A while ago, maybe a decade or so, some people got together and came up with an idea to help reduce the amount of carbon dioxide in the atmosphere. They knew that Phytoplankton, microscopic plant organisms in the Ocean, absorb carbon dioxide through photosynthesis. They figured that if they could increase the amount of Phytoplankton in the Ocean, then it would decrease the amount of carbon dioxide in the atmosphere. They could increase the population of Phytoplankton by fertilizing the Ocean with iron. A good idea right? In theory, yes.
However, when you apply this theory you can get a big mess. Let’s take the Mississippi River, US for example. The Mississippi River runs from Minnesota and cuts south through the midwest until it empties at the tip of Louisiana into the Gulf of Mexico. While it runs through the midwest, the massive river accumulates nutrients from various sources such as farms and waste water treatment plants. The nutrients are emptied into the Gulf of Mexico. In the spring, the Mississippi River flows higher and faster from the extra rainfall and deposits more nutrients into the Gulf. Phytoplankton absorb the nutrients and the population explodes. The phenomenon is called a Spring Bloom and it occurs in most places around the world. There is a larger bloom in the Gulf during the Spring because there are more nutrients (nitrates, phosphates and iron), which help the Phytoplankton grow.
What does the abundance of Phytoplankton have to do with everything? Well, phytoplankton sink to the bottom of the Ocean when they die. Bacteria eat the plankton and absorb oxygen in the process. Animals need oxygen in the water to live. A large bloom such as the one that occurs every spring at the mouth of the Mississippi can cause an oxygen depleted zone at the bottom of the Gulf of Mexico with very little life and very low biodiversity.
Let’s get back to the iron fertilization. If we fertilize the Ocean with iron, phytoplankton will increase in abundance and they will absorb carbon dioxide; however, the plankton will eventually die, sink to the bottom, and be eaten by bateria which use up the oxygen (oh and I forgot to mention that the product of eating the plankton is methane, a compound worse than carbon dioxide when released into the atmosphere).
To summarize, an increase in phytoplankton can cause a large dead zone at the bottom of the Ocean and release methane into the atmosphere. So to pose the question again: Is fertilizing the Ocean with iron a good thing for climate change? I don’t think so.