Huge vents covering the sea-floor – among the strangest and most spectacular sights in nature – pour carbon dioxide and other gases into the deep waters of the oceans.
Last week, as researchers reported that they had now discovered more than 50,000 underwater volcanic springs, they also revealed a new use for them – as laboratories for measuring the impact of ocean acidification on marine life.
The seas are slowly being made more acidic by the increasing amounts of carbon dioxide from factories and cars being pumped into the atmosphere and then dissolved in the sea. The likely impact of this acidification worries scientists, because they have found that predicting the exact course of future damage is a tricky process.
That is where the undersea vents come in, says Dr Jason Hall-Spencer of the University of Plymouth. "Seawater around these vents becomes much more acidic than normal sea water because of the carbon dioxide that is being bubbled into it," he told a meeting of the American Association for the Advancement of Science in San Diego, California, last week. "Indeed, it reaches a level that we believe will be matched by the acidity of oceans in three or four decades. That is why they are so important."
As part of his research, Hall-Spencer has scuba-dived into waters around vents and used submersibles to study those in deeper waters. In both cases the impact was dramatic, he told the conference.
"The sea floor is often very colourful. There are corals, pink algae and sea urchins. But I have found that these are wiped out when the water becomes more acidic and are replaced by sea grasses and foreign, invasive algae.
"There is a complete ecological flip. The seabed loses all its richness and variety. And that is what is likely to happen in the next few decades across the world's oceans."
Hall-Spencer also noted that in acidic seawater a type of algae known as coralline algae – which act as the glue holding coral reefs together – are destroyed.
"When coralline algae are destroyed, coral reefs fall apart," he said. "So we can see that coral islands like the Maldives face a particularly worrying future. Rising sea levels threaten to drown them, while acidic waters will cause them to disintegrate.
"It is a very worrying combination."