Revisiting four scientific debates in ocean acidification research

Abstract. In recent years, ocean acidification has gained continuously increasing attention from scientists and a number of stakeholders and has raised serious concerns about its effects on marine organisms and ecosystems. With the increase in interest, funding resources, and the number of scientific investigations focusing on this environmental problem, increasing amounts of data and results have been produced, and a progressively growing and more rigorous understanding of this problem has begun to develop. Nevertheless, there are still a number of scientific debates, and in some cases misconceptions, that keep reoccurring at a number of forums in various contexts. In this article, we revisit four of these topics that we think require further thoughtful consideration including: (1) surface seawater CO₂ chemistry in shallow water coastal areas, (2) experimental manipulation of marine systems using CO₂ gas or by acid addition, (3) net versus gross calcification and dissolution, and (4) CaCO₃ mineral dissolution and seawater buffering. As a summation of these topics, we emphasize that: (1) many coastal environments experience seawater pCO₂ that is significantly higher than expected from equilibrium with the atmosphere and is strongly linked to biological processes; (2) addition of acid, base or CO₂ gas to seawater can all be useful techniques to manipulate seawater chemistry in ocean acidification experiments; (3) estimates of calcification or CaCO₃ dissolution based on present techniques are measuring the net of gross calcification and dissolution; and (4) dissolution of metastable carbonate mineral phases will not produce sufficient alkalinity to buffer the pH and carbonate saturation state of shallow water environments on timescales of decades to hundreds of years to the extent that any potential negative effects on marine calcifiers will be avoided.