Summary

In this lesson, students will learn about coccolithophores, unicellular marine algae that inhabit the upper layer of the ocean. These phytoplankton form calcium carbonate, calcite, scales called coccoliths and are the biggest calcite producers in the ocean. First, students will observe photos of algal blooms of different types and analyze the photos for similarities and differences. Next, students will be introduced to types of marine algae including coccolithophores and to how ocean pH changes are impacting the availability of carbonate for use in the formation of calcite shells and coccoliths. Students will then plan and carry out a small-scale laboratory to investigate the relationship between the solubility of calcium carbonate and pH. To conclude, students will read an abstract of recent research into coccolithophores and ocean acidification and compare and contrast those findings with their own investigation’s results.

Grade Level

High school

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-6: Refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.
• HS-ESS3-5: Analyze geoscience data and the results from global climate models to make an evidence-based forecast of the current rate of global or regional climate change and associated future impacts to Earth systems.
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Planning and Carrying Out Investigations
  • Constructing Explanations and Designing Solutions

Objectives

By the end of this lesson, students should be able to:

• Describe coccolithophores as marine algae.
• Explain the impact of ocean acidification on the relative levels of carbonate ions, bicarbonate ions, and carbonic acid in the ocean.
• Predict how changes in pH will impact the solubility of calcium carbonate.
• Explain how the availability of carbonate in the ocean could negatively impact calcite forming organisms such as coccolithophores.

Chemistry Topics

This lesson supports students’ understanding of:

• Solutions
• Solubility
• Solubility Equilibrium
• Acids
• pH
• Chemical Reactions

Time

Teacher Preparation: 60 minutes
Lesson: 90-120 minutes

Materials (per group)

• 4-6 pieces of Marble Chips
• 5 mL Vinegar
• Well-plate
• 2 Pipettes
• Balance
• pH paper (broad scale paper)
• Water
• Optional: A drying oven or method of drying samples would be beneficial

Safety

• Reference the SDS for Calcium Carbonate
• Reference the SDS for Vinegar
• Always wear safety goggles when handling chemicals in the lab.
  
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Students should wash their hands thoroughly before leaving the lab.
• When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.

Teacher Notes

• Students should work in groups of 2 to 4 depending upon the size of the class and available resources.
• Calcium carbonate powder or small limestone pebbles could be substituted for the marble chips. If substituting, be sure that the pebbles are small enough to fit into the well plates.
• Small cups or beakers could substitute for the well plates.
• Dropper bottles could substitute for the pipets.

Background:

• The term “marine algae” is used to describe a diverse group of eukaryotic organisms that engage in photosynthesis.
• The types of marine algae include green algae, red algae, brown algae, golden algae, and dinoflagellates. Coccolithophores and diatoms are often grouped into the golden algae category.
• Algal blooms occur when algae or cyanobacteria grow at a rapid pace. They may appear like a film or layer on the surface of the ocean. The color and appearance of the bloom can vary depending upon the type of algae.
• Coccolithophores are unicellular marine algae that live in the photic zone. These phytoplankton form small plates made of calcite across the surface of the cell that are called coccoliths. See The Magical World of Coccolithophores for SEM images of four different species of coccolithophores.
  

Figure 1. Image courtesy of the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

• Coccolithophores contribute from 1 to 10% of the primary productivity at the ocean’s surface.
• They are also the largest producer of calcite sediment in the ocean, serving as a critical means for carbon sequestration as calcite.
• When coccolithophores form an algal bloom, it often appears to be cloudy white or pale blue in the water due to the coccoliths being shed. In the satellite imagery in Figure 1, the coccolithophore bloom has been denoted with a yellow arrow. White clouds in the atmosphere are obscuring some of the bloom. Other algae/phytoplankton would appear green, brown, or even red.

• Ocean pH has decreased from approximately 8.25 to 8.14 since the 1750s. This is attributed to the increased concentration of carbon dioxide gas in the atmosphere due to the combustion of fossil fuels throughout the industrial revolution. The higher the concentration of carbon dioxide in the atmosphere, the more dissolved carbon dioxide exists in ocean water.
• Ocean acidification reduces the availability of the carbonate ion in the ocean for organisms such as coccolithophores for use in the formation of calcite (calcium carbonate).
• As pH decreases, a smaller percentage of inorganic carbon in the ocean is available as carbonate See Figure 2 below for the graph that depicts the relative quantities of carbonate, bicarbonate, and carbon dioxide at different pH levels.

• pH can impact the solubility of an insoluble or slightly soluble ionic solid if the compound contains the conjugate base of a weak acid. If the anion in the solid is basic, changes in pH can cause an increase or decrease of the solubility of the solid due to Le Chatelier’s Principle.

Classroom Management:

• To shorten the activity, the minilab could be adapted so that each group conducts one trial and the data is collected and reported out on a classroom board for analysis and discussion.

Differentiation:

• Teachers may differentiate this activity by the level of inquiry used in the activity. Students needing additional assistance might be provided with a suggested procedure and data table.
• Teachers may also differentiate the activity according to the level of equilibrium calculations used in the experiment. 2^nd year chemistry students would be more able to perform solubility equilibrium calculations.

Helpful Links:

• The Magical World of Coccolithophores from the Joides Resolution
• What is a coccolithophore? NASA Earth Observatory
• What is Ocean Acidification? from NOAA
• Ocean Acidification from the Woods Hole Oceanographic Institute
• US EPA: Understanding the Science of Ocean and Coastal Acidification

References:

Halder, K. (2018, September 25). The Magical World of Coccolithophores. JOIDES Resolution. Retrieved March 7, 2023, from https://joidesresolution.org/t....