Can we do anything to reverse ocean acidification?

Up until now I have spent quite a lot of time looking at what is going on in our oceans and what is likely to happen in the future. The picture hasn’t been too rosy so far, but now I will see if there is anything we can do to combat ocean acidification or if we are just destined to disaster.  Iron fertilisation has been put forward as one of the main mechanisms that could help to reverse the acidifying trend.  Ice cores show that during past glacials iron fertilisation has occurred naturally (for example, dust storms coming from the Sahara towards the Canary islands) and has caused large amounts of CO₂ to be drawn out of the atmosphere (Lampitt et al. 2008). Put simply, it is thought that by adding iron to high nutrient low chlorophyll (HNLC) areas of the ocean it will stimulate the growth of phytoplankton blooms which will take up large amounts of atmospheric carbon dioxide and eventually deposit it into the ocean sediments (Cao and Caldeira, 2010).  There has been quite a large amount of speculation as to whether iron fertilisation will actually cause a reduction in atmospheric and oceanic carbon dioxide levels and several experiments have been run, each reaching different conclusions.  Martin was the first to propose the idea of iron fertilisation and he proposed that 1 ton of carbon added to a HNLC region could cause the sequestration of up to 100,000 tonnes of carbon. More recent, high resolution studies have suggested that iron fertilisation is far less efficient and would only result in a 10ppm reduction in atmospheric CO₂ (Lampitt et al. 2008).  The drop in carbon dioxide is only really found in the surface waters and doesn't extend deeper than about 70m (Cao and Caldeira, 2010).  Cao and Caldeira (2010) also found that even if iron fertilisation was successful by the end of the century it would only reduce the pH change by 0.06.  It is thought that iron fertilisation could produce carbon credits which would be doubly bad news for our oceans as not only would the iron do little to prevent the oceans from becoming acidic, countries would be allowed to increase their carbon dioxide emissions. Many private sector companies are already planning to enrich the ocean in order to gain carbon credits, the moderating of such activities is very difficult, especially away from territorial waters.  There are also several ecological impacts that need to be considered, it is probable that there would be an increase in harmful algae which could cause environments to become toxic.  Microbial shifts could also result in the production of other greenhouse gases such as DMS and methane, both of which are far more potent than carbon dioxide.  Due to monitoring difficulties it is also hard to know if plankton blooms could cause the carbon dioxide to be taken into the deep ocean and sediments.  Iron fertilisation initially sounds like a good idea and some believe that it could cause a large reduction in atmospheric CO₂. There are wide scale ecological effects that could result And the actual reductions in ocean pH and carbon dioxide levels are very low.  More work needs to be done to work out the potential side effects of iron fertilisation and to develop a greater understanding of the movement of carbon dioxide to the ocean sediments.

References

Cao, L. Caldeira, K. (2010). ‘Can ocean iron fertilization mitigate ocean acidification?’, Climatic change, 99, 1-2, 303-311.

Lampitt, R. Achterberg, E. Anderson, T. Hughes, J. Lucas, M. Popova, E. (2008). ‘Ocean fertilisation; a potential means of geoengineering’, Philosophical transactions of the royal society A, 366, 1882, 3919-3945.