Blowing bubbles through oceans may protect coral reefs

US researchers have found that blowing tiny bubbles through sea water could help protect coral reefs and oyster farms from oceans, which have increasingly turned acidic through human activities.

The idea is that tiny bubbles will help cleanse the world's oceans of carbon dioxide (CO2) by drawing the gas out of the seawater and transferring it to the atmosphere. This may provide a relatively inexpensive solution to one of the biggest threats facing coral reefs today.

Ocean acidification harms a variety of marine organisms, but especially those that use calcium carbonate to assemble their skeletons and shells, such as 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," said lead author David Koweek, a doctoral researcher at Stanford University.

The researchers, in the study published online in the journal Environmental Science and Technology, demonstrated that bubbling air through seawater for a few hours in the early morning can enhance the transfer rate of CO2 between the ocean and the air up to 30 times faster than natural processes, resulting in a significant reduction in local marine concentrations of the greenhouse gas.

"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," explained one of the researchers Rob Dunbar, professor at Stanford University.

If timed correctly, bubble stripping could be an effective means of reducing extreme acidity in coastal ecosystems now and in the future.

It could prove useful for protecting small sections of shallow coastline that are ecologically, culturally, or commercially important, the scientists maintained.

Ultimately, bubble stripping could help protect more than just coral. Many coastal ecosystems, including salt marshes, seagrass meadows, and mangroves undergo daily variations in CO2 due to photosynthesis during daylight hours and respiration during nighttime hours.

The team set up a bubbling experiment in a sensor-laden water tank at Stanford's Hopkins Marine Station.

Each night, they would fill the tank with bags of giant kelp -- large seaweed. Throughout the night, the kelp would respire, adding CO2 to the water, and thus acting to simulate the CO2 buildup that occurs from respiration in coastal ecosystems at night.

The team would then arrive the following morning, remove the kelp, and begin to bubble the high CO2 seawater in order to test how bubbling lowers the CO2 concentration.

They found that just two hours of bubble-mediated ventilation could increase the transfer of CO2 from the ocean into the air by 10 to 30 times.