Marine Snow

Marine Snow (Plagiarised from Wikipedia):

In the deep ocean, Marine Snow is a continuous shower of mostly organic debris falling from the upper layers of the water column. Its origin lies in activities within the productive photic zone. Consequently, the prevalence of marine snow changes with seasonal fluctuations in photosynthetic activity and ocean currents. Thus marine snow is heavier in spring, and the reproductive cycles of some deep-sea animals are synchronized to take advantage of this. Marine snow has a composition which includes: dead or dying animals and plants, fecal matter, sand, soot and other inorganic dust. The “snowflakes” are aggregates of smaller particles held together by a sugary mucus, transparent exopolymer particles (TEPs); natural polymers exuded as waste products by bacteria and phytoplankton. These aggregates grow over time and may reach several centimetres in diameter, travelling for weeks before reaching the ocean floor..

Basically, when you are down at The Bottom, Marine Snow is the shit which rains down on you. The amount, and the size of the shit depends on the season.