Sea Ice Impact

Overview

This lesson investigates the impact of melting and freezing arctic sea ice on the properties of salinity, temperature and density that contribute to the stratification of ocean waters. This lesson combines several learning approaches including a hands-on lab, a web-quest and collaboration with other students.

Objectives

1. Students will be able to explain and demonstrate how Arctic sea ice melting and freezing can impact the ocean properties of salinity, temperature and density.
2. Students will be able to explain and demonstrate how these properties contribute to vertical stratification of the deep ocean and the currents of the ocean conveyor belt system.

Lesson Preparation

Background Information: Students should be able to explain what density signifies, how different materials with different densities interact and what effect changes in temperature and pressure have on the density of materials. Students should have a thorough understanding of density concepts prior to completing this lab. I use a series of density labs that could be referenced at the following web address: https://sites.google.com/site/springs8thgradescience/word-of-the-week/general-8-science-files-notes-labs-and-videos. Go to the folder labeled Density Labs.

Procedure

Part I: Main Lesson Intro/Mini-Lesson:

Teacher Intro talk 5-10 minutes with diagram and video. The currents of the Ocean Conveyor Belt System contribute to weather and climate and influence the movement of heat, organisms, nutrients and gases throughout the ocean system. The main cause of ocean currents and vertical stratification involve differences in water temperature due to the uneven heating of the Earth. Another contributing factor is the difference in salinity that results from differential evaporation from the sea surface and uneven freshwater inputs to the ocean. Colder water temperatures and higher salinity both contribute to higher density seawater, which will tend to sink. In this lesson you will be exploring how the formation of Arctic sea ice increases salinity and the density of ocean water and contributes to the process of deep-water formation. By contrast, when sea ice melts, the resulting liquid water is fresher and less dense and contributes to vertical stratification. The use of tea (a form of dissolved organic carbon) will help students understand how materials in seawater (including salt) are excluded from ice when it forms.

• Illustration of the Global Conveyor Belt in the Arctic and Atlantic: http://www.dfo-mpo.gc.ca/science/Publications/article/2006/02-04-2006-eng.htm
• Great Ocean Conveyor Belt: http://nsidc.org/news/press/day_after/q5_ocean_belt.html

Part II: Lab Activity

On a student lab report or in a student science notebook, students should title the experiment: How Sea-Ice Formation and Sea-Ice Melt Influence Sea Water Salinity and Density. Students should continue to follow the Experimental Design Rubric by stating the problem and making a hypothesis based on the problem stated. Students should continue to follow the Experimental Design rubric (B-only; see Resources section) as they write-up and conduct the experiment below, including data tables, graphs, photographs and/or diagrams where appropriate.

1. Fill the cut-off soda bottle to approximately 1 centimeter below the cut-off point, with local or classroom made seawater. Label this bottle, 'seawater'. Fill the other bottle in the same manner with your freshwater and label the bottle 'freshwater'. Measure and record the temperature and salinity of the seawater. Record data collected onto a data table. If equipment is available students can also test for the density of the water with a hydrometer or multi-meter throughout the experiment.
2. Pour the seawater into a beaker and place on a hot plate or burner stand. Add a tea bag and heat the seawater to approximately 60 degrees Celsius or just hot enough to allow the tea to leach easily into the water. Stir and gently put pressure on the tea bag occasionally during this process to increase tea leaching.
3. When the water has darkened with the tea, remove the beaker from the hot plate and let the saltwater tea solution cool approximately to room temperature.
4. Pour the seawater tea back into the cut-off seawater soda bottle.
5. Measure and record the temperature and salinity of the seawater onto the student data sheet.
6. Place the bottle with the seawater tea in the insulated cup holder, or wrap with 2 layers of bubble wrap. Make sure to include 2 bubble wrap cut outs to insulate the bottom of the bottle as well if you're using bubble wrap.
7. Place the bottle with the seawater tea in the freezer and mark the time on the student data sheet. Alternatively, for less time in the freezer, students can set the bottle in an ice bath making sure that none of the ice bath enters the bottle.
8. Leave the bottle in the freezer until about 2-6 centimeters of ice has formed on the top of the water. Freezing time will vary but should take between 2.5-6 hours depending on the starting temperatures. The teacher should test out approximate freezing time well in advance of doing the actual lab with students as freezing times vary greatly depending upon the bottle shape, freezer configuration, etc. Using the ice bath ahead of freezing greatly reduces freezing time. If due to timing students are not available when the correct top layer of ice forms, the teacher may need to conduct this portion of the lab.
9. Remove the bottle from the freezer. Place a thermometer through the ice and into the middle of the water. Determine the temperature of the water and record temperature in the data table.
10. Squeeze the bottle slightly and remove the ice layer. Mark one beaker 'sea ice' and place the ice into the beaker. Mark the second beaker 'seawater' and pour the remaining seawater tea into this beaker.
11. Allow both samples of water to warm to room temperature. (If samples are to be left overnight cover with plastic wrap to decrease evaporation)
12. Measure/record temperature and salinity. Record in the students' data table.
13. Observe the color of each water sample. Students should include drawings of each sample and write a description of what is observed based on the color of the liquids.
14. Students collaborate and compare data to reach a conclusion that relates directly to their original hypothesis. Complete Experimental Design write-up.
15. Students self-edit and peer-edit each other. Complete Experimental Design write-up using the Experimental Design rubric.

Part III: Web Quest and Collaboration

Use the following web-based articles and videos to answer the discussion questions with your lab partner(s).

Articles

1. Density of Ocean Water-Windows To The Universe http://www.windows2universe.org/earth/Water/density.html&edu=high This links with a high reading level. This reading level can be changed with all of the Windows To the Universe readings. Please note the tabs at the top of each web page where you can change to beginner, intermediate or a translated version in Spanish.
2. Thermohaline Circulation: The Global Ocean Conveyor-Windows To The Universe http://www.windows2universe.org/earth/Water/circulation1.html&edu=high
3. The Arctic Ocean Currents-Windows To The Universe http://www.windows2universe.org/earth/polar/arctic_currents.html&edu=high
4. Melting Arctic Sea Ice and the Global Ocean Conveyor-Windows To The Universe http://www.windows2universe.org/earth/polar/icemelt_oceancirc.html&edu=high
5. CTD Instrument-Windows To The Universe http://www.windows2universe.org/earth/Water/CTD.html

Videos

1. Sea ice melt: YouTube: http://www.youtube.com/watch?v=dMgDOSTTXJs&feature=fvwrel
2. Sea ice melt: NASA: http://www.nasa.gov/topics/earth/features/thick-melt.html
3. Dive Discover-Woods Hole Oceanographic Institute: Ocean conveyor belt: http://www.divediscover.whoi.edu/arctic/circulation.html#
4. NOAA Science On A Sphere: Ocean Circulation http://sos.noaa.gov

Extension

• "Module 7:Double Diffusion Salt Fingers". The Salmon Project The Sea-Air-Land Modeling and Observing Network (SALMON) Project is located at the University of Alaska in Fairbanks, Alaska: http://www.ims.uaf.edu/salmon/education/lesson%20plans/mod7.html
• "Par 5" a Windows2Universe.org salt water vs. fresh water density lab: http://www.windows2universe.org/teacher_resources/par5_edu.html

Resources

• Experimental Design Rubric-National Science Olympiad: http://soinc.org/exper_design_b.
• Experimental Design Summary-North Carolina Science Olympiad Coaches Workshop October 2007, Michael Huberty Mounds View High School Arden Hills Minnesota: http://www.sciencenc.com/event-help/experimentaldesign.php

Assessment

• Part II: Students will be assessed based on the Experimental Design rubric and scores from self, peer and teacher review.
• Part III: Students will be assessed based on their responses to the web-quest survey.

Credits

This lesson was developed in a joint effort between educators and researchers during the 2012 Barrow Alaska Arctic Ocean Ecosystem Workshop. Educators Matt Conforti from Barrow High School (Alaska) and Lisa Seff from Springs School (New York) worked in cooperation with research scientists: Dr. Lee W. Cooper, University of Maryland Center for Environmental Sciences; Dr. Matthew Druckenmiller, National Snow and Ice Data Center at University of Colorado at Boulder and Rachel Potter, University of Alaska at Fairbanks, If you have any questions we'd be happy to hear from you: Lisa Seff: lseff [at] springs.k12.ny.us ; Matt Conforti: matthew.conforti [at] nsbsd.org This lesson included adaptations from the following lesson plans:

1. Sea Ice and Salinity: Antarctic Climate & Ecosystems CRC. Lab governed by Australian & International copyright laws. © 2007 ACE CRC.
2. Salinity Experiment: Created by CJ Mundy (University of Manitoba & Shannon Delawsky (Central Middle School, Dawson Creek, BC) 2005 Schools on Board Field Program.
3. Learning through Experimentation: Ice Cubes, Density, Currents. Adapted from Lawrence Hall of Science GEMS "Ocean Currents: Marine Science Activities for Grades 5-8". Activity 5: Ice Cube Demonstration, p. 85.