As plants and animals near the surface of the ocean die and decay, they fall toward the sea floor, just like leaves and decaying material fall onto a forest floor. In addition to dead animals and plants, marine snow also includes faecal matter, sand, soot, and other inorganic dust. The carbon pump.

The decaying material is referred to as "marine snow" because it looks a little bit like white fluffy bits. The "snowflakes" grow as they fall, some reaching several centimetres in diameter. Some flakes fall for weeks before finally reaching the ocean floor.