Figure 2.

Long-term trends in surface ocean pH and CO₂ at station ALOHA in the Central Pacific, along with atmospheric CO₂ from nearby Mauna Loa. Net CO₂ flux was into the ocean, adding carbonic acid and lowering pH. The long-term declining pH trend was highly significant, but is overlain by substantial seasonal variability (Dore et al., 2009). Direct pH measurements agreed well with calculated values based on measurements of total dissolved inorganic carbon (DIC) and alkalinity Surface ocean pH declined by 0.032 pH units from 1989–2006, an approximate 7% increase in H⁺ concentration.