Ventilation and buffering capacity effects on ocean acidification in low oxygen environments.

Abstract

Ocean acidification results from oceanic uptake of anthropogenic CO₂ (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 CO₂ (pCO₂), 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, pCO₂ 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.