Sunday, October 17, 2010

The Great Pacific Garbage Patch

What is the Great Pacific Garbage Patch?

To quote from wikipedia, “The Great Pacific Garbage Patch, also described as the Pacific Trash Vortex, is a gyre of marine litter in the central North Pacific Ocean located roughly between 135° to 155°W and 35° to 42°N. The patch extends over a very wide area, with estimates ranging from an area the size of the state of Texas to one larger than the continental United States […] The Patch is characterized by exceptionally high concentrations of pelagic plastics, chemical sludge, and other debris that have been trapped by the currents of the North Pacific Gyre.”

Do an image search for the Great Pacific Garbage Patch and you will see results like these:

Yes, it is not necessary to dig any further than the second Google Images result to find an image with a city clearly visible in the background, and the fifth result is apparently of someone who felt the need to canoe themselves all the way out to the center of the Pacific Ocean. Viewing the contexts in which these images appear, all of them seem to imply that these are images of the actual Great Pacific Garbage Patch, despite the clear impossibility of them being such.

One group of young environmentalists concerned about the Great Pacific Garbage Patch took a trip out to the center of the North Pacific Gyre in the summer of 2007 and filmed the entire ordeal. Take a look at 1:45-5:40 of this clip to get an idea of what they found.

These young environmentalists said numerous times that they had expected to find a large floating island of garbage as far as the eye could see. What they did find was that after an hour of trawling with a very fine meshed net, they were able to fill a jar with a murky liquid of plastic. Nonetheless, they justify that this is in fact worse than what they had expected. Why would this be?

Plastics do not hold together in direct sunlight. The combination of the constant jostling of salt water and the photodegradation caused by sunlight breaks nearly everything down to microscopic pieces well before it reaches the North Pacific Gyre. The microscopic pieces of plastic remaining in the water column are called neuston plastic. These bits of neuston plastic, along with any impurities they may have contained, can still be eaten by sea life and make their way into the food chain.

A couple of studies have tried to actually measure the amount of this neustonic plastic in the water. The first such study was done from 1985 to 1988. In this study, numerous areas across the entire northern Pacific were studied for the amount of plastic they contained by trawling a 500 micrometer (0.5mm) net behind a ship for 10 minutes at a time. This study found, “Total concentrations of neuston plastic generally were low, with high concentrations recorded at only four stations in Transitional Water, at two stations in nearshore water east of Japan, and at one station in Subarctic Water; total concentrations at the other stations with plastic generally were < 10% of the highest concentration (Fig. 2). The highest total concentration was 3,941.8 g/km2 at lat. 40"00'N, long. 171'30'E near the Subarctic Front in the central North Pacific.” This survey found no clear trend of higher levels in the area typically associated with the Great Pacific Garbage Patch; although, it provided no particularly strong evidence that it wasn't there either. Typical levels found, even in the central region typically associated with the garbage patch, were roughly 400 grams (approx. 1 pound) per square kilometer. Despite the unclear nature of their results, the authors do comment on how the distribution of plastic in the Pacific likely works:

“After entering the ocean, however, neuston plastic is redistributed by currents and winds. For example, plastic entering the ocean in Japan is moved eastward by the Subarctic Current (in Subarctic Water) and the Kuroshio (in Transitional Water, Kawai 1972; Favorite et al. 1976; Nagata et al. 1986). In this way, the plastic is transported from high-density areas to low-density areas. In addition to this eastward movement, Ekman stress from winds tends to move surface waters from the subarctic and the subtropics toward the Transitional Water mass as a whole (see Roden 1970: fig. 5). Because of the convergent nature of this Ekman flow, densities tend to be high in Transitional Water. In addition, the generally convergent nature of water in the North Pacific Central Gyre (Masuzawa 1972) should result in high densities there also.”

This prediction appears to be the origin of the hypothesis that a higher concentration of plastic exists at the center of the North Pacific Gyre.

More recently, in 2001 another group went to the center of the North Pacific Gyre to specifically measure levels of plastic there. They trawled the water with a finer mesh of net (333 micrometers instead of 500) and accordingly they recovered a higher density of plastic per square kilometer than the 1988 study. The nice thing about this study is that in 2002 the same group took the same mesh of nets and went to study the densities of neustonic plastic in the water off southern California. This study was able to make numerous comparisons between waters not considered part of the gyre and what is considered to be part of the garbage patch.

“The density of neustonic plastic along the southern California coast was about three times higher than Moore et al. (2001) found in the mid-Pacific gyre, though the mass was 17 times lower (Table 3). This disparity between density and mass reflects the dramatic difference in size of neustonic debris between the gyre and the coast. Most of the neustonic plastic mass observed in the North Pacific central gyre was large material associated with the fishing and shipping industries. Most of the plastic we observed near the coast were small fragments attributable to land-based runoff.

The average plastic:plankton mass ratio was less in southern California, reflecting its higher plankton density. However, the plastic:plankton ratio on the day after the storm was higher in southern California than in the North Pacific central gyre. This change resulted from an increase in debris following a storm, rather than from a reduction in plankton. Moreover, the ratio in the North Pacific central gyre was driven by large debris. When the comparison of ratios between these two areas is limited to debris smaller than 4.75 mm, which is the fraction that filter feeders are most likely to confuse with plankton, the southern California ratio becomes twice that of the North Pacific central gyre.”

Yes, contrary to what you may expect, there were more pieces, but less plastic mass off the coast of sothern California. The reason for this, as they explain, is because most of the plastic in the gyre was a few large pieces of fishing and shipping waste that they picked up. When we limit the findings to just the smaller pieces, there was far more of this plastic in southern California, and even twice the ratio of plastic to plankton even with the higher levels of plankton.

What should we conclude from this? The hypothesis that slightly higher levels of floating waste accumulates in the North Pacific Gyre certainly sounds like a reasonable one, but at this point I'm afraid we shouldn't treat it as much more than a hypothesis. Even if proves with future research to be true, changing winds, currents, waves, and storms still disperse the floating material enough to make the accumulation modest at best. The amount of small plastic waste we find in our near-costal waters will still be higher in nearly all areas.

There are certainly good reasons to avoid letting our waste leak into the oceans or other large bodies of water. At this point I have seen no research that has been done suggesting levels of any compound of plastic degradation is anywhere near unsafe levels in the North Pacific Gyre, but that doesn't mean such a study couldn't exist. Until I see the results of such research I am inclined to believe we have little more to fear from this area as we do from our oceans as a whole. Remain conscientious of the products you use, but the Great Pacific Garbage Patch is not the reason why you should do this.


  1. Heh? So, where's the plastic island?

  2. Very interesting! Thanks for compiling this information and the video. I always wondered how much plastic you could really see. This, however, seems to be almost more frightening.

  3. It may not be "the" reason, but it is yet one more reason to be conscientious.