Investigating Ocean Acidification

Transcription

1 Investigating Ocean Acidification This four part activity invites students to explore the causes and consequences of ocean acidification. In the first part, students investigate the impact of household substances on eggshells. In the second part, students use data visualizations of ocean ph and remotely-sensed chlorophyll data to identify regions susceptible to ocean acidification. The third part has students read a Scientific American article to connect their findings from parts I and II. In the final part of this lesson students answer a free-response question taken from the 2011 AP Environmental Science Exam. Key Search Words chlorophyll, NASA, ocean acidification, hands-on lab activity, primary productivity, scientific inquiry, primary and secondary data, ph, data visualizations Learning Outcomes Upon completing this activity, students will be able to: Describe the reaction of carbon dioxide & water yielding carbonic acid Describe the impact of increasing levels of carbonic acid on ocean ph and the shells of marine organisms Explain how prior knowledge of acids & ecosystems connects to the larger pattern of global climate change Curriculum Alignment 2010 North Carolina Essential Science Standards Earth/Environmental Science EEn Attribute changes in Earth systems to global climate change (temperature change, changes in ph of ocean, sea level changes, etc.). Climate Literacy Framework Essential Principal 7D: The chemistry of ocean water is changed by absorption of carbon dioxide from the atmosphere. Increasing carbon dioxide levels in the atmosphere is causing ocean water to become more acidic, threatening the survival of shell-building marine species and the entire food web of which they are a part. Materials & Technology For each lab station set-up, you will need: 2 empty chicken egg shells 5 petri dishes 20 ml of the following solutions: Distilled water Cola Lemon Juice Ammonia Vinegar Scale for weighing egg shells Timer ph strips Paper towels Ocean Acidification Investigation Student Worksheet, one per student Copies of Scientific American article The Dangers of Ocean Acidification, one per student Computers with Internet access for each student or student pair Time Required Two, 1.5 hour block periods

2 Student Preparation for Activity This activity is intended to take place after the class has discussed ecosystems, but before the class has discussed climate change at some length. The inquiry nature of this lesson allows for little to no prior knowledge of climate change, as it builds on itself. Procedure 1. Have the necessary equipment available at each student station and divide students in groups of four. 2. Tell students that they will be exploring the effect of different chemicals on eggshells & eventually relating what they find to the impacts of climate change on calcium carbonate containing shells of plankton and other marine organisms. 3. Distribute the Ocean Acidification Investigation Student Worksheet and allow students a few minutes to come up with a hypothesis for Part I in their group. A sample hypothesis might be: The more (or less) acidic the solution the more weight will be lost (or gained) by shells soaked in the solution. 4. Once all groups have formulated a hypothesis, allow them to begin the experiment. 5. Students will then perform the experiment to determine if there is a change in eggshell mass after 15 minutes exposure to each of 5 different chemicals. Allow the eggshells to sit overnight to fully dry out before taking a final mass. 6. Once students have completed the experiment, instruct them to clean up and as a class, review their findings from part I. To culminate the discussion and segue into part II, ask students how their experimental results are relevant to the ocean what marine organisms will be impacted by ocean acidification? Students may not realize that in addition to molluscs and corals, many species of plankton also contain calcium carbonate shells. Plankton form the basis of the food chain in the ocean and thus impacts to calcium carbonate containing shell building plankton could be detrimental to the food chain. 7. [optional] It may be helpful to provide your students with visual evidence that acidic solutions do indeed impact marine organisms with calcium carbonate shells, including mollusks and corals. A demonstration can be set up to enable your students to observe what happens when a seashell is exposed to vinegar for 24 hours. Alternatively, students can drop vinegar onto ground coral (aragonite) where they will observe immediate bubbling as CO 2 is generated and this reaction can be compared with that of inert silica-based sand. See: 8. Prior to having students conduct Part II, discuss how scientists might monitor changes in ocean ph and plankton populations. While students will probably get that the ph of the ocean can be directly measured by sensors (primary data), prompt them to discover that it would take many monitoring stations to assess ocean ph across the globe by relying on primary data alone. Introduce students to the concept of using secondary data to gather indirect evidence of changing ph conditions in the ocean. 9. Next, ask students to complete Part 2, where they will analyze both primary and secondary data to gain a global perspective of ocean ph. What, if any, correlations exist between ocean ph and phytoplankton? 10. For part 2B, care should be taken to look for longer-term trends. One option might be for groups of 2 students to focus on two or three different years that are widely separated in time. Then all of the student groups results could be pooled to look for trends. This might be a good opportunity to discuss the difference between trends and variation. Changes seen between any two years show short-term variations but changes seen over an extend period of time suggest a genuine trend. 11. [Optional] Time permitting, ask students to look at global sea surface temperature data along with chlorophyll data to see if there is also a correlation between sea surface temperature and location of phytoplankton (chlorophyll). Students can compare two data visualizations/animations spanning the same time period (July 2002-December 2013) by visiting: Which parameter appears to be more strongly correlated to the location of phytoplankton, sea surface temperature or ph? 12. Either in class or as an extension activity for homework, have students read the Scientific American article entitled Dangers of Ocean Acidification (see Resources section) and answer the questions in Part 3 of their worksheet. 13. [Optional] Time permitting, ask students to conduct independent research to find updated data to accompany this article. Also, students might enjoy being prompted to investigate how organisms might be adapting to a more acidic ocean (see Resources section). 14. Review Parts 2 and 3 with students and then offer the following summative assessment, either as an in class writing assignment or a homework assignment. Ask students to complete the AP Environmental Science Free Response Question that will require that they apply the information they have learned to coral reefs.

3 This question can be found at: and the scoring guidelines (answer key) at: In conclusion, discuss with students the impact of an increasingly acidic ocean on shell building organisms and its effects on ocean ecosystem dynamics. Expand this discussion to include impacts of global climate change that are not directly observed, or that they might not expect. Use the following prompts for discussion: a. How did the acid affect the eggshells? b. If the ocean becomes more acidic (decreasing ph), how would organisms with shells be affected? c. Zooplankton has shells. If these organisms disappear because of ocean acidification, how will that impact the entire ocean ecosystem? d. What ecosystems are particularly vulnerable to ocean acidification? e. For years, the ocean was viewed as a reliable carbon sink. What are the problems with that view? f. What are some other impacts of global climate change on the oceans? Differentiation Students with Special Needs Split the student worksheet up into each part, following each activity with a discussion. Allow for heterogeneous grouping by ability. English Language Learners Read through the Scientific American article as a class, pointing out and defining difficult words along the way. Begin the activity with an overview of vocabulary words that are relevant to the activity. Gifted & Talented Children Allow students to find and read current scientific journal articles about ocean acidification. Assessment Completion of the Ocean Acidification Investigation Student Worksheet Completion of the 2011 AP Environmental Science Free Response question (either as homework or a formal assessment) Required Resources NASA s MODIS MODIS Data on Chlorophyll Magazine Article: Doney, Scott C. "The Dangers of Ocean Acidification." Scientific American Mar. 2006: AP Environmental Science 2011 Free Response: AP Environmental Science 2011 Free Response scoring guidelines (answer key) Ocean Acidification Educational Tools from NOAA Additional Resources Audio slideshow: Sea drifters Warming will affect phytoplankton differently: evidence through a mechanistic approach 12fd0e66f012

4 Sea Urchins Adapting to Increased Oceanic Acidification (sea urchins- juvenile stages are zooplankton that live in phytoplankton blooms) Global Maps of Sea Surface Temperature & Chlorophyll (MODIS) About the Author Emma Refvem, NBCT, teaches at Riverside High School in Durham, NC. She teaches 9 th grade Earth Science, including an ESL sheltered section, as well as AP Environmental Science. Emma graduated from UNC Chapel Hill in 2009 with a Bachelor Degree in Environmental Science and minor in Geology/Oceanography and she obtained her Masters in Teaching in 2010 also from UNC Chapel Hill. This lesson was reviewed and edited by Dana Haine, MS, K-12 Science Education Manager for UNC- Chapel Hill s Institute for the Environment and Program Director for the NC Climate Fellows Program, a teacher professional development program made possible with support from NASA s Innovations in Climate Education (NICE) project. Acknowledgements Thanks to Linda Schmalbeck, PhD., of the NC School of Science and Mathematics and Karl Castillo, PhD., of the University of North Carolina at Chapel Hill for reviewing this lesson.

5 Ocean Acidification Investigation Student Worksheet Name: Date: Part 1: Investigating Interactions between Carbonate Shells & Household Chemicals You will be investigating the reactions between eggshells (composed mainly of CaCO 3 ) and various household solutions. This experiment will give us a basis to explore complicated chemical interactions in the ocean. 1. In your lab group, predict how exposure to the solutions listed in Table 1 will affect the mass of the eggshells. 2. Formulate a hypothesis based on your prediction: 3. Gather the following supplies and then conduct the experiment by following the procedure below: Egg Shell Pieces 5 Petri Dishes 20 ml of each solution in Table 1 Scale Timer ph strips Procedure A. Record the initial mass of each small piece of shell. B. Fill each petri dish with 20 ml of each solution listed in Table 1 (see below). Be sure to label each dish. C. Using a ph strip, record the ph of each solution in Table 1. D. Simultaneously place the shells in the solutions, and start the timer. E. Soak the shells for 15 minutes, recording qualitative observations in Table 1. F. After 15 minutes, remove the shells and place them on paper towels G. Leave these until tomorrow, when you will record the final mass for each shell. Table 1: Data Collection Solution ph Mass of Shell: t 0 Mass of Shell: t e Change in mass Observations Distilled Water (H 2 O) Cola (H 2 CO 3 ) Lemon Juice (H 3 C 6 H 5 O 7 ) Ammonia (NH 3 ) Vinegar (C 2 H 4 O 2 )

6 Data Analysis 16. Using the graph below and the data from Table 1, plot ph vs. change in mass (be sure to include appropriate units): Change In Mass ph 17. According to your experimental results, what is the relationship between ph and change in eggshell mass? 18. Which solution(s) resulted in the greatest change in eggshell mass? 19. Which of these solutions is the most acidic (has the lowest ph)? 20. Describe how your results confirm/contradict your initial hypothesis. 21. Did you observe anything counterintuitive happening in regards to ph and change in eggshell mass? 22. Define the phrase ocean acidification. 23. Observe the graph below and in your own words interpret the graph. As atmospheric CO 2 increases, what is happening to the amount of dissolved CO 2 in the ocean (pco 2 ) and to seawater ph? 24. Plankton are microscopic organisms that live in water, many of which have shells derived from calcium. Based on your experimental results above, predict how ocean acidification might affect calcium carbonate containing shells of plankton (e.g., cocoolithophores) and other marine organisms.

7 Part 2: Investigating Ocean Acidification & Impacts on Phytoplankton Answer Key 1. Formulate a hypothesis regarding the impact of ocean acidification on phytoplankton based on the experimental results you obtained from Part 1. An example of a student-generated hypothesis might be As the ocean becomes more acidic there will be smaller and fewer phytoplankton blooms. 2. In your group, describe the kind of data you would need to test your hypothesis in the real world to find out if ocean acidification was indeed happening and impacting phytoplankton. Answers will vary but examples of the kind of data that would be needed to test hypothesis include: direct observations of ocean surface ph, satellite imagery of phytoplankton blooms and actual samples of phytoplankton that can be examined under the microscope to assess alterations in shells consistent with decreasing ph levels. Students should grasp that multiple lines of evidence are typically needed in order to adequately test a hypothesis and rule out alternative explanations. 3. In Part 2A below, you will start to test your hypothesis by examining direct observations of ocean surface ph and then in Part 2B you will examine satellite imagery of phytoplankton blooms to assess whether there is any evidence that an acidifying ocean is impacting blooms. Part 2A: Direct measurement of ocean ph 1. Visit: 2. Prior to viewing the animation, observe the ph scale to the right of the data visualization. What would you say was the average ph of the Ocean in 1880? ~8.2 (blue) 3. Next, view the animation that reveals surface ocean ph from 1895 to the present as well as forecasted ocean ph between now and You may need to view this animation several times in order to describe any trends you observe. 4. Describe your observations, and any trends, in the space below. Observations will vary and might include the following: today, average ocean ph is 8 (slightly basic), oceans are forecasted to become much more acidic (lower ph) with the greatest change (lowest ph) occurring in the Northern Hemisphere and Arctic region in the future; areas with corals will see changes in ph; all of the Earth s oceans are forecasted to see a decrease in ph in the future. 5. According to these data (which includes actual data and forecasted measurements) is the ocean becoming more acidic? Yes. Part 2B: Satellite imagery of phytoplankton blooms Scientists can monitor phytoplankton blooms from space due to the photosynthetic pigments (e.g. chlorophyll) present in their cells. Areas with high chlorophyll content are more productive than areas with lower chlorophyll content. Therefore, by looking at the chlorophyll content of the ocean, we can assess primary productivity of the oceans and identify phytoplankton blooms. For this part, you will be looking at data from NASA s MODIS (Moderate Resolution Imaging Spectroradiometer) instrument aboard its Terra and Aqua satellites. Terra's orbit around the Earth is timed so that it passes from north to south across the equator in the morning, while Aqua passes south to north over the equator in the afternoon. Terra MODIS and Aqua MODIS are viewing the entire Earth's surface every 1 to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths (see MODIS Technical Specifications). Satellite data improves our understanding of global dynamics and processes occurring on the land, in the oceans, and in the lower atmosphere. 1. Go to to access the data you will use to examine phytoplankton blooms. 2. Adjust the settings for the data viewer so that you can compare chlorophyll concentrations at a glance. We want Standard, Aqua MODIS Chlorophyll concentration, Seasonal composite, 9km, 44 thumbnails (corresponding to the past 44 seasons). Your settings should look like this when you get done:

8 3. Before you analyze the thumbnails scroll to the bottom of the webpage and take a moment to determine which colors correspond to high and low chlorophyll concentrations. a. High concentration of cholorphyll (basic): orange/red b. Low concentration of cholorphyll (acidic): blue/purple 4. Scan the 44 thumbnails to identify and describe any seasonal trends you notice (remember that summer in the Northern hemisphere corresponds to winter in the Southern hemisphere). Usually there is more chlorophyll production in the summer (phytoplankton are producing more chlorophyll because of more direct sunlight) There is less chlorophyll in the southern pacific in the winter and in the summer, there s more chlorophyll in the Arctic 5. Using colored pencils, compare two different summers between 2003 and Your teacher may tell you which years to analyze so that your class analyzes all years during this activity. Summer Summer

9 6. a. When and where do the lowest chlorophyll levels usually occur? Autumn/Winter in the central Pacific b. While ocean acidification might be one factor contributing to this observation, can you think of any other explanations for this phenomenon? There are many possible explanations for low chlorophyll in this area: (1) nutrients sink out of the photic zone and are not replaced- leading to low productivity (2) lower sunlight levels during winter months lead to less photosynthesis & productivity (3) iron is a limiting factor in plant growth, so a lack of iron can lead to lower productivity despite the presence of nutrients (this area is known as HNLC: high nutrient, low chlorophyll). 7. The Southern Pacific Ocean is acknowledged to be one of the areas most sensitive to decreased ph. Do you notice a trend to lower chlorophyll levels in this region? Yes, purple area present in the fall and winter season reveals less chlorophyll in the Southern Pacific Ocean. 8. Now let s look at annual averages. Set your viewer to: Standard, Aqua MODIS Chlorophyll concentration, Annual composite, 9 km, 12 thumbnails. 9. Focusing on the area on the east coast of Australia (you can click on this region to zoom in) do you notice any annual trends in the chlorophyll levels there? It may be difficult to detect but chlorophyll concentrations are slightly decreasing over time. 10. What ecosystem exists there? Based on your results from Part 1, what might be some impacts on the species dependent on calcium carbonate in that ecosystem? The Great Barrier Reef is present on the coast of Australia, and it is a highly productive coral reef. Species dependent on calcium carbonate for their shells/skeletons will most likely be negatively impacted by decreasing ph levels or increasing acidity. 11. How would you go about determining if this trend towards lower chlorophyll levels in this region is due to ocean acidification and not to a change in one or more variables? You would want to obtain direct measurements of ph for this region to see if ph is indeed decreasing and then you would need collect data to rule out other variables that can also negatively impact growth such as warmer than average sea surface temperature, low nutrient and low iron conditions. Conducting a phytoplankton survey to assess the state of their shells would also be useful. Part 3: Dangers of Ocean Acidification Taken from Doney, Scott C. "The Dangers of Ocean Acidification." Scientific American Mar. 2006: About a third of the CO 2 released by the burning of fossil fuels currently ends up in the ocean. Absorbed CO 2 forms carbonic acid (H 2 CO 3 ) in seawater, lowering the prevailing ph level (which is slightly alkaline) and changing the balance of carbonate & bicarbonate ions at the ocean surface. The shift toward acidity, and the changes in ocean chemistry that ensue, makes it more difficult for marine creatures to build hard parts out of calcium carbonate. The decline in ph thus threatens a variety of organisms, including corals, which provide one of the richest habitats on earth. Within a century, the surface of the Southern Ocean will become corrosive to the shells of tiny snails that form a key link in the marine food chain within this highly productive zone.

10 Read The Dangers of Ocean Acidification from Scientific American. 12. Describe the impact of ocean acidification on marine organisms. a. Lowering ph will hamper the ability of certain (calcifying) organisms to make calcium carbonate, so much so that these organisms will then have difficulty growing or building reefs. b. This article suggests that that lowering ph may cause coral bleaching events but the more significant cause of coral bleaching is increased temperature of sea water. 13. For each organism below, indicate the type of shell that defines the group and summarize the effects of a more acidic ocean on the group: Type of Shell Impact of ocean acidification Foraminifera Calcium carbonate is Will hinder their ability to build shells common material for shells Coccolithophorids Calcium carbonate These phytoplankton will have difficulty growing because they have calcareous plates Pteropods Calcium carbonate- Aragonite Small marine snails will lose their ability to grow, and they constitute a major food source for marine animals Coral Calcium carbonate - Aragonite Coralline Algae Calcium carbonate - magnesium calcite Decreased calcification rates; one study 1 reveals that ocean acidification could contribute to coral bleaching. Highly soluble in acidic ocean, so they are in danger! 14. What impact will ocean acidification have on organisms with aragonite & magnesium calcite shells? They dissolve more easily than shells made of normal calcite, so they may be especially susceptible to harm. 15. What is the saturation horizon, in the context of carbonate ions? The water levels deep in the sea below which shells of marine organisms made of these minerals dissolve. For example, aragonite is much more soluble that calcite so the aragonite saturation horizon is always nearer to the surface than the calcite saturation horizon. 16. How is the saturation horizon changing in response to increased CO 2 levels in the atmosphere? It is shifting closer to the surface; less of the sea will remain hospitable for calcifying organisms. 17. How do your observations from Part 1 & Part 2 connect to what you ve read about ocean acidification? (please elaborate on another page if needed) Answers will vary but include the way acids affect shells, which will affect the growth of plankton and other species that utilize calcium carbonate containing shells. There will be significant food chain implications! 1 Ocean acidification causes bleaching and productivity loss in coral reef builders