ocean. They are nearly unfathomable in size; one could easily fit the entire land area of the United States inside. And they appear to be growing more barren with each passing year.

In a study due to be published in the journal Geophysical Research Letters, two researchers present satellite data showing that the most empty portions of the deserts expanded some 5 million square kilometers of ocean between 1997 and 2007, an area equivalent to about half the land area of all 50 United States.

The readings are based on examining ocean color -- the more green in the ocean, the more chlorophyll there is being produced by microscopic phytoplankton.

Ocean deserts appear very blue to satellites, usually because ocean currents stagnate, reducing the amount of nitrate (NO3) and phosphate (PO4) available for plankton to feed on. As on land, the deserts also appear to be hotter than surrounding areas.

However, the overall area of desert didn't grow appreciably; areas that were already classified as "desert" merely became more lifeless. Scientists are at a loss for what this means for the health of the oceans, and whether or not it will have a negative impact on global fish stocks.

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"On the one hand, yes, these areas appear to be becoming more inhospitable," Andrew Irwin of Mount Allison University in Canada and lead author on the paper said. "But they are low productivity areas anyway. I don't know what the consequences will be for food."

For now, researchers are focusing on determining whether or not human-induced climate change is the driving force behind the expansion.

"It seems like the link with climate is there," Angelique White of Oregon State University in Corvallis said. "It's hard to believe it's not in response to the billions of us living on this planet."

As for the question of food supply, White added "we're not yet able to make predictions with a lot of confidence about what's going to happen 10, 20, or 30 years down the road. No one would say there won't be significant changes in the ocean. The question is how is the biology going to respond?"

Related Links:

HowStuffWorks.com: Fisheries

Get the Wide Angle on Climate Tipping Points

NOAA: Ocean Deserts Expanding

Discovery Earth Pub