As long as there has been marine life, there has been marine snow — a ceaseless drizzle of death and waste sinking from the surface into the depths of the sea.
The snow begins as motes, which aggregate into dense, flocculent flakes that gradually sink and drift past the mouths (and mouth-like apparatuses) of scavengers farther down. But even marine snow that is devoured will most likely be snowfall once more; a squid’s guts are just a rest stop on this long passage to the deep.
Although the term may suggest wintry whites, marine snow is mostly brownish or grayish, comprising mostly dead things. For eons, the debris has contained the same things — flecks from plant and animal carcasses, feces, mucus, dust, microbes, viruses — and transported the ocean’s carbon to be stored on the seafloor. Increasingly, however, marine snowfall is being infiltrated by microplastics: fibers and fragments of polyamide, polyethylene and polyethylene terephthalate. And this fauxfall appears to be altering our planet’s ancient cooling process.
Every year, tens of millions of tons of plastic enter Earth’s oceans. Scientists initially assumed that the material was destined to float in garbage patches and gyres, but surface surveys have accounted for only about one percent of the ocean’s estimated plastic. A recent model found that 99.8 percent of plastic that entered the ocean since 1950 had sunk below the first few hundred feet of the ocean. Scientists have found 10,000 times more microplastics on the seafloor than in contaminated surface waters.