Prior posts have noted the various plastic debris wastes that are located in the oceans. Prior posts have also suggested that there may be plastic waste in the water column, though its quantification was uncertain. A recent assessment suggests that the amount previously estimated using surface sampling techniques may be low by a factor of several hundred percent or much more, depending on wind conditions at the time of the surface sampling.
Researchers used a specialized tow net to capture waste at different depths. The results were then combined into a mathematical model. The model allowed the researchers to calculate the amount of debris at different depths on average as well as look at how that amount changed with different conditions, such as on a windy day. They found 2.5 times more debris in the layers of water below the "surface water" (defined as the top 9.8 inches or 25 centimeters) as was found in that surface section. The debris was distributed down to a depth of about 65 to 82 feet (20 to 25 meters).
The findings mean the estimates of plastic litter in the ocean, as measured solely by skimming the surface water only, may in some cases vastly underestimate the amount of plastic debris which is present. Because churning of the water column affects the distribution of plastic debris, the contrast between surface measurements and measurements at depth can vary considerably. For example, the researchers believe that overall the amount of trash in the water column exceeds surface measurements alone with up to 250%. In high wind conditions, with lots of churning, the differential could be as much as 27 times.
The report can be found at http://www.agu.org/pubs/crossref/2012/2012GL051116.shtml.