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The great Pacific garbage patch

by Donald Prothero, Sep 01 2014
The "Great Pacific Garbage Patch" covers an area many times larger than Texas

The “Great Pacific Garbage Patch” covers an area many times larger than Texas

When I teach Intro to Oceanography this semester and last year, one of the stories that made the greatest impression on my students (and on me, too) was the sad account of the “Great Pacific Garbage Patch.” This is an area of the ocean surface in the North Pacific covering between 700,000 square kilometers (270,000 sq mi) to more than 15,000,000 square kilometers (5,800,000 sq mi), larger than the size of Texas. It is composed nearly entirely of plastic trash, fishing nets, and other floating garbage, at least 80% which comes from the land and is non-biodegradable. The denser areas of garbage are so large they can be seen from satellite views.

Why is so much garbage concentrated in one area? It all has to do with the oceanic currents that I teach my Oceanography students about. The centers of each portion of the ocean is surrounded by a big circular current called a gyre, which usually runs in a clockwise fashion in the Northern Hemisphere and counterclockwise in the Southern Hemisphere (due to the Coriolis effect). In the North Pacific, a huge gyre completely surrounds the center of the northern ocean, with the warm fast Kuroshio Current coming up from the tropics past Japan, and the cold slow California Current coming down the eastern edge from Alaska, connected by currents (North Equatorial, North Pacific) which travel east or west to connect these in the equator and in the polar regions. This spiraling current tends to accumulate a mound of water in the middle (due to the Ekman spiral effect) that is rather stagnant and does not mix or blend with the boundary currents very well. It is also at a latitude with permanent high-pressure over it, so there’s no strong air currents to move it in any particular direction. Consequently, the centers of ocean gyres are slow and stagnant and tend to accumulate stuff that floats into them, and cannot escape. In the North Atlantic, the stagnant center of the gyre is called the “Sargasso Sea” after the huge floating patches of Sargassum seaweed that floats in the region for decades. There are garbage patches of smaller size in most of the other oceanic gyres as well. But in the North Pacific gyre, what stays put is garbage, the largest such patch in the world.

The patch was first discovered in 1997 by Charles Moore during the Transpac sailing race, when he found himself sailing through miles and miles of plastic garbage. Oceanographers have been doing research on it ever since then, analyzing satellite images and taking samples in many areas to determine its density and composition and the size of particles (mostly using nets with different size mesh). Although the  plastic bottles and fishing nets and other debris are more shocking and photogenic, the bulk of the patch is made of tiny plastic debris from abrasives and many other industrial sources. Although the largest portion can clearly be traced to land-based pollution, about 20% of it is thought to be from spills of cargo ships, and other ships dumping their waste. A typical 3000 passenger cruise ship produces over  8 tons of solid waste weekly, most of which is non-biodegradable and ends up in the patch. Recently, more alarming things have been discovered:

Dense areas of the garbage patch, here east of Japan, are visible from space

Dense areas of the garbage patch, here east of Japan, are visible from space

According to one source:

Net-based surveys are less subjective than direct observations but are limited regarding the area that can be sampled (net apertures 1–2 m and ships typically have to slow down to deploy nets, requiring dedicated ship’s time). The plastic debris sampled is determined by net mesh size, with similar mesh sizes required to make meaningful comparisons among studies. Floating debris typically is sampled with a neuston or manta trawl net lined with 0.33 mm mesh. Given the very high level of spatial clumping in marine litter, large numbers of net tows are required to adequately characterize the average abundance of litter at sea. Long-term changes in plastic meso-litter have been reported using surface net tows: in the North Pacific Subtropical Gyre in 1999, plastic abundance was 335 000 items/km2 and 5.1 kg/km2, roughly an order of magnitude greater than samples collected in the 1980s. Similar dramatic increases in plastic debris have been reported off Japan.

The most alarming thing of all, however, it what it does to wildlife. Millions of seabirds are killed, especially if they swallow plastic garbage that resembles food. It’s sickening to cut open dead seabirds and find dozens of plastic items in their stomachs, which kills them. The plastic from six-pack harnesses is also another animal strangler, and the nets often trap dolphins and seals and sea lions and drown them. Worst of all is seeing sea turtles with their shells completely covered in fishing net, some of whom have  grossly-pinched shells as they grew within the net. Even worse, sea turtles around the world are dying because the plastic bags we throw away look like sea jellies to the turtles, and they eat so many their stomachs fill with plastic and they die.

A sea turtle which has been grotesquely deformed by growing up while bound by a fishing net

A sea turtle which has been grotesquely deformed by growing up while bound by a fishing net

What is to be done about this problem? Unfortunately, it’s in international waters, so no one is legally responsible for it, and it would be impossible to determine who dumped which garbage. It’s a classic example of Garrett Hardin’s “Tragedy of the Commons.” Large areas of shared resources, such as our oceans or atmospheres, legally are shared by all of us and no one owns them—but then nobody feels responsible for conserving or protecting this resource, either. Lots of solutions have been suggested, but so far there is no action on the issue.

So keep this in mind the next time you toss a plastic bottle or plastic grocery bag in the garbage. This video says it all:

10 Responses to “The great Pacific garbage patch”

  1. Max says:

    “So keep this in mind the next time you toss a plastic bottle or plastic grocery bag in the garbage.”

    Why? It goes into a landfill. My garbage bag is a plastic bag. I use plastic grocery bags as garbage bags.

  2. Jim S says:

    Donald, I faithfully collect all of the grade-1 plastic, as well as all of the aluminum, tin, glass, cardboard, plastic sacks, and paper waste at my house and take it every few weeks to be recycled. Am I helping the environment at all or just fooling myself?

    • No, any recycling is better than none, and recycling aluminum is the most valuable, since it is 100% imported to the U.S. Plastic bottles and other plastics are important, because they are made from oil, which is only going to become more and more expensive and hard to obtain. And all that paper and cardboard saves trees.
      I have an area where I keep bags full of cans and plastic bottles until I have a big load in six months, then run over to our local recycling yard. I never fail to earn $100 from the aluminum alone.
      In LA and in most of California, there is regular recycling picked up with the real trash once a week, and recycling bins are everywhere. Sadly, it drives me crazy to travel to other states, and have no place to recycle the valuable aluminum or plastic bottles.

  3. Derle says:

    If all goes well, California will finally have a “plastic bag” ban, Yea! At home we try to get as much mileage out of the plastic bags we do bring home, but eventually alas, they do end up in the landfill. I have told myself “at least they are not ending up in the ocean like all that other plastic yuck”, but is this a false illusion (hmm, as apposed to a true illusion…)or do some of my bags end up in the ocean?

    • Max says:

      I don’t get it. They end up in a landfill like all the other trash in trash bags.

    • madscientist says:

      I guess it depends where the landfill is. Birds and prevailing winds are good at scattering plastic bags and flowing water can help too once the birds or wind have moved the bag from the landfill.

  4. Mary Hannah says:

    MUCH plastic is thrown from drivers’ windows – water bottles, candy wrappers, large foam cups, plastic bags that blew like parachutes when released from someone’s hand. A good rain washes some away and no doubt to the ocean.

    I walk a few blocks from my home in a small rural town and carry a bag to pick up trash along the road. It’s dismaying that with so little effort all could be discarded properly.

    Most distressing is learning how innocent animals suffer and die from humans’ actions.

    • Max says:

      Littering is illegal. In California, it’s even illegal to dispose of household batteries, chemicals, and fluorescent light bulbs in the trash. Should all those things be banned because some people break the law?

      • The difference is that plastic bags are disproportionately likely to end up blowing around, blowing into the storm drains and out to the ocean, and disproportionately dangerous to wildlife. In particular, plastic bags floating in the ocean are often mistaken for sea jellies by sea turtles, and end up choking them or filling their stomachs with plastic, killing these magnificent creatures that could live for centuries.

  5. Andre says:

    Thanks for this article, Donald. This is the kind of post why I started following the scepticblog in first place: informative, giving background information to interesting and/or important topics of life and science, and often even a bit humorous.