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Iron Key Unlocks Ocean Ecosystems

September/October 1998

In 1995, oceanographers carefully released half a ton of iron into clear, lifeless waters 800 miles southwest of the Galapagos Islands. Over the next week, the electric blue sea turned green with algae and other phytoplankton. NSF-funded researchers measured a 30-fold increase in phytoplankton growth. The results were clear: In equatorial waters, plant life is limited by a lack of iron.

This was only the beginning. The iron-induced plankton bloom "drew-down" as much as 9,100 tons of carbon dioxide, connecting iron with Earth's atmosphere and climate. The experiment provided guidance for studies of iron-rich paleo-climatic records, as well as phytoplankton growth.

"The confirmation of the iron hypothesis is a paradigm-breaking discovery," says Don Rice, director of NSF's Chemical Oceanography Program. "It links many disparate fields; for example, changes in ocean chemistry lead to changes in ocean biology, which lead to more changes in chemistry, which feed back to changes in the biology and so forth."

Lead scientists Kenneth Coale and Ken Johnson, both from California's Moss Landing Marine Laboratories, estimate that about 20 percent of the world's oceans are high-nitrate low-chlorophyll like the Galapagos' waters. The lack of iron is the limiting factor to growth in these oceans.

"Life evolved in a time when iron was abundant," explains Coale. "But one of the first effects of photosynthesis was to precipitate iron out of the system." Areas once iron-rich lost minerals to the seafloor. Plants that need iron were limited to the continental margins where rivers and coastal erosion dump minerals into the sea.

As a small-scale tool, says Coale, the iron experiment is invaluable. "We need to understand how the ocean works. This is a way for us to probe the biological responses and resulting changes in the geochemistry of these ecosystems."

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