Wednesday, 23 December 2015

Ocean Fertilisation: an enhancement of ocean productivity

1. Ocean Fertilisation Function

This blog aims to assess a CDR geoengineering process, known as ocean fertilisation.  The ocean captures CO2 naturally from the atmosphere in two ways.  The first way involves the ‘solubility pump’, where CO2 is dissolved in seawater due to ocean circulation (Lampit et al 2008).  The second way is the ‘biological pump’, where the production of a phytoplankton plant absorbs CO2 through photosynthesis (Rayfuse et al 2008).  This process will be the focus of this study as the solubility pump is unable to undergo artificial enhancement.

Martin discovered, that adding iron to seawater produces massive algal blooms, which increases CO2 absorption by photosynthesis (Factor 2015).  George (Factor 2015) suggested that enhancement of the biological pump could absorb more CO2 from the atmosphere, as it is an increasing climate change problem.  Hence, the artificial adding of iron in the ocean is known as ocean fertilisation.  Factor (2015) gives a historical context of the trials undertaken for ocean fertilisation, ranging from small laboratory scale processes to large-scale 10,000km2 of ocean experimentation.

Once iron is added to the ocean, an algal bloom is formed, making the ocean a pea green colour.  This algal bloom absorbs CO2 and sinks to the bottom of the sea, below the ocean circulations, where there is no interaction between CO2 and the atmosphere (Lampit et al 2008).  It may take millions of years for this CO2 to resurface (Figure 1). This is a relatively cheap process, Stinger suggests it would cost $2.50 per ton of carbon, whereas, Markerls and Barbier suggest $2 per ton of carbon (Factor 2015).  Hence it may be conceived as a relatively effective process.  However there are many negative side effects that may occur.

Figure 1: Ocean Fertilisation Representation
Source:  MotherJones

2. Side Effects

2.1 Anoxia and Eutrophication

As there is an increase in algal bloom, this creates an excess of iron macronutrients, hence causing eutrophication.  This causes the algal bloom to expand and grow and decreases the biological diversity of the fertilised oceans (Lampit et al 2008).  This is a great concern as eutrophication causes a lack of oxygen ventilation in the ocean and causes anoxia and mortality of marine species (Lampit et al 2008).

2.2 Ocean Acidification

Ocean pH was relatively stable at pH levels of around 8 to 8.3 prior to the industrial revolution.  However, since then the oceans have become more acidic due to the increased levels of CO2 in the atmosphere (Lampit et al 2008).  An increase in algal bloom, will absorb more CO2 and has the potential to make the oceans more acidic.  This occurs due to higher concentrations of CO2 collected in the oceans.  This increases species mortality or forces populations to shift to less acidic oceans (Lampit et al 2008).

2.3 Global macronutrient Balance

Another concern is the increasing input of iron macronutrients to enhance CO2 absorption.  This may redistribute other essential macronutrients in the ocean.  Hence, a lack of nutrients in the oceans may lead to fishery degradation, leading to economic concerns.  Additionally, the marine biological productivity of an area will degrade, as some areas may not have enough nutrients (Lampit et al 2008).

2.4 Modification of global iron balance

It is suggested that iron cannot be applied to surface waters for long periods of time and lasts in oceans for only a few months.  Hence, a, continuous addition of iron micronutrients is required (Lampit et al 2008).  Therefore, questioning the degree of effectiveness that ocean fertilisation will provide in reducing CO2 emissions. 

2.5 Other climate-relevant gases

Moreover, global warming is not only caused by an increase in CO2 levels.  There are various gases that have an impact on global warming, including methane, nitrous oxide and ozone (Lampit et al 2008).  Hence, if algal blooms absorb CO2, they unfortunately have the potential to increase methane levels due to a decrease of oxygen ventilation in the oceans (Table 1).  Hence, this questions to what degree this will reduce the radiative forcing of climate change impacts on Earth.

Table 1: Gases and aerosols affecting the radiative force of the Earth and their potential changes with ocean fertilisation
SourceLampit et al 2008

2.6 Decreasing economic and social sustenance

Changes in the ocean ecosystem can cause a decline in fisheries. Fisheries provide food and economic sustenance for approximately 1.3 billion people.  Hence having social and economic impacts (Lampit et al 2008).  Controversially, ocean fertilisation supporters will argue that an enrichment of CO2 will help fisheries to increase yields.  This may occur as an increase in algal bloom may provide more food for fish species and hence increase their populations.  However, there is great uncertainty on what may happen to fisheries, as computational models have been relatively poor in predicting changes in the community (Lampit et al 2008).  Furthermore, indirect impacts on fisheries need to be assessed as there is a potential of fish communities shifting.

2.7 Benthic Biota

Lastly, it is suggested that only 4% of CO2 absorbed by the oceans is able to sink to the deep ocean and stay there for millions of years.   For this process to be successful, benthic biota are essential (Lampit et al 2008).  Benthic biota, are the organisms that sink to the bottom of the ocean to form sediments. However, with ocean fertilisation, it is probable that benthic biota will decrease in abundance as it is related to the organic matter of the euphoric zone (Lampit et al 2008). Furthermore, most oceanic regions consist of medium to low benthic matter, hence questioning the degree of productivity that ocean fertilisation can provide without the availability of benthic matter (Lampit et al 2008).  Therefore, it is questionable to what degree ocean fertilization will be successful due to its reliance on benthic matter to sink CO2 in the deep ocean without any environmental interactions.

3. Conclusions

I believe when assessing the side effects of oceanic fertilisation, it underlines many probable risks.  Ocean fertilization decreases social and economic benefits and can degrade marine ecosystems.  Furthermore its effectiveness is questionable.  Therefore, I believe ocean fertilisation should not be implemented as it will not be an effective geoegnineering process.  What do you think?


  1. Hi Maria! An excellent review of a geoengineering technique that I too am very sceptical of! I feel that not only could it have potential negative effects such as eutrophication, but I am doubtful of how effective it would actually be for removing carbon dioxide from the atmosphere - the oceans are vast and dynamic, so the algae and benthic biota could just be washed away... What scale would this have to be implemented on to actually make a difference? I feel like any testing that would have been done would be on a much smaller scale than that needed to remove enough carbon dioxide from the atmosphere to counteract climate change.

  2. Hi Shruti! Thank you for your comment and a very good question! Due to ocean fertilisation being assessed at large scales yet not being implemented as a real process, it is hard to say an actual number (in terms of area) required for ocean fertilisation to make a difference. Ocean fertilisation has been experimented with a scale of 10 000km2 and scientists suggest that a larger scale is required to have the desired output. I agree with you that the testing of such geoengineering processes are always smaller than what is needed. In the case of ocean fertilisations, from what I understood, they are thinking of very large areas (more than a few thousands of km2). Moreover, due to not being a process that has been implemented in the world for long periods of time, this may vary highly compared to computational oceanic models. I hope this answers your question!

  3. A very interesting review of ocean acidification! As both of you and Shruti mentioned, I agree that the degree of effectiveness of the geoengineering technique is very unclear. Since we do not fully understand the biochemical interaction in the ocean yet (and I doubt it will ever be), I don't think we should go ahead with it. I guess storing CO2 in biotic components such as algae makes sense to bring the atmospheric CO2 back into the soil as we have been withdrawing energy from the fossilized materials. However, the rate of replenishing the fossil is way slower than it is being consumed. So, my question is, even if we decide to implement any of the above techniques you have discussed, who should decide where and how much particles to be released? Although it is slightly a more political question, I look forward to hearing from you soon!

    1. Hi Satomi! Thank you for your comment. I agree ocean fertilisation has more negative impacts than positive impacts. It is very hard to decide who decides where and to what degree to use geoengineering in general. Any nation can simply decide that they will use a geoengineering method and nobody can stop them really. However, I believe they could make an organisation similar to lets say the united nations where all countries participate with the consultation or participation of a specific scientists representing each country to decide on whether a geoengineering process could be used. You are more an expert on the politics of various nations. I am wondering, do you have a suggestion of how geoengineering processes can be handled?

  4. I am completely unconvinced by this geoengineering technique - it definitely seems to do more harm then good! Is it seriously being considered by some scientists as a viable CDR technique? Do you think it would be implemented anywhere? I wonder - as the ocean is so dynamic, would this technique have transboundary implications? As in, if a country bordering another decided to use it, do you think the neighbouring country would be negatively effected due to loss of fishing stocks etc?

    1. Hi Celia thank you for your comment! I completely agree with you! I think bordering countries will definitely be affected. Due to the oceans circulating, no matter how fast iron fertilisation sinks to the bottom of the ocean, not all will be able to sink fast enough and the oceans will be impacted, hence influencing neighbouring countries also. I believe fish yields will definitely decrease or be negatively affected due to ocean acidification that may occur from other countries in the nearby area of this process. I hope this answers your question :) On a positive note, enhanced weathering is a process that may actually decrease human induced ocean acidification so feel free to check it out :)