Could blowing tiny bubbles through seawater help protect coral reefs and oyster farms from increasingly acidic oceans? New research from Stanford University points toward "yes."
The idea is that tiny bubbles will help cleanse the world's oceans of carbon dioxide by drawing the gas out of the seawater and transferring it to the atmosphere. This, researchers say, could provide a relatively inexpensive solution to one of the biggest threats facing coral reefs today.
Ocean acidification is largely driven by human activity and carbon dioxide emissions. Researchers say as much as 30 to 60 percent of all the coral reefs have died since the Industrial Revolution.
Carbon dioxide absorbed into the ocean poses serious risk to a variety of marine organisms - especially those with calcium carbonate shells or exoskeletons, including coral, mussels and oysters.
"Ocean acidification is particularly troublesome for coral reefs because the entire structure of the ecosystems is built upon the calcium carbonate skeletal remains of dead coral," explained David Koweek, lead author of the study and a doctoral candidate at Stanford's School of Earth, Energy & Environmental Sciences. "Ocean acidification makes it difficult for corals to calcify and makes it easier to erode these skeletal remains, threatening the integrity of the entire reef."
Coral reef systems also provide a home for thousands of organisms and protect island communities from surging waves and damaging tropical storms. Therefore, further coral reef loss could have catastrophic impacts on marine ecosystems. That's where researchers' innovative technique using air bubbles comes into play.
Koweek and his team found that bubbling air through seawater for a few hours in the early morning makes the transfer rate of carbon dioxide between the ocean and the air up to 30 times faster, compared to natural processes. This, in turn, effectively reduces local marine carbon dioxide concentrations.
"The nice thing about the bubble pulse method is that it provides an engineering technique that can help bring us closer to conditions that coral reefs were used to 100 years ago, and to which they've been adapted for many thousands of years," said Rob Dunbar, study co-author and professor of earth science at Stanford.
In a series of bubbling experiments, researchers would fill a sensor-laden water tank with bags of giant kelp. This was designed to simulate the carbon dioxide buildup that occurs in marine environments overnight from plant respiration. In the morning, the team would then remove the kelp and blow bubbles in the seawater to lower carbon dioxide levels. If the bubbles have lower concentrations of carbon dioxide than the surrounding water, the gas will naturally diffuse into the bubbles.
It is believed that this bubble stripping technique, as it has been named, could be useful in small sections of shallow coastline. On such a small scale, researchers say the benefits of lowering ocean acidity in marine environments would greatly outweigh the relatively small amount of atmospheric carbon dioxide generated by the bubbling process and by the compressors used to produce the bubbles.
"If this idea takes off, you could imagine people running these compressors on solar power. In the tropics, where there's a lot of sunlight, you could charge your compressors with solar energy during the day and then bubble at night," Koweek said, adding that the technique could help protect more than just coral. "Many coastal ecosystems, including salt marshes, seagrass meadows, and mangroves undergo daily variations in carbon dioxide due to photosynthesis during daylight hours and respiration during nighttime hours."
Their study was recently published in the journal Environmental Science & Technology.
