Apparently if you dump powdered iron into the ocean, it turns into fish food over night:
Iron Into Fish
In July they spread the iron additions over a week's time. The result was described by Kenneth Coale, one of the scientists, as "like driving through the Mojave Desert and coming on a rain forest." It turned the ocean into green soup! "The oceanographers watched in awe as the R. V. Melville plied Pacific waves dyed a soupy green by a bumper crop of tiny ocean plants. ... Only a day before, this patch of water near the Galapagos Islands had sparkled with electric blue clarity, a quality owed to the general absence of ... phytoplankton."
[...] A rough and ready calculation suggests that catching 10 tonnes of fish removes about a pound of iron from the ocean. Have fishermen been "mining" the oceans for iron all these centuries, as farmers mined their soil of minerals before widespread use of fertilizer? Would supplying iron restore historical levels of fishery productivity? Would it boost productivity far beyond anything in history?
If a normally cruising boat can fertilize one-half square kilometer per hour (say an area 50 meters wide by 10 kilometers long), the application rate would only have to be about a pound of iron per hour. It would add only trivially to the cost of running a boat. If iron fertilization became routine practice among fishermen, lesser rates might be needed.
Iron Into Fish
Tags: doomed, mad science
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There's actually an article about this in last months Scientific American.
The Ocean's Invisible Forest (By Paul G. Falkowski)
It's an interesting piece, focusing more on phytoplanktons ability to clean CO2 from the air than the fact that fish eat it.
Incidentally, quite a lot of minerals are being returned to the ocean through fertilizer seepage into watersheds. This leads to lots of weird stuff happening with the "lower" forms of life, who tend to you know, breed until they kill everything around them in the water. Oops.
That article said that the phytoplankton (plants) eating CO2 is counteracted by the zooplankton (animals) who sprout up to eat the plants, so the O2/CO2 deal is a wash. But, you end up with more critters overall.
The exchange isn't exact-- things that die without being eaten, as well as incomplete predator digestion, can sink from the surface waters and continue decomposing down below the thermocline, where most of the CO2, iron, and other minerals in the ocean hang around (wierdly enough, considering the solute potential is higher in warm water, but there are more minerals down deep). So there is a net CO2 absorbtion, just not as large as you would expect.
And to belabor the obvious, the hot spots in ocean life are around upwelling points (trenches, sharp continental shelves, etc) where the low-layer, mineral rich water surges to the surface. There are some eco-nerds out there who want to build floating cities, in dead ocean zones, running thermal exchange pumps to bring those deep waters to the surface for acquatic farming.
am I the only one who saw this and thought 'agh algae bloom danger'?