Marine snow is a continuous shower of organic material drifting from the ocean’s upper layers to the deep sea. This phenomenon resembles a gentle snowfall, appearing as white, fluffy bits suspended in the water. While visually similar to terrestrial snow, marine snow is a diverse collection of particles, not frozen water.
Formation and Composition
Marine snow forms from a variety of organic and inorganic materials that aggregate in the water. Its primary components include dead or decaying plankton, such as phytoplankton and zooplankton, along with fecal pellets from marine organisms. These aggregates also incorporate other debris like mucus secreted by zooplankton, sand, dust, and even soot. The composition can vary based on location, depth, and seasonal changes in ocean productivity.
The aggregation process often involves sticky, gel-like substances called exopolymers, which are natural polymers exuded by microorganisms like phytoplankton and bacteria. These exopolymers act as a binding agent, causing smaller particles to clump together and form larger aggregates. This clumping increases the size and density of the particles, which helps them sink faster through the water column. Marine snow aggregates can grow to several centimeters in diameter, and their formation is often enhanced during phytoplankton blooms.
Role in Ocean Ecosystems
Marine snow serves as a food source for organisms living in the deep ocean. This continuous rain of organic matter provides nutrients and energy for a wide array of deep-sea life, from bacteria and filter-feeding invertebrates to larger animals. Many deep-sea creatures, such as sea cucumbers and brittle stars, rely on marine snow as their primary source of nutrition.
The sinking of marine snow is a mechanism for transporting organic carbon from the surface waters to the deep ocean, a process known as the biological carbon pump. This process helps regulate Earth’s climate by sequestering carbon dioxide from the atmosphere into the deep ocean, where it can be stored for hundreds to thousands of years. Annually, the biological pump transfers approximately 10.2 gigatonnes of carbon into the ocean’s interior. Marine snow also contributes to nutrient cycling by carrying elements like nitrogen and phosphorus to deeper waters, which can then be released and recirculated.
Journey to the Deep
As marine snow forms in the sunlit surface waters, it begins its descent through the water column. While some particles can fall for weeks to reach the ocean floor, larger and denser aggregates sink more rapidly. During this journey, a substantial portion of the marine snow is consumed or broken down by microbes, zooplankton, and other filter-feeding animals in the upper 1,000 meters of the ocean. This consumption recycles nutrients and carbon within the water column, supporting diverse marine communities throughout various depths.
Despite consumption during its long fall, a considerable amount of marine snow eventually reaches the seafloor. There, it accumulates and forms a layer of organic-rich sediment, often called “ooze.” This sediment nourishes benthic (bottom-dwelling) organisms, providing a sustained food supply. The deposition of marine snow contributes to the formation of sedimentary layers that can preserve historical records of ocean conditions.