Several myths have grown up about the "garbage patch," worth clarifying here:
(1) It's not really a "garbage patch," e.g., a floating landfill. Rather, the debris consists mostly of small bits of plastic suspended throughout the water column. A good analogy is that it is more like flecks of pepper floating throughout a bowl of soup, than a skim of fat that sits on the surface. There are three major garbage patches stretching to the west from the coast of southern California and Baja: the Eastern Garbage Patch, the Western Garbage Patch out near the Kuroshio current, and, further north between these two, a subtropical convergence zone.
|Graphic is from Tomczak, M., and Godfrey, J.S., 2002,|
Regional Oceanography: an Introduction, online version.
A is a convergence zone; E is a coastal upwelling
divergence zone. Black arrows are winds; green arrows
indicate water movement. This graphic from
this WWW site.
In an interesting post on May 16 by the NOAA Office of Response and Restoration, the question "Is there a garbage patch in the Great Lakes?" is asked. In an understatement, NOAA points out that "The Great Lakes are no mere group of puddles. They contain nearly 20% of the world's surface freshwater and have a coastline longer than the East Coast of the United States."
|Average summer water circulation in the Great Lakes.|
From Beletsky et al., 1999 as posted by NOAA here.
In the Great Lakes system, water flows from the big Lakes Superior and Michigan in the west into Lake Huron, through Lake St. Clair (not shown**) and the Detroit River into Lake Erie. It exits through Niagara Falls and Lake Ontario into the Saint Lawrence River and then out to the Atlantic Ocean. Within each Lake, the "current" breaks down into numerous eddies (convergence zones similar to those discussed above) whose geometry is determined by the elevation differences (highest in the west, lowest in the east), the geometry of the Lake beds, wind, solar energy, differences in density in the water column due mostly to the temperature differences, and the shorelines. There is now a project based at the University of Waterloo in Canada, partnered with COM DEV (a designer and manufacturer of space and remote sensing technology) to develop and test remote sensing methods for detecting plastics in the Great Lakes. Here's Sarah Opfer's blog on this topic for more information.
**Lake St. Claire is the small nearly-circular feature shown on this map between Lake Huron and Lake Erie.