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Snow on Sea Ice
Overview
In this activity, students discuss the potential correlation between the thickness of sea ice and the thickness of the snow cover. They graph data acquired in the field to examine the correlation and draw conclusions based on the interpreted data.
Pancake ice in Ross Sea. Photograph by S. Shipp.
Rationale
Sea ice is the thin, floating crust of ice that forms from sea water each winter as the air temperatures drop and the surface of the ocean cools. Antarctic sea ice is 1 m thick on average, growing to cover 20,000,000 km2 each winter - an area twice the size of the United States - and melting each spring back to a mere 3,000,000 km2 (1,153,200 to 7,688,000 mi2). Until recently, scientists originally thought that sea ice was a flat, white layer of monotonous ice. Once avoided and feared, research expeditions now place costly ice-breaking vessels squarely in the middle of the winter pack ice. These investigations have only begun to reveal the amazing secrets of this seasonal event. Sea ice moderates our climate, acting as a blanket that keeps the ocean heat from escaping and warming the chilly polar atmosphere. Sea ice formation helps define our ocean circulation through the formation of the coldest, saltiest water in our global ocean - setting in motion a water flow that cools the air of tropics and warms the polar atmosphere. Sea ice is the haven for communities of microscopic organisms that, when released with the spring melt, help create one of the richest feeding grounds in the ocean for the likes of krill, penguins, seals and the far-traveling whales.
USCG
Glacier plowing through thin sea ice in Antarctic waters. Sea
ice can form a hazard to shipping and to towing scientific equipment. Photograph
courtesy of John B. Anderson, Rice University.
Scientists are trying to understand the feedback systems of the sea ice formation and our global ocean, atmospheric, and ecological systems. By understanding the components and how they interact, we can better predict how they may change in the future. One piece of the system is snow cover on sea ice. Snow cover may have profound effects upon the sea ice. Snow has a different reflectivity than sea ice, thus snow may impact how quickly the sea ice grows and melts. Scientists have discovered that the depth of accumulated snow may affect both the salinity and the crystalline structure of sea ice on the surface of the sea ice. The weight of snow on the sea ice frequently overcomes the buoyancy of the ice, causing the sea ice to flood with a thin layer of seawater. Finally, snow cover can influence biological activity within and underneath the sea ice by affecting the amount of available light.
Two seals lounge on the pack ice. Is the seal on the left checking for
killer whales before diving into the icy water?! Sea ice plays an important role in the
ecosystem. Not only does it serve as a resting place for penguins and
seals, but it is critical in the annual cycle of algae growth in
Atarctica. Algae are incorporated into the sea ice as it forms in the
winter. In the summer, as the light increases and the sea ice melts, the
algae are released back into the water and "bloom." Photograph courtesy of John Anderson, Rice University .
Grade Level/Discipline
High School, Physical Science, Earth Science, Physics, Math
Objectives
Students will:
predict trends in sea ice thickness with respect to snow thickness
use a graphing calculator to graph the thickness of sea ice and snow data
interpret the graphs to determine the relationship between snow thickness and sea ice thickness.
National Standards
Teacher Preparation for
Activity
Materials
Sea ice thickness and snow cover transect data
TI-83 Graphing calculator (or equivalent)
Time Frame
1 Class Period
Teaching Sequence
Engagement and Exploration (Student Inquiry Activity)
Each fall season, a thin cover of sea ice begins to form on the surface of the water around Antarctica. As the temperatures cool into the winter, this floating ice layer gets thicker and thicker. Why does it get thicker? Some of the increase in thickness is due to freezing of sea water onto the sea ice, some is due to pieces of ice being shoved up on top of each other, and some thickening is caused by snow fall.
Work with the students to develop a hypothesis that addresses the question: "What correlation, if any, may exist between the thickness of Antarctic pack ice and the depth of snow cover on the ice?"
What data do the students need to answer this question? What graph format will best show the results?
Elaboration (Polar Applications)
Ask the students to examine the data table. How do they plan to graph the data to show the difference between the snow thickness and sea ice thickness?
One way the students can prepare the graph:
x-axis: ice thickness in centimeters
y-axis: snow depth in centimeters
Plot ice and snow data on the same graph.
Draw a "best fit" line through the data points.
DATA
Date: 09/19/94
Latitude: 69o36'31.2"S
Longitude: 110o50'36.6"W)
| Transect Dist. (m) | Snow Depth (cm) | Ice Thickness (cm) |
|---|
| 5 | 75 | 320 |
| 10 | 78 | 170 |
| 15 | 70 | 130 |
| 20 | 77 | 250 |
| 25 | 69 | 320 |
| 30 | 61 | 138 |
| 35 | 50 | 140 |
| 40 | 49 | 182 |
| 45 | 75 | 175 |
| 50 | 68 | 160 |
| 55 | 65 | 300 |
| 60 | 70 | 118 |
| 65 | 45 | 118 |
| 70 | 44 | 118 |
| 75 | 38 | 128 |
| 80 | 30 | 128 |
| 85 | 35 | 105 |
| 90 | 39 | 130 |
| 95 | 38 | 125 |
| 100 | 37 | 127 |
Exchange (Students Draw Conclusions)
Ask the students to work in groups to compare their results:
What, if any, relationship exists between snow depth and ice thickness?
What might be the cause(s) of the observed trends?
What environmental factors and conditions might affect the snow / ice characteristics?
How could more confidence be developed in the findings? Explain.
Evaluation (Assessing Student Performance)
Authors
Marge Porter, Woodstock Academy, Woodstock, Connecticut
Background
Resources
Student Reproducible Masters
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