(Fe)rtilisation: Fantasy or Fear?

"Give me half a tanker of iron and I will give you an ice age' (Martin, 1988)

Stated John Martin at the Woods Hole Oceanographic Institution lecture in 1988. By this, he was referring to the proposed geoengineering method of iron fertilisation. Although previously touched upon, this post will concentrate on understanding how it works and assessing its future viability.

Between 1993-2009, 13 small iron fertilisation studies were carried out in a range of oceanic environments with the sole purpose to determine if phytoplankton growth in the surface ocean was limited by iron availability. Interestingly, none of these studies were designed as geoengineering trials. However, all projects concluded that biological production across a range of oceanic regions is limited by iron shortages (Williamson, 2012). In each case, the addition of iron increased phytoplankton biomass which led to reduction of CO2 levels in surface waters, thus promoting CO2 drawdown from the atmosphere (Watson et al, 2008). Although the magnitude of carbon sequestration varied amongst experiments, all indicated that levels were insignificant in achieving an offset for anthropogenic carbon production.

A simple explanation of how iron fertilisation works with the best and worst case scenario for its outcome (Source:http://bloggie-360.blogspot.co.uk/)

During these investigations a range of side-effects were noted and now form part of the argument against iron fertilisation as a viable geoengineering option.

The Fear:

1. Production of Climate-Relevant Gases:

Currently, there are uncertainties about unwanted production of nitrous oxide and methane gases as a spin-off effect of iron fertilisation. Although research on this matter remains sparse, studies by Jin & Gruber, 2003 show small increases in both gas levels following iron addition. These gases have warming potentials of 320 and 20 times greater than CO2 respectively. Therefore, if release occurs, this can completely offset any carbon sequestering occurring from the fertilisation itself.

2. Ocean Acidification:

Although a reduction of atmospheric CO2 levels will contribute to reduced acidification of the ocean surface, the issue is simply relocated rather than solved. Cao & Caldeira, 2010 found that further CO2 sequestration in the deep ocean can cause increased acidification of ocean interior waters, possibly degrading the habitat of benthic, shell building organisms due to a lack of bio-minerals.

3. 'Nutrient Robbing':

This term was first coined by the Royal Society in (2009) and refers to downstream changes occurring from ocean fertilisation. The Royal Society suggested that the iron additions in open oceanic waters can lead to reduced productivity around islands and nations that may not be partaking in the fertilisation activity. This leads to issues of governance and can result in conflict between countries. Furthermore, the biodiversity losses from this can be severe and result in the extinction of a large number of marine species.

4.  Anoxia:

Due to increased photosynthesis, there will be a decrease in oxygen availability. Where fertilisation is over large areas, there can be widespread oxygen depletion and even regions with anoxic waters. Chan et al, 2008 suggests that the rate of mortality of marine organisms following this could be catastrophic.

5. Toxin Production:

Trick et al (2010) discovered, through a range of shipboard experiments, that phytoplankton producing the toxin domoic acid can increase in abundance following iron fertilisation. In addition to this it was found that their rate of toxin production increases in fertilised conditions. This toxin is said to accumulate in shellfish and when eaten can be fatal to all predators, including humans.

A natural phytoplankton boom off the coast of Argentina. Will this be a more common sight in the future? (Source: http://www.whoi.edu/oceanus)

Conclusion:

In my opinion, iron fertilisation is a fantasy with too many uncertainties to be implemented as a carbon management method.  Where field experiments have been conducted, it has shown potential in reducing atmospheric levels but the magnitude at which it works is too small to make a significant difference. The side effects are severe and under-researched to justify large scale study of this method. Therefore, although an interesting idea on paper, iron fertilisation should not be considered when designing a geoengineering approach to manage climate change.