The Other CO2 Problem: Ocean Acidification
Grades: 6-12
INTRODUCTION: Here, we present two activities relating to the global problem of Ocean Acidification.
These activities can be used and/or adapted for a range of grade levels, esp. grades 6-12.
BACKGROUND: Global climate change is often perceived as the CO2 problem. Although sea levels are
rising and the Earth’s climate is warming because of increased levels of carbon dioxide (CO2) in the
atmosphere, there’s another serious problem related to this:
When there is excess CO2 in the atmosphere, some of it gets dissolved in the ocean. The dissolved CO2
then mixes with the water (H2O) in the ocean and forms carbonic acid (H2CO3). This causes the ocean to
become more acidic (that is, have a lower pH).
This process is called ocean acidification, and is a huge problem for marine ecosystems! Read on to
learn why!
Why is ocean acidification a problem for marine ecosystems?
Well, for two reasons. Many marine organisms (such as coral and
some plankton) have calcium carbonate shells. One problem is calcium
carbonate (calcareous) shells dissolve in acid. Moreover, ocean
acidification inhibits these organisms from creating their calcareous
shells.
Ocean acidification affects:

CALCAREOUS ORGANISMS: Marine organisms, such as corals and
certain plankton like pteropods and coccolithophores, rely on
their calcareous shells to grow and defend themselves.

ALL OTHER MARINE LIFE: When the survival of calcareous
organisms is threatened, it has a knock-on effect on all other
marine life. For example, corals provide shelter for many other
marine creatures. When corals die or retreat, the whole
ecosystem suffers.
Also, pteropods (tiny planktonic snails) are eaten by a wide
variety of fishes and some marine mammals, like whales. A
reduction in pteropod population would cause a cascading effect
up the marine food web.

Figure 1. Pteropod (Image:
http://www.pmel.noaa.gov)
Figure 2. Coccolithophore (Image:
http://www.nhm.ac.uk/index.html)
TERRESTRIAL ANIMALS AND HUMANS: Marine phytoplankton
produce over half the oxygen on Earth. Thus, humans and other
terrestrial animals are inextricably linked to the marine
environment.
Figure 3. Coral reef (Image: Ron
Vave/ Marine Photobank)
Stn. ALOHA
How do we know this is really happening?
Scientists from the Hawaii Ocean Timeseries (HOT) program have been taking
seawater measurements at Station ALOHA
monthly since 1988! Station ALOHA is a
research station in the Pacific Ocean,
located 60 miles north of the Hawaiian
island of O‘ahu. These HOT data tell us how
ocean chemistry has changed over time. For
example, the HOT data tell us that the
ocean’s CO2 is increasing while its pH is
decreasing
Figure 4. Station Aloha (Image: http://cmore.soest.hawaii.edu/cruises/biolincs/)
FOR FURTHER READING:
NOAA Pacific Marine Environmental Laboratory (PMEL) Carbon Program:
http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F
Woods Hole Oceanographic Institution:
http://www.whoi.edu/main/topic/ocean-acidification
Hands-on Activities:
Activity 1: Analyzing Station ALOHA Data
Activity 2: Ocean Acidification Yeast Experiment
Activity 1: Analyzing Station ALOHA Data
Driving Question: How has Ocean Chemistry Changed in the past 25 years?
Activity: Using Hawaii Ocean Time-Series data to graph CO2 and pH with time
Introduction: In this activity, students graph Hawaii Ocean Time-Series (HOT) data from Station ALOHA
either by hand or electronically (e.g., with Microsoft Excel) to reproduce the graph below, which shows
that the ocean’s CO2 has increased and its pH has decreased since the HOT program began collecting
data in 1988. If desired, you can also plot the atmospheric CO2 data on the same graph.
Figure 1. TOP: Time-series data of atmospheric CO2 (red) and oceanic CO2 (blue). BOTTOM: Time-series
data of oceanic surface pH (blue). Atmospheric data were collected at the Mauna Loa observatory and
oceanic data were collected at Station ALOHA, located 60 miles north of O’ahu.
Materials
 Computer with Microsoft Excel
 Excel data file with two spreadsheets: (1) HOT data of oceanic CO2 and pH, and (2) NOAA data of
atmospheric CO2 from the Mauna Loa observatory. Download Excel file from:
cmore.soest.hawaii.edu/education/teachers/documents/HOT_and_NOAA_%20data_FINAL.xlsx
Graphing
A) Create a scatter plot showing how pH and CO2 data change with time
1. Create basic graph. Open Excel file and click on the “HOT” spreadsheet tab (lower left corner of
the Excel file). Highlight the 3 data columns (date, CO2 and pH). Click on "Insert" tab and insert
a “scatter plot” (scatter with straight lines). Do you see a graph with 2 sets of data that are
scrunched together and hard to read? Reformatting the axes will definitely help!
2. Reformat the x-axis. Right click on x-axis and “format axis”. Under "Axis options", set the
minimum value to 32000, maximum to 41500, and major unit to 365. Under "Alignment", set
custom angle to -45 degrees. [What did this accomplish? What do you think the numbers
represent?]
3. Create two y-axes (one per data set). Right click on the upper dataset on the graph (CO2 values).
Click on “Format Data Series”, “Secondary Axis” then “Close”. [What did this accomplish?] Do
you see two overlapping data sets (pH and CO2)? To make it easier to read, we can adjust the yaxis ranges so they don't overlap.
4. Reformat the left y-axis. Right click on the left y-axis and “Format axis”. Under “Axis Options”,
set the minimum value to 8.04,maximum to 8.28, and “Close”. [What did this accomplish?]
5. Reformat the right y-axis. Repeat the above step for the right y-axis, but set the minimum to 195
and the maximum value to 410. [What did this accomplish?]
6. Adding trendlines. To add trendlines to the data, right click on the upper data series. Click on
“Add Trendline” and select “Linear”. Adjust Line Color and Line Style to your liking. Click “OK”.
Repeat for the other data series.
7. Examine the graph. What do you notice about the two datasets?
B) Plot the atmospheric CO2 data (if desired).
8. Add data series. To add the atmospheric CO2 values to the graph right click on the chart and
choose “Select Data”. Click the “Add” button and type the series name (e.g. Atmospheric CO2).
To add X values click in the box then go to the NOAA worksheet tab (lower left corner of the
Excel file) and highlight the dates. Do the same for Y values, but highlight the Atmospheric CO2
column instead. Click “OK”.
9. Examine the graph. You should see now see a third data series of atmospheric CO2 values added
to the graph. How do the trends of the atmospheric and oceanic CO2 values compare?
C) Add some finishing touches.
10. Change x-axis values to years, for easier reading. [Hint: “Format axis”, “Number” and type
"yyyy" for "Format Code"]
11. Add axis labels & a title [Hint: “Chart Tools” and "Layout"]
12. What other finishing touches would you like to add?
Questions (partial list; please add your own!)
1. Why do you think the atmospheric data fluctuate in such a regular (saw-toothed) pattern?
2. The oceanic and atmospheric CO2 both generally increase with time. Why?
3. The oceanic CO2 and pH data appear to be mirror images of each other. Why?
4. About how much has the atmospheric CO2 increased from 1988 to 2011?
Increase in ppm: _________
Percentage Increase: _____________
5. About how much has the ocean CO2 increased from 1988 to 2011?
Increase in ppm: _________
Percentage Increase: _____________
6. About how much has the ocean pH decreased from 1988 to 2011?
Decrease in pH units: _________
Increase in acidity*: _______________
*Note: the pH scale is logarithmic: a decrease from 9.0 to 8.0 equals a 10x increase in acidity.
7. Hypothetically, at some point in the future, suppose the pH of the ocean decreased to 8.0. How
much of an increase in acidity would that represent (from 1988)?
8. What could be done to prevent the scenario in the above question from happening?
Answer key:
For an answer key to the above questions, please contact oceanfest@soest.hawaii.edu. In the body of
your email, please provide your name, school, subject(s) and grade level(s) taught.
For Further Reading:
Bruno, B.C. and J.L.K. Wren (2014). Climate change, sea level rise, and ocean acidification. The Earth
Scientist, Vol. XXX (1), 9-11.
Hawaii Ocean Time-series (HOT) program: http://hahana.soest.hawaii.edu/hot/
Activity 2: Ocean Acidification Yeast Experiment
Introduction: This activity familiarizes students with the causes and consequences of ocean acidification:
the process by which our ocean is becoming increasingly acidic. In this experiment, we simulate ocean
acidification by activating yeast with warm water and sugar. The CO2 gas produced is directed into two
separate chambers: one that contains air and one that contains water. Over about a 20 minute period,
we measure both the increase in gaseous CO2 and the decrease of the water's pH using electronic
probes connected to a data recorder.
These lessons provide students with experience:
• How to use the scientific method
• How to generate a hypothesis
• Data collection through hands-on experimentation
• How to analyze results
Materials:
1. Vernier LabQuest data recorder
2. Electric kettle
3. 1 pH probe, stored in solution
4. 1 CO2 probe
5. 2 round 500 ml bottles
6. 1 square 125 ml bottle
7. 1 BioChamber (bottle with hole in the side)
8. 1 funnel
9. 1 timer
10. 1 piece of rubber tubing connected with straight connectors to a small, black stopper (#6) at one
end and a large, white stopper at the other (#8)
11. 1 piece of rubber tubing connected with a straight connector at one end to a large, white
stopper (#8)
12. Sugar packets
13. Yeast packets
14. Extra pH storage solution
Standards – Ocean Literacy: Essential Principles and Fundamental Concepts
The following Principles and Concepts may be addressed using this lesson:
Ocean Literacy Principle #2: The ocean and life in the ocean shape the features of the Earth.
2d. Sand consists of tiny bits of animals, plants, rocks and minerals. Most beach sand is eroded from
land sources and carried to the coast by rivers, but sand is also eroded from coastal sources by surf.
Sand is redistributed by waves and coastal currents seasonally.
Ocean Literacy Principle #3: The ocean is a major influence on weather and climate.
3a. The ocean controls weather and climate by dominating the Earth's energy, water and carbon
systems.
3e. The ocean dominates the Earth's carbon cycle. Half the primary productivity on Earth takes place in
the sunlit layers of the ocean and the ocean absorbs roughly half of all carbon dioxide added to the
atmosphere.
3f. The ocean has had, and will continue to have, a significant influence on climate change by absorbing,
storing, and moving heat, carbon and water.
Ocean Literacy Principle #6: The ocean and humans are inextricably interconnected.
6b. From the ocean we get foods, medicines, and mineral and energy resources. In addition, it provides
jobs, supports our nation's economy, serves as a highway for transportation of goods and people,
and plays a role in national security.
6c. The ocean is a source of inspiration, recreation, rejuvenation and discovery. It is also an important
element in the heritage of many cultures.
6e. Humans affect the ocean in a variety of ways. Laws, regulations and resource management affect
what is taken out and put into the ocean. Human development and activity leads to pollution (point
source, non-point source, and noise pollution) and physical modifications (changes to beaches,
shores and rivers). In addition, humans have removed most of the large vertebrates from the ocean.
6g. Everyone is responsible for caring for the ocean. The ocean sustains life on Earth and humans must
live in ways that sustain the ocean. Individual and collective actions are needed to effectively
manage ocean resources for all.
Advance Preparation
1. Check that the yeast packets have not past their expiration date; replace as needed.
2. Make sure the Data Recorder is fully charged before beginning this activity (it takes ~8 hours to
fully charge). It is not necessary to calibrate the equipment.
3. Prepare 500 ml (~16 oz) of hot tap water just before the start of the experiment. If hot tap
water isn't available, use the electric kettle to heat water. Note: boiling water is too hot to
activate yeast, so it will need to be cooled to ~100°F.
4. Have 100ml (~4 oz) of room temperature water available for the pH measurements.
pH Set-up:
5. Fill the square 125ml bottle to the red line with room temperature water.
6. Remove the pH probe from its storage container by unscrewing the lid and
then gently pulling the sensor out of the top. Be careful not to spill the
storage solution. Insert the sensor into the square bottle as in the photo to
the right. Submerge the tip (blue end) of the probe in the water. The black part of the pH
probe must remain dry!
7. Connect the pH probe to the port labeled CH1 on the back of the
Data Recorder. Turn on the Data Recorder by pressing the silver
button in the upper left corner. A box should appear on the screen
labeled CH 1: pH.
8. The sensor will need to equilibrate before beginning the experiment. Gently swirl the probe in
the water for ~3 minutes; during this time the pH should rise. Watch the readings on the Data
Recorder, and wait for the pH reading to settle. The pH reading should be stable for at least 1
minute before beginning the experiment. It is very important that the sensor equilibrate, so be
patient! The sensor should give a pH of approximately 6–8. The pH of pure water is 7, but tap
water often contains harmless, dissolved minerals that can affect its pH.
CO2 Set-up:
9. Lay the biochamber bottle on its side, and insert the probe horizontally through the bottle top,
as in the photo at right. Collect the rubber tubing with stoppers at both
ends. Place the small black stopper in the hole in the side of the
BioChamber. Make sure the seal is tight. The CO2 probe cannot get
wet.
10. Set the CO2 probe to high (switch is at the top of the probe). Connect
the CO2 probe to the port labeled CH2 on the back of the Data Recorder.
11. A box should appear on the screen labeled CH 2: CO2. Let the sensor equilibrate for a few
minutes. The sensor should give a CO2 concentration somewhere between 300–600 ppm
(higher if the ventilation is poor). Allow a few minutes for the sensor to produce a stable value.
Instructional and Experimental Procedures
1. Start by explaining that human activities such as burning fossil fuels put CO2 in the air, and some
of this excess CO2 dissolves in the ocean where it gets converted to an acid. This process of
"ocean acidification" is harmful to many types of marine life. Explain that this experiment
simulates ocean acidification. You will activate yeast to produce CO2, dissolve the CO2 in water
and measure the acid that forms in the "ocean".
Activating the Yeast:
2. Fill both round 500 ml bottles up to the white line with water that is hot to the touch.
3. To each bottle, add 3 packets of sugar, and then add 1 packet of yeast. Stir by swirling the
bottles for 5 seconds (This is the only time you need to stir the solution. Do not overmix!),
then QUICKLY insert a white stopper (attached to tubing) into the top of each bottle. Make sure
the seal is tight.
4. Place the loose end of the rubber tubing into the room-temperature water with the pH sensor.
Ensure it is submerged.
Data Collection:
5. Ask students to make a prediction: After the yeast is activated, what will happen to the pH and
CO2 levels over time? Record the hypothesis on the data sheet using the dry erase marker.
6. Have a student record the initial CO2 and pH readings on the data sheet. The values may jump
around on the Data Recorder, so watch the range of values for 5 seconds, and record the
highest value.
7. Continue to record measurements every 3 minutes.
8. When the foam reaches the red line on the bottle, stop the
experiment by removing both stoppers from the bottles. Do not let
the foam pass the red line.
9. To see how this relates to current C-MORE research, refer to the
Station ALOHA Curve (located in the Ocean Acidification Straw
Experiment section).
Clean up
1. Unplug the probes from the Data Recorder.
2. Rinse all bottles. DO NOT wash the probes.
3. To store the pH probe, remove the top of the storage bottle, insert the probe through the top,
and then screw the top back onto the storage bottle. The tip of the pH probe should be
immersed in storage solution, but should not touch the bottom of the storage bottle. The pH
probe must be stored vertically in the outreach box.
4. Wipe the data sheet with a damp tissue so that it can be re-used again.
Trouble-shooting
1. If the yeast doesn't bubble up, it may have been old or got overmixed. Alternatively, the water
may have been too hot. Water should not be so hot as to cause burning. Try again with a new
yeast packet and new sugar packets.
2. If the yeast bubbles up but the CO2 reading doesn't increase, check your seals on the CO2 set-up.
3. If the yeast bubbles up but the pH isn't decreasing, check your seals on the pH set-up. Also
check that the tubing from the yeast bottle is submerged in the water in the square bottle (you
should see bubbles coming out of the water). If the pH is increasing, the pH probe may not have
had sufficient time to equilibrate.
4. If your data recorder isn't displaying the sensor values, check that the probes are connected
properly. Alternatively, the battery may need charging; test this by plugging it in.
Set-up of Ocean Acidification Yeast Experiment
Ocean Acidification Data Sheet
1. Make a prediction! After the yeast is activated, what will happen to the pH and CO2 levels over
time? Record your hypothesis here:
2. Record your data in the table below.
Time
(minutes)
0
3
6
9
12
15
18
21
pH
CO2
(ppm)
Observations