Corrosive Water on the West Coast: How NOAA Found Ocean Acidification Decades Early

Richard Feely on the deck of the research vessel Wecoma during the 2007 survey off the Washington–Oregon coast. NOAA.

By the spring of 2007, oyster growers in the Pacific Northwest were in trouble. Pacific oyster larvae normally swim for two or three weeks before settling on a shell to grow, but in the region around Willapa Bay, Washington, millions were dying before they got that far, in the wild and in hatcheries. The growers blamed a bacterium, Vibrio tubiashii, which was turning up in the seawater at nearly 100 times its normal level. Nobody knew why.

Richard Feely, a senior oceanographer at NOAA's Pacific Marine Environmental Laboratory in Seattle, had a suspicion. He had spent decades tracking something that could make seawater hostile to anything that builds a shell.

Carbon dioxide goes into the sea

Feely came to Seattle in 1974 to start a chemical oceanography programme at NOAA. Scientists were then trying to work out where all the carbon dioxide released by burning fossil fuels was going; some of it seemed to be missing, perhaps taken up by the oceans or by plants. In 1981 Feely's programme began measuring carbon dioxide in seawater, to complement the records kept in the air since the late 1950s. There were no standards for such measurements, so the team developed its own.

On research cruises they saw the first signs: water with more carbon dioxide and a lower pH than expected. When carbon dioxide dissolves in seawater it forms carbonic acid, which lowers the pH. Feely published these findings in the mid-1980s, but few people noticed — tiny changes in a few places seemed unimportant in so vast an ocean.

The pH scale. On it 7 is neutral; each whole unit is a tenfold change. NOAA.

Feely suspected the change was worldwide. In the early 1990s he and his colleagues, joined by oceanographer Christopher Sabine, launched an international survey: on 99 cruises over 10 years they collected nearly 72,000 seawater samples from every ocean. In 2004 they published the results in two papers in Science. The ocean, they found, had absorbed about one-third of the carbon dioxide emitted by human activities. That slows global warming, but it changes the water. The surface ocean's average pH, historically about 8.2, had fallen to 8.1 since the Industrial Revolution, and was expected to reach 7.8 or 7.7 by the end of the century.

The second paper, led by Feely with biologists and ecologists, showed what that meant: acidified water can corrode the calcium carbonate that oysters, clams, scallops, lobsters, crabs, shrimp, corals, sea urchins, tiny swimming snails called pteropods and some plankton use to build shells and skeletons. In laboratory experiments, some of these animals grew malformed.

Modelled availability of calcium carbonate 10 metres below the surface, where most corals live, over the coming century: blue is plenty for shell-building, deep red corrosive. Based on models by James Orr of the Laboratory for the Sciences of Climate and Environment, Paris. NOAA.

There was hope in it too. Computer models predicted that corrosive water would take many years to reach the surface — time, perhaps, to cut emissions. Feely wanted to check.

The 2007 survey

In May 2007 Feely and Sabine boarded the research vessel Wecoma with scientists from Canada and Mexico for the first large-scale carbon survey of the West Coast, two months of sampling from Canada to Mexico. The ship zig-zagged along thirteen lines running out from the coast past the edge of the continental shelf, stopping at seven or eight stations on each. At every stop the crew lowered a CTD rosette — sensors for conductivity, temperature and depth on a wheel of 24 sampling bottles — almost to the seafloor, then closed the bottles one by one on the way up to sample different depths.

The Wecoma's track and sampling stations, 2007. NOAA.

The weather that made the work hard was the reason for it. Gusts of 35 knots blew for much of the cruise. Each spring, northwesterly winds strengthen off the coast, push warm surface water out to sea and draw cold water up from the depths to replace it. The team feared that this upwelling could lift the corrosive deep water they had found before onto the shallow continental shelf — something no one had ever observed there.

It did. After the fifth line, near the Oregon–California border, the data showed corrosive water reaching all the way to the surface less than 20 miles from shore. Shell-building animals there were facing acidified water now, not 50 or 100 years in the future. The team's paper appeared in Science in June 2008.

Back to the oysters

The larvae in Willapa Bay, which supplies about a sixth of the nation's oysters, failed for a fourth summer in a row, and hatchery managers began calling Feely. He could not say for certain that acidified water was to blame; other problems, including a low-oxygen dead zone off Oregon, might play a part. But the pattern fitted. Hatcheries reported die-offs after spells of persistent northwesterly winds, when deep water welled up into the bay and the hatchery intakes; the water could be corrosive enough to dissolve the larvae's fragile shells; and Vibrio tubiashii seemed to thrive in it. Feely believed corrosive water was the main cause, worsening the bacterial outbreaks.

Scientists began working with a hatchery to record the pH of the water it pumped in, and Feely proposed a network of moorings along the coast — about $3 million to build — to warn hatcheries when corrosive water came close to shore.

The first buoy built to monitor ocean acidification, anchored in the Gulf of Alaska. It measures ocean pH and carbon dioxide and sends the data by satellite. NOAA.

The first buoy dedicated to measuring both ocean pH and carbon dioxide was already at sea, in the Gulf of Alaska. Many questions remained open: which parts of the ocean would change most, which species would suffer, and whether they would adapt or move. Feely stayed hopeful: once a problem and its causes are understood, he said, it can be monitored, and people can decide to cut their carbon dioxide emissions and protect the ocean.

Sources

• NOAA Climate.gov, "An Upwelling Crisis: Ocean Acidification"; rewritten in hubnx's own words, as the situation stood in 2009. Photographs and graphics from NOAA; pictures whose owner the page does not name are left out.
• R. A. Feely and others, "Evidence for Upwelling of Corrosive 'Acidified' Water onto the Continental Shelf," Science 320 (2008); R. A. Feely and others, "Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans," and C. L. Sabine and others, "The Oceanic Sink for Anthropogenic CO2," Science 305 (2004).