The implications and impacts from ever increasing greenhouse gases emitted into our atmosphere are profound. It is the responsibility of scientists and policy makers to find methods of reducing these emissions and increasing the worlds carbon sinks. The oceans are one of the largest natural carbon sinks in the world, absorbing around 30-50% of anthropogenic emissions per year. With this in mind, scientists have come up with a way of potentially enhancing the amount of carbon that can be sequestered by the ocean by using iron to increase the amount of photosynthesis that occurs in surface waters. This method is known as iron fertilisation.
What is the Iron Fertilisation hypothesis?
Some areas of the world oceans are known to be rich in nutrients but have very little growth. In the late 1980’s Scientist John Martin claimed that iron was a limiting factor in growth in these areas and by adding iron he could stimulate phytoplankton growth in surface oceanic layers (Buesseler et al. 2003). Phytoplankton use carbon dioxide during the process of photosynthesis, therefore, by adding iron to oceanic waters and increasing the phytoplankton growth, this would also increase the amount of CO2 absorbed through the oceans.
What evidence supports the hypothesis?
John Martin needed to prove that iron was a limiting factor in phytoplankton growth. He studied the depth profile of iron throughout the oceans and found that iron acted in the same way as nitrogen and phosphorus, both micronutrients. It has a high surface depletion, indicating that something is taking it out of the surface waters; furthermore iron is regenerated at depth due to bacterial decomposition. This signifies that iron is a micronutrient and can be a limiting factor from growth.
Twelve oceanic iron experiments were carried out to test whether iron enrichment would increase primary productivity in areas of high nutrients but low productivity (Boyd et al. 2007). Buesseler and Boyd (2003) studied three experiments all with locations in the southern ocean. They stated that all of the experiments produced noticeable increases in biomass and associated decreases in dissolved inorganic carbon and macronutrients. Powell (2008) also reported that all 12 experiments reported up to a 15 fold increase in chlorophyll content in the surface of the oceans.
The 12 experiments verify that iron enrichment does enhance primary productivity in high nutrient but low chlorophyll areas of the oceans and therefore iron has a fundamental role in photosynthesis.
However, very little work has been carried out to test whether the amount of carbon taken up in the surface waters during these experiments has been transported down throughout the water column, and sequestered into the seafloor or deep layers of the ocean. If this process is not completed then the carbon will re-emerge later in a different location.
What are the impacts of iron fertilisation?
Iron fertilisation is a popular notion in carbon sequestration as it has been portrayed as a cheap, fast and easy way to mitigate climate change. However uncertainties and doubts regarding this method of geo-engineering have increased dramatically since John Martin first came up with concept.
So far only 12 small scale experiments and computer models have been used to predict the impacts and benefits of large scale long term iron fertilisation. While this is a fairly risk free process of assessing the costs and benefits of this method of carbon sequestration, it by no means can replicate the effects of a large scale experiment.
Creating large scale phytoplankton blooms could change the balance of the oceans food chains and could increase the number of large predators including fish, jellyfish and algae concentrations. The increase in fish and commercially available food could lead to an increase in the world’s fisheries. However some phytoplankton blooms are toxic and could therefore be harmful to the whole food chain, including human consumption.
The fertilisation of the oceans could cause deficits in oxygen or nutrient in far removed areas of the ocean, due to the oceanic circuits. Areas that have been enriched with iron months or even years previously will be lacking in nutrients as they will have already been consumed.
The UN Convention on Biodiversity states that precautionary action must always apply in the face of uncertain consequences. This applies to iron fertilisation experiments in the oceans, and it is now forbidden for any iron enrichment to take place within a countries coastal waters. Furthermore the London Protocol against marine pollution could also apply to the input of dissolved iron as the consequences of this are still mostly unknown.
According to Boyd (2008) the costs of iron fertilisation have been severally underestimated. The amount of carbon that can be absorbed by iron fertilisation in the long run has greatly decreased over the past 20 years by 5-20%. Especially when compared to the amount of fossil fuel emissions that are emitted into our atmosphere, iron fertilisation alone, can be considered to make little difference to the greenhouse gas effect.
Conclusion
Iron fertilisation is an interesting concept of geo-engineering and is successful at drawing carbon out of the atmosphere in short periods of time. However the impacts of large scale experiments, or even the commercialisation of iron enrichment to reduce the effects of climate change, are largely unknown and high in risks. It is unlikely that iron fertilisation will ever occur to the scale that will achieve significant impacts in aiding the efforts to reduce the amount of greenhouse gases in the atmosphere. However, every little does help in terms of reducing these gases, especially carbon dioxide so why not have a look at our tool to help you consider your footprint?
References
Buesseler, K. et al. (2008) Ocean Iron Fertilisation –Moving Forward in a Sea of Uncertainty. Science Vol: 319. P: 162
Powell, H. (2008) Will Ocean Fertilisation Work? Oceanus Magazine. Vol: 46. P: 10-13
Boyd, P. (2008) Implications of large scale Iron fertilisation of the Oceans. Marine Ecology Progress series. Vol: 364. P: 213-218.
