July 22nd, 2012 by Michael Ricciardi
Results of the most recent iron fertilization experiment are giving scientists good reason for renewed hope in the great, global challenge of capturing carbon: A team of biologists and oceanographers, working out of the Alfred Wegener Institute for Polar and Marine Research in Germany, seeded 167 square kilometers with 7 metric tons of iron sulfate particles and were able to generate lasting phytoplankton blooms that penetrated to significant depths.
The iron fertilization technique was first proposed by marine scientist John Martin whose colleagues provided the first ‘proof of concept’ of the technique (Ironex) back in 1993, off the coast of the Galapagos Islands. However, with one exception (EIFEX), eight of the nine subsequent coastal and open ocean fertilization experiments (some using iron, some nitrogen) failed to produced lasting effects or significant results (there is also evidence of disproportionate triggering of harmful planktonic blooms). Clearly, the geoegineering technique needed serious refinement.
The solution, devised by team leader Victor Smetacek, involved finding the right oceanic environment — the right location — in which to “spew” the iron sulfide brew. Smetacek realized that this key environment was ocean eddies — whirlpools that are relatively independent from the larger, more dispersive, oceanic currents.
In these eddies*, the iron particles could remain bio-available longer, giving sufficient time for enough planktonic life to absorb them and spur on large population growth. Such iron “seeding” strategies are only worthwhile if they can trigger sufficiently massive plankton blooms — blooms large enough to be seen from space — and consequently absorb enough carbon dioxide that will sink to the bottom when the plankton die (this is referred to sometimes as carbon “draw down”).
“Give me half a tanker of iron, and I’ll give you the next ice age.” John Martin (deceased) of Moss Landing Marine Observatories, California, 1988.
Operating in the Southern Indian Ocean near Antarctica, and following a circular patch of eddying ocean, the team dispersed its load of iron sulfate (via the ship’s propeller wash system) in a total concentration amounting to .01 gm per square meter (of surface water). This concentration is equivalent to the naturally-occurring concentration of iron particles from an iceberg’s meltwater.
Following a five week period which included periodic “supplements” of the iron sulfide, experimenters found some twelve different species of diatom phytoplankton had indeed experienced sizable blooms. Amongst the species identified were Chaetoceros atlanticus, Corethron pennatum, Thalassiothrix antarcticus, and nine others, and their blooms were found at a depth of 100 meters. This depth is reassuring in that it shows that these blooms are not just superficial surface blooms.
During the third week of the experiment, the iron sulfate seeding was stopped, which choked off the diatoms growth, causing massive numbers to die off — 34 times faster than any laboratory-tested decay process. The die-off was tracked to 500 meters in depth, with at least 50% of this making it past 1000 meters and possibly to the ocean floor (at 3000 meters) in the form of mucilaginous aggregates of entangled cells and chains, or “layer of fluff.”
The team takes credit for this fluff. According to Smetacek:
“Since the aggregates sank so rapidly and the water column was more or less ’empty’ on day 50, they must have settled out. Layers of fluff have been reported from various regions, including the Southern Ocean.” [quote source]
Further measurements showed that less than 10 percent of the eddy’s water was siphoned off to the surrounding ocean, meaning that the effect was concentrated in a defined region that could be monitored, if not completely controlled.
* And not all eddies are equal, either. The team had to locate ideal water conditions; effective fertilization requires more acidic (lower pH) levels, specifically, higher levels of silicic acid which is essential for diatom growth.
The team’s research (‘Deep carbon export from a Southern Ocean iron-fertilized diatom bloom’) was published in Nature on July 19. For further reading, check out this Sci Am article.
The Future of Carbon Capture and Geoengineering
The big problem with geoengineering solutions is that because of the large scale of the effect needed they cannot be conducted in traditional laboratory settings. They must be conducted in the ‘real world’ of complex and dynamic systems, like our oceans. And that makes things more complicated, and more expensive.
Carbon Capture and Sequestration (CSS) strategies are the subject of a great deal of thought and theoretical speculation these days. Of these, the most promising seems to be those involving iron fertilization of the oceans — discounting the previous failures and potential ecological problems. Fortunately, a combination of good science, ingenuity and political will allowed development and implementation of this newest approach.
But even with this recent success story, such sequestration of carbon lasts, at best, for a couple of centuries before natural ocean recirculation brings it back to the surface (and possibly into the atmosphere). It is estimated that at most only one billion metric tons of carbon per year could be stored this way. This is maybe one eighth of the total carbon emitted each year by humans (but that is nothing to sneeze at).
Despite these limitations, the strategy is far safer than terrestrial storage (which could leak rapidly and cause mass death; see Lake Nyos, Cameroon), has great appeal and potentia,l and, is the only geoengineering strategy that has been tested in the real world to date.
Engineering algal blooms of this scale translates into more chlorophyll, more organic carbon storage, and ultimately more “sequestration” of atmospheric carbon to the bottom of the sea.
Such problems as promoting fish-poisoning plankton (or disrupting ecosystems) are being weighed against potential long-term benefits from this form of CSS. It may be that such harmful blooms are isolated and transient.
Additionally, carbon storage could be extended if these “layers of fluff” could also be buried beneath seafloor sediments. This approach will add to the technical challenge, and cost, of this sequestration strategy.
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