Marine snow is a continuous descent of organic and inorganic marine particles from the upper layers of the ocean to the deep seafloor. This phenomenon appears as a shower of white, fluffy bits against the dark backdrop of the deep ocean, resembling snowfall. The term “marine snow” was coined by explorer William Beebe, who observed this phenomenon from his bathysphere. It is a pervasive feature throughout the world’s oceans.
What Sea Snow is Made Of
Sea snow is composed of a diverse array of organic and inorganic materials. A significant portion consists of dead or dying microscopic marine organisms, such as phytoplankton and zooplankton. These tiny plants and animals are primary producers and consumers in the ocean’s sunlit surface waters.
The composition also includes fecal matter produced by various marine organisms, contributing nutrient-rich particles to the mix. Discarded larval casings, decaying animal bits, and organic debris like mucus secreted by zooplankton (such as salps and appendicularians) also become part of the aggregate. Inorganic components like dust from land, sand, and silt get incorporated, adding to the density of the particles.
How Sea Snow Forms and Sinks
The formation of sea snow begins with smaller, dispersed particles in the upper ocean clumping together. This aggregation process is facilitated by sticky extracellular polymeric substances (EPS), which are natural polymers exuded primarily by phytoplankton and bacteria. These sticky substances act as a glue, binding various organic and inorganic components into larger aggregates.
Once these aggregates grow sufficiently large and dense, they begin their descent through the water column. While the journey to the deep ocean can take weeks, larger, denser particles sink faster than smaller, less dense ones. This process transports material from the sunlit surface waters, where photosynthesis occurs, towards the aphotic zone below, which lacks sunlight.
Ecological and Climate Significance
Sea snow serves as a primary and continuous food source for organisms inhabiting the deep ocean, an environment devoid of sunlight where primary production is impossible. Deep-sea creatures, including bacteria, various invertebrates like sea lilies and brittle stars, and fish such as halibut, filter these falling particles from the water or scavenge them from the seafloor. This constant supply of organic matter forms the base of the deep-sea food web, sustaining a diverse range of life in otherwise dark and nutrient-scarce conditions.
Beyond its ecological role, sea snow plays a significant part in regulating Earth’s climate through its contribution to the “biological carbon pump.” This process transports carbon from the surface ocean, where carbon dioxide is absorbed from the atmosphere, to the deep ocean and seafloor. As organic matter in sea snow sinks, it carries carbon with it, sequestering it away from the atmosphere for potentially hundreds to thousands of years. Estimates suggest that the ocean’s biological pump removes around 10-20 petagrams of carbon per year from the atmosphere, with sea snow accounting for a substantial portion of this carbon export.