Ocean Acidification: Global Warming’s Evil Twin
Earth’s oceans are carbon sinks, removing carbon dioxide from the atmosphere and helping prevent global warming, right? Unfortunately, carbon dioxide turns into an acid in the ocean, causing its pH to rise–a process called ocean acidification. Those who’ve heard of this phenomenon often associate it with declining coral reefs in the tropics. However, one of the best places to observe this effect is in Oregon, where a unique ocean environment creates seasonal peaks in acidity that are causing huge losses in the oyster industry. The Pacific Coast Shellfish Growers Association has estimated the loss at $34 million since the problem started in 2006.
“We’ve linked together high carbon dioxide water with the failures in those hatcheries,” said George Waldbusser, assistant professor of ocean ecology and biogeochemistry at Oregon State University. “They were basically on the verge of failure in 2008.”
The problem is seasonal. During the summer, hot days in the valley coincide with windy, foggy days on the coast due to summer winds. These winds drive dense, cool water up toward the ocean surface–a process known as upwelling. Upwellings bring nutrient-rich water to the surface, but the water is also richer in carbon dioxide. Combined with higher baseline levels of carbon dioxide from increases in the atmosphere, the upwellings today are too acidic to support young oysters. Specifically, the water interferes with their ability to grow shells and develop normally.
“If they’re exposed to water that has high carbon dioxide it seems that it is harder for them to grow a shell. It also affects their overall growth–it marks that larvae for life,” said Waldbusser.
“It’s really hitting them at the basic level of their biology,” added Francis Chan, an assistant professor in OSU’s zoology department. “They’ve evolved to develop shells; we’re making it harder and harder for them to do so every day.”
During the upwellings, levels of carbon dioxide approach 2,000 parts per million. To put this in perspective, consider that the current level in the atmosphere is about 400 parts per million. The Natural Resources Defense Council reports that ocean acidity has increased by 30 percent over the last 250 years; potential consequences range from species extinction to disruptions in the food web and impacts on fishing and tourism.
Oregon’s hatcheries have started taking adaptive measures, pumping water selectively and using precise equipment to monitor the water coming in. They fill tanks during times when the water is not too acidic, and add sodium carbonate to the high-acid water to buffer it, or reduce its pH.
As time goes on, normal ocean water will become more and more of a rare thing. The problem we’re seeing today isn’t a consequence of current emissions, but rather emissions that went into the atmosphere 30 or 50 years ago when that water was in contact with the atmosphere before going into the ocean’s interior. This means that we have not yet seen the effects of today’s increased levels of carbon emissions on the ocean.
“The ocean chemistry that we see today is a reflection of things that we’ve done in the past in terms of adding carbon dioxide into the atmosphere,” said Chan. “The changes we’re going to see are already built into the system.”
“The concern the industry has is whether the recent failures are the tip of the iceberg,” commented Waldbusser.
Oysters aren’t the only ocean life that will be affected. Many other organisms build shells and skeletons of calcium carbonate, which dissolves in acidic water.
Francis Chan of OSU mentioned coralline algae as another potential loser in an acidic ocean–plus the organisms that rely on them in turn. Numerous other species grow upon coralline algae, which has a skeleton even more sensitive to drops in pH than the oyster’s.
It’s a complicated process of figuring out future effects–not just which organisms, but at which life stages they’re vulnerable. Some species might thrive–such as competing algae. Specific effects on organisms are also unknown; no one would have guessed that it prevents clownfish from being able to sense their predators in the tropics. It’s unknown whether there’s a safe level of change that the system can absorb, or whether we’re approaching a tipping point.
“At OSU we’re doing a ton of work to try and get a handle on this issue,” said Chan. “The $64,000 question is how much can they cope with?”
For now, the acidic upwellings on the Oregon coast provide a sneak peek of what might happen elsewhere as ocean acidification continues.
“Oregon is one of the ground zeros for looking at this fairly large change in ocean chemistry,” Chan said. “We get an early glimpse of things to come.”
By Jen Matteis