Ocean fertilisation for carbon capture

For this blog post I am going to look at the concept and implementation ocean fertilisation for carbon capture as a form of geo-engineering to reduce carbon levels in the atmosphere – one of the key greenhouse gases that is causing climate change.

So what exactly is ocean fertilisation? Ocean fertilisation refers to the adding of iron or other nutrients to the ocean at a large scale to enhance algal growth in order to increase the uptake of atmospheric CO2. When the algae die, they sink to the sea bed, taking the carbon with them and storing it in the deep ocean. This would benefit the planet as a reduction in atmospheric CO2 would reduce the amount of heat reflected back to Earth thus reducing or reversing the current trend of a warming planet. In order to boost this algal growth, nutrients such as nitrogen (N), phosphorous (P) and iron (Fe) could be added to the ocean waters to stimulate this growth and thus trigger the uptake of more Carbon Dioxide. Figure 1 below shows the biological pump, the process by which carbon dioxide is transferred between the atmosphere and the ocean. Stimulation of this cycle with nutrients is the purpose of ocean fertilisation.

Figure 1: The Biological Pump

One major question with regards to the implementation of ocean fertilisation is the feasibility of it. A study from 2014 looked into the feasibility of ocean iron fertilisation in the Southern Ocean using simulations with a Global Climate Model. This paper concluded that the Southern Ocean would be one of the best areas of ocean iron fertilisation worldwide which could have a noticeable effect on atmospheric carbon dioxide levels. In addition to this, other studies have involved data from a Southern Ocean-Iron Experiment (SOFeX). From this research, ocean fertilisation is a geo-engineering method that is difficult to achieve as the amount of iron required and the frequency to achieve the level of carbon sequestration (uptake of carbon by oceans) that is necessary to influence the climate is difficult to achieve. There are suggestions that commercial ships could deposit iron along the major shipping routes but these ships would be unable to carry the amount of iron needed.

The concept of ocean fertilisation sounds promising but there are a number of other drawbacks that need to be considered. One of the key concerns is ocean acidification. Carbon is a key cause of ocean acidification and by using ocean fertilisation, the oceans would be taking in more carbon, lowering the pH of the water. This can have severe consequences of marine wildlife and coral. In addition, there is a problem known as outgassing which refers to the fact that not all the carbon transferred to the deep ocean will remain there. Carbon is returned to the surface through ocean upwelling and evaporation transfers it into the atmosphere. One piece of research, found that within 100 years, around two-thirds of the carbon transferred to the deep ocean by ocean fertilisation returns into contact with the atmosphere because it is redistributed through the world’s oceans. This emphasises the fact that ocean fertilisation is not a long-term geo-engineering solution unless it is sustained. The process of ocean fertilisation is also slow and therefore it may not be the solution necessary to quickly react to anthropogenic climate change. The use of ocean fertilisation can also reduce oxygen levels in the ocean. This can lead to a loss of marine wildlife and a reduction in biodiversity because they are not well adapted to low oxygen (anoxic) waters. This can kill fish which has a knock on effect for commercial farmers.

So is ocean fertilisation a suitable Geo-Engineering solution? On the surface, ocean fertilisation seems to be a reasonable method of addressing the effects of climate change at a small scale. It is possible to implement quickly and effectively, and at relatively little cost. However, when looking at this method in greater depth, it is clear that there are a great number of problems with it and the suitability of this technique is questionable. In my own personal opinion, I do not feel that ocean fertilisation is the best possible geo-engineering as it is slow, has relatively little effect on global climate and has a number of negative environmental impacts that are difficult to avoid. The focus should be on protecting current ecosystems not destroying one to save the others.