Read: How plastic cleanup threatens the ocean’s living islands
In another way, though, all the plastic in the deep ocean is not a surprise. Scientists estimated the amount of plastic going into the ocean, and the number far exceeded what they were seeing in the water. “We’ve known for a long time if we just sample from the ocean surface, it doesn’t add up, so it must be going somewhere,” says Tamara Galloway, an ecotoxicologist at the University of Exeter who was not involved with the study. Where the missing plastic went was down.
The team also found microplastics as deep as they could sample with their ROV, which was 3,200 feet. Earlier this year, another group found plastic fibers in the guts of animals that live in the 36,000-foot-deep Mariana Trench, the lowest point on Earth. The Monterey Bay study suggests that microplastics are not just present below the surface of the ocean, but may be abundant.
Choy says it’s unclear exactly why most of the plastic seems to be hanging out in the 200-to-600-meter zone. There could be physical explanations, such as the density of the plastic and the movement of water. There could also be biological explanations, such as the way plastic moves through the food web. Choy and her team’s ROV also collected “sinkers,” which are sticky mucous houses that animals called larvaceans build and discard every day. Larvaceans use their mucous houses to filter feed, and they invariably catch microplastics. As sinkers fall through they water, they bring nutrients down to the deep sea. Anglerfish, vampire squid, and deep-sea cucumbers all eat sinkers and, consequently, they all eat microplastics.
When animals eat microplastics, they are, obviously, not eating food. The material can clog their guts. The chemistry of plastic also means the material tends to attract pollutants in the ocean water, making it even more dangerous to eat.
Read: A troubling discovery deep in the ocean
After Choy and her colleagues collected all of their microplastic pieces, they wanted to identify the kind of plastic, too. “That was a very—oh my gosh, that was a very manual effort, if you’d like,” she says, clearly remembering exactly how much work it took. Her co-authors at Arizona State University sorted hundreds of pieces of microplastic by hand and identified the plastic using a laser. They found that most of the plastic was polyethylene terephthalate, the type that goes into single-use plastics such as food packaging.
As the problem of plastic pollution has gained attention, so have viral solutions, such as the Ocean Cleanup, a 2,000-foot-long floating boom meant to collect plastic on the surface. The tube broke in testing, without collecting much plastic (a result experts could have predicted). The deep ocean is harder to reach, dark, cold, and under immense pressures. It’s hard to imagine how to even begin removing plastics there. “The best approach is to stop chucking so much in the ocean in the first place,” Galloway says. “That’s always going to be the best approach.”
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is a staff writer at The Atlantic.