In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below. The term was first coined by the explorer William Beebe as he observed it from his bathysphere. As the origin of marine snow lies in activities within the productive photic zone, the prevalence of marine snow changes with seasonal fluctuations in photosynthetic activity and ocean currents. Marine snow can be an important food source for organisms living in the aphotic zone, particularly for organisms which live very deep in the water column.

Composition

Marine snow is made up of a variety of mostly organic matter, including dead or dying animals and plants (plankton), protists, fecal matter, sand, soot and other inorganic dust. Most trapped particles are more vulnerable to grazers than they would be as free floating individuals and can be classified as "olive green" or "gray body" cells, which are plant parts and degrading plant material. A majority of marine snow composition is actually made up of aggregates of smaller particles held together by a sugary mucus, transparent extracellular polysaccharides (TEPs). These are natural polymers exuded as waste products mostly by phytoplankton and bacteria. Mucus secreted by zooplankton (mostly salps, appendicularians, and pteropods) also contribute to the constituents of marine snow aggregates. These aggregates grow over time and may reach several centimeters in diameter, traveling for weeks before reaching the ocean floor.