It's no snow job

Salt spray peppers Alice Alldredge's face as her little rubber Zodiac crests a wave and slides into the trough of a six-foot swell. Under a blue sky, the wind whines and yelps in 15-to 20-knot gusts across the Pacific. It makes a bumpy ride out of the 300-yard trip from the mother ship to the deep-water dive spot chosen by the marine biologist and her fellow researchers. A familiar queasiness stirring in the pit of her stomach tells her the scopolamine patches are failing. Silently she urges on the Zodiac--and prepares for the inevitable.

"She gets terribly seasick on the Zodiac in a rough sea," says Chris Gotschalk, Alldredge's research associate at the University of California at Santa Barbara and dive partner. "But she's a very determined person. She dives anyway; says she feels better in the water."

A soothing calmness awaits her only a short distance below the white-capped waves. "There's an incredible peace about floating in blue water," says Alldredge. "It's the most wonderful part of my job."

Down the weighted, depth-marked dive line swim the neoprene-clad hunters. All the scuba divers are connected by 30-foot-long white cords to keep them from wandering or venturing too far into the gloom below. At a depth of 50 feet, they fan out. Their quarry glitters in shafts of filtered sunlight all around them--the seemingly insignificant particles constantly raining from the surface, which scientist-author Rachel Carson termed the "most stupendous snowfall the earth has ever seen."

Armed with small jars and syringes, Alldredge painstakingly collects various samples of marine snow--the tiny leftovers of animals, plants, and nonliving matter in the ocean's sun-suffused upper zone. Among these particles are chains of single-celled plants called diatoms, shreds of zooplankters' mucous food traps, soot, fecal pellets, dust motes, radioactive fallout, sand grains, pollen, and pollutants. Microorganisms also live inside and on top of these odd-shaped flakes.

Marine snow consists of small and large particles found in all oceans. Under some conditions, the particles produce a blinding underwater storm. "I have seen it so thick that you cannot see more than a few feet in front of you," says Alldredge.

Until the mid-1970s, most marine scientists considered snow a nuisance, if they considered it at all. Consensus was that, except...