Unit 2: Ocean Acidification
Students will be provided with seawater pH and carbon dioxide concentration (pCO2) data spanning as far back as 1850. They will describe trends in pH, pCO2 and atmospheric CO2 concentration, outline why these parameters are related, and predict how changes in these parameters will affect marine biology. Each group of students will be given a different set of data from different regions and asked to compare with other groups to determine if seawater pH change is a global or regional phenomena. This unit will provide students with an understanding of the pH buffering system and an opportunity to interpret real climate data.
- Describe carbon dioxide dissolution and solubility in the context of the ocean carbon system;
- Explain how the ocean carbon system buffers the ocean against rapid changes in seawater pH;
- Interpret real seawater pH and pCO2 data.
This unit directly supports multiple InTeGrate guiding principles and addresses grand challenges by introducing students to how human activities are connected to the overall health of the ocean, providing a global perspective of seawater pH, and encouraging interpretation of real scientific data.
Context for Use
This unit can be used as a stand-alone unit or as part of the Ocean Sustainability Module. It can be used in an introductory oceanography or environmental science course. This unit is designed to be used in a classrooms of six or more students over the course of one 50-minute class period. Most work is completed in-class, but a pre-homework assignment is available.
Description and Teaching Materials
Pre-lecture Homework Assignment 1: Estimating your carbon footprint
So that students can understand their role in ocean acidification, the instructor should assign pre-lecture homework on using a carbon footprint calculator. The Nature Conservancy provides a great calculator that can be used for either individual or family carbon footprint calculations: http://www.nature.org/greenliving/carboncalculator/. Below is a set of questions that can be used as a pre-lecture homework assignment. This assignment should also be completed by the instructor so that his/her carbon footprint estimate can be included in the PowerPoint lecture.
Pre-lecture homework 1 files:
Pre-lecture Homework Assignment 2: Plotting seawater data
This pre-lecture homework assignment can be assigned to help students see where to access and learn how to plot real scientific data. The National Oceanic and Atmospheric Administration (NOAA) is a great place to access such data. In the following assignment, students are led through a data base to access data, then asked to plot that data in Excel and identify trends.
Pre-lecture homework 2 files:
- Unit 2_pre-homework 2 (.doc) (Microsoft Word 2007 (.docx) 171kB Nov16 16) } Unit 2_pre-homework 2 (.pdf) (Acrobat (PDF) 97kB Nov16 16)
Instructor answer keys:
Activity 2.1. What happens to carbon dioxide after it is taken up by the ocean? (25 min total)
In this activity, students will be introduced to the solubility cycle, then use what they learn to complete a solubility cycle flowchart for carbon in the ocean. They will use this flowchart to interpret real-world data provided to them in Activity 2.2.
10 min: Break students up into groups of 2–4 and have students compare their carbon footprints within their group — understanding that their carbon footprint does not just affect the atmosphere will motivate students to understand the ocean carbon cycle. Introduce the carbon cycle and review basics of the solubility cycle using the PowerPoint provided below or your own short lecture. These slides provided cover the basic marine carbon cycle and how dissolved CO2 changes seawater pH.
15 min: Stop on "Solubility Chart Exercise" lecture slide and provide students with solubility cycle charts. Students can practice the steps of CO2 dissociation using by filling in a solubility cycle flowchart individually for ~8 minutes. At the end of 8 minutes, the instructor should direct them to compare with their neighbors (think-pair-share format). Note to students: the word bank contains some terms that will not be used.
Activity 2.2. How has increased carbon dioxide changed ocean chemistry? (25 min total)
In this activity, students will be provided with data sets of pCO2 and pH (one data set also includes atmospheric CO2), asked to describe the relationship between these parameters, determine the implications these data have for the ocean's ability to buffer against pH changes with modern fossil fuel usage, and predict the implications these data have for organisms that precipitate carbonate shells or skeletons. They will use the carbon cycle flowcharts they made in Activity 2.1 to help them interpret the data sets from the Caribbean Sea, Northern Atlantic Ocean, and Pacific Ocean (see data sets below).
5 min: Review slides 11–14. Slides 11–14 are used to transition to Activity 2.2 and show data that students will be working with in this activity.
20 min: Have students split up into groups. Provide each group of students (3–4 in each group) with one seawater pH and pCO2 data set (Caribbean Sea, Northern Atlantic or Pacific) and guided questions (provided below). Each group is asked to describe the data they are provided in terms of what parameters are given, what trends exist, and how the parameters are related. In smaller classes, groups should compare their data set with nearby groups that have a different data set. In larger classes, have groups summarize their findings for the class.
All groups should work through the guided questions using their data set. Question #6 in the guided questions requires groups to communicate with nearby groups that have different data sets — in the case of smaller class sizes, students may need to move around. In the case of larger class sizes, sub-groups will communicate with each other.
Activity 2.1 and 2.2 files:
- Unit 2 Powerpoint (.ppt) (PowerPoint 2007 (.pptx) 14.5MB Oct25 16) *Note: The lecture provided contains 14 slides (plus two "bonus" slides). The first 10 slides will be used for this activity, slide 11 will be used to transition to Activity 2.2, and slides 12–14 will be used for Activity 2.2.
- Activities 2.1-2.2 (.doc) (Microsoft Word 2007 (.docx) 78kB Jul25 18) | Activities 2.1-2.2 (.pdf) (Acrobat (PDF) 138kB Oct25 16)
- Activity 2.2_data (.ppt) (PowerPoint 2007 (.pptx) 3.5MB Oct26 16) | Activity 2.2_data (.pdf) (Acrobat (PDF) 3.9MB Oct26 16)
Instructor answer keys:
Teaching Notes and Tips
To encourage students to internalize the carbon cycle for themselves, Activity 2.1 should be treated as a think-pair-share exercise. Students should begin to work on the solubility chart on their own for at least five minutes, then share their answers with neighboring classmates after they have had a chance to think on their own. During this activity, the instructor should walk around to make clarifications and answer questions regarding the exercise.
While students are working on Activity 2.2, the instructor should walk around the classroom and ask group members to explain out loud to each other the connection between atmospheric carbon dioxide concentration, partial pressure of carbon dioxide in seawater, and pH.
Assessments for Activity 2.1 gauge whether students can describe the carbon cycle. Assessments also assess whether students are able to describe and interpret real scientific data regarding modern changes in the marine carbon cycle and describe how the ocean is buffered against rapid changes in seawater pH.
References and Resources
- 5th Assessment Report, Synthesis Report, (2014) IPCC
- Dore, J.E. et al. 2009. Physical and biogeochemical modulation of ocean acidification in the central North Pacific. Proceedings of the National Academy of the Sciences, USA 106: 12235-12240.
- Gonzalez-Davila, M., and J. M. Santana-Casiano. 2009. Sea Surface and Atmospheric fCO2 data measured during the ESTOC Time Series cruises from 1995-2009. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, US Department of Energy, Oak Ridge, Tennessee. doi: 10.3334/CDIAC/otg.TSM_ESTOC
- Muller-Karger, F. E., L. Lorenzoni and Y. M. Astor. 2012. Carbon Dioxide, Hydrographic and Chemical Data Measured during the CARIACO Time-Series Cruises. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, US Department of Energy, Oak Ridge, Tennessee. doi: 10.3334/CDIAC/OTG.CARIACO_TS.