A 20-year study of the Pacific Ocean waters northwest of Hawaii has documented a sustained rise in the water’s acidity caused by air pollution, a change that could lead to a cascading effect on ocean life if not checked.
“Only by doing it in this long-term fashion can we say confidently that the ocean is getting more acidic,” said John Dore, lead author of the study recently published in the Proceedings of the National Academy of Sciences. Dore is a professor in the Department of Land Resources and Environmental Sciences at Montana State University who has been working on the Hawaii Ocean Time-series project for 18 years.
He said fluctuations in ocean acidity occur naturally, making it difficult for researchers to separate out the increase from the “background noise.” But with 20 years of data, the rise was easier to document.
“It’s surprising how difficult it is in practice to refute this or confirm it,” Dore said. “There’s a lot of debate about if it’s going on and the effects.”
The increase in acidity results when carbon dioxide in the atmosphere, which is produced by the burning of fossil fuels, dissipates in ocean water.
“Animals grow shells by precipitating calcium carbonate,” said Steve Running, a climate change expert at the University of Montana. “When you have a more acidic solution, the shells just won’t form. That’s becoming the big issue for ocean scientists.”
Shellfish such as shrimp and clams as well as coral all rely on calcium carbonate.
“This is a mechanism that is so fundamental that if we do reach that point there could be an incredible cascade through the whole ecosystem,” Running said.
He added that a decade ago, the big concern was warming ocean temperatures, but ocean acidification has risen as a bigger issue since then.
“It’s really a more fundamental change in the chemistry that supports ocean life, and that’s stronger than temperature effects and more all-pervasive,” Running said.
Dore started his work on the project as a student in 1989. Even though he’s leaving the project, he said the goal is to maintain the study funded by the National Science Foundation because of its long-term recording of data.
“This data has been so scientifically eye-opening that there’s been a push to keep it going,” he said. “Beyond confirming the progression of acidity at the surface of the ocean, we found other things that were a bit surprising.”
Year-to-year variations in the ocean’s acidity are significant, Dore said, and it appears to be driven by changes in climate and the effect of currents mixing in the ocean.
“Another thing we found is the rate at which the ocean is getting more acidic is actually greater at deeper portions,” he said. “That was surprising.”
Dore said one possible explanation of higher acidification deeper in the ocean is that currents move water from the north, where the water is more acidic. Those waters are then mixed into the water northwest of Hawaii.
Another possibility is that the ocean’s biology is creating the changes. As algae grow and die during the peaks and troughs of acidification, they transfer the carbon dioxide from the ocean’s surface to its depths.
“It’s probably a little of both,” Dore added. “So when they put it in models, they really have to take into account the biology, not just the chemistry.”
Should the dispersal of atmospheric carbon dioxide stay on its current track, the effects could be substantial.
“Estimates are that, certainly by the end of this century at the CO2 trajectory we’re on now, that the ocean will be acidic enough that the majority of shellfish wouldn’t make it,” Running said.
Dore is a bit more conservative in his predictions.
“Acidification is proceeding right on target,” Dore said. “The changes are small and slow, but they are expected to increase and over decades could impact the ocean biology.”
Brett French, Billings Gazette, 31 July 2009. Article.
