Plastic in oceans underestimated, UW researcher finds
Skimming-based estimates questioned, following study of winds' effects on debrisMay 10th, 2012
While working on a research sailboat gliding over glassy seas in the Pacific Ocean, oceanographer Giora Prosku-rowski noticed something new: The water was littered with confetti-size pieces of plastic debris, until the wind picked up and most of the particles disappeared.
After taking samples of water at a depth of 16 feet, Proskurowski, a researcher at the University of Washington, discovered that wind was pushing the lightweight plastic particles below the surface. That meant that decades of research into how much plastic litters the ocean, conducted by skimming only the surface, may in some cases vastly underestimate the true amount, Proskurowski says.
Reporting in the journal Geophysical Research Letters last month, Proskurowski and co-lead author Tobias Kukulka, of the University of Delaware, say data collected from just the surface of the water commonly underestimates the total amount of plastic in the water by an average factor of 2.5. In high winds, the volume of plastic could be underestimated by a factor of 27.
"That really puts a lot of error into the compilation of the data set," Proskurowski says. The paper also details a new model that researchers and environmental groups may use to collect more accurate data.
Waste in the oceans is a concern because of the impact it might have on the environment. For instance, when fish ingest plastics, it may degrade their liver functions.
Proskurowski gathered data on a 2010 North Atlantic expedition where he and his team collected samples at the surface, plus at an additional three or four depths, to as deep as 100 feet.
"Almost every tow we did contained plastic regardless of the depth," he says.
By combining the data with wind measurements, Proskurowski and his co-authors developed a simplified mathematical model that potentially could be used to match historical weather data, collected by satellite, with previous surface sampling to more accurately estimate the amount of plastic in the oceans.
In addition, armed with the new model, organizations and researchers in the future might monitor wind data and combine it with surface collections to estimate better how much plastic waste is in the world's oceans.
"By factoring in the wind, which is fundamentally important to the physical behavior, you're increasing the rigor of the science and doing something that has a major impact on the data," Proskurowski says.
The team plans to publish a "recipe" that simplifies the model so that a wide range of groups investigating ocean plastics, including those who aren't oceanographers, can use the model. Following the recipe might encourage some consistency among the studies, Proskurowski says.
"On this topic, what science needs to be geared toward is building confidence that scientists have solid numbers and that policy makers aren't making judgments based on CNN reports," he says. Descriptions of the so-called great Pacific garbage patch might have led many people to imagine a giant island of garbage, when in fact the patch is made up of widely dispersed, millimeter-size pieces, he says.