New UC Davis research suggests that assumptions used for 50 years in reconstructing some aspects of Earth's climate history have lacked a critical variable: fluctuations in the acid-base balance of the ocean.

The discovery could help explain why atmospheric carbon dioxide has increased since the last ice age and improve understanding of the ocean's role in global warming.

"If the changes that we see in the fossil record were due to changes in the ocean's pH, it means we'll have to take a hard look at the ocean's carbon-buffering system as a controller of greenhouse gases," says lead researcher Howard Spero, an associate professor of geology. "It will reinforce the notion that oceanic processes drive climate."

The Spero group discovered the importance of ocean pH during studies of living marine organisms called foraminifera. Many long-standing conclusions about ancient climate are based on analyses of stable isotopes in fossil foraminifera shells.

"The entire community of geologists, paleogeologists and paleoclimatologists have been using these stable-isotope tracers to reconstruct Earth's climate history. But there's always been something missing," Spero says. "Using this new environmental parameter will allow them to more completely tell their stories."

The journal Nature will publish the findings on Thursday, Dec. 4. Spero's co-authors are Davis geology graduate student Bryan Bemis and collaborators from UC Santa Barbara and Germany.