It’s snow time in the Northern Hemisphere, the season of winter wonderlands and skiers’ delight. But most landlubbers don’t realize—as I didn’t until recently—that it’s always snowing in the sea.
This underwater downfall, known as marine snow, drifts through every ocean on the planet. The term was coined in the early 1950s by Japanese researchers who described “snowflakes” swirling in waters stirred by their submersible. Invisible from shore and rarely noticed even by sailors, the silent drizzle helps keep the oceans productive and the planet healthy.
Unlike the pristine flakes that dance in the sky, marine snow is a jumble of odds and ends: the soft remains of microscopic life, fragments of shells and molts, fecal pellets, dust and soot from the atmosphere. Once the tiny drifters form near the surface, gravity begins to tug them downward—if they’re not eaten along the way. In the so-called “twilight zone,” hundreds of yards below, hungry foragers such as jellyfish and crustaceans nibble on the floating buffet.
On their own, particles sink at a glacial pace—barely a hundredth of a mile per hour—taking weeks to reach the bottom. But many are surprisingly sticky—more like wisps of spiderweb than grains of snow. As they drift, they snag other bits, including dense materials like calcium carbonate (the stuff of shells), and grow into larger bundles called aggregates. These heavier clumps plunge far more quickly, dropping hundreds of yards a day.
The snowflakes that reach the depths feed an entirely different cast of characters: sea cucumbers, worms, brittle stars, and other bottom-dwellers that vacuum them from the water or scavenge them from the seabed. The remainder settle into the soft, muddy ooze that blankets much of the ocean floor, accumulating at a pace so slow that it’s measured in yards per million years.
Here, microbes take over. Bacteria dismantle the last traces of organic matter, releasing its components back into basic chemical form: carbon dioxide, nitrate, phosphate, silicate, ammonium—the raw ingredients of life. These nutrients dissolve into the deep.
This burial is one reason marine snow matters far beyond the ocean. By carrying carbon from the surface into the sea, it helps regulate Earth’s climate. Carbon that might otherwise circulate in the atmosphere—trapping heat and warming the planet—is instead packaged, weighted, and locked away for centuries. In this way, the ocean acts as a vast carbon bank; marine snow is one of its most effective deposit systems.
The story doesn’t always end at the bottom. Along certain coasts, including Northern California’s, seasonal winds and Earth’s rotation disrupt the ocean’s orderly water column. In a process known as upwelling, cold, nutrient-rich water rises from the deep toward sunlit waters. There, long-buried chemicals, reunited with light, spark blooms of phytoplankton (the ocean’s equivalent of terrestrial grass) and reboot the annual growth cycle.
In the snowbound places where I’ve lived—upstate New York, New England, Chicago—even blizzards were fleeting. Snow fell and lingered but eventually melted. Marine snow keeps moving: feeding what lives below, rising again to fuel what lives above, binding the ocean, from surface to seafloor, into a single, breathing whole.
