Researchers measured the acidity of seawater off the Pacific Northwest coast for eight years. Every half hour, so there’s plenty of data.
"Professor Timothy Wootton from the department of ecology and evolution, University of Chicago, in Illinois, says such dramatic results were unexpected as it was thought that the huge ocean systems had the ability to absorb large quantities of CO2.
‘It’s been thought pH in the open oceans is well buffered, so it’s surprising to see these fluctuations,’ he said.
The findings showed that CO2 had lowered the water pH over time, demonstrating a year-on-year increase in acidity."
Findings were reported in the journal PNAS. The BBC article is available here.