Voyage to ocean's 'Twilight Zone'

On a mid-January night, the Kilo Moana's floodlit deck glistens under a thin veneer of water drained from sampling bottles and dripping from nets, topped by a fine spray kicked up as the ship rides the swells.

Standing at the stern rail, Brian Guest points to foot-long squids darting just below a foam-mottled surface. The squids are looking to make meals of the fish attracted to the ship's lights.

"That's why I like working night watches," the engineer from the Woods Hole Oceanographic Institution says quietly, as he awaits the return of some sampling equipment pulled up from the ocean's depths. "You get to see so much just looking over the side."

The squids represent more than an evening's diversion, however. They also testify to the ocean's ability to draw carbon from the atmosphere and store it in the water and in its inhabitants.

As human activities pump more heat-trapping carbon dioxide into the atmosphere, researchers are trying to understand how effectively the ocean will continue to function as a long-term "safe-deposit box" for carbon dioxide. Creatures big and small - through their carbon-rich detritus that sinks to the bottom- drive most of this long-term carbon storage.

Scientists on board the Kilo Moana hope to begin the process of determining how much and how fast this material moves into deep waters or onto the ocean floor, as well as how those processes change as the climate changes.

For marine biologists and geochemists, results from the two-year project, dubbed VERTIGO, are expected to yield a wealth of insights into a little-studied layer of ocean: the "twilight zone," which ranges from 1,640 to 3,281 feet deep.

The movement through this region of carbon-rich castoffs from shallower depths is the key driver in the ocean's biological carbon pump, says Ken Buesseler, the project's chief scientist.

For climate researchers, the results are expected to help enhance computer simulations of the ocean carbon cycle and its effect on climate. More accurate simulations not only are needed to improve forecasts of climate change, scientists say, but they also could help gauge the value of controversial proposals to stimulate plankton growth on the ocean's surface. The plankton would then draw more carbon dioxide from the atmosphere for storage in the deep ocean and perhaps help slow global warming.

In June, researchers will return to this site, roughly 65 nautical miles north of Oahu, to begin more detailed studies. Then in 2005, they will move to sites near Japan.

The project comes at a time of increasing interest in the ocean's smallest, most biologically productive inhabitants and the factors that govern their survival. While surface-dwelling phytoplankton use carbon in photosynthesis, they also soak up nutrients such as iron, nitrogen, and phosphorus. So researchers are learning about the large-scale movement of other nutrients, in addition to carbon.

For example, the Southern Ocean, which rings Antarctica, has long been recognized as a rich food source for a range of local marine life. Yet a study published in the journal Nature last month and led by Jorge Sarmiento at Princeton University suggests that the Southern Ocean is the source of basic nutrients for the entire Southern Hemisphere and North Atlantic. Another "hot spot," located in the Northwest Pacific's Sea of Okhotsk, appears to play the same role for the North Pacific.

Indeed, the same processes of falling detritus that draw carbon into the deep ocean do the same for nutrients, which are redistributed by deep-sea circulation and brought back to the surface, Dr. Sarmiento says. Though not part of the VERTIGO collaboration, he suggests that data gathered from VERTIGO may also be used to track the factors that affect nutrient flows from the surface through the "twilight zone" and into the deep ocean.

The link is not lost on the VERTIGO team, which also will be trying to look at the relative speed with which carbon and nutrients move.

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