Northeastern professor Aron Stubbins says to find plastics “well-distributed throughout the ocean is surprising.”
After a decade of testing, Northeastern researchers have uncovered a “light smog” of microplastics drifting below the surface of the world’s oceans — revealing far more plastic pollution in deep-sea waters than previously known.
Published in Nature, the study combines data from nearly 2,000 ocean sampling stations collected between 2014 and 2024. The findings show that microplastics are not just floating on the surface but are spread throughout the ocean’s depths.
The research is not a global analysis. Sampling for microplastics occurs the most in northern ocean waters, where there is more land and people fringing the water. But in those areas, data shows that plastics are accumulating rapidly.
“Plastics are more or less everywhere,” said Aron Stubbins, professor of marine and environmental sciences, civil and environmental engineering, and chemistry and chemical biology at Northeastern. “We’re finding them deposited in the Antarctic, in the Himalayas, carried by the wind, but to find them well-distributed throughout the ocean is surprising.”
It was already known that plastic debris accumulates in subtropical gyres — or swirling eddies — that trap and concentrate trash on the ocean surface. The new research reveals that below the surface, plastics are floating, suspended, all the way to the ocean floor.
“You’ve got these accumulations on the surface, and the same processes concentrating and leading to accumulations below the gyres into a sort of lens,” Stubbins said.
Plastics like polyethylene and polypropylene are buoyant, so they float on the surface. Other plastics, like the polyethylene terephthalate used to make water bottles, are dense and are more likely to sink to the ocean floor. The fact that microplastics are found everywhere between the surface and the sea floor might be explained by size, Stubbins said.
“One rationale is that when something is small enough, its density becomes less important than its drag,” he said.
The overall abundance of plastic, Stubbins added, leads to questions about the ocean’s capacity to absorb carbon dioxide from the atmosphere and sequester it in the deep sea. Through this process — called a biological carbon pump — the ocean currently takes up about 25% of carbon dioxide emitted from fossil fuels.
Plastics may reduce the ocean’s ability to offset carbon dioxide, Stubbins said. He is among a group of researchers leading a $1.3 million National Science Foundation grant to study this question further.
Debris on the ocean’s surface is visible — images of a massive garbage patch in the North Pacific Ocean were first widely published in 1988 — and previous research has been limited to surface water pollution.
Documenting plastic pollution in the ocean’s depths is much harder. While this research establishes benchmark numbers for subsurface plastics, Stubbins said that further study is needed to standardize how data is collected at depth and to answer questions about whether plastic concentrations are increasing slower or faster in deep waters than in surface waters.
“Plastics is an emergent field,” he said, “and there are concerns about how the changing physical environment of the deep ocean may have impacts on how the ocean functions as part of the Earth’s system.”
Microplastics at depth are unlikely to have a direct impact on humans, he said, but they could easily end up in the food supply. Abundant plastic materials smaller than 20 microns — smaller than the width of a human hair — may be eaten by zooplankton, which is food for bigger marine animals.
“In terms of the food chain, there could be interaction,” Stubbins said. “Organisms could be feeding in these zones and ingesting these plastics and also the toxic passenger molecules they carry, which could distribute into fish tissue, and we end up consuming them.”