Nav: Home

Plastic below the ocean surface

April 21, 2016

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.

Troubling tiny travelers

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.

"You have stuff that's potentially poisonous in the ocean and there is some indication that it's harmful to the environment, but scientists don't really understand the scope of this problem yet," explains Kukulka, an expert on ocean waves and currents, and associate professor in the College of Earth, Ocean, and Environment's School of Marine Science and Policy.

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."

Ocean turbulence explained

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

In the ocean, wind and waves act like a spoon, generating turbulence and mixing this surface layer of the water.

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

The study findings provided evidence that turbulence from waves and currents plays a critical role in whether plastics stay at the surface or get mixed deeper into the ocean. Surface heating from the atmosphere, due to seasonality, latitude or night/day cycles, also had a significant effect.

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.

"If we really want to go after this problem and quantify the amount of plastics in the ocean and think about distribution and impact, then we need to keep in mind that turbulence is influenced by heating and, therefore, the distribution of plastics is too," Kukulka said.

Comparing model results to actual field observations by his colleagues from the subtropical Atlantic, Kukulka corrected the surface measurements taking into account turbulence models and mixing processes, revealing new measurements that are significantly higher.

Big picture perspective

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.

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

"Even though the plastic pieces are buoyant, cleanup might not be as simple as skimming the surface," he said.
-end-
The scientists reported their findings in the March issue of the Journal of Physical Oceanography, a publication of the American Meteorological Society. Co-authors on the work, titled "Evidence for the Influence of Surface Heat Fluxes on Turbulent Mixing of Mircoplastic Marine Debris," include Kara L. Law, a sea education associate with Woods Hole and Giora Proskurowski, a research scientist at University of Washington.

This work was supported by the U.S. National Science Foundation (Grant OCE-1352422).

University of Delaware

Related Pollutants Articles:

Bacteria-coated nanofiber electrodes clean pollutants in wastewater
Cornell University researchers may have created an innovative, cost-competitive electrode material for cleaning pollutants in wastewater.
Lab on a chip could monitor health, germs and pollutants
Imagine wearing a device that continuously analyzes your sweat or blood for different types of biomarkers, such as proteins that show you may have breast cancer or lung cancer.
US streams carry surprisingly extensive mixture of pollutants
Many US waterways carry a variety of pollutants, but not much is known about the composition or health effects of these chemical combinations.
Melting snow contains a toxic cocktail of pollutants
With spring finally here and warmer temperatures just around the corner, snow will slowly melt away, releasing us from the clutches of winter.
Pollutants in the Arctic environment are threatening polar bear health
A new analysis has found that although the risk of persistent organic pollutants (POPs) in the Arctic environment is low for seals, it is two orders of magnitude higher than the safety threshold for adult polar bears and even more (three orders of magnitude above the threshold) for bear cubs fed with contaminated milk.
Evolution in action: How some fish adapt to pollutants
New genetic analyses of fish reveal how some have managed to evolve and adapt to live in polluted water.
Why air pollutants make some people vulnerable to atopic dermatitis
Researchers announce the results of a study into why air pollutants cause some people to be more susceptible to atopic dermatitis, a kind of skin inflammation.
Can early life exposure to pollutants predispose for disease?
Some studies indicate that early life exposure to pollutants such as PCBs and phthalates can predispose people to disease.
Exposure to particulate air pollutants associated with numerous cancers
Researchers have found that long-term exposure to environmental pollutants was associated with increased risk of mortality for many types of cancer in an elderly Hong Kong population.
Exposure to particulate air pollutants associated with numerous types of cancer
Long-term exposure to ambient fine particulate matter, a mixture of environmental pollutants, was associated with increased risk of mortality for many types of cancer in an elderly Hong Kong population.

Related Pollutants Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Bias And Perception
How does bias distort our thinking, our listening, our beliefs... and even our search results? How can we fight it? This hour, TED speakers explore ideas about the unconscious biases that shape us. Guests include writer and broadcaster Yassmin Abdel-Magied, climatologist J. Marshall Shepherd, journalist Andreas Ekström, and experimental psychologist Tony Salvador.
Now Playing: Science for the People

#513 Dinosaur Tails
This week: dinosaurs! We're discussing dinosaur tails, bipedalism, paleontology public outreach, dinosaur MOOCs, and other neat dinosaur related things with Dr. Scott Persons from the University of Alberta, who is also the author of the book "Dinosaurs of the Alberta Badlands".