Ocean Acidification: Geologic Record Adds New Warning

As humans continue to pump carbon into the air, a closely related problem–the accumulation of carbon in the oceans–is gaining attention. In the last hundred years, we’ve raised atmospheric carbon levels by 30 percent and lowered the pH of the oceans (increasing their acidity) by an equivalent percentage. While the amount of carbon in the air and oceans has fluctuated naturally over time, a new study in Science finds that the oceans may be acidifying faster today from industrial emissions than they did during four major extinctions in the last 300 million years when carbon levels spiked naturally. The study is the first of its kind to survey the geologic record for evidence of ocean acidification over this vast time period.

“What we’re doing today really stands out,” said study lead author Bärbel Hönisch, a paleoceanographer at Columbia University’s Lamont-Doherty Earth Observatory.  “We know that life during past ocean acidification events was not wiped out—new species evolved to replace those that died off. But if industrial carbon emissions continue at the current pace, we may lose organisms we care about—coral reefs, oysters, salmon.”

The oceans act like a sponge to draw down excess carbon dioxide from the air; the gas reacts with seawater to form carbonic acid, which over time is neutralized by fossil carbonate shells on the seafloor. But if CO₂ goes into the oceans too quickly, it can deplete the carbonate ions that corals, mollusks and some plankton need for reef and shell-building. The study in Science examines the fossil record for signs of ocean acidification during the big extinctions of the last 300-million years. Their findings are summarized in this press release.

Today, the effects of ocean acidification are currently overshadowed by other problems, ranging from sewage pollution and hotter summer temperatures that threaten corals with disease and bleaching. However, scientists trying to isolate the effects of acidic water in the lab have shown that lower pH levels can harm a range of marine life, from reef and shell-building organisms to the tiny snails favored by salmon. In a recent study, scientists from Stony Brook University found that the larvae of bay scallops and hard clams grow best at pre-industrial pH levels, while their shells corrode at the levels projected for 2100. Off the U.S. Pacific Northwest, the death of oyster larvae has recently been linked to the upwelling of acidic water there.

“It’s not a problem that can be quickly reversed,” said Christopher Langdon, a biological oceanographer at the University of Miami who co-authored the study on Papua New Guinea reefs. “Once a species goes extinct it’s gone forever. We’re playing a very dangerous game.”