Modern Ocean Acidification Outpaces Ancient Climate Change by 10 Times

Ocean acidification may be impacting our world's seas today, but it also occurred in the past. Now, scientists have taken a closer look at the extent of ocean acidification that occurred millions of years ago, and have found that we may be in for a catastrophic event of our own as waters continue to acidify.

About 56 million years ago, a massive pulse of carbon dioxide that surged into the atmosphere sent global temperatures soaring. As this gas dissolved into the ocean, it became more acidic; carbonate sediments, including the shells of animals, dissolved as organisms went extinct or evolved to cope.

In order to better understand this ancient event, the researchers examined seafloor sediments drilled off of the coast of Japan. More specifically, they analyzed the shells of plankton that once lived at the surface of the ocean during the Paleocene-Eocene Thermal Maximum (PETM), a period of intense warming on land and throughout the oceans. In the end, they found a massive change of pH which caused a series of environmental shifts.

"This could be the closest geological analog to modern ocean acidification," said Barbel Hornisch, one of the researchers, in a news release. "As massive as it was, it still happened about 10 times more slowly than what we are doing today."

In fact, the oceans have absorbed about a third of the carbon that humans have pumped into the air since industrialization. In the last 150 years or so, the pH of the oceans has dropped from 8.2 to 8.1, which is equivalent to a 25 percent increase in acidity. In fact, by the end of the century ocean pH is projected to fall to 7.8. A comparable pH drop during the PETM happened over a few thousand years.

"We are dumping carbon in the atmosphere and ocean at a much higher rate today-within centuries," said Richard Zeebe, one of the researchers, in a news release. "If we continue on the emissions path we are on right now, acidification of the surface ocean will be way more dramatic than during the PETM."

The findings reveal that ocean acidification may be a huge problem today. In the past, species changed location and even went extinct, and acidification was happening a lot more slowly than it is today. It's crucial to take steps to reduce the amount of greenhouse gases in the atmosphere in order to help curtail the massive increase in acidification in the future.

The findings are published in the journal Paleoceanography.