Plan to Slow Global Warming By Dumping Iron Sulphate into Oceans

ananyo writes "In the search for methods of geoengineering to limit global warming, it seems that stimulating the growth of algae in the oceans might be an efficient way of removing excess carbon dioxide from the atmosphere after all. Despite attracting controversy and a UN moratorium, as well as previous studies suggesting that this approach was ineffective, a recent analysis of an ocean-fertilization experiment eight years ago in the Southern Ocean indicates that encouraging algal blooms to grow can soak up carbon that is then deposited in the deep ocean as the algae die. Each atom of added iron pulled at least 13,000 atoms of carbon out of the atmosphere by encouraging algal growth which, through photosynthesis, captures carbon. The team reports that much of the captured carbon was transported to the deep ocean, where it will remain sequestered for centuries — a 'carbon sink' (abstract)."

Comments

Re:Ending badly?

[Anonymous Coward]

And the side effects are not all bad: it should increase the amount of fish that can be sustainably harvested.

The 2 side effects mentioned in the article both kill fish. Toxic algal blooms poison fish, either causing them to grow abnormally or death. Depleted oxygen levels does the same thing to the fish as it does to you, suffocation.

The Risks of Iron Fertilization

[catchblue22]

I took a course on oceanography a few years ago, and we actually studied this. I'll summarize my professor's powerpoint notes as best I can.

Iron is a limiting nutrient in phytoplankton growth. This is not in dispute. However if we are to add iron to the ocean in order to increase phytoplankton counts, and thus to increase CO2 uptake then we must consider several things. Firstly, how much CO2 will be semi-permanently transported to the ocean floor. In terms of percentages, if increased phytoplankton counts caused a CO2 flux in the surface layer of 50 Gt Carbon / year, the corresponding CO2 flux to the ocean floor would be about 0.7 Gt Carbon / year. This is due to the fact that the mechanisms of carbon transport from the surface to the sea floor (the "biological pump") is quite inefficient. Thus the increase in phytoplankton at the surface would have to be HUGE to transport meaningful amounts of CO2 to the sea floor.

Secondly, there may be dire unintended or undesired consequences of increasing the surface phytoplankton counts. Imagine we put significant amounts of iron in the ocean and imagine that surface phytoplankton counts increased significantly. At the surface we could get increased CO2 uptake and O2 production. But what happens when those phytoplankton die? They sink. And when they sink to deeper layers, other organisms would decompose them. Those decomposers would be oxygen breathers and would consume oxygen at the deeper layer. If their numbers increased due to increased dead phytoplankton, the decomposers could deplete the O2 levels in that level, creating anoxic zones at deeper levels in the ocean. In addition, some of these decomposers might be methane producing bacteria, especially in the absence of oxygen. That methane might make its way into the ocean. The worry is that the imbalanced increase in phytoplankton might result in an anoxic jellyfish ocean that would be rather unfriendly to fish like salmon, tuna, and the other common species that currently exist.

Unless the above arguments have been refuted, I don't know why iron fertilization is still being pushed as a realistic option. It seems to me that many decision makers are nearly completely illiterate in science.