Ocean’s deserts – biological dead zones – expanding

Ocean’s deserts – biological dead zones – expanding

Scientists are seeing an expansion of the regions of the ocean that support the least ocean life. These are biological dead zones, or ocean’s deserts.

These are regions of warm water at the centers of the world’s oceans. Scientists often refer to them as the ocean’s biological deserts.

Jeff Polovina of the U.S. National Marine Fisheries Service studies a measure of phytoplankton – ocean plant life – estimated from a satellite. Polovina has seen these biological deserts in the oceans expand by 15% – or 6.6 million square kilometers – over the past 9 years.

Jeff Polovina: To see a similar and persistent expansion of the regions that have the least productivity was quite surprising.

These regions in the ocean – places lacking in ocean life – happen naturally. They occur when nutrients from the bottom of the sea are not mixed up towards the surface. It’s thought that warming ocean surface temperatures, or changes in wind patterns, could keep nutrients in nearby waters from mixing. If so, that could explain why these ocean deserts are expanding.

Jeff Polovina: It’s consistent with what we know about global warming, that as the oceans warm, we would expect this phenomena to happen. It’s happening at a little faster rate than we thought.

If the expansion of these ocean ‘deserts’ is linked to climate change…

Jeff Polovina: Then we’re looking at changes that will persist and increase over time, that will result in large areas of the ocean declining in productivity.

The major impact of this phenomenon is that it reduces the ocean’s ability to support large animals and fish. It may also affect fisheries, which are double-stressed from overfishing top predators, and loss of production from the bottom.

Jeff Polovina: If it were part of natural fluctuation, you might see it fluctuating in one direction in one ocean, and another direction in another ocean, the way a lot of natural variability does occur. But what we’re seeing is the same trend over all four of our ocean basins.

Our thanks today to NASA: explore, discover, understand.

Our thanks to:
Jeff Polovina
U.S. National Marine Fisheries Service
Honolulu, Hawaii

August 30, 2008

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