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UD professor finds plastic pollution in ocean may be grossly underestimated

Surface trawling has long been used to estimate the level of plastic pollution in the ocean, from plastic soda bottles to disposable bags, but it turns out this method of measurement only scratches the surface of the problem… quite literally.

High winds cause plastic debris to mix well below the surface where more than half of the ocean’s plastic pollution has swirled about, uncounted, according to Tobias Kukulka, a University of Delaware assistant professor of physical ocean science and engineering.

UD professor finds plastic pollution in ocean may be grossly underestimated
Dr. Tobias Kukulka
UD assistant professor of physical ocean science and engineering.
(Credit: University of Delaware)

In still water, plastic is buoyant, inevitably rising to the ocean surface, Kukulka explained in an email interview. “However, in a wind-driven turbulent ocean, this buoyant upward transport is balanced by a downward transport because plastic particles “catch a ride” with the turbulent motion,” he said.

Kukulka and co-lead author Giora Proskurowski, oceanography scientist at the University of Washington, published the results of a study of plastic pollution of the world’s oceans in the latest issue of Geophysical Research Letters.

In the ocean, winds pushing down on the surface of the water cause a similar disturbance to shaking a snow globe. Thousands of plastic particles that should in theory float on the surface of the salt water are thrust deeper into the water column.

In order to begin to understand just how much debris penetrates below the surface, Kukulka’s and his team spent a month cruising the North Atlantic Ocean off the coast of Bermuda during the summer of 2010. While aboard the 134-foot Brigantine, SSV Corwith Cramer, the 33-person research team collected samples at varying depths and hand-sorted over 48,000 pieces of plastic gathered in the ocean.

While plastic concentrations decrease with depth, collective sampling from various depths in a single water column found just as much, if not more, plastic churning underwater as floating on the surface, wrote Kukulka.

UD professor finds plastic pollution in ocean may be grossly underestimated
Plastic particles found in the ocean resemble colorful confetti. Thousands of these millimeter-sized fragments can emerge in a single tow.
(Credit: Sea Education Association, Marilou Maglione)

Analysis of the debris at depths up to 100 feet below the surface indicate that surface sampling can represent as little as three percent of the true concentration.

Understanding the extent of plastic pollution in the ocean is a vital part of assessing the health of the world’s oceans, the largest biome on the planet.

Public education campaigns have highlighted some of the effects on marine life posed by plastic refuse. For instance, sea turtles can mistake plastic bags floating on the surface for jellyfish and may choke while attempting to eat them. (Some municipalities have banned plastic bags for this reason.)

Such encounters with marine life only represent the beginning of life on the high seas for a plastic bag, disposable cup, or yogurt lid.

Measuring Plastic at Depth with the Tucker Trawl, courtesy of Sea Education Association.

Measuring Plastic at Depth with the Tucker Trawl, courtesy of Sea Education Association.

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UD professor finds plastic pollution in ocean may be grossly underestimated

While it takes at minimum decades for plastic to truly break down, items such as bottles, straws, and six-pack rings are easily torn, crushed, and shredded into tiny pieces. These millimeter-sized fragments make up the bulk of the plastic found in the oceans.

Each of those bits of plastic can become a vehicle on which microbes and contaminants can hitch a ride to non-native waters. This problem can occur near the shore where ocean waters mix with fresh water bodies, and potentially at various depths of the ocean, as well.

To better understand the movement of plastic particles in the ocean Kukulka and his team will be creating a three-dimensional simulator to study particle motion and ocean turbulence. Such a simulator can help Kukulka to study the physics involved in ocean mixing which can inform future study within the natural ecosystem.