Scientists run into a problem while trying to create a phytoplankton bloom in the ocean in order to gobble up or sequester some of the excess carbon dioxide (a greenhouse gas) produced by people.

Furthermore, in related news, scientists have found that a “warming climate is changing the numbers and composition of phytoplankton—the base of the food web—along the western shelf of the Antarctic Peninsula.” Declining plankton blooms and diversity could have disastrous impacts on Antarctic wildlife, because phytoplankton are the foundation of the food chain in the ocean. If this foundation is disrupted or weakened, then it causally impacts everything else up the food chain. From the Economist.com:

The growth of phytoplankton is kept in check by the amount of sunlight available for photosynthesis and the supply of crucial nutrients such as iron. In the Southern Ocean, iron is indeed often the limiting nutrient. As a result, when iron levels increase naturally (for example when a dust storm dumps large amounts of it into the sea) giant blooms of phytoplankton can suddenly appear. Previous studies have shown that adding iron artificially can also create algal blooms. The expedition’s researchers wanted to find out how many of the extra algae end up on the sea bed.

Those researchers, led by Wajih Naqvi and Victor Smetacek, created a bloom of phytoplankton by fertilising an area of 300 square kilometres with six tonnes of iron sulphate, which dissolves in water. In two weeks the bloom’s mass doubled. But it also proved to be extremely tasty for small crustaceans called copepods, which gobbled the phytoplankton up so quickly that even with further iron fertilisation the bloom stopped growing. As a result, only a small amount of CO2 was dispatched to the ocean floor.

The problem lay with the species of phytoplankton in the bloom. In previous experiments the blooms had consisted of a group of algae known as diatoms. As diatoms have shells made of silica they are protected from copepods and so are more likely to die without being eaten and thus take take their carbon to the ocean floor. But in the area where the researchers were working natural blooms had already depleted much of the silicic acid, which the diatoms use for shellmaking. The result was that the beneficiaries of the iron were instead groups of algae such as Phaeocystis, which are among the most heavily grazed by copepods.

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