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
Source: Lampit 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?