Victor Smetacek and colleagues at the European Iron Fertilization Experiment in the Southern Ocean  say the phytoplankton blooms triggered by fertilising iron-poor waters resulted in sinking particles - some of which they tracked - carrying at least half of the bloom biomass to below 1000 metres.

Potentially, the carbon in the microscopic phytoplankton, which die and sink, could be stored in the ocean depths for centuries. But the researchers say that it is too soon to start geoengineering to combat global warming.

Further experiments would be needed to try to get a handle on the knock-on effects on ecology and climate and how the processes that determine the composition of the environment would be affected.

The SMC contacted New Zealand experts for further comment on the research and its implications:

Dr Cliff Law, principal scientist at National Institute of Water and Atmospheric Research (NIWA), was a recipient of the 2011 Prime Minister's Science Prize for his work on iron fertilisation. He comments:

"The paper reports on an experiment that extends the observations and understanding developed from the previous iron experiments.

"As a result of longer occupation on site, and a measurement framework more focussed upon particle export than previous experiments, the authors have identified that a significant proportion of the "extra" carbon fixed by the iron-fuelled phytoplankton growth is transferred into the deep ocean.

"As this carbon will be isolated from the atmosphere for decades to centuries, the results have implications for understanding of both past and present climate change.

"That this experiment recorded a stronger phytoplankton bloom than any previous iron experiment highlights the importance of timing and location

"The 12 previous experiments to date have taken placed in different regions and shown a broad range of responses, with the lowest response recorded on the NZ SAGE experiment at the same time of year and same latitude (in New Zealand waters) as the experiment reported in Nature

"Indeed a subsequent larger iron addition experiment carried out by Smetacek et al in the same region of the South Atlantic at the same time of year in 2009 saw only a modest increase in carbon export.  So location and timing of an iron experiment is critical.

"The paper may re-open the debate around geoengineering, although the authors do not link their results to this.

"Tracking the response to iron addition is required, not only in terms of fate of the extra carbon, but also the knock-on effects such as oxygen depletion, nitrous oxide (a greenhouse gas) production, and loss of nutrients in waters that support production in other regions.

"Observation and verification of these impacts represent huge technological challenges which will require significant financial investment to support major operations. Until this is achieved and the knock-on effects proven to be minor compared to the benefits of iron-induced carbon sequestration, then iron fertilisation cannot be considered as a viable geoengineering approach".

Professor Philip Boyd at Otago University's NIWA Centre for Chemical and Physical Oceanography:

"It's 'location, location, location'.

"Not all blooms are made equal... This bloom is an end-member [an eddy] where conditions permitted a very efficient export of material to the deep ocean.

"Other blooms export much less material - such as our SERIES  bloom that CLiff Law and I led in the NE Pacific in early 2000's.  

"I don't think this changes anything in this geo-engineering debate.  

"What we need to better understand is what controls the export efficiency of different blooms".  

Our colleagues at the UK SMC collected the following expert commentary.

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

"This is an extremely interesting result and one that is sure not only to renew interest in the potential for deliberate (iron) fertilisation for sequestering fossil fuel CO2 in the future - a geoengineering proposal not only currently banned under international regulations and 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::

"The group ... 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:

"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."

 

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