Density of the Great Pacific Garbage Patch

The Great Pacific Garbage Patch (GPGP) is a huge region of ocean trash twice the area of Texas. I’m trying to understand how dense it is, and running into contradictory information.

This article describes a project, Ocean Cleanup, that aims to clean up half the GPGP in five years. How could you possibly clean up a garbage patch bigger than Texas in five years? That made me suspect the GPGP isn’t as dense a garbage patch I imagined, and it’s not.

The article mentioned above says Ocean Cleanup would remove 5.5 metric tons of trash a month, and clean up half the GPGP in five years [1]. (I hope they can!) That implies the GPGP contains 660 metric tons of trash. Wikipedia says it contains 80,000 metric tons of trash. Somebody is off by two orders of magnitude! If Wikipedia is right about the mass, and if Ocean Cleanup is right that they can remove half of it in five years, then they’ll have to remove 700 tons of trash per month.

Not exactly a garbage patch

The Wikipedia article on the GPGP does say that “garbage patch” is misleading.

There has been some controversy surrounding the use of the term “garbage patch” and photos taken off the coast of Manila in the Philippines in attempts to portray the patch in the media often misrepresenting the true scope of the problem and what could be done to solve it. Angelicque White, Associate Professor at Oregon State University, who has studied the “garbage patch” in depth, warns that “the use of the phrase ‘garbage patch’ is misleading. … It is not visible from space; there are no islands of trash; it is more akin to a diffuse soup of plastic floating in our oceans.”

Density

So how dense is it? Let’s assume 80,000 metric tons over an area twice the size of Texas. The area of Texas is 700,000 km² , so that’s 8 × 1010 grams of trash over 1.4 × 1012 square meters, or 57 milligrams per square meter.

An empty water bottle weighs about 20 grams, and an American football field covers 5300 square meters, so this would be the same density of plastic as 15 empty water bottles scattered over a football field. This is an average. No doubt the density is higher in some areas and lower in others.

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[1] The video in the article says Ocean Cleanup would remove half the GPGP every five years, implying that the rate of clean up will decline exponentially.

10 thoughts on “Density of the Great Pacific Garbage Patch”

1. Rich Gillin

Isn’t it more than just man-made materials? Would it help grow, retain or collect biological mass as well?

2. I’ve heard that the GPGP is a habitat for some living things, but that seems less plausible now that my understanding of its density has gone down. Maybe in places of high density there are things living in it. I’ve heard that a lot of the mass comes from fishing nets, and they’d hold together big clumps of trash. If it is that clumpy, and the average density is milligrams per meter, large portions of the GPGP must be nearly free of garbage.

I’m no expert on this, and I’m just going by what I’ve heard.

Maybe there are things living in the GPGP, but the 80,000 ton estimate is just the estimate of the plastic mass.

3. 15 empty water bottles scattered over the area of a football field? The garbage density on Houston freeways has to be at least 100 times of that amount.

4. The exponential recovery rate seems about right. I’ve been associated with some radiological cleanups that have exponentially decreasing thresholds for their removal criteria. The main problem is the sensors don’t see the small stuff when big stuff is around (SNR), so multiple passes are mandatory.

In the case of the GPGP, the stuff moves around, so collection must be repeated over the same area as density decreases.

5. Saurish Chakrabarty

About the 15 bottles: It may be more insightful to get an estimate of the highest density in a Dallas-sized region within the Texas-sized region where the average density is ~15bottles/football field. Alternatively, if the Texas-sized region contains almost all the garbage, what is the garbage density in the region that contains, say, 50% of the garbage. The density may be too low near the boundaries of the region.

6. Jonathan T

The cleanup rate may not decline, if new plastic is added at a fast enough rate

7. Michael Watts

The exponential decline in cleanup seems pretty expected on the assumptions that (1) no new plastic comes in to the patch; and (2) the project processes a fixed amount of water every year.

8. Brian Coates

Dr. Cook,
I may have missed it in the article, but what is the “normal” garbage density of open water? Has any sampling been done elsewhere? How does the garbage density of the Garbage Patch compare to other areas of the planet?Thanks,
brian