Failure sells. That’s the only explanation I could come up with when I read last week’s reports on the Indo-German LOHAFEX expedition: every story I saw focused on how the iron-fertilization experiment didn’t manage to pull large amounts of carbon dioxide from the atmosphere, sequester it on the sea floor, and provide a ready-made solution to global warming. But I’ve got news for you -- just because an experiment doesn’t turn out the way you really really really hope it will doesn’t actually make it a failure. In fact, if you take the time to read through the reports posted on the expedition website, it’s clear that the scientists who designed the project thought through several logical alternative outcomes to the experiment, and the whole point was to find out which one of those hypotheses also described the real world.
So the expedition carried out a classic, if very large, perturbation experiment: they took an environment – in this case a patch of ocean in the South Atlantic, they changed one part of it – dropping a total of 20 tons of iron sulfate into the iron-poor water, and they watched and measured what happened in response for as long as they could. And because so little is known about the ecology of open ocean habitats, pretty much any data they collected that could shed light on natural interactions in these free floating communities was going to be of value.
As expected, soon after the seeding photosynthetic plankton took advantage of the higher iron concentrations, rapidly growing and breeding. As they grew, they built their bodies out of sugars they manufactured from carbon dioxide dissolved in the water. And as the phytoplankton pulled CO2 from the water, more CO2 entered the water from the atmosphere. Eventually, the phytoplankton used up the iron. From this point, the team had predicted two possible outcomes: if most of the photosynthetic plankton died and sank, they would take the carbon they built themselves out of with them. But if most of the phytoplankton stayed near the surface, they would attract grazers which would attract predators…. and the food chain would kick the CO2 right back into the atmosphere. The second hypothesis won out: as the phytoplankton bloomed, grazing zooplankton like copepods congregated to eat them, followed by amphipods coming to eat the copepods.
So ocean seeding isn’t a magic bullet to suck CO2 out of the atmosphere. Big deal. The experiment revealed a little more about how ocean ecologies react as trace elements are blown in from land. And as these floating plankton communities may ultimately feed both the bigger fish that we like to eat and the biggest filter-feeding whales, understanding them is hardly a waste of time.
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