Lab 6: Ocean Acidification

The lab activity described here was developed by Candace Dunlap of TERC for the EarthLabs project.

Use the button at the right to navigate to the student activity pages for this lab. To open the student pages in a new tab or window, right-click (control-click on a Mac) the "Open the Student Activity" button and choose "Open Link in New Window" or "Open Link in New Tab."

Investigation Summary and Learning Objectives

Image caption. Image source: MBARI

Students learn more about the impact of increased levels of carbon dioxide in the ocean. The most worrisome result may be the changing pH level: the ocean is becoming more acidic. The carbonic acid that results from the reaction of water with carbon dioxide is dissolving the shells of sea-dwelling critters from oysters to the single-cell coccolithophore.

After completing this investigation, students will be able to:

Explain what ocean acidification is and why it is happening.
Describe ways in which individual species and marine ecosystems may respond to ocean acidification.
Describe how ocean acidification may impact the ability of oceans to sequester carbon.

For more information about the TOPIC, read the section titled Background Information under Additional Resources below

Activity Overview

In Part A: Students analyze time series graphs to search for relationships and trends in atmospheric CO₂, dissolved seawater CO₂ and changes in ocean pH. They are introduced to a chemical understanding of pH. Students then carry out a class experiment on the effects of increased amounts of CO₂ on pH of water.

In Part B: Students read an ABC news report on ocean acidification and oyster farming off the coast of Oregon. Then, they watch a movie on ocean acidification narrated by the actress Sigourney Weaver that will introduce them to ocean acidification and its predicted impacts on marine organisms.

In Part C: Students review and analyze the results of research compiled by the Woods Hole Oceanographic Institute on the effect of ocean acidification on a variety of marine organisms. They then read research on the importance of echinoderms in the carbon sink and carry out a Virtual Lab on the effect of increasing acidic sea water on sea urchin larvae.

Printable Materials

To download one of the PDF or Word files below, right-click (control-click on a Mac) the link and choose "Save File As" or "Save Link As."

ABC News Article: Ocean Acidification Hits Northwest Oyster Farms (Acrobat (PDF) 146kB Jul6 11)
Doc _______
Stop and Think Questions lab 6-A (Microsoft Word 2007 (.docx) 67kB Mar13 12) Lab 6-B (Microsoft Word 2007 (.docx) 38kB Mar13 12) Lab 6-C (Microsoft Word 2007 (.docx) 100kB Mar13 12)
Lab 6-A (Microsoft Word 2007 (.docx) 77kB Mar13 12) Lab 6-B (Microsoft Word 2007 (.docx) 47kB Mar13 12) Lab 6-c (Microsoft Word 2007 (.docx) 101kB Mar13 12) Suggested Answers to Stop and Think Questions

Teaching Notes and Tips

In Part A:You may want to project this graph on the board and help students work through the various data sets. They are looking for trends - either increase, decrease or no change. They will need to be reminded that a decrease in pH (or a lowering in pH) means an increased acidity. its very easy for students to get confused.

To save time, you can do the BTB experiment as a demo. Regardless, make sure the BTB solution you have works before the lab. You can order aqueous solutions of BTB or you can make your own. It has a limited shelf life so make sure what you are using works. Alternately, you could boil some red cabbage and use that. Y

Bromthymol blue is an indicator used to show the presence of an acidic solution. Low levels of acid will result in the bromthymol blue solution remaining blue, while higher levels of acid will result in the bromthymol blue solution taking on a yellow tint. Bromthymol blue is also used to measure photosynthetic activity (solution turns blue as CO2 is used) or respiratory activity (solution turns yellow as CO2 is added to the solution).

Aqueous version

Add 0.1g Bromthymol blue into 16ml of 0.01N NaOH
Mix in a mortar or small tube
Dilute to 250ml with distilled water
Use 5 drops in 10ml of test solution
Alcohol version

Add 0.5g of Bromthymol blue into 500ml of 95% ethanol and dissolve
Add 500ml of distilled water
Filter and store at room temperature

In Part B:

This is a good section to give students as homework. Have them come into class the next day with answers to the Stop and Think question. This questions would be a good DO NOW as they come in.

In Part C:

Part C will take two class periods. Have them fill in the table when they read the Oceanus Article: A Risky Shell game.

Be sure to familiarize yourself with the Virtual Sea Urchin website and Part 2 which students will be using. Make sure they do the pre-lab section in class so you can identify any issues students might have using this interactive. Depending on your class, you may want to give students the virtual lab as homework and have them bring in their data to share the next day. They can then graph the class data and write a conclusion.

The Stop and Think questions #2 and # 3 are both formative assessments that you may choose to do. Encourage students to go back to the carbon cycle interactive in Lab 2 if they need to.