Learning the main facts about ocean acidification, watching movies, reading scientists' blogs from the Arctic may raise curiosity a lot on this topic - but going further into understanding the phenomena involved gains a lot from actually experimenting these phenomena.

In this perspective EPOCA and CarboSchools joined forces to test and describe hands-on experiments for science teachers interested to illustrate ocean acidification in their classrooms. This page introduces thirteen experiments, generally designed for pupils from 10 to 18 years old, potentially adaptable to any age group within that range as well as for museum presentations:

1) one preliminary experiment to familiarize students with basic knowledge on pH: What is pH?

2) one experiment offering an overview of the main phenomena involved in ocean acidification: "Atmospheric CO₂ can produce ocean acidification" - pupils will observe a seawater acidification by introducing CO₂ directly on seawater or by increasing CO₂ in air above it with a candle. They will also observe that CO₂ can pass from seawater to air. Effects on shells can also be observed.

3) Six experiments illustrating the physico-chemical laws which cause ocean acidification: how CO₂ travels between the atmosphere and the water, and how temperature and salinity influence this.

CO₂ and pH: this experiment shows the influence of the CO₂ absorbed by water on its pH.

• Interaction at the Air-Water Interface demonstrates gas exchange and equilibration at the boundary layer between air and water. In part 1, pupils observe acidification of water due to CO₂ introduced directly in the water. In part 2, pupils observe that a high atmospheric CO₂ concentration will produce water acidification.
• How does temperature affect the solubility of CO₂ in water? This experiment explores the effects of water temperature on the solubility of CO₂ in water.
• Effects of Increased CO₂ in the Air on Seawater and Distilled Water. Pupils compare the effect of increasing atmospheric CO₂ concentrations on seawater and freshwater, thus investigating the influence of salinity on variations of pH.
• pH-Regulation of Seawater: The Role of Carbonate (CO₃) and Bicarbonate (HCO₃). This simple experiment uses an indicator solution to enable pupils to visualise the buffering capacity of seawater. This activity will help pupils understand how the different dissolved inorganic carbon ions affect the pH of distilled water and seawater.

4) Two experiments addressing the key biological question with OA: what could be the consequences of the decrease of seawater pH for marine organisms?

• What could be the consequences of an acid pH for living beings? highlights the effects of a very low pH (not existing in natural conditions) on the shell of calcifying animals.
• Long term shells experiment shows the influence of a decreasing pH on shells of marine organisms mainly made of limestone.

5) Two additional experiments on the role of plants in the marine carbon cycle:

• Uptake of Carbon Dioxide from Water by Plants shows the potential role of marine plants in mitigating the acidification caused when CO₂ is dissolved in water.
• Carbon Dioxide Fertilization of Marine Microalgae (Dunalliela sp.) Cultures illustrates the impact of carbon dioxide on microalgal growth in the aquatic environment.