In 2004, a team of scientists traveled by ship to an enormous whirlpool in the ocean near Antarctica. Their goal was to find out if a risky strategy for fighting climate change might work. The plan: Dump iron in the water to trigger the growth of organisms called algae. Then let the algae soak up carbon dioxide, a gas that contributes to global warming. Finally, watch to see if the organisms drift to the seafloor. This iron fertilization of algae
appears to have been successful,
an international team of
researchers reports in the July 19
issue of Nature. Algae indeed
removed carbon dioxide from the
atmosphere, then sank deep into
the ocean. Some scientists still
aren’t sure if iron fertilization is a
good idea, but this study is one
step toward showing that the
tactic for fighting global warming holds promise.
Climate change is a major problem facing the planet. As cars and factories release gases such as carbon dioxide that trap heat, Earth slowly warms. Rising temperatures can melt glaciers and ice sheets, causing sea levels to rise. Some plants and animals may go extinct if they can’t adapt to a warmer world.
One way to solve this problem is to cut the amount of carbon dioxide released through human activities. But it would also help to suck some of the extra carbon dioxides out
of the atmosphere.
Iron fertilization is one method that scientists have proposed to do so.
If people add iron to the ocean, the thinking goes, more algae will grow. After sucking carbon dioxide out of the atmosphere, these algae may eventually sink and carry that carbon to the ocean floor. Once the carbon is at the bottom of the ocean, it could remain buried there for centuries.
Other experiments have shown that the first part of the process works — that adding iron promotes the growth of algae, which then removes some carbon from the atmosphere. But scientists have had a hard time proving that this carbon later sinks, rather than just reentering the atmosphere again.

To test the second part of the process, the research team dumped the iron powder into a whirlpool in the Southern Ocean. Because the whirlpool traps material instead of letting it drift to other parts of the ocean, the scientists could more easily track the carbon.
Sure enough, a giant bloom of algae called diatoms grew. Diatoms are tiny organisms with a shell of a hard material called silica. After a few weeks, many of the diatoms died.
The researchers collected water samples at various depths to monitor the organisms. Much of the dead diatom mass sank 1,000 or more meters, and a lot of it probably reached the bottom of the ocean. The team calculated that more than half of the carbon absorbed by the diatoms probably also sank to the seafloor.
Iron fertilization is not a perfect solution. The researchers’ experiment removed only a tiny fraction of the carbon dioxide released through human activities each year. And iron fertilization might put other organisms in danger by increasing levels of algal poisons in the ocean.
Key Terms
algae A large group of organisms ranging from meters-long seaweeds to single-celled microorganisms. Most algae are photosynthetic, meaning that they use light and carbon dioxide to make sugar and oxygen.
diatom A microscopic type of algae with a shell of a hard material called silica.
carbon dioxide A gas made of one carbon atom and two oxygen atoms.
fertilization The addition of chemicals that encourage growth.
Questions:
1. What is the problem?

2. What is the hypothesis?

3. What is the independent variable?

4. What is the dependent variable?

5. Was the hypothesis correct?

6. Why is iron fertilization not a perfect solution?