Scientists are aware that iron in the ocean can play a role in reducing atmospheric carbon dioxide (CO2) through a process called iron fertilization. In 1988, oceanographer John Martin suggested that using metal fillings into the ocean could be an ideal practice for carbon capture. The basic idea is that by adding iron to certain parts of the ocean, it can stimulate the growth of phytoplankton, which are tiny marine algae.
Through the biological process of photosynthesis, phytoplankton absorbs CO2 from the atmosphere during their growth. When these phytoplankton die, they sink to the ocean floor, taking the captured carbon with them. This process effectively sequesters carbon from the atmosphere in the deep ocean, reducing atmospheric CO2 concentrations and mitigating climate change.
However, the concept of iron fertilization as a large-scale geoengineering solution to combat climate change is a subject of debate and controversy. While scientists agree that introducing iron can lead to phytoplankton blooms, it can alter the local marine ecosystem and potentially cause harmful algal blooms, which can harm other marine life. Also, the effectiveness of iron fertilization is uncertain, and the amount of carbon that can be sequestered and for how long is still a topic of research and debate.
Asked whether it’s a good idea to dump iron in the sea in order to slow climate change, Marion Fourquez, polar oceanographer at the Mediterranean Institute of Oceanography in France, said: “The answer is both yes and no, and it should not be tested again.”
Early experiments proved the “iron hypothesis” — sprinkling huge amounts of iron into the ocean — did increase algal growth. Since then, there have been over a dozen experiments in the ocean to test its impact, though these have generated controversy as the scientific consensus has solidified against the idea.
“We’ve learned that dumping iron into the ocean actually helps to absorb CO2 from the atmosphere,” Fourquez added. But she says it’s far more complicated than that. Experiments measuring how much carbon has fallen into the deep ocean from these artificial fertilisations have consistently shown that the math simply doesn’t add up.
Fourquez went on explaining the difference of natural and unnatural iron in the ocean and how the natural form of iron alone is a key factor maintaining the ecosystem’s health. “A lot of sources are a lot more efficient at stimulating phytoplankton compared to iron dumped into the ocean,” Fourquez said, referring to the Southern Ocean, where iron comes from upwelling, as well as sea ice and surface ice melt.
Fears mount as to the potential consequences of attempting to engineer the ocean’s natural cycle. “We can’t recreate the complexity of what nature offers at the moment,” Fourquez warned. Even if it’s theoretically possible to continue experimenting with iron fertilisation, Fourquez defends it’s best not to test it any more in the ocean – not for a long time, and possibly never.