The poster-child of global warming, apart from the hockey-stick graph is melting ice-mass, be it bergs, or sheets on Greenland (named so, because it once was a lush and verdant land) or the Antarctic peninsular. However, in a twist of irony has emerged a new discovery that when this ice melts, tiny particles of iron are released , leading Professor Rob Raiswellfrom Leeds University to comment, "The Earth seems to want to save us." Personally I doubt the Earth gives a toss about us, but the finding does emphasise the intricate and interconnected manner of nature, and that by tampering with one aspect, she may respond in an altogether unexpected way through another mechanism.
Schemes have been proposed before to deliberately dump vast quantities of iron filings into the ocean as a nutrient to promote the growth of phytoplankton, which through photosynthesis might sequester billions of tonnes of CO2 from the atmosphere as a carbon capture strategy, and if when these algae die they are harmlessly dumped onto the ocean floor (and stay there!) this might become a viable and extensive approach to carbon sequestration - i.e. locking up that carbon for centuries to millennia. There are many issues in the negative to be addressed, including the dubious influence of so much adventitious iron on natural ecosystems etc. For the algae to flourish, it is necessary that there be sufficient of other nutrients, mainly nitrogen and phosphorus, present to form the body of what is effectively plant material in a water-borne environment.There is also research that indicates that less carbon is transferred to the sea-bottoms during a period of luxuriant algal growth than during more fallow periods .
However, in the light of the discovery of a natural source of iron from melting ice, the decision has been taken to "mimic nature" by adding several tons of iron sulphate to the ocean off South Georgia (which remained British after the war with Argentina in 1982), taking the view that this is part of the natural CO2 regulation mechanism that has been functioning for millions of years within the waters of the Southern Ocean, which are relatively isolated from other sources of iron. I note as a small aside, the idea that desertification may actually act to force algal growth in the oceans, since the drying land turned to wind-blown dust, rich in iron, can act as a natural fertiliser for ocean phytoplankton, and so perhaps we have another feedback defence mechanism that is switched-on by global warming.
The aim of the experiment (to be begun next month) rests on some pretty spectacular figures. Since the Southern ocean covers 20 million square miles (about 50 million square kilometers) it is reckoned that if all of it could be treated with iron, the resulting algae (covering all of it???) would remove 3.5 billion tonnes of CO2, which is equivalent to one eighth of all the emissions that can be blamed on humans for inconsiderately burning fossil fuels of various kinds.
I shall watch this with interest, but I can imagine that the usual scale-up problems will prevail, even if it does look promising. I estimate that the full implementation would need around 90 million tonnes of iron to be dumped into the ocean. Presumably this would be an ongoing strategy, say dumping 9 million tonnes/year for 10 years. It is not clear what effect this might have on other forms of life there including fish and there is the matter of what to do with all that algae, which would severely attenuate the influx of light much beyond the surface.If the algae doesn't sink as hoped, because say of that "leaky biological pump" , it may well rot on the surface and produce methane rather than CO2, which has 100 times the global warming potential of CO2.
I am always uneasy over tampering with nature, especially on the large scale - as we may have already done with CO2 and various other unnatural additions to the environment. Indeed there may be some natural symbiosis between ice and CO2 which cycles over far longer timescales than those over human civilisation can be measured, and perhaps there are buffers to making rapid change e.g. to carbon levels that we are as yet unaware of. Whatever we do, I am sure that nature will "sort the planet out", but it may take thousands of years and not be too interested in whether there are still humans around to witness her wonders or not.