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:
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.
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: