A neutrally buoyant sediment trap is lowered into the waters off Hawai'i from the research vessel Kilo Moana. The device drifts on the deep currents as it collects organic particles that sink toward near-perpetual storage on the ocean floor. KEN BUESSELER | Woods Hole Oceanographic Institution   Foraminifera are single-celled marine organisms that form a shell around their tiny bodies. MARY WILCOX SILVER | UC Santa Cruz

Researchers are using an intricate sediment trap that drifts on the deep currents as it collects the falling "snow." After several days, the device, which has been called a "Twilight Zone Explorer," rises to the surface and reports its position to a satellite, so that a ship can come and collect it.

Initial results, reported in the April 26 issue of the journal Science, have been surprising: The efficiency of this natural carbon-storage system varies dramatically in different parts of the ocean. In the nutrient-deprived waters off Hawai'i, very little carbon makes it to the ocean floor, while near Japan, roughly 2.5 times as much does.

A team of international scientists, including University of Hawai'i oceanographers Robert Bidigare and Dave Karl, have been working to determine how efficiently this "oceanic biological pump" shoves carbon deep into the ocean — since that could be critical to understanding how the planet naturally locks up excess carbon. This, in turn, is key to understanding how our planet responds to rising levels of carbon dioxide in the atmosphere.

A CLOSER LOOK AT THE 'BIOLOGICAL PUMP'

The researchers used their "explorer," also called a neutrally buoyant sediment trap, in the waters north of O'ahu at a research site called Station ALOHA, and in the western Pacific off northern Japan at a site called K2.

Karl said the "biological pump" works like this: Carbon dioxide from the atmosphere dissolves in the ocean, where tiny marine plants — phytoplankton — use it during photosynthesis. The stored carbon moves up the food chain as microscopic animals — zooplankton — feed on the plants, and bigger animals in turn feed on them. Eventually, fin fish eat those creatures. But during this process, some material is lost. Dead marine plants, fecal pellets and other aggregates of organic matter sink through the water column.

As this marine snow drops to several hundred feet below the surface, there is no longer enough light to support photosynthesis and it can continue sinking unless bacteria or other deep sea creatures consume it.

MARINE 'SNOW' DIFFERENT IN ISLES, JAPAN

In studying the contents of the marine snow, scientists have found that there are fundamental differences between the microscopic oceanic life off Hawai'i and off Japan. In the northern waters, the marine organisms are bigger, as shown by a marine snow dominated by the fecal matter of shrimps and small animals called copepods, Karl said. Off Hawai'i the snow is so fine that it's difficult to determine its source, and there is far less of it.

Karl said that may be the result of differences in oceanic nutrients — more nutrients mean bigger creatures, and that's why the fishing grounds off continental areas are richer than those off isolated islands like Hawai'i. And because there is so little nutrient availability around Hawai'i, marine life has become extremely efficient at using what's available, he said.

"These are the most efficient systems on the planet. Everything is hungry, everything is waiting for food, and when it is produced, it gets consumed," he said. With little waste, there's not much lost to the marine snow, he said.

"There is very little storage" of carbon in Hawai'i's warm waters, he said.

For the scientific community, the research shows that oceanic carbon movement is more complicated that previously thought, and that there is no simple way to model the amount of carbon that the oceans lock up.

"We can't just use a simple relationship to model the global ocean," Karl said. "We need to refine our models, and we need to caution our policy makers."