Ocean fertilisation....a viable approach?

Hey all,

So while we have looked at Geoengineering approaches aimed at reducing the amount of short wave radiation absorbed by the earth, other options include increasing the amount of long wave radiation emitted from the earth, through capturing and storing carbon!

Thanks to Viv’s lecture, the scientific basis for this post, has been provided. However, we will do a quick overview!

The carbon cycle is made up of a series of stocks and fluxes. Currently, the stock of CO₂  in the atmosphere is increasing, this is trapping increasing amounts of longwave radiation and causing temperatures to rise. Therefore, to increase the amount of longwave radiation emitted from the earth rather than trapped, CO₂  needs to be removed/transferred to other stocks.

The ocean is a large carbon sink. The Northern Hemisphere and Southern Hemisphere oceans store on average 2.2GtCyrˉ¹. Through the concept of the biological pump, shown in Figure 1, CO₂  is dissolved in the oceans and taken up by phytoplankton through the process of photosynthesis. When these organisms die, the organic carbon is transported to the sea floor.

Figure1:

Two decades ago, scientists realised that the amount of CO₂  absorbed by phytoplankton , and transported to the deep oceans could be enhanced by adding  iron, which is often a limiting nutrient for growth (Raven and Falkowski, 1999).  Numerous experiments have since been conducted in regions where waters are replete with light and  major plant nutrients, yet phytoplankton stocks are low. Several examples of these regions are shown in Figure 2.

Figure 2:

Although most experiments show noticeable decreases in dissolved inorganic carbon, carbon sequestration, whereby particulate organic carbon sinks to the ocean floor is limited. Once absorbed by the algae, only minimal amounts of carbon are sequestered while the rest is recycled back into the atmosphere. Several studies question whether iron fertilisation would make any significant reductions to the stock of CO₂ in the atmosphere. (Zahriev, et al., 2008; Martin, et al., 1994; Busseler, et al., 2004). Buesseler and Boyd (2003) estimate that the sequestration of the 30% of the carbon produced by human activities would require an area larger than the Southern Ocean. Consequently, more research is needed to determine the perfect conditions that may allow optimal carbon sequestration. However, there is a growing concern over scaling up experiments. Ocean ecosystems are still poorly understood in comparison to terrestrial ecosystems, tampering the food chain could lead to a domino of undesired impacts e.g. De-oxygenated waters, depletion of vital nutrients, all of which would severely affect fish stocks (Davis, 2006).