Ocean acidification worst in 300m years – scientists

2 Mar 2012

Surface of the Atlantic Ocean meeting the Earth's planetary boundary layer and troposphere

Scientists at Columbia University in the US have led pioneering new geologic research on ocean acidification. And according to their findings, the world’s oceans may be turning acidic faster today as a result of human carbon emissions than they did during four major extinctions in the last 300m years.

The findings of the study, which was carried out at Columbia University’s Lamont-Doherty Earth Observatory, have been published in Science.

The U.S. National Science Foundation funded the research, which Columbia is terming the first study of its kind to explore how carbon emissions are affecting the planet’s oceans.

According to the scientists, even during extinctions during the past 300m years, when natural pulses of carbon would have sent global temperatures soaring, no period in history even compares to the levels of C02 emissions that are affecting oceans as swiftly as now.

Planet Earth might lose organisms

The lead author on the study Bärbel Hönisch, a paleoceanographer at Lamont-Doherty Earth Observatory, spoke about how the geologic research is so pivotal.

“We know that life during past ocean acidification events was not wiped out as new species evolved to replace those that died off,” she said.
Hönisch added that if industrial carbon emissions continue at the current pace, Planet Earth might lose organisms such as coral reefs, oysters and salmon.

The scientists explained how the world’s oceans act like a sponge to draw down excess carbon dioxide from the air. The CO2 then reacts with seawater to form carbonic acid, which over time is neutralised by fossil carbonate shells on the seafloor.

However, 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. According to the scientists this is what is happening now.

Great Barrier Reef – Australia

Satellite image of part of the Great Barrier Reef adjacent to the Queensland coastal areas of Airlie Beach and Mackay

Satellite image of part of the Great Barrier Reef adjacent to the Queensland coastal areas of Airlie Beach and Mackay. Last week it was revealed that scientists will be studying the health of coral on the Great Barrier Reef, which is located in the Coral Sea, off the coast of Queensland, Australia

So how did the scientists carry out such expansive geologic research on the world’s oceans?

A team of researchers hailing from five countries reviewed hundreds of paleoceanographic studies. They said they found evidence for only one period in the last 300m years when the oceans changed even remotely as fast as today. This was the Paleocene-Eocene Thermal Maximum (PETM), which happened some 56 million years ago when global temperatures rose by about 6°C.

In the early 1990s, scientists extracted sediments from the seafloor off Antarctica. What they found was a layer of mud from this PETM period wedged between thick deposits of white plankton fossils.

Carbon surge

In a span of about 5,000 years, they estimated that a surge of carbon doubled atmospheric concentrations, pushing average global temperatures up by about 6°C. And the result? The scientists said carbonate plankton shells littering the seafloor dissolved and as many as half of all species of single-celled organisms (known as benthic foraminifers) went extinct.

Study co-author Ellen Thomas, a paleoceanographer at Yale University, who was on that Antarctic cruise in the 1990s, said it suggested that organisms higher in the food chain might have also disappeared.

“It’s really unusual that you lose more than 5 to 10pc of species over less than 20,000 years,” she said. “It’s usually on the order of a few percent over a million years.”

During this time, scientists estimate that ocean pH – a measure of acidity – may have fallen by as much as 0.45 units.

Flash forward to the last 100 years and atmospheric CO2 has risen by about 30pc, and ocean pH has fallen by 0.1 unit, to 8.1. Hönisch said this acidification rate is least 10 times faster than 56 million years ago.

Oceanic predictions

Meanwhile, the Intergovernmental Panel on Climate Change is also predicting that pH may fall another 0.3 units by the end of the century, to 7.8. The scientists said this raises the possibility that we may soon see ocean changes similar to those observed during the PETM era.
They indicated, however, that it may take decades before the effect of ocean acidification’s reveals its true impact on marine life.

“These studies give you a sense of the timing involved in past ocean acidification events — they did not happen quickly,” said Richard Feely, an oceanographer at the National Oceanic and Atmospheric Administration, who was not involved in the study. “The decisions we make over the next few decades could have significant implications on a geologic timescale,” he added.

Carmel Doyle was a long-time reporter with Silicon Republic