While there was marine life, there was also sea snow – a constant rain of death and debris sinking from the surface into the depths of the sea.
Snow begins as particles that collect in dense, flocculant flakes that gradually sink and drift past the mouths (and mouthpieces) of the wipers below. But even the sea snow that is swallowed will most likely be snowing again; squid intestines are just a stop to rest on this long journey to the deep.
Although the term may imply winter whites, sea snow is mostly brownish or grayish, including mostly dead things. For eons, debris contains the same things – plant and animal carcass stains, feces, mucus, dust, germs, viruses – and transports carbon to the ocean to be stored on the seabed. However, sea snowfall is increasingly infiltrated by microplastics: fibers and fragments of polyamide, polyethylene and polyethylene terephthalate. And this false fall seems to be changing the ancient cooling process of our planet.
Every year tens of millions of tons of plastic enter the oceans of the Earth. Scientists initially speculated that the material was intended to float in garbage and carousels, but surface studies have accounted for only about one percent of the calculated plastic in the ocean. A recent model found that 99.8 percent of the plastic that entered the ocean since 1950 sank below the first few hundred feet of the ocean. Scientists have found 10,000 times more microplastic on the seabed than in polluted surface water.
Sea snow, one of the main roads connecting the surface and the depths, seems to help plastics sink. And scientists are just beginning to unravel how these materials interfere with deep-sea food webs and the ocean’s natural carbon cycles.
“It’s not just that sea snow carries plastics or plastic aggregates,” said Louisa Galgani, a researcher at the Atlantic University of Florida. “It’s that they can help each other get to the deep ocean.”
The sunlit surface of the sea blooms with phytoplankton, zooplankton, algae, bacteria and other small life, all feeding on the sun’s rays or with each other. While these microbes are metabolized, some produce polysaccharides that can form a sticky gel that attracts the lifeless bodies of small organisms, small pieces of larger carcasses, shells of foraminifera and pteropods, sand and microplastics that stick together to form larger scales. “They are the glue that holds all the components of sea snow together,” said Dr. Galgani.
Sea snowflakes fall at different speeds. The smaller ones have a lower descent – “slow by a meter a day”, says Anela Choi, a biological oceanographer at the Scripps Institute of Oceanography at the University of California, San Diego. Larger particles, such as thick faecal pellets, can sink faster. “It’s just rising to the bottom of the ocean,” said Tracy Mincher, a researcher at the Atlantic University of Florida.
The plastic in the ocean is constantly degrading; even something as large and floating as a jug of milk will eventually disintegrate and disintegrate into microplastics. These plastics develop biofilms from different microbial communities – the “plastisphere”, said Linda Amaral-Zetler, a scientist at the Royal Dutch Marine Research Institute who coined the term. “We think plastics are inert,” said Dr. Amaral-Zetler. “Once it enters the environment, it is quickly colonized by microbes.”
Microplastics can house so many microbial hitchhikers that they counteract the natural buoyancy of plastics, causing their raft to sink. But if the biofilms then degrade on the way down, the plastic can float back up, which will potentially lead to the purification of microplastics in the water column. Sea snow is anything but stable; as scales fall freely into the abyss, they continually harden and disintegrate, torn by waves or predators.
“It’s not that simple: Everything falls all the time,” said Adam Porter, a marine ecologist at the University of Exeter in England. “It’s a black box in the middle of the ocean because we can’t stay there long enough to understand what’s going on.
To study how sea snow and plastics are distributed in the water column, Dr. Mincher began sampling deeper water with a dishwasher-sized pump full of filters that hangs on wire from a research boat. The filters are arranged from a large net to a small one to filter fish and plankton. Running these pumps for 10 hours reveals nylon fibers and other microplastics distributed in the water column below the South Atlantic subtropical circle.
But even with a research boat and its expensive and cumbersome equipment, a single piece of sea snow cannot be easily extracted from deep water in the real ocean. Pumps often disturb the snow and disperse fecal pellets. And the flakes themselves give little idea of how fast some snow melts, which is vital for understanding how long plastics stay, yo-yo, or sink in the water column before settling on the seabed.
“Is it decades?” Dr. Mincher asked. “Is it hundreds of years?” Then we can understand what we are here for and what the problem is. “
To answer these questions and work on a budget, some scientists have made and manipulated their own sea snow in the lab.
At Exeter, Dr. Porter collected buckets of seawater from a nearby estuary and filled the water into ever-rolling bottles. Then sprinkle with microplastic, including polyethylene beads and polypropylene fibers. The constant stirring and spraying of sticky hyaluronic acid encouraged the particles to collide and stick together in the snow.
“Obviously we don’t have a 300-meter pipe to make it sink,” Dr. Porter said. “As you roll it, what you’re doing is creating an endless pillar of water through which particles can fall.”
After rolling the bottles for three days, he examined the snow and analyzed the number of microplastics in each flake. His team found that each type of microplastic they tested aggregated in sea snow, and that microplastics such as polypropylene and polyethylene – usually too floating to sink on their own – sink easily after being incorporated into sea snow. And all the sea snow contaminated with microplastic sinks significantly faster than natural sea snow.
Dr Porter suggests that this potential change in snow speed could have huge implications for how the ocean traps and stores carbon: faster snowfalls could store more microplastics in the deep ocean, while slower snowfalls could make plastic-laden particles more accessible to predators, potentially starving food webs deeper. “Plastics are a weight loss pill for these animals,” said Karin Quayle, a carbon scientist at GNS Science in New Zealand.
In experiments in Crete, funded by the European Union’s Horizon 2020 research program, Dr. Galgani tried to mimic sea snow on a larger scale. She released six mesocosms – huge bags, each containing nearly 800 gallons of seawater – and recreated the natural movement of water – in a large pool. Under these conditions, sea snow forms. “Mostly you make observations in the field,” said Dr. Galgani. “You have so little space and a limited system. In the mesocosm, you are manipulating a natural system.
Dr. Galgani mixed microplastics in three mesocosms in an attempt to “recreate a sea and perhaps a future ocean where you can have a high concentration of plastic,” she said. Microcosms loaded with microplastics not only produce more sea snow, but also more organic carbon, as plastics offer more surfaces for colonizing microbes. All this can engender the deep ocean with even more carbon and change the ocean’s biological pump, which helps regulate climate.
“Of course, this is a very, very big picture,” said Dr. Galgani. “But we have some signals that there may be an effect. Of course, it depends on how much plastic there is. “
To understand how microplastics can travel through deep-sea food webs, some scientists have turned to evidence creatures.
Every 24 hours, many species of marine organisms embark on a synchronized migration up and down the water column. “They do the marathon equivalent every day and night,” said Dr. Choi. Guillermo W.B. Ferreira, a researcher at the Rural Federal University of Pernambuco in Brazil, wonders: “Is it possible for them to transport plastics up and down?”
Dr. Ferreira and Anne Justino, a doctoral student at the same university, collected vampire squid and medium-sized squid from a section of the tropical Atlantic. They found an abundance of plastics in both types: mostly fibers, but also fragments and beads.
This made sense for medium-sized squid that migrate to the surface at night to feed on fish and copepods that eat microplastics directly. But vampire squid, which live in deeper waters with less microplastics, have even higher levels of plastic, as well as foam, in their stomachs. Researchers have suggested that the main diet of sea snow vampire squid, especially the more fleshy fecal pellets, may direct plastic into their bellies.
“This is very worrying,” said Ms. Justino. Dr Ferreira said: “They are one of the most vulnerable species to this anthropogenic impact.”
Ms. Justino has dug up fibers and beads from the digestive tract of lanterns, axes and other fish that migrate up and down in mesopelagics, from 650 to 3,300 feet down. Some microbial communities that settle on microplastics can bioluminesce, attracting fish as bait, Dr. Mincher said.
In the canyon of Monterey Bay, Dr. Choi wanted to know if certain types of filter feeders absorb microplastics and transport them into food webs in deeper water. “Sea snow is one of the main things that connects food networks across the ocean,” she said.
Dr. Choi turned to the giant larva Bathochordaeus stygius. The larva looks like a tiny poppy spoon and lives inside a palace bubble of mucus, which can reach a meter in length. “It’s worse than the worst bastard you’ve ever seen,” Dr. Choi said. When their snot houses become clogged with food, the larvae are removed and the heavy bubbles sink. Dr. Choi discovers that these mucus palaces are crammed with microplastics that head to the depths along with all their carbon.
Giant larvae are found across the world’s oceans, but Dr. Choi stressed that her work is focused on the Monterey Bay Canyon, which belongs to a network of marine protected areas and is not representative of other, more polluted seas. “It’s a deep bay on one side of the country,” Dr. Choi said. “Zoom in and think about how vast the ocean is, especially deep water.”
The individual scales of sea snow are small, but add up. A model created by Dr. Quayle estimated that in 2010 the world’s oceans produced 340 quadrillion units of sea snow, which can transport up to 463,000 tons of microplastic to the seabed each year.
Scientists are still studying exactly how this plastic snow is sinking, but they know for sure, Dr. Porter said, that “everything eventually sinks into the ocean.” Vampire squid will live and die and eventually turn into sea snow. But the microplastics that pass through them will remain, eventually settling on the seabed in a stratigraphic layer that will mark our time on the planet long after humans are gone.