Since the 1980s, Smetacek has taken regular expeditions from his home port of Bremerhaven to the Southern Ocean aboard the sturdy icebreaker Polarstern. He goes to study the plankton that fill the sea from top to bottom, extending even into the sediments of the sea floor. Plankton is our planet’s most prolific life form, and the food it generates makes up the base layer of the global food chain. . . .Smetacek's trials seem to show that his method works: adding iron sulfate to the ocean leads to an increase in plankton, some of which drops to the ocean floor, taking carbon with it. But this is hugely controversial:
That these tiny creatures could affect such massive change is not as unreasonable as it sounds. Much of the oxygen we breathe comes from just one species of cyanobacteria, Prochlorococcus. This species was not even discovered until the 1980s: it is so tiny that millions can fit into a single drop of water and no one had produced a sieve small enough to catch it. The oxygen made by these tiny marine plants dwarfs that produced by the Amazon rainforest and the rest of the world’s woodlands combined. By taking in CO2 and exhaling oxygen, these tiny creatures serve as the planet’s lungs, whose steady breathing is limited only by nutrition. . . .
And yet, environmentalists – the very people who care the most about climate change – were outraged by Smetacek’s project, and tried hard to stop it. A subsequent research cruise in 2009 was held up by international outcry before being permitted to execute a limited follow-up study. Environmental activists stoked fears about unknown side effects. Some worried the iron could lead to a toxic algal bloom, like those that have poisoned sea lions and other sea life off the coast of California. Others floated the possibility that the experiment could lead to a dead zone, like the one created each summer by the algal bloom in the Gulf of Mexico, where the fertilisers that support Midwestern cornfields gush out of the Mississippi river’s mouth and into the ocean. When that algae dies, other microbes consume the corpses, using up all the available oxygen in the surrounding waters. When the oxygen shortages hit, fish flee, but slower-moving sea life such as crabs and worms suffocate and die in droves.All of these fears are legitimate: we really don't know what would happen if various amounts of various mixtures of iron were added to the sea. Which is why, I think, we ought to keep experimenting. How else are we going to find out?