Ocean ‘deserts’ are expanding, say scientists
(Credit: Michael Strande. Some rights reserved.)
Scientists are seeing an expansion of the regions of the ocean that support the least ocean life.
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.
Additional Teacher Resources
NASA: Lesson Plan – There are Algae in Your House!
In this lesson, students investigate common foods they eat, such as ice cream, pudding and cheese, to determine what algae (phytoplankton) derivatives they contain. Teacher background information is provided. (Grades 3-8)
NASA: Lesson Plan – Ocean Currents and Sea Surface Temperature
In this lesson, students discover the link between ocean temperatures and currents as related to our concern for current climate change. (Grades 8-12)
NOAA: Study Shows Ocean Deserts are Expanding
This article discusses how the least biologically productive areas of the oceans are expanding much faster than predicted. The evidence of this expansion comes from data collected by a sensor aboard NASA’s orbiting SeaStar spacecraft. The article includes satellite images of the oceans.
NASA: Nine Years of Ocean Chlorophyll
About half of the oxygen we breathe is produced by phytoplankton. Phytoplankton are tiny, single-celled plants that live in the ocean, and they serve as the base of the oceanic food chain. The interaction of phytoplankton with our planet has only recently been studied on a global scale. The satellite sensor that has pioneered the study of phytoplankton globally is the Sea-viewing Wide Field-of-View Sensor (SeaWiFS).
