Ocean Acidification

Seawater acidification can be induced both by absorption of atmospheric carbon dioxide (CO₂) and by atmospheric deposition of sulfur and nitrogen oxides and ammonia. Their relative significance, interplay and dependency on water-column biogeochemistry are not well understood. Using a simple biogeochemical model we show that the initial conditions of coastal systems are not only relevant for CO₂-induced acidification, but also for additional acidification due to atmospheric acid deposition. Coastal areas undersaturated with respect to CO₂ are most vulnerable to CO₂-induced acidification, but are relatively least affected by additional atmospheric deposition-induced acidification. In contrast, the pH of CO₂-supersaturated systems is most sensitive to atmospheric deposition. The projected increment in atmospheric CO₂ by 2100 will increase the sensitivity of coastal systems to atmospheric deposition-induced acidification by up to a factor 4, but the additional annual change in proton concentration is at most 28%.

Hagens M., Hunter K. A., Liss P. S. & Middelburg J. J., in press. Biogeochemical context impacts seawater pH changes resulting from atmospheric sulfur and nitrogen deposition. Geophysical Research Letters. Article (subscription required).