Feeding the Phytoplankton

While many forms of geoengineering involve counteracting global warming with induced cooling, others move closer to the source of the problem and target the CO2 increase. By artificially boosting the strength of natural carbon sinks, it might be possible to suck CO2 emissions right out of the air. Currently around 30% of human emissions are absorbed by these sinks; if we could make this metric greater than 100%, atmospheric CO2 concentrations would decline.

One of the most prominent proposals for carbon sink enhancement involves enlisting phytoplankton, photosynthetic organisms in the ocean which take the carbon out of carbon dioxide and use it to build their bodies. When nutrients are abundant, phytoplankton populations explode and create massive blue or green blooms visible from space. Very few animals enjoy eating these organisms, so they just float there for a while. Then they run out of nutrients, die, and sink to the bottom of the ocean, taking the carbon with them.

Phytoplankton blooms are a massive carbon sink, but they still can’t keep up with human emissions. This is because CO2 is not the limiting factor for their growth. In many parts of the ocean, the limiting factor is actually iron. So this geoengineering proposal, often known as “iron fertilization”, involves dumping iron compounds into the ocean and letting the phytoplankton go to work.

A recent study from Germany (see also the Nature news article) tested out this proposal on a small scale. The Southern Ocean, which surrounds Antarctica, was the location of their field tests, since it has a strong circumpolar current that kept the iron contained. After adding several tonnes of iron sulphate, the research ship tracked the phytoplankton as they bloomed, died, and sank.

Measurements showed that at least half of the phytoplankton sank below 1 km after they died, and “a substantial portion is likely to have reached the sea floor”. At this depth, which is below the mixed layer of the ocean, the water won’t be exposed to the atmosphere for centuries. The carbon from the phytoplankton’s bodies is safely stored away, without the danger of CO2 leakage that carbon capture and storage presents. Unlike in previous studies, the researchers were able to show that iron fertilization could be effective.

However, there are other potential side effects of large-scale iron fertilization. We don’t know what the impacts of so much iron might be on other marine life. Coating the sea surface with phytoplankton would block light from entering the mixed layer, decreasing photosynthesis in aquatic plants and possibly leading to oxygen depletion or “dead zones”. It’s also possible that toxic species of algae would get a hold of the nutrients and create poisonous blooms. On the other hand, the negative impacts of ocean acidification from high levels of CO2 would be lessened, a problem which is not addressed by solar radiation-based forms of geoengineering.

Evidently, the safest way to fix the global warming problem is to stop burning fossil fuels. Most scientists agree that geoengineering should be a last resort, an emergency measure to pull out if the Greenland ice sheet is about to go, rather than an excuse for nations to continue burning coal. And some scientists, myself included, fully expect that geoengineering will be necessary one day, so we might as well figure out the safest approach.


3 thoughts on “Feeding the Phytoplankton

  1. Thanks for this post. Agreed there will need to be some serious changes.

    However engineering should target the ethics and attitudes of the fossil fuel industry – it is still cranking out the carbon. “The first thing is to stop digging the hole” An easy step is to follow the tobacco industry – every sale comes with a warning and advice. Stop.

    The challenge amounts to human engineering – and when money, governments and Madison Avenue decide humans will change, then change will happen. Maybe soon, since denial is not really working anymore.

  2. “The challenge amounts to human engineering – and when money, governments and Madison Avenue decide humans will change, then change will happen. Maybe soon, since denial is not really working anymore.”

    richard pauli

    As we have seen with the banking crisis and the economic woes of Spain, Greece, Portugal et all;
    It is NOT the corporates, those who are causing the problem, who will pay the bills to implement human engineering and fix the additional problems that will most likely result, it is the middle and lower economic classes that bear the burden. Surely all can agree that human engineering may well result in another “cane toad” situation. These people have no power to fend off the bill collectors when corporates sell solutions which cause more harm than good.
    What corporate or government official would disagree on a human engineering solution if they knew that they would not have to pay the piper?

    I am not against research and data collection that reveals the workings of Gaia. But I do suggest that we have not the knowledge or wisdom to human engineer ourselves out of tragic situations that we knowingly create out of an almost total disrespect for the behaviour of a living Earth.

  3. “Very few animals enjoy eating these organisms, so they just float there for a while.”
    Might want to check this. Phytoplankton, along with zooplankton, are the basic building blocks of the marine food web. They represent roughly half the primary production of the planet. Yes, in large blooms, significant numbers will die and sink before being eaten, but phytoplankton health is absolutely critical to the health of the oceans. And since they provide roughly half the oxygen in the atmosphere, they’re pretty important for everything else as well.

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