Garbage Patches
6,350-245,000 metric tons of plastic waste are floating on the ocean's surface.
What is a garbage patch?
Garbage patches are large collections of marine debris - mostly plastics - that are found in the middle of the ocean, not islands made of plastic which is what many people imagine. The best known garbage patch is called that Great Pacific Garbage Patch and spans from the Western coast of North American all the way to Japan. The Great Pacific Garbage Patch is actually compromised of two separate garbage patches, the Western garbage patch and the Eastern garbage patch. All of the Great Pacific Garbage Patch is enclosed in the North Pacific Subtropical Gyre, the gyre is the reason that so much trash and debris has been brought into the middle of the ocean.
The North Pacific Garbage Patch is actually made up of two different garbage patches. The smaller of the two sits between Japan and Hawaii and the larger one, estimated to be about the size of Texas, sits between Hawaii and California.
How do currents and gyres affect garbage patches?
The mix of pollutants and water does not move indefinitely across the earth’s surface. Eventually it encounters a landmass, which the prevailing wind can traverse, but the water cannot. When this happens the water, still deflected by the Coriolis force, piles up against the land and deflects more significantly, right in the north and left in the south. This turns the circulating water until another prevailing wind can pick it up, which finally results in the vast dirty whirlpool of a Garbage Patch. [1]
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The final complexity is that this explanation of how currents, gyres, and the Coriolis effect connect to garbage patches only covers the surface. The 45-degree deflection as described on the What are they? page is an average impact at the surface, where the wind fully acts on objects and the water. Farther down the water column the relative influence of the Coriolis Effect is greater than that of wind, and the deflection angle relative to the wind direction is greater.
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On average, items suspended in the water column move at 90 degrees to the angle of the wind. This has important implications when studying the impact of different solid pollutants, as scientists cannot find the middle of a garbage patch, via satellite sensing for example and sample it at all depths to determine the pollutant concentration.[2] At the surface, samples of light plastics and Styrofoam would be accurate, but as the depth increases the researcher must sample for less buoyant pollutants such as drifting nets and microplastics at increasing deflections from the prevailing wind. They then estimate the degree of deviation through complex hydrodynamic calculations. Since these calculations are not exact, it requires many samples to be sure, increasing the cost and time required for such studies.
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[1] National Oceanic and Atmospheric Administration Marine Debris Program, 2016 Report on Modeling Oceanic Transport of Floating Marine Debris, Silver Spring, MD, 21pp.
[2] Interestingly, the water at the center of the Gyre is actually higher than at the outside, an effect caused by the deflection of the water toward the center by the flow around the center. While only about a meter even for the vast Pacific garbage patches, this difference can be observed from space by sensitive satellites and Garbage Patches are monitored by both visual means and by measuring the ocean height.
National Oceanic and Atmospheric Administration Marine Debris Program, 2016 Report on Modeling Oceanic Transport of Floating Marine Debris, Silver Spring, MD, 21pp.
