Rate of ocean acidification may accelerate, scientists warn

Last summer, scientists met at the University of Washington to address alarming findings concerning the rapid acidification of the world’s oceans. Experts at that symposium warned that wildlife in the Salish Sea, from salmon to shellfish, may start to see significant effects from changing water chemistry within the next 10 to 20 years. This article summarizes the symposium’s key findings and was commissioned and edited by the Washington Ocean Acidification Center which hosted the gathering. Funds for the article were provided by the Washington state legislature. [A version of this article was originally published by the Washington Ocean Acidification Center.]

Ocean acidification, which threatens sea life throughout the world, is affecting Pacific Northwest waters — including the Salish Sea — sooner than most regions around the globe, according to ongoing studies.

Even more alarming is new research now causing oceanographers to predict that the changes in ocean chemistry will soon pick up the pace, causing the rate of ocean acidification to accelerate.

“If we continue down the road we are on, we will see very dramatic changes in the next 10 to 20 years,” said Richard Feely, senior scientist at NOAA’s Pacific Marine Environmental Laboratory in Seattle.

Ocean acidification, caused by the absorption of more and more carbon dioxide from the atmosphere, can affect the survival, growth and behavior of all kinds of sea creatures. New evidence suggests that ocean acidification impairs the sense of smell in salmon, impedes growth in herring and other critical prey species, and can affect plankton populations, thereby altering the food web.

Most notable in the struggle for survival amid ocean acidification are species that form shells of calcium carbonate — including succulent oysters that support a vast industry, solitary corals that live in local waters, and a wide variety of tiny animals that serve as food for others.

These new predictions are the result of a growing understanding of the chemical changes taking place in different parts of the ocean, said Feely, who presented the latest findings during a 2019 Ocean Acidification Science Symposium in Seattle. Of particular concern, he noted, is what could become a dangerous weakening of the ocean’s buffer system — an elegant set of chemical reactions that have so far inhibited an even faster rate of ocean acidification.

Researchers at the symposium also presented new findings about the effects of ocean acidification on salmon, herring, Dungeness crabs, plankton and eelgrass, while others talked about future conditions and what can be done to turn things around.

Ocean chemistry

Over several decades, scientists throughout the world have been joining forces to better understand ocean acidification and its ecological consequences. The Global Ocean Acidification Observing Network, known as GOA-ON, has been compiling and sharing data from a vast array of sources —from stationary monitoring buoys to ocean-going research vessels to merchant ships that carry sensors while delivering cargo around the world.

Researchers have long understood that the ocean is far from uniform when it comes to absorbing and transforming excess carbon dioxide, said Feely, who has been studying ocean acidification for 37 years. New information is helping to explain why Northwest waters are so vulnerable to acidification and why the perils are growing greater as time goes by.

“We’re not there yet, but we’re at a turning point,” he said. “We have to make a decision about what we are going to do. The result (for marine life) will be a function of our decisions.” — Richard Feely, NOAA

As carbon dioxide increases in the atmosphere from the burning of fossil fuels and from deforestation, about 25 to 30 percent of it gets absorbed into the ocean, where it is transformed into other carbon compounds.

In the North Pacific, subsurface currents along the West Coast carry acidified water northward, where upwelling brings corrosive low-oxygen water up from the depths. That’s why shell-bearing creatures in Washington, Oregon and Northern California are especially vulnerable to ocean acidification.

New studies on pteropods — free-swimming sea snails — have revealed that the shells of these tiny animals collected along the coast are fully one-third thinner than those of pteropods collected in the open ocean, says Nina Bednaršek, senior scientist at the Southern California Coastal Water Research Project. Such studies raise concerns not only for the survival of pteropods but also for the multitude of species that eat them.

New evidence also suggests that acidification has already begun to upset the chemical balance of the ocean, including its ratio of buffering chemicals, which so far have helped to quell the rate of acidification. But buffering has its limits. Once a threshold is reached, the rate of acidification is expected to accelerate, like a brakeless freight train on a downhill track.

The chemistry of the ocean is complex, but buffering can be viewed as a balance between two closely related compounds — with carbonate and bicarbonate being the key partners. They can readily change form from one to the other as acidity increases or decreases. This partnership helps to maintain a fairly stable pH — the common measure of acidity.

Buffering comes into play as the ocean absorbs carbon dioxide through direct contact with the atmosphere. As CO2 gas enters the water, it readily converts to carbonic acid and begins to influence the buffer, turning carbonate into bicarbonate. As carbonate is consumed, the rate of acidification increases.

At the same time, the increase in carbon dioxide also influences calcium carbonate  — the material of shells. Higher acidity tends to dissolve calcium carbonate molecules into separate calcium and carbonate ions. Thereafter, the reduced concentration of carbonate ion makes this critical mineral less accessible to shell-forming animals. At low concentrations of carbonate ion, favorable chemical reactions can actually run in reverse, dissolving the shells of living creatures.

If concerns about coastal waters are running high, trends for Puget Sound and the entire Salish Sea are raising the loudest alarm bells, Feely said. That’s because freshwater flowing in from rivers and streams lowers the buffering capacity even further through dilution.

Christopher Dunagan, Salish Sea Currents Magazine, 15 December 2019. Full article.

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