to open a new window into the difficult-to-explore twilight zone. They successfully used a wide array of new tools, including an experimental device that overcame a longstanding problem of how to collect marine snow falling into the twilight zone. The problem is that particles sink slowly, perhaps 10 to a few hundred meters per day, but they are swept sideways by ocean currents traveling many thousands of meters per day. To collect sinking particles, scientists use cones or tubes that hang beneath buoys or float up from seafloor. That, Buesseler said, "is like putting out a rain gauge in a hurricane." Buesseler and WHOI engineer Jim Valdes developed Neutrally Buoyant Sediment Traps (NBST)-free-floating devices that sink to a programmed depth within the twilight zone and neither sink nor rise. They are swept along with the currents for several days, collecting particles, and then programmed to resurface, transmit their position via satellite, and wait for recovery, more than 10 to 20 miles away from where they were dropped into the ocean. "It's a bit like finding a needle in a haystack, since they are so small and difficult to spot, especially in rough seas that are common in the open ocean," Valdes said. On their first scientific mission for VERTIGO in 2004, Buesseler and Valdes could only wait and hope their devices would work. "Seven NBSTs went in the water and all seven came back with their precious cargo-a first in ocean sciences history," Buesseler said. Why more carbon reached the depths in the northwest Pacific might be due to many factors. Waters there are full of silica that plankton incorporate to make shells. Do the silicaladen plankton weigh more and thus sink faster, giving bacteria less time to break them down? Do lower water temperatures in the northwest Pacific slow down the breakdown of organic carbon? Do different populations in the food webs at different sites change how organic matter is broken down and marine snow is produced? Scientists will continue to explore these regional differences in the ability of carbon to reach the deep sea. In June, Buesseler and colleagues head to Bermuda to examine seasonal changes in the rain of carbon through the twilight zone. They will repeatedly sample at a single site, using a new and improved NBST called the Twilight Zone Explorer. www.seadiscovery.com Marine Technology Reporter 21
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