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John also realized that the iron limitation could be caused by the limited delivery of iron-carrying atmospheric dust to these waters. He further reasoned that the differential availability of iron between past glacial and interglacial periods could have played a role in regulating the productivity during those periods, and therefore in regulating climate.

So that's where this now-famous quote--"Give me a half a tanker of iron and I'll give you the next Ice Age"--came from. John recognized the potential coupling between iron and climate through marine productivity. He said this at a lecture in Woods Hole, where I just happened to be. I remember very clearly the reaction of the audience, which was a non-reaction. I mean, people chuckled, but nobody had any idea that this was the moment, really, when it all began.

Well, soon after John made that statement, the press and the broader scientific and engineering community got interested in this idea. Suddenly, it became clear to some people that maybe you could actually intentionally fertilize the oceans to regulate climate. This became the subject for an article in Discover magazine, which triggered a whole series of articles. A lot of oceanographers, and limnologists who had spent their careers studying the effects of nutrients on lake ecosystems, started to get very concerned about the momentum of the idea. They had spent their careers studying the effects of nutrient enrichment on aquatic ecosystems, and had been trying to reverse the consequences of anthropogenic eutrophication of lakes and coastal waters.

imageThis is a picture of an experimental lake area in Canada, in which a lake in its natural state is shown next to one that has been intentionally fertilized to study the effects of nutrient enrichment on food webs. The results of these and other studies have sown that nutrient enrichment of lakes and coastal waters from sewage and fertilizer runoff cause undesirable algal blooms in these ecosystems. Because of this we have gone to great efforts to reverse nutrient input into lakes, and create buffer zones to take up the nutrients before they run off agricultural lands into river systems and coastal waters.

 

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So these and other environmental concerns about ocean fertilization triggered a symposium in 1991 where a group of oceanographers and limnologists gathered to talk about the evidence for iron limitation of the oceans and the potential and risks of using this knowledge for to try to regulate climate. The results of that symposium were published in a special issue of the journal of Limnology and Oceanography, and it culminated in this resolution: "That iron fertilization is a scientifically uncertain mitigation measure to reduce rising CO2 levels. It would likely, at best, postpone the impending climate change by a few years." This statement was based on computer modeling efforts in which the entire Southern Ocean was fertilized with iron for 100 years, such that all of the available N and P were used up and converted to organic carbon. The group concluded, therefore, that "Ocean fertilization should not be considered as a policy option that significantly changes the need to reduce CO2 emissions."

So that was the resolution back in 1991. The other outcome from that symposium was generate interest in the iron hypothesis. It became clear that doing some very small-scale fertilization experiments in the ocean would be very useful in helping us understand not only what regulates productivity in ocean ecosystems, but also the changes in climate during glacial/interglacial transitions.

imageThree such experiments have been done, unequivocally proving that iron does limit productivity in the Equatorial Pacific and the Southern Ocean. Kenneth Coale will describe the results of those experiments, and Dave Karl will then discuss the biological details and all of the uncertainties involved in the 'biological pump'.

The experiments have proven that this is a powerful new approach to oceanography, which for the first time allows us to manipulate the food web so we can better understand how it works. They have also shown us how very small amounts of a nutrient can trigger major changes in the ocean ecosystem. Finally, they have catalyzed interest in ocean fertilization as a carbon sequestration tool.

imageThere are many reasons to worry about what this type of technology might do, not only to the marine ecosystem, but also to other regulating mechanisms in the climate system.

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