SILVER wants to know what role snow plays in transferring nutrients into the deep sea. The abundant life below the surface requires sustinence, she says, but "we really don't know how [food] gets into the deep sea."
     Thanks to researchers like Silver, though, we do know that marine snow is likely a major food source for life in the abyssal deep.
     Marine snow forms when plant and animal detritus floating about in the ocean sticks together. The binding substance is mucus, which ocean dwellers make a lot of. The mucus glues together scraps of crustacean shells, remnants of plants, and excrement of animals. The particles are all different shapes and denser than the surrounding ocean, but have many cavities.
     And while the particles have to be at least one-half millimeter in diameter to be considered snow, they can grow to be quite large, on the order of feet. But since the snow is fragile, the large marine snow grows only in calm waters.
     The construction of a good snow particle requires a nucleus--a solid chunk of sticky matter to serve as the basis for the growing particle. A common base for snow in the open ocean is the cast-off houses of the giant larvacean, a small, tubelike hemichordate (which is not quite an invertebrate and not quite a vertebrate) that weaves a chambered house around itself. The chambers collect food for the larvacean nestled within--so effectively, in fact, that a larvacean must drop its house up to four times a day and start again. The released houses shelter living bacteria and plankton and collect other matter on their way downward.
     Another starting point for snow--especially common in the Monterey Bay--is a colony of diatoms. These single-celled algae build walls of opal (a type of silica), and some species can form long chains. When the colonies grow old and die, they "get goopy," Silver explains. Goopy clumps are perfect for collecting dead organisms and waste.
     The turbulence of the water drives the formation of snow and determines the ultimate size of the particles. "Intermediate" turbulence favors snow growth by bumping the particles into each other. Too much turbulence, however, fragments the flimsy aggregates, Silver says.
     Small sea creatures swimming through the snow also influence the size of the particles. Alice Alldredge, a professor of marine biology at the University of California, Santa Barbara, studies how some marine organisms, such as the centimeter-long shrimp-like krill, break up the snow into smaller particles. She wants to understand the relationship between the turbulence caused by various krill activities--like swimming and eating--and the size of snow particles. If krill swimming can affect the size of snow, then perhaps other marine organisms can as well. Ultimately, the size of the particles determines how much of it reaches the bottom of the ocean.

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