Ocean Acidification and the Souring of Our Waters

All predictions suggest that the atmospheric CO2 will continue to rise into the next century, with a concomitant progressive reduction in oceanic pH. The impact on phytoplankton is complicated. Phytoplankton have carbon-concentrating mechanisms that buffer their sensitivity to changes in CO2, but these mechanisms operate differently for different types of phytoplankton. Changing CO2 and pH levels also impact rates of calcification for calcifying algae and rates of N2 fixation for N2–fixing cyanobacteria. Understanding how future oceans may change requires recognition and quantification of not only the direct effects of the single stressors (rising CO2 levels and decreasing pH levels), but how such effects change when multiple stresses, such as nutrient limitation or warming, are also imposed. This chapter first explores the effects of increasing CO2 on ocean chemistry. Then, the complex effects of rising CO2 and decreasing pH on phytoplankton photosynthesis, N2 fixation, calcification, algal toxicity, and community interactions are discussed.