Ocean Acidification Driven by Local Factors as Well, Study Finds

The discovery of dramatic yet natural short-term increases in a North Carolina estuary's acidity is bad news for the fragile ecosystem and others like it, all of which are already facing long-term ocean acidification due to climate change.

Writing in the journal PLOS One, researchers from Duke University explain how, by measuring the acidity of a North Carolina inlet every week for a year, they were able to identify a range of natural factors contributing to temporary spikes in acidity. These included shifts in temperature, water flow and biological activity, among others things.

"The natural short-term variability in acidity we observed over the course of one year exceeds 100-year global predictions for the ocean as a whole and may already be exerting added pressure on some of the estuary's organisms, particularly shelled organisms that are especially susceptible to changes in pH," said Zackary I. Johnson, an assistant professor of molecular biology at the school's Nicholas School of the Environment and lead author of the study. "For vulnerable coastal marine ecosystems, this may be adding insult to injury."

The researchers carried out the study at the Pivers Island Coastal Observatory at the Duke Marine Lab in Beaufort, N.C., gathering measurements from Beaufort Inlet sometimes daily and even hourly in addition to their weekly observations. Doing so allowed them to detect shifts on multiple time scales and revealed that while some changes in acidity took place over an entire season, others lasted days and, in some cases, mere hours. 

"Understanding to what extent pH naturally varies in coastal ecosystems worldwide will be essential for predicting where and when the effects of increasing ocean acidity will be most profound, and what organisms and ecosystems may be most affected," said Dana Hunt, an assistant professor of microbiology and co-author of the study. "Our research demonstrates we have to take into account a wide range of environmental variables, not just pH."