The ocean absorbs billions of tons of carbon every year, and the process is accelerating, study shows

Author Evan Bush

Newly published research analyzed more than 100,000 seawater samples worldwide and found the oceans are absorbing about 31 percent of human-caused carbon emissions. It’s “a huge service the oceans are doing,” says a co-author, in Seattle.

Richard Feely has spent years of his career at sea, casting packages of plastic tubes into its void, and pulling up seawater from its depths while exploring how carbon emissions are changing the world’s oceans.

Feely, a senior scientist at the National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory in Seattle, has sampled Antarctic waters, passed through Tahiti and ridden out “huge” storms aboard ocean-class research vessels.

Most days on these scientific cruises, which last more than a month, there’s no other boat in sight.

“You see an occasional whale or some birds,” he said. “It’s a big ocean.”

It’s hard, tedious work.

But the data collected by Feely and other scientists throughout the world are now telling us just how much carbon humans have put into the ocean and what that might mean for our future.

Research published Thursday in the peer-reviewed journal Science analyzed more than 100,000 seawater samples worldwide collected from 1994 to 2007 and taken from nearly every corner and depth of ocean.

The analysis found the oceans are absorbing about 31 percent of the carbon humans are spewing into the world. For context, the weight of the carbon seeping into the ocean each year, on average for the period of study, is roughly equivalent to 2.6 billion Volkswagen Beetle cars, Feely said.

It’s “a huge service the oceans are doing,” said Feely, who is listed as a co-author on the study. “That significantly reduces global temperature.”

But that temperature buffering comes at a cost. The ocean has continued to acidify, and changes in its chemistry are already affecting ecosystems in the Pacific Northwest. Adding carbon lowers seawater’s pH level, making it more corrosive. The research by Feely and others found the uptake of carbon in the world’s oceans has kept pace with worldwide CO2 emissions into the atmosphere.

“The amount of carbon in the ocean, that rate is increasing, because the amount of CO2 we’re releasing into the atmosphere is still increasing,” Feely said.

To scientists, the results of the Science study were less a revelation and more of an affirmation. Thousands of physical measurements painstakingly collected over 13 years in nearly every reach of the ocean matched what they already knew.

“The oceans have been taking up carbon dioxide recently in exactly the way we thought they would,” said Curtis Deutsch, a University of Washington associate professor of oceanography, who was not involved in the research.

During 13 years of data collection, scientists took more than 50 cruises and collected more than 100,000 seawater samples, according to NOAA senior scientist Richard Feely. (NOAA)

“There’s nothing really surprising about the results, but they are super important in confirming that we really do understand the system and the way it operates.”

Scientists have long relied on climate models to forecast our warming future. In the ocean, the models consider factors like circulation, biological processes and the chemistry of carbon dioxide and water.

“Those models all turned out to be correct and that’s really an important fundamental step in the scientific process: that you verify predictions that are made based on basic principles of ocean circulation,” Deutsch said.

Those circulation patterns are incredibly important, and scientists are keenly watching for large-scale changes, he said.

The Atlantic Ocean, for example, is about half the size of the Pacific Ocean, but the research shows the Atlantic absorbs nearly as much carbon. That’s because ocean circulation patterns in the Atlantic churn waters down to greater depths than in the Pacific, which means the effects of human-caused carbon emissions can be detected more than a mile below the ocean surface.

If ocean circulation were to slow down, some scientists have hypothesized, the ocean would not be able to absorb as much carbon. That could intensify the rate of global warming because additional carbon would remain in the atmosphere and not be absorbed by the ocean.

The data analyzed in the Science paper hints at a slowdown in circulation, Deutsch said, but because the length of study is only 13 years, the cause is not clear, and it could be natural and benign.

“We think this is more in line with natural variability than long-term change at this point in time,” Feely said. “That remains to be seen.”

The Pacific Northwest could be particularly sensitive to increases in carbon in the ocean.

“Here in the Pacific Northwest, there are some somewhat unique factors that result in our experience of ocean acidification being more intense than in other places,” said Jan Newton, a UW oceanographer who co-directs the Washington Ocean Acidification Center.

Pacific Northwest waters — teeming with respiring life that gives off carbon dioxide — naturally contain more dissolved carbon than other seas, Newton said.

Along the Washington coast in the summer, upwelling, an ocean pattern that surfaces deep water, brings up waters high in nutrients and CO2 and low in oxygen, Newton said. Meanwhile, in Puget Sound, tidal mixing brings up carbon-rich deep water.

So, humans are adding carbon to waters that are already naturally more corrosive.

“It can be noticeable,” Newton said. “We’re starting to see some of these effects more quickly than other places in the world.”

Ocean acidification already has hampered the shellfish industry. A more acidified ocean can prevent oysters and other shellfish from forming their shells.

UW research has shown that high-CO2 water can erode the ability of some salmon to process smells, critical for the fish to avoid predators.

More-corrosive waters have been shown to reduce the reproductive success of krill, Newton added.

“Some organisms are going to be resilient and adapt, but it’s an overall stress” to have additional carbon in the water, Newton said. “At some point, there becomes a limit and that’s the part that, to some extent, is impossible to know. And that’s the part we really need to be considering.”

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