University of Alberta scientists discover volcanic eruptions on the ocean floor caused a drop in CO2 concentrations and a mass extinction of marine life

It sounds like a science fiction movie: a warm and watery North Pole, high carbon dioxide levels, giant clams trolling ocean floors, and volcanoes as large as a Canadian province. Then, a massive wipeout of ocean life.

This dystopia is not fiction, but an episode in Earth's long history, occurring 94 million years ago during the Cretaceous period. A geological mystery for years, recent discoveries have enabled two University of Alberta scientists to shed light on what caused this large-scale extinction.

Steven Turgeon, one of the leading researchers in the study that has garnered international attention and whose findings are now largely accepted, said he is "97 per cent" sure that it was volcanic activity in the ocean bed that triggered a chain reaction, ultimately resulting in the widespread extinction of marine life.

"Previously there was some speculation that it might have been caused by a meteorite," said Turgeon, who worked with Robert Creaser, also an Earth and Atmospheric Sciences professor. "Both volcanism and meteorites have the same isotopic signature. But we now know from our analysis of deposits that what caused the dinosaurs to die off did not cause this."

The particular volcano that caused the extinction was spread over an extensive area, most likely in the Caribbean region. Its eruption resulted in anoxia, a dramatic depletion of oxygen in the ocean. Dying marine life accumulated at the bottom of the ocean, forming what is called black shale.

The volcano spewed magma in bursts for thousands of years, but as Turgeon explained, due to oceanic stratification, it actually took 23 thousand years for ocean life to become extinct.

"If this event were to happen today, the effects would be seen much faster because there is more mixing between the top and bottom layers of the ocean," Turgeon warned.

While some species became extinct forever, it took 80 million years before the rest of the marine world recovered. Turgeon noted that the effects of this giant volcano also extended to the atmosphere.

"Carbon dioxide concentrations of the ocean and the atmosphere dropped because of this huge burial of organic carbon. The surface temperatures dipped as well, so it was like a global cooling. With the passage of time though, the atmospheric carbon dioxide concentrations went back to their original levels and the temperatures also increased."

Turgeon also acknowledged that these findings have intriguing implications for current global warming debates.

"A lot of people think it's okay to pump more carbon dioxide into the atmosphere. They rationalize that because of this there will be more carbon dioxide in the ocean and so an increase in plant life, like an acceleration of the natural cycle," he observed.

"This organic matter would take up the extra carbon dioxide and then be buried at the bottom of the ocean. That might happen, that might not happen, but we don't want to be around to actually try it." He emphasized that the cooling effect during the Cretaceous period as a result of the burial of organic matter ultimately reversed.

The research fills in important gaps in Earth's history and will force scientists to revisit other episodes of mass extinction and their relationship to volcanism, but it may also aid predictions about the planet's future.

"I don't have a crystal ball but what we do know from history with some confidence is that oceans have limited buffering capacity for all the carbon dioxide that is being emitted today."