Abstract
Ocean acidification results from oceanic uptake of anthropogenic CO(2) (ΔC(ant)). Weak carbonate buffering capacity (high Revelle factor, RF) amplifies acidification, but its role in persistently low-oxygen, poorly ventilated regions is unclear. Here we compare preindustrial to present changes in partial pressure of CO(2) (pCO(2)), hydrogen ion concentration ([H(+)]), pH, aragonite saturation state (Ω(ara)), and RF within permanent oxygen minimum zones (OMZs) versus well-ventilated regions. We find that acidification is negligible in the least-ventilated, poorly buffered lower OMZs, but detectable in moderately ventilated upper OMZs. In upper OMZs, pCO(2) and [H(+)] increase faster while Ω(ara), pH, and RF change more slowly than in adjacent well-ventilated regions. Our analysis reveals that limited ΔC(ant) delivery by ventilation ultimately constrain acidification in low-oxygen regions. Accordingly, low-oxygen regions with poor ventilation will experience less acidification than well-ventilated regions, and different metrics (notably [H(+)] versus Ω(ara)) respond distinctly due to their different definitions and sensitivities.