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expert reaction to new research on iron fertilisation

Nature published a paper suggesting carbon could potentially be transported to the bottom of the ocean, and stored there, by sinking microscopic phytoplankton following iron fertilization.


Professor John Shepherd, Chair of the Royal Society’s Geoengineering the climate report, said:

“The Royal Society’s 2009 report on geoengineering concluded that iron fertilisation was likely to have only a relatively small capacity to sequester carbon and would be likely to have unintended and probably deleterious consequences. Whilst the new research is an interesting and valuable contribution in this evolving field, it does not address the potential ecological side effects of such a technology and it still just a single study in what is a poorly understood field.

“It is important that we continue to research these possible technologies but governance of this research, through projects such as the Solar Radiation Governance Initiative, is vital to protect the oceans, wider environment and public interests. The successful management of this research experiment vindicates the strategy by the London Convention that seeks to prevent large or uncontrolled experiments or deployment, whilst allowing useful small scale field experiments.”


Prof Andrew Watson FRS, Royal Society Research Professor at the University of East Anglia, said:

“Victor Smetacek and his colleagues report an ocean iron fertilization experiment that resulted in a big export of carbon to the deep ocean.

“Previous experiments have not been able to show that. However, the carbon buried in the deep sea in this experiment came from the surface ocean, not from the atmosphere. It’s quite unclear how much, if any, was removed from the atmosphere, but it would be too small to affect the amount of CO2 there unless fertilization was carried out on a very large scale and over a very long time.

“This experiment helps us understand why CO2 might have been lower in the ice ages – when for thousands of years the iron supply to the oceans from atmospheric dust was increased – but artificial iron fertilization would not be a very effective way to combat modern climate change.”


Prof Andy Ridgwell, Professor in Earth System Modelling at the University of Bristol, said:

“The authors have obtained direct evidence for efficient and rapid carbon export to the deep ocean when stimulating phytoplankton growth with the nutrient iron. This is an extremely interesting result and one that is sure not only to renew interest in the potential for deliberate Fe fertilization for sequestering fossil fuel CO2 in the future – a geoengineering proposal not only currently banned under international regulations but previously assumed to be an inefficient way of sequestering carbon – but also in the understanding of past climates.

“Exactly why atmospheric CO2 concentrations during the last glacial were approximately one third lower than the current interglacial average is still hotly debated. The results of this study hint at a greater importance for higher glacial dust (and iron) fluxes to the surface ocean in strengthening the ocean carbon pump and hence in lowering atmospheric CO2.”


Dr Michael Steinke, Lecturer in Marine Sciences at the University of Essex, said:

“This article by Victor Smetacek and his co-workers provides the very first evidence of a man-made conduit between the increasingly CO2-burdened atmosphere and the deep sea. Like plants on land, the photosynthetic floating phytoplankton of the sea take up CO2 at the ocean’s surface and, once they die, sink to the bottom of the sea where much of this material is buried in the deep sediments for hundreds of years. This transfer of CO2 assists with cooling our climate and keeping temperature at a level to facilitate life on our planet.

“The group embarked on a 5-week research cruise in 2004 and managed to add 7000kg of iron fertilizer to just the right part of the Antarctic Ocean to stimulate phytoplankton growth, increase the uptake of CO2 from the atmosphere and, crucially, demonstrate that at least half of this material disappeared into the deep sea. Several other scientific experiments tried this before but the oceanographic conditions were such that the CO2 from the decay of phytoplankton was transferred straight back into the atmosphere so that no additional cooling was produced from fertilising the sea.

“Will this open up the gates to large-scale geoengineering using ocean fertilisation to mitigate climate change? Likely not, since the logistics of finding the right spot for such experiments are difficult and costly! Of the twelve fertilisation experiments of this kind carried out since 1993, many showed the desired increase in CO2 drawdown from the atmosphere but this group’s experiment is the only example to date that demonstrates the all-important carbon burial in the deep sea sediments, away from the atmosphere.”


Dr Dave Reay, Senior Lecturer in Carbon Management at the University of Edinburgh, said:

“If the 50% figure for algal bloom biomass sinking to the deep ocean is correct then this represents a whole new ball game in terms of iron fertilisation as a geoengineering technique. Maybe such deliberate enhancement of carbon storage in the oceans has more legs than we thought but, as the authors acknowledge, it’s still far too early to run with it.”

‘Deep carbon export from a Southern Ocean iron-fertilized diatom bloom’ by Victor Smetacek et al., published in Nature on Wednesday 18th July.

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