In this activity, students build on their growing knowledge of ice and glacier growth. The students examine images of core samples and make observations about the decreasing size of gas bubbles with increasing depth in the core. The students model permeability. From this experiment, the students develop an understanding of the movement of air through snow and ice and why this information is critical to researchers studying the past climate of our Earth.
Middle School; Earth Science, Environmental Science, Physical Science, Chemistry
Teacher Preparation for Activity
The students may want to read about Sandy Shutey's experience at Siple Dome in Antarctica. They can access her project description, daily journals, and images from the field.
The class will need:
Each group of 4 to 5 students will need:
One to two class periods
Engagement and Exploration (Student Inquiry Activity)
How might the students demonstrate which material has the highest permeability? The students will measure how fast water flows from the top to the bottom of the container. Provide each group with a stopwatch, ruler, beaker of water, pencils, and graph paper.
How will the students want to measure permeability? What factors should they keep constant? The students should recognize that they need to pour the same amount of water into each container, start timing at the same time, etc.
What do the students expect to happen? Through which container will water flow the fastest? The slowest? Have the students record their hypotheses.
Have the students mark their containers with the ruler in one-centimeter intervals. Each group should assign a recorder to note the time and distance the water has traveled, a time keeper to monitor the time, and a distance keeper to keep track of how far the water travels. When the students are ready, they should start with the finer grained sand; flow will be slower and will allow them to coordinate their method. of measurement. The group will pour 500 ml of water over the sand and keep track of how fast the water moves downward through the sand. The students may find it is easiest to have the distance keeper state when the water passes a centimeter interval and the time keeper can then state the time increment. Have the students repeat the procedure for each container.
When they have completed collecting data for all containers, have the students graph the results. Ask them to graph the results on a single sheet of paper, using a different color for the different sands.. What are the constants? Variables? What goes where on the graph? What kind of graph is appropriate? What scale is appropriate? What labels are needed?
Elaboration (Polar Applications)
What do the graphs show?
Through which container did the water flow the fastest? The slowest? What does this mean about the permeability of the different sands? Which is most permeable? Least? What does this have to do with grain size? Have the students look at the ice core sections again. How do they relate their experiment findings to the ice data? Inside each layer there is a definite size snow crystal. The larger the snow crystal the larger the air passages around it and the easier the air can flow around the snow crystals. As the crystals get smaller, so do the spaces around them*.
*Teacher Note: This relationship holds true for the upper part of the core - and it is very important with respect to how the ice "records" the climate/atmosphere signal and how the research teams sample the ice. With greater depth, ice crystals actually grow at the expense of air bubbles and each other - ice crystals can reach the size of a football with time and under extreme pressure.
Exchange (Students Draw Conclusions)
Have the groups present their results to the class. Are the results the same? Why or why not?
What do the experimental results tell the scientists? If a scientist was trying to get a sample of the atmosphere today, where would they sample? Just at the top? Can they sample a little further down the core, because the atmosphere gases can move through the core? What does this mean when the scientist samples further back in time? They need to know how quickly the ice "seals" and "traps" the atmosphere sample to be able to acquire samples at the right spacing.
Evaluation (Assessing Student Performance)
Sandra Shutey, Butte High School Butte, Montana and Stephanie Shipp, Rice University, Houston Texas
In the Arctic and Antarctic, the snow piles up and up each year. The more snow on top the greater the chance for the firn (snow flakes with out their edges) to be pushed closer and closer together. When they get pushed together they do not allow air to pass between them easily. The more air that can go between the firn the less they have been compacted. Scientists test ice cores in the frozen parts of the world to see how much air will pass between the firn. From this they can try to figure out what happened in the layers of ice above and in the atmosphere
Sandy Shutey worked at Siple Dome, Antarctica. From Sandy's daily field journals:
...Siple Dome is actually situated on a dome of ice that is about 1000 meters thick. The Dome is moving about 1 meter a year. The landscape is flat and white in all directions that you turn. The sun is rolling about at a 25 to 30 degree angle from the horizon. It is about the same amount of light all day long. Even at 2 or 3 in the morning the sun is bright and one is able to see for ever....You can almost see the curve to the earth as you look out along the flat white horizon. It seems that here at Siple you can see for a very long distance in any direction but it is all white with small tints of blue where the snow has been cleared. Siple Dome is a small community of dark green/ brown Jamesways (a type of Quonset hut) and a sea of yellow and blue or blue and purple tents....
...I will be working with Dr. Mary Albert...on a core experiment dealing with the gases found in the core....we are doing research on the chemical composition of the core. With this information, a model of what has happened with our atmosphere in the past and now will help us understand the possibility of a green house in the earth's future. These projects are a part of the project being done with Dr. Ken Taylor and Dr. Gregg Lamorey and the WAISCORE project. Check out the science on www.maxey.dir.edu/WRC/waiscores.
...Since the day was a quiet one; it gave me a chance to reflect on the continent as a whole and the science that is being done here. There is so much to be learned and never enough time or money to do it . I have learned that what we do with our atmosphere usually can be recorded here in the ice. They have a record even of the radiation fallout from the testing of the atomic bombs in our atmosphere from the 1950's. They have also found traces of volcanic lava in layers of the ice that can be discovered only by drilling ice cores. Most of the science that I have seen deals with the ice cores....
...The cores this year to be drilled are small ones of only 20 meters that we will use to find permeability of the ice. They are hoping to drill a larger core later in the season...This core will be around one thousand feet long. They have even built a special under-ice trench to house the core in so that it will not melt before the scientist will be able to study it. Much of the core may be sent away from the ice to be studied at a later date by scientists....
...Permeability allows the scientist to discover at what rate gas is transmitted through the layers of ice. Each layer can have a different rate of gas movement since some of the ice layers are denser than others. Layers closer to the surface of the ice will probably allow gas to move through more rapidly because these layers have not been compressed by overlying snow and ice....
... Dr. Albert has some mini projects dealing with a pit that she and her assistant, Nancy Cloud, dug. They have done the stratigraphy and grain sizes on the ice layers. She has even taken pictures of the crystals to measure the grain sizes for more accuracy to her science. She has traced the permeability of the layers and is doing thermal conductivity on the pit. Dr. Albert has also had Dr. Joe McConnell analyze the pit for an age. They are checking the hydrogen peroxide in the layers. From the amounts of hydrogen peroxide in the layer they can tell if the layer is a spring or winter layer. There is more peroxide in the spring, summer, and especially in the fall time of the year than in the winter. By counting these layers, they get an approximation of the age of the ice. Often times, isotopes such as Oxygen 18 can also be used to determine the age of the ice.
... The drillers from PICO came out to the site today to start drilling core for Dr. Albert. She needed 15 meters of core to test the permeability of the snow. Permeability is finding the air spaces between the firn of the core. Ideally the deeper the core, the less space there should be between the firn crystals. The deeper and the less space between the firn gives the scientist and idea about the size of the firn crystal. Usually they are smaller with depth due to the compacting of the ice. The drillers brought with them a drill called a side winder that they could put into the ground and bring up the needed ice core...
...Joey and I begin working on the core in late afternoon. We had to measure the cores, which should have come in about 1 meter long, than we cut them into 10 cm. lengths. We, then, placed them in a tube that is pressurized to form a tight fitting membrane about the core. Once this is in place we simple apply gas to the system allowing it to flow both on the outside and the inside of the core. The gas flow should be smooth called laminar in the core. Once we have adjusted the flow, we take readings and place them in a formula to find the permeability of the ice core. Darcy's law is used for this purpose from a spread sheet on the computer. The permeability are graphed according to depth and then Dr. Albert can analyze the data...
Student Reproducible Masters
Past Climates from Ice Cores
Antarctica holds a special key to the mysteries of Earth's past climate. As snow falls, it traps water from the clouds and gases and dust from our atmosphere. The snow gets a "chemical signature" of the atmosphere as it falls.
In some places, like Antarctica, the temperature is so cold, most of the snow does not melt - it accumulates as glaciers and ice sheets. The snow and ice crystals fall layer on layer, year after year. The snow gradually turns to ice. The tiny parcticles and chemicals that fell with the snow are trapped in the ice.
The ice holds a record. The deepest part of the ice fell as snow thousands and thousands of years ago. The ice contains chemicals and parcticles from our Earth's atmosphere from thousands and thousands of years ago. The top of the ice fell as snow more recently - it contains chemicals and parcticles from our recent atmosphere. The top The deeper in the ice that the core goes, the tinier the air bubbles. By drilling through the ice and collecting an ice core, we can sample the record of Earth's changing atmosphere. The oldest ice sampled so far in Antarctica, at Vostok Station, is over 300,000 years old!
An ice core ready for sampling. What are the dark bands? Often the ice cores show layers of dust or volcanic material from a volcanic eruption. Because volcanic eruptions spread ash for many, many miles, the layers are time markers and help scientists relate the age of one ice core to another.
Fold in an ice core.
Before collecting an ice core the research team must know about the place they want to drill. Ice flows. It can fold and fracture. To collect a core with a complete history, the research team must make sure they know how the ice has flowed. The longer the core and the older the time the scientists want to study, the harder it is to find a site. Even cores for the last few thousand years must be placed carefully; snow accumulation rates can be very different from place to place and flow patterns can be very different over a tiny distance!
Drilling a core is hard work and requires careful planning! Even before drilling, the research team conducts many investigations. Automatic weather stations are used to provide information about the prevailing wind direction and temperatures. The shallow layers of the ice are studied by cutting and sampling ice pits. The researchers examine annual accumulation of the snow and ice and investigate chemical properties. The deeper layers of ice are investigated using airborne radar (radio-echo sounding profiles). This a picture of what the layers look like and help the scientists figure out how the ice is flowing.
Snowpit in Greenland. Two pits are dug, one next to the other. The scientist works in one pit, with a cover over the top. The second pit is left open, and light from that pit penetrates the thin ice wall between the two, illuminating the layers in the snow! Why is the ice wall blue? The summer layers are indicated with arrows. In the summer the sun heats the snow at the surface, causing it to evaporate (sublimate). This makes the layers very coarse grained. In the winter, the sun does not shine, so the layers stay fine grained and densely packed (darker blue).
Once a location is selected, the research team really goes into high gear. The season for drilling is short. Often the perfect site is far from an established research base, so a temporary base has to be put in place and supplies and people have to be flown back and forth.
Drilling rig at Newall Glacier. The rig is not protected from the weather; acquiring the ice cores is hard, cold work! The covered area to the right of the drill rig is the area where the cores are placed after they are drilled. It offers protection from the sun before the cores are prepared for travel.
Empty sections of pipe, or core barrel are attached to the drill nose. As the drill nose spins, it cuts into the ice, going deeper and deeper. The core barrels fill with the clean cut ice core. This ice is extracted and an empty barrel is attached and sent back down the hole to drill the next section.
Once collected, the ice core section is taken to the clean area for preparation.
The science team carefully maneuvers a core just collected. The ice core is handled very carefully - each core piece represents many, many hours of work and dollars of support money! If a core is lost in shipping or melts, there may never be another chance to collect a replacement! The cores are measured and stored carefully and then shipped back to the home laboratory for sampling. All through shipping, the cores must be kept at the proper temperature. Why is one person wearing a mask and "clean suit?"
Sample of ice being prepared for examination under a microscope.
Once back in the lab, the research team begins to sample the layers in the core. They extract the chemical signature of the atmosphere hundreds and thousands of years ago. This helps scientists determine climate properties such as the temperature, the snow accumulation rate, patterns of ocean and atmosphere circulation, and the concentrations of greenhouse gases, like carbon dioxide and methane, when the snow fell. If we can understand how these properties affected our climate in the past, we can make some good predictions about how our climate may change in the future, especially as humans change these properties.
Thin section of ice viewed through special filters under a microscope. This sample is from a Greenland ice core at a depth of 80 meters. Each of the different colored ice crystals are about 1 millimeter across.
Many thanks to Mark Twickler of the University of New Hampshire's Climate Change Research Center, and Richard Alley of Pennsylvania State University's Earth System Science Center for providing these images!
From Ice and Air to Glacier - History in a Bubble!
Below are several samples from an ice core. You are looking at them as they are seen under a microscope. The microscope is using white light that is transmitted, or shining through the sample from behind. The samples have been stained, one with brown stain, and three with blue stain, so that the ice crystals show up better.
Before the slides were made, each sample was treated with a special material so that the empty spaces (air pockets) would have a filler and would not squish. The slides were then cut on a saw and shaved until they were very thin. The filler in the air pockets is stained blue (remember, one is brown rather than blue!). Blue is air, white and gray are ice!
Which sample is from near the top of the ice core? Which is the next deepest? The next deepest? The very deepest? How can you tell?
Thanks to Richard Alley of Pennsylvania State University's Earth System Science Center for providing these terrific images!
We look forward to hearing from you! Please review this activity.
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