Geologic record testifies to unprecedented changes in ocean chemistry, USC researcher says

In a sense, the ocean is choking on greenhouse gases. As much as a third of the carbon in the atmosphere is saturating seas, making them more acidic. Rowan Martindale, a doctoral student in earth sciences at USC, thinks about that when she dives to coral reefs; She says her fellow scientists have begun to see coral, plankton and shellfish weaken: “Biological experiments being conducted today show that even small changes can cause things to have a really hard time building a skeleton or shell or for their larvae to grow or for them to reproduce.”

A new and sweeping survey of science about geologic history has revealed no time in 300 million years when the chemistry of the oceans has changed as fast as it’s changing now. Columbia University paleo-oceanographer Bärbel Hönisch and 20 other authors published their findings in the journal Science; Rowan Martindale is one of several researchers with California connections.

Martindale reviewed studies of the geologic record, studies about ancient times when the ocean’s chemistry became more acidic. “The events that are most similar to the event that happened today caused huge extinction events. Really really big extinction events,” Martindale said.

Her event — the one she examined — she calls big and bad. A quarter of a BILLION years ago, evidence suggests, a continental shift began to unleash a series of volcanic eruptions in “the huge volcanoes from Iceland, from Newfoundland, all the way down to Morocco.” It’s believed those volcanoes spewed carbon and other climate-changing gases — gases that then, like now, saturated the sea. “And so the hypothesis is that those gases then went into the ocean and through various chemical reactions took the ocean to a more acidic state.”

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Around that same time, something called the Triassic-Jurassic extinction event wiped out more than half the planet’s species. Martindale says an acidic ocean may have played a role. Recorded in layers of sediment and rock, geologic history testifies that corals died out, as some are starting to do now. “There’s a gap in the rock record where you don’t have corals and coral reefs for something like 300,000 years.”

Martindale says what happens to coral today is well worth keeping a close eye on. Corals are keystone species; then, as now, part of the foundation for biological diversity in the sea. “If you lose your reefs, you lose your fishes that go along with the reefs, and you lose anything that needs a reef to spawn or to host their young, so there would have been some very dramatic ecosystem consequences of such an acidification event.”

What the past says about the future has its limits. A key conclusion of the new paper is that none of the events examined, not the one Martindale studied, not one that happened 55 million years ago, are good enough analogs to what’s happening now. Oceans are already twice as acidic as they were 150 years ago. And that, say the authors of this paper, means we’re moving into uncharted waters.

April 19, 2012: A caption in a photo appended to this story has been corrected to correctly reflect that Pomona College did not contribute research to the study on which this report is based.