Plastic below the ocean surface

http://www.eurekalert.org/pub_releases/2016-04/uod-lbt042116.php

Public Release: 21-Apr-2016
Plastic below the ocean surface
Current measurement methods may be vastly underestimating the amount of plastic in the oceans.
University of Delaware

Plastics are all around us. They are found in containers and packing materials, children's toys, medical devices and electronics.

Unfortunately, plastics are also found in the ocean.

A 2015 paper published in Science estimates that anywhere from 4.8 million to 12.7 million metric tons of plastic were dumped into the ocean in 2010 alone. One metric ton equals approximately 2,200 pounds, roughly the weight of a Mazda Miata.

As we celebrate Earth Day on Friday, April 22, new research by University of Delaware physical oceanographer Tobias Kukulka provides evidence that the amount of plastic in the marine environment may be greater that previously thought.

Plastic in the ocean becomes brittle over time and breaks into tiny fragments. Slightly buoyant, these microplastics often drift at the surface where they can be mistaken for food by birds, fish or other marine wildlife. Microplastics have turned up in the deep ocean and in Arctic ice, too.

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One technique scientists use to try and quantify how much plastic is in the marine environment 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 considered representative of the amount of plastic in the area.

But Kukulka isn't so sure this method provides an accurate picture of what's happening.

"My research has shown that ocean turbulence actually mixes plastics and other pollutants down into the water column despite their buoyancy," Kukulka said. "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."

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In the summer, for example, 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. When the surface cooled, the water density increased and caused the plastic to sink into the water column.

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While the research team's findings shed new light on the growing plastics problem, Kukulka said the research also can be applied to oil and other pollutants, even to the distribution of nutrients in the water and phytoplankton, ocean drifters that form the base of the marine food web.

"Broadly, these plastics pieces can be used as a physical tracer to help answer bigger questions about ocean processes and their implications for other ocean pollutants," he said.

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