Planet Earth Online

Massive volcanoes trigger climate change

12 August 2009

Until now researchers couldn't explain the sudden change in climate. Things seemed to be going well on Earth. The oceans were warm and foraminifera - tiny marine creatures - flourished. But then the climate cooled for no obvious reason.

Dr Sev Kender from the British Geological Survey and colleagues from the British Antarctic Survey, University College London and BP suggest huge volcanoes that spewed both carbon dioxide (CO₂) and sulphur dioxide were responsible for triggering the climate to cool.

Chain reaction

They say that once the climate started cooling, this effect set off a chain of reactions that ultimately led to long-term cooling that is still going on today.

Kender and his team report in Geology how they analysed sediment cores taken from the Congo Fan region off the west coast of Africa, an area few scientists have studied before. 'This region is dominated by industry, but there have been very few academic studies done there,' says Kender.

They found vast quantities of ancient foraminifera in the sediment. Not only that, but the type of foraminifera they found lived during two brief episodes of the Earth's history and would only have existed if the ocean in this region had been acidic.

'These reflect a more productive ocean, where large quantities of planktonic algae flourished over the Congo Fan. Our results show that they were abundant 16 and 15.5 million years ago. The obvious question was, why was the ocean both productive and acidic at these times?' says Kender.

When they trawled through other geological records, they discovered that the oceans were acidic at exactly the same time the Columbia River region of North America was going through huge volcanic activity. 'The Columbia River volcanoes were above a deep molten plume known as a 'hot spot' - in a similar way that Yellowstone is today,' says Kender.

'Sulphuric acid from the Columbia River area volcanoes would've stopped a large amount of sunlight from reaching the Earth's surface, which would've triggered cooling in the climate,' says Kender.

The researchers suggest the change in climate led to windier conditions off the west coast of Africa. 'Wind churns up the oceans and brings nutrients closer to the surface. Algae, which live near the surface, use these nutrients to grow, so you end up getting huge algal blooms,' explains Kender.

Algae pull CO₂ out of the atmosphere, so more algae in the oceans means more CO₂ gets absorbed by the oceans, essentially leading to long-term cooling.

Other researchers have seen evidence for increased rainfall over North Africa at exactly the same time, and the expansion of ice sheets in eastern Antarctica, both evidence for a changing climate. 'It looks like the volcanic eruptions were so big that they changed the climate all over the world.'

'But these eruptions were far larger than anything we've seen in recent history, so we don't think the same thing is likely to happen again in the foreseeable future,' adds Kender.

Keywords: Africa, Atmosphere, Environmental change, Geology, Hazards,

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