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 km^2 , so that's 8 i- 10¹⁰ grams of trash over 1.4 i- 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.