The ocean is filled with microscopic creatures that thrive in the sunshine. These bacteria and plankton periodically clump up with detritus, like waste produced by fish, and then drift softly downward, transforming into what scientists call marine snow.
In the inky depths of the ocean that the sun can’t reach, other creatures depend on the relentless fall of marine snow for food. Those of us living on land depend on it, too: Marine snow is thought to store vast amounts of carbon in the ocean rather than letting it heat Earth’s atmosphere. Once those particles of marine snow arrive at the ocean bottom, their carbon stays down there for untold eons.
It has long been assumed that marine snow falls like any other particle of a given size. But scientists recently made an unexpected discovery: Many particles are sporting parachutes made of mucus.
Researchers observed this phenomenon when they brought a newly invented type of microscope out on the open ocean to watch the snow fall. They found that gooey, transparent parachutes considerably slow the snow’s descent, suggesting that marine snowfall is a delicately tuned process controlled by bacteria and plankton that are far from passive.
These findings are described in a paper published last week in the journal Science.
It is difficult to study marine snowfall in a lab, explained Manu Prakash, a bioengineer at Stanford University who worked on the research. The particles are fragile, and laying them under a microscope in a dish is a poor substitute for seeing them in their natural environment. So Dr. Prakash and his colleagues developed a device they call “the Gravity Machine,” in which a wheel is filled with seawater and continually rotates.
“A ring of fluid is an infinite fluid,” Dr. Prakash said. Placed in the device, a particle of marine snow can sink unobstructed and without interruption just as it usually would in the ocean.
By using a microscope to examine the water in the wheel, the team tracked individual particles as they moved. And by mounting the whole system on a gimbal, the researchers were able to study marine snow on a ship in the ocean as it rocked and rolled, allowing the team to observe seawater samples immediately after they were plucked from the waves.
During their efforts, the researchers spotted something surprising. Invisible gobs of mucus, sometimes nearly as large as the particles themselves, were trailing above the fragments of snow. “Wait a second,” Dr. Prakash said he remembered thinking. “They are making parachutes.”
The bigger the mucus gob, the scientists found, the slower the particle’s fall.
Researchers knew from previous work that mucus, made by bacteria and plankton, was a component of marine snow. But Dr. Prakash said it had been assumed that the mucus was mainly a glue holding particles together.
If mucus slows the fall of marine snow — and in some cases observed in this study, it took the rate from 200 meters a day to near total stillness — that means the organisms living in the snow have control over how long they hang out in the upper parts of the ocean. They may tarry there for far longer than anyone thought, taking advantage of the sunlight and warmer temperatures. And that, in turn, means that the organisms in the marine snow may emit more waste and therefore store less carbon on the ocean floor than accounted for by existing models used to study the planet’s changing climate.
If mucus parachutes are commonly seen in oceans across the world, as follow-up expeditions by Dr. Prakash and his colleagues suggest, then a potentially enormous quantity of carbon is making its way into the atmosphere rather than heading to the ocean floor.
A back-of-the-envelope calculation by Lionel Guidi of the French National Center of Scientific Research and B.B. Cael of the National Oceanography Center in England, neither of whom were involved in the study, supports the finding that vastly less carbon gets sequestered by particles with mucus parachutes than by those without.
“We already know that our representation of marine snow in climate models needs revising,” Dr. Cael said. “This study elucidates a way to making one of those necessary revisions. That should improve the accuracy of projected changes in Earth’s carbon cycle.”
The mucus parachutes reflect a larger truth about the ocean, Dr. Prakash said. Many of its most fundamental processes are likely to be controlled, on some level, by its very smallest inhabitants.
“Unless we get serious about the microbes and the microbial context,” he said, “we are blind.”
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