EarthLabs for Educators > Climate and the Carbon Cycle > Lab 7: Ocean Acidification- Too much of a good thing?

Lab 7: Ocean Acidification

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

Open the Student Activity in a New Window 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:

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 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."

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. It is very easy for students to get confused.

Bromthymol blue(BTB) is an indicator used to show the presence of an acidic solution. Low levels of acid will result in the BTB solution remaining blue, while higher levels of acid will result in the BTB solution taking on a yellow tint. BTB 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).
To save time, you can do the BTB experiment as a demo. BTB solution has a limited shelf life so make sure your BTB solution works before you begin the lab. You can order aqueous solutions of BTB from any school science supply company or you can make your own. Alternatively, you could boil some red cabbage and use that.

Recipe for aqueous version of BTB

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
Recipe for alcohol version of BTB

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:

Part B 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.

Student Notebooks

Student notebooks are optional. Here are just a few suggestions for what to include in student notebooks for Lab 7: Note: You may want to separate actual data collection and analysis into a Lab Notebook.


There are several options for assessments of students understanding of material produced in this Lab. Teachers can choose from the following list or create their own assessments.

Assessment Options:

  1. Assess student understanding of topics addressed in this investigation by grading their responses to the Stop and Think questions.
  2. Grade lab reports to the Virtual Urchin Lab.
  3. Written Test for Lab 7 (Microsoft Word 2007 (.docx) 150kB Feb10 14) Answer Key (Microsoft Word 2007 (.docx) 228kB Feb10 14))

National Science Teaching Standards

Lab 7 supports the following Next Generation Science Standards (NGSS):

Science and Engineering Practices

4. Analyzing and Interpreting data

5. Using Mathematical and Computational Thinking

Disciplinary Core Ideas

LS2.B. Cycles of matter and Energy Transfer in Ecosystems

LS2.C Ecosystem Functioning, Dynamics and Resilience

Cross-Cutting Concepts

1. Patterns

2. Cause and Effect

5. Energy and Matter: Flows and Cycles

7. Stability and Change

Additional Resources

Background Information

An excellent resource is a webinar given by Dr. Gretchen Hofmann. You can find this at Webinar at Once at this site, you can download Dr. Hofman's slides and listen to the audio.

Nature Knowledge Project/ Scitable article Ocean Acidification

Oceanus articles on ocean acidification

FAQs about ocean acidification This site contains links to many other informative sites.

Content Extension

  • How has ocean acidification research changed over time?
  • What organisms have been researched?
  • Are there an contradictory findings in newer research versus older research?
  • Are there some surprises?
  • What new technologies are being used and how do they impact results being collected? (example: mesocosm experiments compared to lab bench experiments)

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