“Give me half a tanker of iron, and I’ll give you an ice age”

Iron fertilisation of the oceans is by no means a modern idea. It works through dumping extremely large quantities of iron filings into the ocean which act as a catalyst to the production of phytoplankon blooms. These phytoplankton are photosynthetic and consequently sequester CO₂ from the atmosphere. However, this is by no means as simple as the late John Martin makes it sound when he famously made the remark that i have used in the title of this post (Oceanus).

So far 12 iron fertilisation experiments have been completed and most have unequivocally concluded that iron is in fact the main limiting factor controlling phytoplankton biomass in the worlds oceans (1). One of the most influential of these is the Southern Ocean Iron RElease Experiment (SOIREE) which took place in November 2000. Through artificial supply of iron within small experimental areas the levels of primary productivity and consequent chlorophyll-a concentrations were seen to rise significantly (from 48-56 to 231 mg Chl-a m²) (Gervais et al.)

    

                                                   Satellite image of a phytoplankton bloom

But it’s not all good! There are many unanswered questions and concerns which are hindering iron fertilisation from taking the leap from mesoscale experiments to macro-scale implementation.

• Much of the phytoplankton bloom is swiftly consumed by zooplankton and the carbon sequestered makes its way up the food chain and through decomposition makes it’s way back into the atmosphere.
• Changes in the foundations of the food chain could affect fish stock (maybe for good....maybe not)
• The bloom will not only consume iron but also significant amounts of nutrients. This is likely to work as a limiting factor in the growth of plankton populations down current of the ‘fertilised’ area
• Algal blooms will block light from penetrating the deeper water which could affect corrals and benthic plankton. 
• Decomposition of phytoplankton might also starve oceans of oxygen and could increase inputs of CH4 into the atmosphere

“You might make some of the ocean greener by iron enrichment, but you’re going to make a lot of the ocean bluer”    Robert Anderson

In 2009, an article in Nature cast further gloom on the concept as a viable option in the fight against climate change. It concluded that the extent of carbon sequestration was considerably lower than previously thought and on the most part only a short term effect. Plankton that sink to the seabed can act as a CO₂ sink for millions of years but more commonly it only remains in middle waters where it will only be stored for a couple of decades at most (Pollard et al., Bowie et al.). 

IRON FERTILISATION : RISKY, EXPENSIVE AND TEMPORARY

For the time being at least, I believe that the risks involved are far to great to warrant the implementation of what may only be a temporary solution to a very permanent problem

If anyone is particularly interested in this then might I suggest reading the article by Boyd et al. (2000). It gives a very in depth overview of SOIREE, the ‘iron hypothesis’ and all the different responses to artificial inputs of iron into the ocean.