This new research concludes that the top 200 meters of the Atlantic Ocean are positively packed with microplastics, with serious implications for the rest of the water column. For instance, microplastic particles are known to accumulate a biofilm of organic matter as they float around, which could weigh them down until they fall to the sea floor. This means that the plastics don’t stay at the top of the ocean—they have a chance of raining down into ocean ecosystems at all depths. “Another mechanism is plastic particles can be mistaken for food, and organisms at the very bottom of the food chain will be consuming it,” says Pabortsava. “As they excrete the material, that fecal material is very dense and it sinks, carrying plastics all the way down.”
Pabortsava thinks that one of the reasons why the millions of metric tons of plastic bags and bottles that humanity unloads into the sea each year seem to disappear is due in part to sampling techniques. Pabortsava filtered down to a resolution of 25 micrometers (25 millionths of a meter). But because this field of research is so new, there isn’t a standardized technique both for the fineness of the filters used to collect the particles, and the methods for counting them in the lab. So one group of researchers might be counting smaller particles than another, giving them different quantifications of microplastics in a given part of the sea.
“The reason we previously were not able to account for about 99 percent of what we have been putting in,” says Pabortsava, “is either because we haven’t been collecting the right size of particles in the surface ocean, or because it actually fragments and is transported down below the surface as a result.”
By scaling up their counts of microplastics across those dozen sample sites, Pabortsava says they can account for all that missing plastic, and even revise that figure upwards. “Our small microplastics alone, with just those three polymer types, can actually balance the inputs for the past 65 years and even surpass it,” Pabortsava adds. That is, Pabortsava says that even more plastic might have flowed into the environment than scientists previously believed.
But hold up, says Jennifer Brandon, a researcher at the Scripps Institution of Oceanography, who studies microplastics but wasn’t involved with this research. “There are some big leaps in their calculations,” she writes in an email to WIRED. “One of the largest is that they took their transect that curves right through two subtropical gyres (the most densely polluted areas of the Atlantic Ocean) and extrapolated those numbers for the entire Atlantic Ocean. You can’t get an accurate number doing that: It’s like taking the eye of a hurricane and saying that that is what the whole hurricane’s pressure field is like.”
“There is a lot of variability even within the subtropical gyres in terms of plastic abundance,” Pabortsava agrees, and points out that their paper describes some regions holding less plastic than others. For example, in the Atlantic subtropical gyres, they found no increase in microplastic. But this is where larger objects like bags, the precursors of microplastics, tend to accumulate.
So, says Richard Lampitt, an oceanographer at the National Oceanography Centre and coauthor on the paper, those gyres might not be so loaded with microplastics. “There isn’t actually strong evidence that these are massive repositories for plastics,” he says. Also, he notes, he and Pabortsava sampled from 12 areas up and down the Atlantic. “That’s one of the great attractions, is that it was covering a wide variety of environments, not just looking at the coastal and not just again the subtropical gyres,” Lampitt says.