Southern Ocean's acidification may threaten marine life

November 2, 2015

Ocean acidification from atmospheric carbon dioxide is expected to rapidly change the Southern Ocean's chemistry during the next few decades. The onset of harmful conditions will be too abrupt and the duration of these events too long for some organisms to adapt, according to a study published today in the journal Nature Climate Change.

The ocean absorbs excess carbon dioxide from the atmosphere. This process consumes carbonate ions, which are necessary for some marine organisms to build and maintain their shells. If the carbonate ion concentration drops below a threshold, or becomes “undersaturated,” these organisms end up fighting dissolution.

Using a number of Earth system models, University of Alaska Fairbanks researcher Claudine Hauri and colleagues from the University of Hawaii at Manoa explored how the uptake of anthropogenic carbon dioxide and the resulting ocean acidification will affect the Southern Ocean over the next century.

The study projects that the duration of undersaturation events will increase abruptly from one month to more than six months, in less than 20 years upon their onset, and could reach nearly year-long durations by the end of the century in large parts of the Southern Ocean. (Watch animations here.)

“This is a clear warning sign. Given the projected rapid expansion and prolongation of these harmful conditions, it remains very uncertain whether tiny sea snails, called pteropods, and other vulnerable marine organisms will be able to adapt,” said Hauri, a chemical oceanographer at the UAF International Arctic Research Center and lead author of the study.

The pteropod is one of the most threatened marine organisms, a tiny, shell-building sea snail that serves as a staple food for plankton, fish, whales and seabirds. Pteropods are also an important component of the food web in Alaska's seas and can make up an important part of the diet of young salmon.

“Because oceans in polar regions have naturally low levels of carbonate ion concentrations, seas around Alaska are also close to this critical threshold,” added Hauri.

Increased freshwater discharge from sea ice and glacier melt due to rising temperatures decreases the level of carbonate ion concentrations even further. “This in turn enhances the problem even more,” she said.

“Other organisms that build their shells or skeletons with carbonate ions, such as oysters, mussels and corals, may be in danger as well,” added Hauri.

As some organisms are affected, the predator-prey dynamics in the food web will change, influencing yet other organisms.

With five times more coastline than any other state, Alaska depends heavily on the ocean. Ocean acidification’s potential impact on subsistence and commercial fisheries, for example, can be very serious.

“Only an immediate and substantial reduction in human-induced carbon dioxide emissions would relieve the risks of ocean acidification to our marine organisms and the livelihoods that depend on them,” Hauri concluded.

Photo by NOAA/Nina Bednaršek. The figures show the duration of harmful surface events for today, 2055 and 2095.. Inset: Example of pterapod showing in situ dissolution due to ocean acidification.

The study, “Abrupt onset and prolongation of aragonite undersaturation events in the Southern Ocean,” funded by the National Science Foundation Ocean Acidification Program (OCE-1314209), was published today in the journal Nature Climate Change.

ADDITIONAL CONTACT: Claudine Hauri, 907-474-7059, chauri@alaska.edu.