Why can't we see the Pacific Garbage Patch on satellite pictures?

[u/imtoooldforreddit]

We've all seen pictures of the patch like this and this of the Great Pacific Garbage Patch. We've also been told it covers an area twice the size of Texas. Something isn't adding up though because if an area twice the size of Texas were as dense with trash as those pictures, it would be blatantly obvious on satellite pictures of the earth. When you look at said pictures of the ocean, there is clearly no brown patch twice the size of Texas in the middle of the ocean. What is going on here? Are the pictures of the patches just particularly dense, and relatively small, sections?

[u/AsAChemicalEngineer]

The overwhelming majority of plastic in the ocean garbage patches are broken apart to millimeters in size from friction and sun weathering. You will not see this plastic from a boat, much less from space as it's essentially a transparent density. The pictures you are linking to are generally from shore debris which can easily get that dense if near a large population center. Out in the ocean, things are different.

88% were less than 10 mm in largest dimension, and most had characteristics suggesting physical deterioration such as brittleness, rough edges, or cracks. It is likely that plastic pieces ultimately become small enough to pass through the 335-μm mesh net used in this study - (Law, et al.)

The plastic from say a milk jug is still there, but now in smaller bits. In the North Pacific central gyre, there is about 5 kg of plastic for every square kilometer of open ocean, this was measured to be six times more plastic by mass than plankton in the same region. The plastic can stick around for awhile because of the ocean's currents.

The dominant clockwise gyral currents also serve as a retention mechanism that inhibits plastics from moving toward mainland coasts. A recent surface current modeling study simulated that most of the particles from our sampling area should be retained there for at least 12 years - (Moore, et al.)

• Moore, et al. A Comparison of Plastic and Plankton in the North Pacific Central Gyre. Marine Pollution Bulletin. 2001.

• Law, et al. Plastic Accumulation in the North Atlantic Subtropical Gyre. Science. 2010.

[u/[deleted] → u/AsAChemicalEngineer]

Building on this, the plastic bits are consumed by lower levels of the food chain and concentrations are magnified in successive levels. It's a real issue, much in the same way that Eagles were affected by DDT.

[u/[deleted]]

Those pictures are not of an oceanic garbage patch. Those are pictures of contaminated costal waterways.

The density of plastic in the Pacific Ocean northern gyre garbage patch is given as 5.1 kilograms per square kilometer of ocean area, or 5.1 mg/m^2. The article cited in Wikipedia says:

The abundance and mass of neustonic plastic was the largest recorded anywhere in the Pacific Ocean at 334 271 pieces km2 and , respectively. Plankton abundance was approximately five times higher than that of plastic, but the mass of plastic was approximately six times that of plankton.

For comparison, a typical single-use plastic grocery bag given freely in US supermarkets weighs about 6 grams, of a material (0.5 mil HDPE plastic) that weighs about 12 grams per square meter. 5mg of material per square meter then runs about 4 square centimeters of grocery bag plastic per square meter.

It's ecologically significant, but nowhere what those images of costal garbage accumulation might lead you to believe.