There is snow at the bottom of the ocean. Submersible cameras trawling the depths capture scenes reminiscent of winter nights: endless black, punctuated with picturesque drifts of swirling white flakes. But what looks like frozen water is really anything but. Marine snowflakes are made up of tiny bits of dead animals, molted shells, and poop—all of which becomes a banquet for the multitudes of still-living creatures lucky enough to be snowed on.
For a very long time, people assumed that nothing could survive in the deepest parts of the ocean. Without sunlight, there could be no phytoplankton, and without phytoplankton, what would form the bottom of the food chain? When naturalists began dredging the sea floor in the mid-1800s, they found that the barren landscape they envisioned was actually crawling with critters.
The mystery of the food chain remained. What were these animals eating? The stomachs of dissected deep-sea animals contained a few smaller animals, but were mostly filled with sticky sludge. What was this sludge, and how had it reached those depths?
Answers began rolling in during the 1970s, when the first-ever deep-sea sediment trap was recovered from the bottom of the Sargasso Sea. The trap’s contents revealed specks of decaying plant and animal matter, fecal pellets, mucus, and shells. But each speck of garbage was tiny. How could they sink to such great depths? By sticking together.
Let’s Stick Together
Each speck might start off on its own, but as it sinks through the water column, it gloms on to others like it, growing heavier and heavier, and gaining velocity as it falls. Passing fish and marine mammals eat these clumps and poop them out again, adding even more bulk and weight and hastening the smooshy snowflake’s descent. Flakes that would have taken years to sink alone—if they sank at all—can touch down in a matter of weeks.
Marine snow is resourceful but indiscriminate, and will aggregate with anything that bumps into it. Earlier this year, scientists learned that the higher-than-average marine snowfalls in the Gulf of Mexico were likely due to the 2010 BP oil spill. With more sticky material—in this case, oil—to build around, marine snowflakes were falling even more quickly than usual.
Manna from Heaven
Marine snow is a hugely important food source for sea floor residents. By the time it reaches the black, a snowflake is a tidy package of carbon, calcium, and other, er, recycled nutrients. Baby eels, for example, are completely dependent on marine snow during their four-month larval stage. They won’t eat anything else, which has presented quite a challenge for the scientists trying to start eel farms.
But the mushy marine snow is more than just baby food. Vampyroteuthis infernalis, the "vampire squid from hell," may look like a killer, but it’s actually quite content to snarf snowflakes. The vampire squid has even evolved special sticky filaments, which work almost like a spider web, trapping falling particles of marine snow in what has to be the laziest hunting ever. Once its filaments are full, the squid squeezes them through its arms to collect the goodies. It envelops its catch in a juicy glob of mucus, then eats the parcel whole.
Not every snowflake gets eaten. Those that don’t will join their predecessors, settling into the thick blanket of sludge that blankets the ocean floor.