Ocean Acidification, Global Warming’s ‘Evil Twin’

The shells of pea-sized pteropods, also known as sea butterflies, dissolve in water with increasingly lower pH. Image Credit: Nina Bednaršek

The shells of pea-sized pteropods, also known as sea butterflies, dissolve in water with increasingly lower pH. Image Credit: Nina Bednaršek

On a bitterly cold February morning in 1972, a young graduate student at Texas A&M University boarded the research vessel Alaminos in Galveston, Texas, and headed out into the Gulf of Mexico. It was Richard Feely’s first time at sea. It was also the first time the 25-year-old Minnesota native had set eyes on the ocean.

“I was filled with wonder about how vast and pristine the ocean was,” Feely recalls. “I was amazed to find out how quickly I couldn’t see land and how big the waves could really get.”

They got even bigger when the expedition hit a particularly rough patch of weather. The 108-foot long ship pitched and rolled so much that Feely, racked by sea-sickness, vowed he would never go to sea again.

Time, and the pursuit of a doctorate, helped Feely get beyond that first queasy encounter with the ocean. Today, as senior scientist at the National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory (PMEL) in Seattle, Washington, Feely has made more than 50 scientific voyages for a total of three years spent at sea. But it was on those first ocean voyages that Feely discovered his calling: literally charting how humans are altering the fundamental chemistry of the ocean.

Scientists like Feely call the process global warming’s Evil Twin. “Every year,” he explains, “mankind releases about 10 billion tons of carbon in the form of carbon dioxide, primarily by burning fossil fuels.”

About 40 percent of the CO2 stays in the atmosphere with the remaining 60 percent split roughly equally between land and the ocean. When most people hear the phrase “climate change,” they think of the atmosphere, the thin layer of gases surrounding our planet. But the surface of the ocean and the atmosphere are constantly interacting, forming a single system.

Dr. Richard Feely, senior scientist, NOAA, Pacific Marine Environmental Laboratory. Image Credit: Climate.gov

Dr. Richard Feely, senior scientist, NOAA, Pacific Marine Environmental Laboratory. Image Credit: Climate.gov

On land, plants absorb CO2 and act as sinks for carbon, reducing the effects of climate change. The ocean also removes CO2 from the atmosphere. Feely’s seminal work proved the ocean’s role as a carbon sink – a steep price for marine life to pay for human activities.

“The ocean environment is rapidly increasing its acidity as CO2 reacts with seawater in a process known as ocean acidification,” says Feely. Our understanding of ocean acidification and its effects on sea life is still rudimentary. In fact, when Feely began studying these changes, the term ocean acidification hadn’t even been coined. It first turns up in scientific literature in 2001 and didn’t become widespread until 2003 when a paper in the journal Nature ran with this stark prediction: “The coming centuries may see more ocean acidification than the past 300 million years.”

In a 2004 cover article for Science, Feely and his co-authors for the first time presented an overview of the impact this massive influx of CO2 is having on the ocean. Feely sums up the most important change simply: “We are lowering the pH of the ocean, and we’re doing it extremely rapidly” (The lower the pH, the greater the acidity).

Changes in ocean acidity occur naturally over time, but the pace of change is happening as much as 100 times faster than at any time in the last 800,000 years.

Since humans first began burning fossil fuels on a large scale, the ocean has increased its acidity by 30 percent. To put that into perspective, imagine biting into an apple and discovering it’s as acidic as vinegar. Worse, says Feely, the trend has been accelerating as more and more CO2 is emitted.

“If we continue on the same trajectory,” he cautions, “by the end of this century we will see a 100-to-150 percent increase in the acidity of the ocean.”

Changes in pH over the last 25 million years. Image Credit: Turley, et al., 2006.

Changes in pH over the last 25 million years. Image Credit: Turley, et al., 2006.

There are winners and losers from the increased levels of CO2 in the ocean. Some species, like sea grasses, could benefit from the change. But the situation is very different for corals, snails, clams and oysters. These organisms have one thing in common, says Feely: “They produce a calcium carbonate shell or skeleton.”

OA makes it harder for marine creatures like oysters to build and maintain their shells, a change that threatened to wipe out the oyster industry in the Pacific Northwest (See Altered Waters).

The problem was first noticed in 2006, when oyster larvae in hatcheries were having difficulty producing shells. Many were dying within their first two days of life. By 2009, the problem had become a crisis for the shellfish industry in Washington, which contributes $100 million annually to the state’s economy. U.S. Sen. Maria Cantwell, D-Washington, obtained $500,000 in funding for NOAA to find out what was killing the larvae. Using water sensors, the researchers determined that acidified waters were causing the die-offs. By making a few simple changes, including adding sodium carbonate to the hatchery waters, industry and scientists were able to reverse the problem.

“It’s a fabulous story,” says Feely. “The industry would have died without those actions.”

Feely is quick to add that the success was a “stopgap measure.” Their efforts worked in enclosed hatcheries where the chemistry of the water could be controlled. “But,” he says, “it does nothing to help the shellfish farmers who have to cope with the increasing CO2 concentrations in embayments. We have to come up with additional adaptations for the shellfish farmer.”

“Of course if [coral reefs] are going under because of water quality then warming and OA means they won't stand a chance. Sadly, the combined effects are worse than one on its own. ” - Dr. Carol Turley, Plymouth Marine Laboratory, U.K. Image Credit: Jim Maragos/U.S. Fish and Wildlife Service

“Of course if [coral reefs] are going under because of water quality then warming and OA means they won’t stand a chance. Sadly, the combined effects are worse than one on its own. ” – Dr. Carol Turley, Plymouth Marine Laboratory, U.K. Image Credit: Jim Maragos/U.S. Fish and Wildlife Service


And it’s not just oysters that are hurt by OA. Researchers have found that this change in ocean chemistry makes corals more prone to rapid bleaching, a potentially fatal condition in which the coral polyps expel their food-producing symbiont. OA appears to affect the neurotransmitters of some fish, causing changes in behavior responses that make them more vulnerable to predators. OA also impairs reproductive success in other marine creatures and interferes with respiration in squids.

In their first year of life, fish like salmon rely on a diet that includes pteropods, tiny marine snails, to survive. Pteropods build calcium carbonate shells so delicate that they’re transparent and are tremendously sensitive to OA. Their shells are already dissolving. “That,” says Feely, “doesn’t bode well for the entire food chain in the ocean.”

A critical first step in dealing with OA is monitoring. That’s because ocean chemistry, including pH level, varies depending on a number of factors including water temperature and salinity.

For example, “CO2 goes into the oceans more readily in colder water,” says Feely. That means that pteropods and other creatures at high latitudes that are sensitive to ocean acidification are feeling the effect of OA sooner than similar organisms in warmer waters.

This interactive map offers the best information available on the current inventory of global OA observing platforms. Image Credit: Global Ocean Acidification Observing Network

This interactive map offers the best information available on the current inventory of global OA observing platforms. Image Credit: Global Ocean Acidification Observing Network

The Global Ocean Acidification Observing Network (GOA-ON) is a recent internationally coordinated effort to monitor levels of carbon in the ocean around the world. Scientists have been coordinating ocean observations since the United Nations Intergovernmental Conference on Oceanographic Research, held in Copenhagen, Denmark, in 1960. In preparation for the conference, Roger Revelle, then-director of the Scripps Institution of Oceanography, stressed the need for such an international effort. More than two decades before anthropogenic climate change entered public discourse, Revelle wrote:

“In general, oceanographic research, like many other kinds of research, is best done by individuals or small groups working independently. However, there are some research problems that require international co-operation … Scientific problems that require nearly simultaneous observations over a wide area or over the entire ocean also demand international co-operation in taking the observations, and co-ordination to ensure comparability of results.

“An example is the present attempt to determine the total carbon dioxide content in the atmosphere and the change in this content with time as a result of the input from fossil fuel combustion and the loss to the ocean and biosphere. One of the questions we are asking is: Where is the carbon dioxide absorbed by the ocean? Does it remain in the surface layers or does it extend throughout the ocean volume?”

Over the next 30 years, 1 million measurements of ocean carbon were made. By 2010, researchers like Feely were recording 1 million such measurements a year.

Today, GOA-ON participants collect daily readings from several countries and uses sensors on ocean buoys, dedicated research vessels, and ships. Feely directs the U.S. West Coast monitoring system for NOAA, working with states and eight federal agencies.

“We’re working to expand our monitoring capability throughout the waters of the United States,” he says, while stressing the need to keep expanding monitoring efforts internationally. Scientists are making headway studying the problem in many countries, including in the European Union and North Africa, but many other regions still lack the necessary infrastructure to monitor OA.

“That’s the next big push,” says Feely. For all the very real progress that has been made since 1960, the task of understanding OA throughout the global ocean still presents an enormous challenge to scientists. And the stakes, Feely emphasizes, couldn’t be higher.

“One in seven people on the planet depend on seafood for protein,” he adds.“Clearly, we have our work cut out for us.”

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