Article Summary: 'Who ate all the algae?'

Article: Who ate all the algae?

Date: March 26^th 2009

Publisher: The Economist

URL: http://www.economist.com/science/displaystory.cfm?story_id=13361464

It seems that scientists are willing to try most anything these days in order to reduce carbon dioxide (CO₂₎ in the atmosphere. One of these attempts at reducing CO₂ is a joint project, the largest geo-engineering experiment ever, being conducted by India’s National Institute of Oceanography and the Alfred Wegner Institute for Polar and Marine Research in Germany. It is an expedition that consists of pouring 6 tons of iron sulphate into the Southern Ocean, an area surrounding Antarctica, to create a bloom of phytoplankton.

Phytoplankton is a type of algae that depends on certain conditions, such as sunlight (for photosynthesis) and iron (a crucial nutrient). Increases and decreases in iron levels in the Southern Ocean, that normally occur naturally, therefore play a role in determining the size of the phytoplankton population. Tests have shown that adding iron artificially creates algal blooms. One advantage of creating these blooms is that phytoplankton absorbs CO₂ as it grows and locks up small amounts of the gas when it dies and sinks to the ocean floor. Therefore, in theory, creating large blooms of phytoplankton would lead to more CO₂ being sent to the bottom of the ocean.

However, first results of this experiment have shown that there are certain factors that hinder its success. Though the iron sulphate that was poured into the water, covering an area of 300 km², did lead to the creation of a phytoplankton bloom that grew to double its size within 2 weeks, the bloom eventually stopped growing since it was being eaten by copepods (small crustaceans). The problem was the type of phytoplankton; the bloom consisted of a group of algae called Phaeocystis, which are heavily grazed by copepods. Diatoms, another group of algae, are protected from this by shells made of silica and therefore are more likely to die and sink to the ocean floor than get eaten. Had this type of algae been present, the results regarding CO₂ absorption would have been better.

The results suggest that the experiment won’t be as successful in removing CO₂ from the atmosphere as had been expected; however, this has given researchers a lot of material to work with. So maybe it wasn’t all for nothing after all.