Between a rock and a hard place? A last-ditch approach to slow ocean acidification may involve spreading a mineral along coastlines to suck acidifying protons out of the water.
Earth’s oceans are now 25 per cent more acidic than they were before the industrial revolution, due to excess carbon dioxide in the air dissolving to form carbonic acid. Acidification is threatening a wide range of marine organisms, including corals, mussels, sea urchins and oysters, because it makes it harder for them to build their skeletons and shells.
As a potential solution, Francesc Montserrat of the Royal Netherlands Institute for Sea Research and his colleagues are exploring whether a natural mineral can mop up unwanted acid in seawater.
“We’re trying to put some numbers on the table so that if politicians decide that we need to do this in 10 to 15 years’ time, the research is there and we can say, ‘here are the problems you might be dealing with’,” he says.
Rock to the rescue
Olivine is a magnesium silicate mineral that is mainly found in Earth’s subsurface and has been previously suggested as a way to soak up atmospheric CO2. The amounts needed to make a real difference globally are too high, but less of it would be required to reduce ocean acidification locally. When it is placed in seawater, it gradually swaps its magnesium ions for protons, thereby helping to remove acidity.
Montserrat and his colleagues studied this effect in seawater tanks 1 cubic metre in size, which contained living creatures and were designed to mimic the marine ecosystem. When the mineral was ground up and applied as a 1.5 centimetre layer over a base of natural sediment, the pH of the seawater increased by the desired amount, with no adverse effects on life.
However, when a 3 centimetre layer of olivine was used, the lug worms and other marine organisms inhabiting the sediment died. This may be because the pH change was too great, or trace amounts of nickel present in the mineral poisoned the organisms.
“This goes to show that it is a sensitive process that we have to work out,” says Montserrat, who presented the work at the International Symposium on the Ocean in a High-CO2 World in Hobart, Australia in early May.
Ocean engineering on the table
The researchers are currently in early talks with the Netherlands government about testing the safety and efficacy of applying a thin layer of ground-up olivine to a real-world coastal environment.
“There are of course a lot of legal issues to tackle, because you’re talking about dumping this material in the sea,” Montserrat says. “But it suggests that even at a government level, people are interested.”
Several scientific and government bodies are starting to consider these kinds of environmental engineering approaches for softening the blows of climate change, says Andrew Lenton of Australia’s national research body, CSIRO.
“The fact that we’re already starting to see detectable changes in our oceans suggests that we certainly need these sorts of tools in our arsenal,” he says.
One of the key issues to address is whether the effects of olivine could be reversed if it began to harm the environment, Lenton says.
“What happens if some kind of unforeseeable problem pops up and we need to stop it?” he says. “That’s a really important question that we need to get a handle on.”
Earth’s climate has been edging towards a scene usually reserved for a post-apocalyptic movie. Some posit geoengineering as a radical fix to climate change. Others say the risks are too high and its proponents mad. Welcome to the debate where science fiction meets climate science.