Ocean Acidification: Investigation and Presentation of the Effects of Elevated Carbon Dioxide Levels on Seawater Chemistry and Calcareous Organisms

Ocean acidification refers to the process by which seawater absorbs carbon dioxide from the atmosphere, producing aqueous carbonic acid. Acidic conditions increase the solubility of calcium carbonate, threatening corals and other calcareous organisms that depend on it for protective structures. The global nature of ocean acidification and the magnitude of its potential impact on marine ecosystems and the industries they support make it an important and engaging topic to explore in the undergraduate laboratory. In this multiweek experiment, designed for second year analytical and environmental chemistry courses, artificial seawater samples containing pieces of seashell or coral were prepared. One sample was pressurized with carbon dioxide and stirred for 1 week, while the other was stirred without carbonation. Mass and pH measurements and carbonate, bicarbonate, calcium(II), and magnesium(II) titrations were performed on samples before and after treatment. Through data analysis and a rigorous consideration of the acid base and solubility equilibria involved, students concluded that carbonation significantly decreased seawater pH and caused appreciable seashell and coral dissolution, which raised the bicarbonate and calcium(II) concentrations. Minimal change in the seawater chemistry or carbonaceous material was observed for the noncarbonated sample. Overall, the experience provided a meaningful experimental context for titration analyses and a practical application of the conceptual treatment of a multiequilibrium system. In addition to the experiment, a corresponding oral presentation assignment is presented, in which students produced a video designed to educate a general audience on the topic of ocean acidification by using their experimental results as support. Through this assignment, students reflected on the broader ecological and societal ramifications of ocean acidification and developed the ability to communicate scientific knowledge to a nonscientific audience, a critical collaborative skill for addressing such multifaceted issues.