The Amount of Plastic in the Ocean May Be Severely Underestimated

April 26, 2016 | Joanne Kennell

Plastic washed up on the beach
Photo credit: Hllary Daniels/flickr (CC BY 2.0)

How much plastic that gets dumped into the ocean each year will shock you!

Plastics are everywhere. They are used in food packaging, children’s toys, medical devices, electronics, and even clothing. And unfortunately, plastics are found in the oceans too.

According to a paper published in Science back in 2015, anywhere from 4.8 million to 12.7 million metric tons (10.5 billion to 27.9 billion pounds) of plastic were dumped into the ocean in 2010 alone. Adding to the alarm, a report published in January revealed that there could be more plastic than fish, pound per pound, in the oceans by 2050.

However, new research by University of Delaware physical oceanographer and associate professor, Tobias Kukulka, has provided evidence that the amount of plastic in the marine environment may be a lot higher than previously thought.

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Over time, plastic in the ocean becomes brittle and breaks into tiny fragments, and since these microplastics are slightly buoyant, they drift at the surface and can be mistaken for food by birds, fish, and other marine wildlife.

One current technique scientists use to quantify how much plastic is in the sea is to drag a tow net over the surface for a few miles, then count the number of plastic fragments. This number is then used to calculate a concentration that represents the total amount of plastic in the area.

However, Kukulka is not so sure that this method paints an accurate picture of what is really going on.

"My research has shown that ocean turbulence actually mixes plastics and other pollutants down into the water column despite their buoyancy," Kukulka said in a press release. "This means that surface measurements could be wildly off and the concentration of plastic in the marine environment may be significantly higher than we thought."

A good way to understand ocean turbulence is to think about adding cream to your coffee: If you pour the coffee gently, you need a spoon to generate turbulence to mix the two liquids. However, if you pour the cream quickly, as the liquid descends into the coffee, it naturally generates turbulence and mixes.

Now in the ocean, winds and waves act like a spoon, generating turbulence and mixing this surface layer of the water.

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Working with collaborators at the Woods Hole Oceanographic Institute and the University of Washington, Kukulka used computer modeling to look at the effect that waves and heating of the ocean surface had on where plastic was found.

The study, published in the Journal of Physical Oceanography, showed that turbulence from waves and currents play a critical role in whether plastics stay at the surface or get mixed deeper into the ocean. They also discovered that surface heating from the atmosphere, due to seasonality and latitude, also had a significant effect.

In the summer, strong surface heating by the sun warms up the ocean’s top layer, decreasing the water’s density and trapping the plastic at the surface. However, when the surface cools, the water density increases, causing the plastic to sink.

Kukulka compared the model results to observations made by his colleagues from the subtropical Atlantic. Correcting for surface measurements that accounted for turbulence and mixing processes, his new measurements were significantly higher. However, the paper did not supply any numbers.

Some scientists have suggested dragging nets through ocean's surface waters to remove the plastic, but Kukulka cautioned that in areas with strong turbulence, scientists "may want to consider spending our energy and efforts elsewhere."

Nevertheless, the results provide more insight on the ever-growing plastics problem. Kulkula even said the research could be applied to oil, pollutants, and even the distribution of nutrients and phytoplankton.

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