The sample map, shown above, displays ice velocities, paleo-ice stream locations and minimum grounding line extent at the last glacial maximum.
This activity is suitable for students in grades 9-16.
After completing this chapter, students will be able to:
- Describe how multi-beam sonar works
- Outline multi-beam sonar findings around Antarctic
- State a rationale for study of Antarctica's glacial history
- Download, install and use GeoMapApp
- Construct a variety of geospatial data visualizations
- Compare the position of WAIS today with its position during the last glacial maximum
- Define several key terms relevant to study of glacial geomorphology
- Use evidence to defend an argument about the past history of glaciers
Access to Antarctic research affords new opportunities for teachers and students to improve their understanding of a range of topics including: climate change timing and intensity during the past 34 million years, use of multi-beam sonar to infer past glacial extent, and application of GIS tools to understand the physical environment. Teaching with data and using technology prepares students for real world tasks and helps develop critical thinking and evaluation skills central to science.
Searching for evidence of ancient ice sheets
Antarctica is the most inhospitable and remote place on Earth yet it has been the focus of intensive scientific study over the last half century. Much of this research has concerned the evolution of the massive ice sheet that obscures most of the continent. The ice sheet has a surface area of over 12 million km2 and is the single largest control on world sea level (1). According to the National Snow and Ice Data Center, the 30 million km3 of ice represents a 60-meter sea-level rise if completely melted. Antarctica's ice cover is divided by the Trans Antarctic Mountains into two distinct ice sheets: the land–based East Antarctic Ice Sheet and a faster moving, smaller sheet called the West Antarctic Ice Sheet (WAIS).
The focus of this EET chapter is on the West Antarctic Ice Sheet (WAIS). This marine-based ice sheet is grounded below sea level. Due to the potential for under-shelf melting where the ice sheet is in contact with the ocean, it is less stable than the larger East Antarctic Ice Sheet (2). Scientists estimate the WAIS contains enough ice to equal up to five meters of sea-level rise. This is important in light of concern about anthropogenic (human-caused) warming and recent observations of retreat of ice sheets in Antarctica. Melting in the West Antarctic Ice Sheet, and other large ice sheets globally, has the potential for economic and social disruption in low-lying coastal areas worldwide. Improving our knowledge of the changes of the WAIS since the last glacial maximum (LGM) is crucial to the development of scientific models that will enhance our understanding of current and future ice sheet conditions and associated potential contributions to sea-level changes.
Where is the research effort located?Direction of WAIS drainage.×
As shown in the image, right, almost half of the WAIS drains into the Ross Sea and is comprised of two major components: a floating ice shelf that is forms a fringing edge to a grounded ice sheet. The WAIS is typically in contact with the seafloor at depths of more than 800 meters below sea level. In deeper waters, as ones moves towards the sea, the ice shelf thins and begins to float. The point at which and ice sheet is no longer in contact with the seafloor is called the grounding line.
What is a grounding line and why are scientists studying ancient grounding lines in Antarctica?
The grounding line demarks the transition from ice sheet to shelf. The current position of the WAIS's grounding line on the Siple Coast runs roughly between the 150W meridian and the 160W meridian (1).Ice streams×
The WAIS is drained by rapidly moving ice streams (see image right) that continue into the floating ice shelf. Ice stream velocities vary over the continent with a bi-modal distribution peaking at 4-5 meters per year for East Antarctica and more than 250 meters per year for fast flowing ice streams and shelves such as those in the Ross Sea area (3). Many researchers suggest that the potential instability of the WAIS hinges on the fact that sea-level rise can cause a landward shift of the grounding line and result in enhanced under-ice melting. This may be amplified by positive feedbacks within the system such as acceleration of the ice streams and loss of equilibrium between ice accumulation and ablation that, in turn, has the potential to further raise sea-level.
Clues to past ice sheet locations
As it turns out, there is ample evidence that the grounding line has shifted dramatically in the past. Earth has gone through many glacial/interglacial cycles in its history. At times the configurations of sea level and ice cover have been radically different than they are today. For example, at the time of the last glacial maximum (LGM), around 20,000 years ago, ice sheets covered vast areas of northern Europe and North America and sea level was much lower than today (4). Therefore, it stands to reason that the extent of grounded ice in Antarctica would have also been much greater during the LGM.
When ice sheets retreat they leave behind large scratches, or striations, in the bedrock on which they once covered. Since they were first observed in Landsat images of northern Canada, shown below, almost in the mid-1990s, mega-scale glacial lineations (MSGL) have been hypothesized to be the result of fast-flowing paleo-ice streams associated with the retreat of the North American Ice Sheet (5). These geologic features are massive waveforms in the landscape running parallel to ancient ice flow. Typically MSGLs range from 8 to 70 kilometers in length with widths of 200 to 1300 meters and spacing ranging from 300 meters to 5 kilometers (5).
While debate continues on the exact mechanism of MSGL development, their current formation beneath the WAIS has been confirmed (6). Mega-scale lineations have also been revealed across several troughs in the Ross Sea by high-resolution multi-beam swath measurements (see image, right) begun in the 1990s (7). Amongst researchers, there is broad agreement that mega-scale glacial lineations are direct evidence of the extent and flow direction of grounded ice during the Last Glacial Maximum.
How do we know how fast the ice sheet is retreating?Grounding zone wedges (GZW) are end moraine features that occur at an ice stream's transition from grounded ice to floating ice. As the base of an ice sheet ice comes into contact with warmer seawater and melts, sediment falls out of suspension and accumulates to form wedge shaped fans or till deltas wherever the grounding line of the ice sheet pauses for extended periods. Along with MSGL features the location of these piles of debris, can be used to infer the maximum extent of grounded ice. More importantly, grounding zone wedges provide insight about the manner and timing of glacial retreat (8). While GZWs can be revealed by bathymetric data they are best shown with seismic stratigraphy. These data clearly show a series of broad, low-relief GZWs along the axes of paleo-ice-stream troughs on the outer continental shelf (8). Scientists infer these features to represent a series of pauses and liftoff retreats of the WAIS ultimately resulting in today's configuration.
Key Terms and Prerequisite Knowledge
Ross Sea, glacier, grounded ice, ice stream, multibeam sonar, seismic profile, glacial trough, till, moraine, grounding zone wedge (GZW), last glacial maximum (LGM), eustacy, climate change, ice sheet, ice shelf, mega-scale glacial lineations (MSGL), West Antarctic Ice Sheet (WAIS)
- Computers with Internet access, GeoMapApp, and Excel
- Research report criteria (see Part 3)
- Printed copies of the following articles:
This EET chapter is divided into four sections: a video and discussion introduction, a reading-based Case Study, a set of step-by-step instructions that will guide students in the use of GeoMapApp, and a final research report.
If this is the first climate related activity of the class teachers may want to ask students what they have heard about climate change. Ask students how scientists know about the Earth's past climate by focusing on the most recent "ice age." Ask students if they can think of any local evidence of the last ice age in their home region. (Note: common examples include glacial striations and erratics.) Discuss the difference between seasonal ice and snow and year-round ice, like that found in Greenland and Antarctica. (See Going Further for additional background activities and related EET chapters.) Ask students if they can think of any place that is still in an "ice age."
After introducing this EET chapter and research goals, set the stage by showing students the video "Antarctica's Ice on the Move" available at Antarctica's Climate Secrets. (linked below). This NET Nebraska series includes five short (7-minute) YouTube videos detailing the work of Antarctic scientists on climate change. Although the selected video doesn't feature the collection of bathymetric data such as that used in this activity, it does give a good overview of the difference between ice sheets and shelves along with a convincing argument on the need for continued Antarctic research. As time allows, students may wish to view other episodes and should be encouraged to cite the video in their reports.
After the video, give students an opportunity to review the material presented in the background and Case Study section of this activity. This can be done either as a reading assignment or lecture/discussion format. Teachers should make sure that students gain exposure to key terms, concepts, and imagery in the background.
Case Study and Background Reading
Prior to this part of the activity, teachers should print sufficient classroom copies of each of the following two articles:
- Multibeam Sonar
- Seeing the Seafloor
Divide students into reading groups of approximately four. Have them read the Case Study section of the chapter and then give the group members copies the two different articles. As they read the articles, ask them to highlight key information. Allow 20-40 minutes for the reading and note-taking.
After students finish their reading they should discuss with their group the important points in the article. (Teachers may want to remind students of the activity goals related to this reading.)
Next, each student should pair off with a member from a group who read the other article. Students should take turns explaining to each other the main points of their respective articles.
When students have completed reading and discussion, gather as a class to review key points, concepts, and terminology in the articles.
Step-by-step instructions for GeoMapApp (Parts 1 and 2)
Before beginning the step-by-step portion of this activity, teachers should take time to familiarize themselves with GeoMapApp. This can be done by trial and error interactions with the toolbar or by utilizing the tutorials under the education menu at the top of the GeoMapApp page. Several related EET chapters, listed in the Going Further section, can be used for review.
Most students have probably used geospatial tools such as Google Earth and thus will be familiar with the GeoMapApp toolbar since it has a similar layout and icons. Students may need to be reminded about latitude and longitude coordinate systems and different map projections. It is doubtful that students have ever used south polar projections such as they will use in this lesson. Care should be taken to familiarize students with the map and its cardinal directions. For example, in a polar projection of the Ross Sea region northwest will be at the bottom right of the map. It is helpful to have a globe handy to clear up confusion students may encounter.
Teachers should distribute the research paper outline (see Part 3) and review the scoring guide with students before beginning the step-by-step instructions. Teachers may need to remind students that they already have two sources they can cite and a good start on the rationale and multi-beam sonar overview.
Teachers have the option to print and distribute the step-by-step instructions for GeoMapApp or direct students to the EET chapter pages.
In addition to assessing key vocabulary, student understanding can be gauged prior to the activity with the following questions:
- How does multi-beam sonar work? What has it revealed about the seafloor?
- Why do scientists study past Antarctic ice sheets?
- What geologic formations can be used to piece together glacial history?
- How has the West Antarctic Ice Sheet changed in the last 20,000 years?
In Part 3 of this EET chapter, students will build a research report that shows evidence that they can: use the key vocabulary correctly, explain the physical science basis and application of multi-beam sonar, communicate the relevance of glaciology in today's world and use data to support inferences of past glacial conditions. Students will also be assessed on the quality of geospatial imagery they produce to illustrate their findings. An outline for the report is provided in Part 3 of this chapter. Papers can be scored using the free rubric provided at LabWrite Excel grading rubric for lab reports.
Learning ContextsThe material and activities explored in this chapter would be suitable for a high school earth science or college-level introductory geology or oceanography class. The chapter could be used in conjunction with a unit on plate tectonics, climate change, or glaciology.
Science StandardsThe following National Science Education Standards are supported by this chapter:
- 12ASI1.1 Identify questions and concepts that guide scientific investigations.
- 12ASI1.3 Use technology and mathematics to improve investigations and communications.
- 12ASI1.6 Communicate and defend a scientific argument.
- 12DESS3.2 Geologic time can be estimated by observing rock sequences and using fossils to correlate the sequences at various locations. Current methods include using the known decay rates of radioactive isotopes present in rocks to measure the time since the rock was formed.
- 12DESS3.3 Interactions among the solid earth, the oceans, the atmosphere, and organisms have resulted in the ongoing evolution of the earth system.
- ESS1.C The history of planet Earth: The rock record resulting from tectonic and other geoscience processes as well as objects from the solar system can provide evidence of Earth's early history and the relative ages of major geologic formations.
- ESS2.C The roles of water in Earth's surface processes: The planet's dynamics are greatly influenced by water's unique chemical and physical properties.
- ESS2.D Weather and climate: The role of radiation from the sun and its interactions with the atmosphere, ocean, and land are the foundation for the global climate system. Global climate models are used to predict future changes, including changes influenced by human behavior and natural factors.
- ESS2.E Biogeology :The biosphere and Earth's other systems have many interconnections that cause a continual co-evolution of Earth's surface and life on it.
- ESS3.D Global climate change: Global climate models used to predict changes continue to be improved, although discoveries about the global climate system are ongoing and continually needed.
- PS4.C Information technologies and instrumentation: Large amounts of information can be stored and shipped around as a result of being digitized.
Geography StandardsThe following U.S. National Geography Standards are supported by this chapter:
The World in Spatial Terms
1. How to use maps and other geographic representations, tools, and technologies to acquire, process, and report information from a spatial perspective.
2. How to use mental maps to organize information about people, places, and environments in a spatial context.
3. The physical processes that shape the patterns of Earth's surface.
4. The characteristics and spatial distribution of ecosystems on Earth's surface.
Time Required 3-4 class periods
Case Study and Background: 40 minutes
Part 1: 20 minutes
Part 2: 40 minutes
Part 3: 40-60 minutes
AntarcticGlaciers.orgprovides a web-based introduction to key concepts in Antarctic glaciology. These are explored in Science Themes, and include descriptions of different types of glacier, ice shelves, and ice streams. This website also explores the recent rapid environmental changes happening today in Antarctica, and how changes in atmospheric and ocean temperatures has led to ice-shelf collapse, rapid glacier recession and sea level rise.
Antarctica's Climate Secrets YouTube video series
LabWrite Excel grading rubric for lab reports
References and Additional Resource Materials
Alley, R.B., Bindschadler, R.A., 2001. The West Antarctic Ice Sheet and Sea-Level Change. Antarctic Research Series (AGU), Vol 77: 1-11.
Anderson, J.B., Wellner, J.S., Lowe, A.L., Mosola, A.B., Shipp, S.S., 2001. Footprint of the Expanded West Antarctic Ice Sheet: Ice Stream History and Behavior. GSA Today: 4-8.
Bart, P.J., De Santis, L., 2012. Glacial Intensification during the Neogene: A review of seismic stratigraphic evidence from the Ross Sea, Antarctica, continental shelf. Oceanography 25(3): 166-183.
Bart, P.J., Owolana, B., 2012. On the duration of West Antarctic Ice Sheet grounding events in Ross Sea during the Qaternary. Quaternary Science Reviews 47, 101-115.
Clark, C.D., 1993. Mega-scale glacial lineations and cross-cutting ice-flow landforms. Earth Surface Process. Landforms, 18: 1-29.
King, E. C., Hindmarsh, R.C.A., Stokes, C.R., 2009. Formation of mega-scale glacial lineations observed beneath a West Antarctic ice stream. Nature Geoscience Vol 2: 585-588.
Mosola, A.B., Anderson, J.B., 2006. Expansion and rapid retreat of the West Antarctic Ice Sheet in eastern Ross Sea: possible consequences of over-extended ice streams? Quaternary Science Review 25, 2177-2196.
Nitsche, F.O., Wellner, J.S., Bart, P.J., O'Hara, S., Gavahan, K., 2012. Seeing the seafloor: Discoveries of the RVIB Nathaniel B. Palmer multibeam systems. Oceanography 25(3): 136-139.
Pollard, D., DeConto, R. M., 2009. Modelling West Antarctic ice sheet growth and collapse through the past five million years. Nature 458, 329-332.
Rignot, E., 2006. Influence of ocean warming on glaciers and ice streams. Glacier Science and Environmental Change, Knight, P.K., ed., Blackwell Publishing, Malden, MA, 136-137.
Rignot, E., Mouginot, J., Scheuchl, B., 2001. Ice flow of the Antarctic ice sheet. Science 333, 1427-1430.
Ruddiman, W.F., 2008. Earth's Climate; Past and Future, New York, NY: W.H. Freeman and Company, 381 pgs.
Ship, S., Anderson, J., Domack, E., 1999. Late Pleistocene-Holocene retreat of the west Antarctic ice-sheet system in the Ross Sea: part 1 – geophysical results. GSA Bulletin 111, 1486-1516.
Stanley, S.M., 2009. Earth System History, New York, NY: W.H. Freeman and Company, 551 pgs.
Vaughn, D.G., 2006. The Antarctic Ice Sheet. Glacier Science and Environmental Change, Knight, P.K., ed., Blackwell Publishing, Malden, MA, 209-220.
Wellner, J.S., Heroy, D.C., Anderson, J. B., 2006. The death mask of the Antarctic ice sheet: Comparison of glacial geomorphic features across the continental shelf. Geomorphology 75, 157-171.