An eight-year German research effort has shown that under the right conditions seeding the ocean with iron can trigger phytoplankton blooms that suck carbon out of the air and trap it deep in the ocean, a potentially important breakthrough in the nascent field of climate geoengineering. Reporting in the journal Nature, scientists from the Alfred Wegener Institute for Polar and Marine Research said that adding 14 tons of iron sulfate to the Southern Ocean near Antarctica resulted in a significant phytoplankton bloom extending more than 300 feet deep. That bloom consisted of large masses of algae, mainly composed of diatoms, which absorbed carbon dioxide from the atmosphere. More than 50 percent of the carbon-rich algae then sunk to a depth of more than 3,000 feet, where it is likely to be trapped for centuries. The German research team conducted the iron-seeding experiment in 2004 and then spent eight years analyzing the data. Previous iron-seeding experiments have had difficulty tracking the path of CO2 pulled out of the atmosphere because of swirling currents and other complications. But the Wegener team said its experiment had succeeded because scientists found a 40-mile-wide column of water that was isolated from other ocean currents.