Ocean Iron Fertilization: Is pumping iron the answer?

From land based geoengineering to ocean based geoengineering. You may remember four years ago when Russ George, the American businessman labeled a ‘geo-vigilante’, released 100 tonnes of iron sulphate into the ocean, contravening UN regulations and making headlines. Russ worked with indigenous Canadians to fertilize the plankton with the intention of boosting the ecosystem and to take out carbon from the atmosphere. This is ocean iron fertilization (OIF).

OIF works on the fact that phytoplankton in the surface ocean use macronutrients (e.g. phosphorus and nitrogen) and micronutrients (e.g. iron) to convert carbon into biomass, which then sink out of the surface layer. This is the ‘biological pump’ which acts to remove inorganic carbon from the atmosphere to the ocean. OIF releases iron in oceanic ‘high-nitrate, low chlorophyll (HNLC)’ areas where the biological pump is not working at full capacity because it lacks iron. Therefore, the increased iron stimulates the growth of phytoplankton in the surface layers of the HNLC areas and the phytoplankton remove more carbon dioxide from the air. The general idea is summarised in the video, which is advertising a ‘container floater’, a particular way of releasing iron into the oceans.



Part of the biological pump (Whoi, 2015)

I have shown similar video clips in earlier blog posts. However, I find statements such as ‘it can be stopped at any time ’rather misleading. On my geoengineering journey there has emerged a common theme of uncertainty surrounding the impacts and OIF is no different with large uncertainties surrounding the reversibility of any large scale OIF.  

Feasibility

The study by Zeebe and Archer (2005) outright dismiss large-scale OIF as a feasible solution. They used models based on small scale experiments to work out the amount of OIF required to reduce atmospheric CO₂ by 15 parts per million (ppm) by 2100. Their scenario has global CO₂ concentrations set at 700ppm, which is considerably higher than the 400ppm now and the predicted 450ppm of a 2^oC warmer world, so their calculations may be a stretch. They suggest all of the world’s HNLC areas would have to be fertilized 15 times a year until 2100 to achieve -15ppm. This would require a minimum of 5,500 chemical tankers transporting an average of 10,000 tonnes each. However, Aumount and Bopp (2006) suggest double this amount of CO₂ removal could be achieved if the oceans were fertilized year round, rather than 15 times per year.



Global carbon dioxide concentrations in relation to a future scenario, data derived from Zeebe and Archer (2005) and Tollefson (2015) 

Consequences

Despite Zeebe and Archer (2005) dismissing OIF methods, further investigations have still gone ahead with 12 major experiments to date. Oschlies et al (2010) have identified OIF could in fact lead to increases in other greenhouse gases, such as nitrous oxide (N₂0) and methane (CH₄), if not implemented properly. N₂0 is a greenhouse gas 300 times more powerful than CO₂ and CH₄ is 12 times more powerful than CO₂. They suggest that more of these gases could be released from the Southern Ocean (the ‘best’ region for OIF) because the increased organic matter from the phytoplankton bloom increases remineralisation and methane producing bacteria, releasing more N₂0 and CH₄ respectively. It is suggested that this effect could be reduced to an equivalent loss of 15% efficiency, if implemented properly, which would still make the overall method useful.

Oschlies et al. (2010) also highlight the issue of permanence. In the video above OIF is referred to as a ‘natural way to reduce CO2’. Although I would argue that dumping millions of tonnes of anything into the ocean is unnatural, it is enhancing a natural process where iron (e.g. in dust) enters the ocean and causes a planktonic bloom. However, Oschlies et al (2010) identify that the ocean can take carbon out of land sinks as well as the atmosphere because it is a ‘natural’ process. This could mean up to 8% of the extra carbon taken up by the ocean is not from the atmosphere because of changes in the carbon cycle.

What's more, they suggest that stopping OIF would result in carbon being lost to the atmosphere. Aumount and Bopp (2006) take this idea even further and suggest OIF would have to be implemented continuously to avoid carbon being re-released to the atmosphere. Therefore, if this occurred in the tropics, the combined effects of N₂O release and re-release of CO₂ could result in a loss of greenhouse gas emissions equivalent to those taken out by OIF. Despite these impacts, Oschlies et al (2010) do not dismiss the idea of OIF, rather they stress the importance of modelling the global impacts and implementing OIF in the right areas.

Aside from the climatic consequences of OIF there would clearly be huge implications on marine ecosystems, for instance, increasing ocean acidification. Nutrient robbing is also cause for concern, especially if only selected regions are fertilized. This results in the targeted area boosting productivity to such an extent that it ‘robs’ other areas of nutrients such as nitrogen and phosphorus, resulting in decreased biological productivity elsewhere.

Ocean acidification cartoon (Water-Is-Life, 2013)

I’ve surprisingly found myself siding with Zeebe and Archer (2005). I don’t think the predictive removal of CO₂ is enough to warrant risking the negative effects to get to the 2^oC climate target. I understand that every little helps but if we reach 700ppm, a reduction of 15 ppm is not going to make a huge difference and it certainly is not going to get us to 2^oC.