Ocean Acidification Series

Ocean Acidification: The Unknown Reality of Climate Change

Plankton Life Already Weakened by CO2

The Luck of the Fish: for How Long?

Finding a Cure Despite Uncertainties

The Hopes of Ecosystem Modelling

Finding a Cure Despite Uncertainties

Fishermen on Goree Island, Senegal- credit: Laurene Mainguy

By Laurene Mainguy, May 2009

Coral degradation would be dramatic for fish and invertebrates that find shelter and reproduce in coral reefs. It would also be a great threat to people who depend on tourism and coral trade to make a living.

Ocean acidification could have catastrophic consequences for those communities. In a recent study, a group of economists tried to evaluate the impact of ocean acidification on coral reefs in four climate scenarios, defined by the International Panel on Climate Change (IPCC). They found that 16% to 27% of corals will disappear by 2100, a loss that could be worth $870 billion.

The rest of the world population would be affected too. The ocean provides food, jobs and incomes to millions of people worldwide. In 2006, the total production of fish and mollusks was worth 170 billion dollars, according to the Food and Agriculture Organization.

Small changes are already happening. The lives of microorganims and pteropods already show signs of disruption. Those issues are likely to become more problematic affect more species through food web changes, although no one knows exactly how. â€At this moment, it is very difficult, probably impossible to answer this question,â€â€ said Atsushi Ishimatsu, a fish scientist at Nagasaki University.

Ecosystems with a great biodiversity might be better off than others, said Stephen Widdicombe, a benthic ecologist at the Plymouth Marine Laboratory. â€When you have lots more species than "jobs" [breaking down plant material, eating other species, altering the environment in some ways] you will have each job being done by several species. Therefore, if you lose a few species, the jobs still get done and ecosystem function is not affected,†he said in an email. But the relationships between biodiversity and ecosystems are not yet clearly understood.

The scientific community has tried to come up with solutions to mitigate the effects of ocean acidification. One of them is iron fertilization. The idea is to spread iron dust into the sea to stimulate plankton growth, which in turn eat up carbon dioxide.

John Raven, a plankton biologist and former chair of the Royal Society working panel on ocean acidification, said iron fertilization could only be a minor contributor to atmospheric CO2 mitigation.

.Phytoplankton bloom off the coast of Florida- credit: NASA Visible Earth

''In terms of keeping carbon dioxide in the atmosphere below whatever threshold- we were talking about450 ppm- it migh have an effect. Maybe 20 ppm CO2, that sort of range,'' he said.

But we don't know if iron fertilization would work on a large scale because only small-scale experiments have been done so far, Raven said. It can also be hard to track the effects of fertilization because the iron sometimes just disappear. ''It gets mixed and widely diluted. The iron gets stuck on mineral particles and precipitates, onto organsisms, so it gets lost in one way or another,'' Raven said.

Philip Boyd, a researcher at the New Zealand National Institute for Water and Atmospheric Research, agrees. He said iron fertilization expeditions can be unpredictable. ''The first experiment shut down after only five days when a mass of less dense water moved over the iron-fertilized water, pushing it far below the sunlit surface and ending the iron-induced bloom prematurely,'' he told the Woods Hole Oceanographic Institution.

Buoy delineating the ocean patch fertilized with iron in the Lohafex expedition- credit: Patrick Martin NOCS, Alfred Wegener Institute

Lohafex, the latest iron fertilization expedition, was carried out in Antarctica in February. The crew fertilized 186 miles square of the southern ocean with 4 tonnes of dissolved iron for 39 days. They found that phytoplankton doubled their biomass and ate up more CO2 during the first two weeks, after which they did not grow any further and were grazed by more predators than usual.Contrary to previous expeditions, the CO2 impact of Lohafex was quite small and scientists are still trying to understand why. ''The mechanisms await further analysis,'' said Uli Bathmann in an email.

Even if iron fertilization produced significant plankton blooms, it might fail to store CO2 permanently. ''After the organisms have broken down in the deep ocean, that will bring the carbon dioxide back to the surface, said Raven. '' It's quite difficult to breack that connection between the precipitate and the carbon.''

Environmentalist and Gaia theorist James Lovelock had another idea. Rather than adding extra nutrients to the ocean, he suggests to recycle deep waters that are already rich in nutrients. His idea is to have floating pipes sucking deep waters up to the surface, where plankton will eat the nutrients, photosynthesize and absorb excess carbon dioxide.

The pipes would work like a pump running on wave energy.The upward movement of the waves would open a valve located at the end of the pipe, to let deep waters in and mix with surface waters. The downward flow would close the valve and block surface waters out.

Critics say such a system would not only bring nutrients up to the water surface, it would also bring back carbon dioxide. ''It is sufficient to acidify that bit of water,'' said Raven. ''And there is a chance that some of that CO2 actually comes out of the solution into the atmosphere.''


Polarstern research vessel of the Lohafex expedition- credit: Alfred Wegener Institute

The system would also be quite dangerous and costly to run, Raven said. ''As people who are extracting oil and gas from the ocean know, running any device like that in the ocean is high risk and expensive. It doesn't involve a complicated apparatus, but the maintenance, and hurricanes, cyclones, typhoons...''

Lovelock conceived the idea, now he would like people to test it and see if it works, Raven said. ''I'd like to see that too.''

More about the ocean acidification series:

Part 1: Ocean Acidification: The Unknown Reality of Climate Change

Part 2: Plankton Life Already Weakened by CO2

Part 3: The Luck of the Fish: for How Long?

Part 4: Finding a Cure Despite Uncertainties

Part 5: The Hopes of Ecosystem Modelling