Dear EarthTalk: What are these “ocean deserts” I’ve been hearing about? Also, didn’t I read that there was a huge mass of plastic bottles floating around somewhere on the ocean surface?
-- Wally Mattson, Eugene, OR

So-called “ocean deserts” or “dead zones” are oxygen-starved (or “hypoxic”) areas of the ocean. They can occur naturally, or be caused by an excess of nitrogen from agricultural fertilizers, sewage effluent and/or emissions from factories, trucks and automobiles. The nitrogen acts as a nutrient that, in turn, triggers an explosion of algae or plankton, which in turn deplete the water’s oxygen.

According to the Ocean Conservancy, a dead zone in the Gulf of Mexico—where the Mississippi River dumps untold gallons of polluted water every second—has expanded to over 18,000 square kilometers in the last decade. Many other such dead zones have also undergone rapid expansion in recent years.

A recent study by German oceanographer Lothar Stramma and a team of prominent international researchers confirms this phenomenon and also points the finger at global warming. Their data show that oxygen levels hundreds of feet below the ocean surface have declined over the past 50 years around the world, most likely a result of human activity. And as ocean waters warm due to climate change, they retain less oxygen. Furthermore, warmer upper layers of water stifle the process that brings nutrients up from colder, deeper parts of the ocean to feed a wide range of surface-dwelling marine wildlife.

The expansion of these dead zones is bad news for most marine inhabitants and the ecosystems they thrive in. Thousands of different species already stressed from over fishing and other threats, now must contend with expanding hypoxic areas throughout regions that once constituted healthy habitat.

The accumulation of plastic debris and other trash in the ocean is not necessarily related to hypoxic zones, but is yet another major problem facing the world’s fragile marine ecosystems. California-based sea captain and ocean researcher Charles Moore discovered what is now known as the Eastern Garbage Patch—an aggregation of plastic and other marine debris occupying some 700,000 square kilometers in the North Pacific Ocean—during a crossing of the North Pacific in 1997. In a 2003 article in Natural History Magazine, Moore reported being astounded that he couldn’t be further from land anywhere on Earth yet he could see plastic bags and other debris coating the ocean’s surface as far as the eye could see.

Individuals can help the oceans and their inhabitants by making smart daily choices that can have collective, positive impact. Lowering your carbon footprint—driving less, biking more, donning a sweater instead of turning up the heat—is one way to help stem the spread of hypoxic zones, which is directly related to industrial activity and the amount of greenhouse gases we spew into the atmosphere.

And limiting plastic and plastic bag use is the best way to prevent such litter from ending up swirling around mid-ocean. Some countries, such as China, and many large cities—San Francisco, for example—have banned plastic grocery bags. If your city hasn’t yet taken this step, pressure them to do so—and in the meantime bring your own reusable bags to the market and avoid plastic wherever else you can.

CONTACTS: Ocean Conservancy, www.oceanconservancy.org; Natural History Magazine, www.naturalhistorymag.com.

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5 Comments

1. 1. doug l 12:52 PM 10/23/08

   I curious. I've heard that when debris floats in the ocean for long periods it begins to serve as an anchor for barnacles and othe sesile animals and plants which filter/feed on plankton and sunlight and that they draw other fish to the areas and in some cases act almost like floating oases. The saragasso sea of plastic bottles. I'm aware that fishing tackle and plastic bags do entrap and endanger some animals, birds and turtles especially, but are ther other communities thriving beneath these mats of floating bottles and chunks of polyfoam?

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2. 2. TravisH82 02:21 PM 10/23/08

   HaHa!! That's a pretty funny idea.. I have no Idea if it is true though... Although we do sink battleships and such to create underwater reefs. Even if there was millions of pages of documented information regarding this and days of video footage.. Good luck trying to get the tree-hugging group to admit that "Evil Humans" could possibly have inadvertently helped out the environment though our "Horrible Neglect" of our "On the brink of Global Extinction" ecosystem

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3. 3. bethfreeman 03:37 PM 10/23/08

   I started keeping track of the plastic in my life and it is in absolutely *everything*. How can we avoid it? It's one thing to avoid plastic bags; another to avoid plastic. We know plastic is incredibly harmful to the environment and it continues to be legal to make things with plastic. Can we talk about alternatives to plastic rather than just saying "avoid it"? The only way to reduce plastic is to vote with our pocket books and for that, we need viable alternatives. For example, what would I do instead of buying a plastic toothbrush? Or a tube of toothpaste? Or a package of crackers with plastic wrap on the inside of the box? Or... the list is endless.

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4. 4. bethfreeman in reply to doug l 03:40 PM 10/23/08

   After 40 or 50 years, plastic starts to break down into particles that are small enough for sea life to ingest. At that point, plastic enters the food chain. So, while plastic may provide oases for "life" for a period, when it breaks down and is ingested by sea life, and then you ingest that sea life, then you will be eating plastic. Sounds pretty unappetizing to me, especially since plastic is toxic for ingesting. Plastic never "goes away". It simply breaks down until the particles are too small to see.

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5. 5. Derick in TO in reply to doug l 03:55 PM 10/23/08

   There's a world of difference between a gigantic patch of floating garbage in the middle of the ocean and a battleship that has been carefully stripped of most or all of its toxic materials and sunk near a coastline. For one thing, it's a hell of a lot easier for a sea bird to mistakenly eat a piece of refuse (say a pop bottle top or a tampon applicator) than to mistakenly eat a battleship. And I doubt anything larger than a colony of bacteria is going to find a plastic bag to be a safe habitat.

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