Decades of Data And Discoveries

Christopher Sabine on a field study in the Southern Ocean aboard the NOAA Research Vessel Ronald H Brown. Photo courtesy of NOAA.

Feely moved to Seattle in 1974 to start a chemical oceanography program at NOAA. At that time Earth scientists were just beginning to understand our planet as a global system. They had new abilities to measure Earth processes and represent them with computers. To build models of the physical world they needed to know where the carbon dioxide emitted into the atmosphere from the burning of fossil fuels was going, but they could not account for all of it. They thought that the “missing” carbon dioxide might be absorbed by the oceans or by land plants.

In 1981, Feely’s program began measuring the amount of carbon dioxide in the ocean to complement the records of atmospheric carbon dioxide that had been taken since the late 1950s. Getting started was difficult. There were no existing standards for measuring carbon dioxide in seawater, so Feely and his team had to develop their own.

As part of this investigation, Feely and his colleagues participated in research cruises along coastlines and across ocean basins studying ocean carbon chemistry at a range of locations and depths. During these cruises, the team saw the first indications that seawater was storing excess carbon dioxide — some of water samples had higher-than-expected concentrations of carbon dioxide and lower-than-expected pH values. When carbon dioxide reacts with seawater, carbonic acid forms. The acid mixes and reacts with other constituents of seawater, reducing its pH.

pH is a measure of acidity. On the pH scale, 7.0 is neutral, with points higher on the scale being “basic” and points lower being “acidic.” Historically, the ocean has had an average pH of 8.16 but it is predicted to fall by as much as 0.4 units by 2100. Because the scale is logarithmic, a difference of one pH unit represents a tenfold change. Even small decreases in the surface ocean’s pH could cause abrupt and large changes for many sea creatures. Image: Cartifact, Inc.

Feely published these findings in the mid-1980s, but few people noticed. The science community wasn’t too concerned about tiny changes in pH in a few areas of the world’s vast ocean. Yet Feely suspected that the problem could be worldwide; if so, even small changes in pH could lead to large changes in the marine ecosystem. “Over the past 20 million years, ocean ecosystems have evolved in a very stable pH environment,” Feely explained. “I’m worried that if concentrations of carbon dioxide continue to rise, the ocean could undergo large and rapid changes in pH.” Feely decided to launch a global investigation. In the early 1990s, he and his team of researchers expanded their observation program from the Atlantic and Pacific Oceans to launch a worldwide effort involving laboratories from several countries. On 99 oceanic cruises over a 10-year period, they collected nearly 72,000 seawater samples from all over the world. Feely invited oceanographer Christopher Sabine to join him at NOAA’s Pacific Marine Environmental Laboratory and, together, they began the arduous task of analyzing the thousands of samples to characterize the global ocean’s carbon dioxide content.

In 2004, they published the results of this colossal effort in two articles in the prestigious journal Science. In the first of the two studies, Sabine and Feely and their colleagues found that the ocean has absorbed about one-third of the carbon dioxide emitted by human activities. This absorption slows the rate of global warming by removing carbon dioxide from the atmosphere, but it also changes the chemistry of seawater. Historically, the average pH of seawater around the globe has been approximately 8.2, a value that is slightly basic. Since the Industrial Revolution, the average pH of surface oceans has decreased to 8.1, which means the seawater is becoming less basic—more acidic. Based on current and projected concentrations of carbon dioxide in the atmosphere, the pH of surface waters is expected to decrease to 7.8 or 7.7 by the end of this century.

Watch Dr. Feely talk about how increased carbon dioxide in the atmosphere is making the oceans more acidic, and how that will affect ocean ecosystems and the marine animals that inhabit them.

Feely led the second of the two Science studies, which was a cross-disciplinary collaboration with biologists and ecologists to assess the potential impact of ocean acidification on marine life forms. The scientists found that in some conditions, acidified water “eats away,” or corrodes, calcium carbonate minerals that many calcifying, or shell-building, organisms rely on to build their shells and skeletons. This study alerted biologists that acidified waters could begin to interfere with marine organisms’ abilities to form their protective armor.

The three maps show model data of how the availability of calcium carbonate is predicted to decrease over the next century at a depth of 10 meters in the ocean—where most corals occur. Blue indicates surface waters are sufficiently saturated with calcium carbonate; organisms have enough material to build their protective shells. Areas that are deep red are expected to be sufficiently acidic to dissolve shell-building organisms. Graph based on models by James Orr of the Laboratory for the Sciences of Climate and Environment in Paris. Image courtesy of the NOAA Environmental Visualization Laboratory.

Feely was dismayed by the list of organisms at risk from ocean acidification. The list included seafood favorites such as oysters, clams, scallops, lobsters, crabs, and shrimp as well as creatures less familiar to humans such as sea urchins, free-floating snails called pteropods, and some types of microscopic plankton. Coral reefs, already stressed by increasing ocean temperatures, made the list as well. Corals rely on calcium carbonate to build their skeletons. When exposed to water with a high carbon dioxide concentration in lab experiments, some of these calcifying organisms showed malformed growth. In the wild, such malformations would make it harder for the creatures to survive and reproduce.

Calcifying organisms come in many shapes and sizes. Crustaceans, such as the blue crab shown at right, and shellfish, including oysters (left) and mussels (center), are popular favorites at any seafood restaurant. Photo at left courtesy of Wikimedia Commons; photo at center courtesy of Claude Covo-Farchi, Wikimedia Commons; photo at right courtesy of Derek Parks, NOAA.

The 2004 studies gave reason for alarm, but also for hope. Ecologically, a large-scale loss of calcifying organisms, that form the base of the marine food chain, could distress populations of larger fish that feed on them, successively disrupting the entire marine food web. However, experiments conducted with computer models after Feely’s findings were published predicted it would be many years before the corrosive waters would start showing up in surface waters. If the models were correct, then there was still time for humans to reduce carbon emissions and avoid the worst consequences of ocean acidification.

Feely wanted to see if the models were right. He continued monitoring the ocean’s changing chemistry, knowing that there might still be some surprises along the way…