Hakai Magazine

Coastal science and societies

plastics floating in water
By blocking sunlight, floating plastics limit the energy available for photosynthesis. Photo by Cavan/Alamy Stock Photo

How Enough Floating Plastic Could Change the Sea

Many plastics float, block sunlight, and do not degrade—a recipe for altering the physical properties of the water underneath.

Authored by

by Maria Bolevich

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Some damage caused by plastic waste is dramatic and well known: every year, plastic is an accomplice in the deaths of millions of marine birds, mammals, turtles, and fish. But as new research suggests, plastic pollution may soon have far more insidious effects. A study led by Renjith VishnuRadhan, a postdoctoral researcher at the Indian Institute of Technology Bombay, outlines ways in which plastic may affect the physical processes in the ocean. Even a thin coating of plastic, VishnuRadhan and his colleagues write, could prevent solar radiation from penetrating into the ocean’s depths, with consequences from the surface to the seafloor.

Drawing on existing research into ocean processes, rates of pollution, the reflectance of different types of plastics, and other related topics, VishnuRadhan and his colleagues explore how floating plastic pollution may, in the coming decades, impact physical and biogeochemical processes, and possibly even the climate.

Obscuring sunlight is not unique to plastic, says Boris Worm, a marine ecologist at Dalhousie University in Halifax, Nova Scotia, who was not involved in the new paper. “Clearly any material that is optically dense will change the optical properties of ocean surface waters,” he says.

Many plastics absorb sunlight from the infrared, visible, and ultraviolet parts of the spectrum—just like many other small floating objects such as phytoplankton or dissolved organic matter. But unlike these other objects, plastic is stubbornly persistent.

According to VishnuRadhan, plastic isn’t causing a noticeable effect yet. But it could within the next few decades. Once this happens, one effect could be a change in the depth of the thermocline—a band of ocean where the temperature changes rapidly. The report explores how plastic in the ocean could also affect the exchange of gases between the ocean and the atmosphere; the marine carbon, nitrogen, and oxygen cycles; the stability of the water column; and the ocean’s heat balance and energy budget.

In his own work studying anthropogenic pressures on deep sea ecosystems, Alex David Rogers, a zoologist at the University of Oxford, United Kingdom, who was not involved in the new study, says that in some areas of the ocean plastics already reach sufficiently high concentrations that they can scatter sunlight, limiting its availability for photosynthesizing organisms.“The results of the paper are important,” Rogers says. It offers yet “more evidence that plastic is extremely harmful to the health of the ocean.”