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Full NSF Report
Authors and Credits
Robert W Jacobel ; Saint Olaf College
Siple Dome Glaciology and Ice Stream History
Undergraduate student(s): Anna L Weitzel; Andrew I Malm; Peter I Pearson; Andrew M Fisher; Nancy M Sundell; Victoria J Reuter
University of Washington: Collaborative Research
University of Colorado at Boulder: Collaborative Research
Activities and findings:
This project supported glaciological studies of Siple Dome and its surroundings between Ice Streams C and D. There were two major goals: (1) To characterize the dynamic environment and ice stratigraphy with the specific mission of assessing Siple Dome as a potential deep core site; and (2) to determine whether the configuration of ice stream flow in the region was different in the past than now. Both these goals are relevant to understanding the dynamics of the West Antarctic Ice Sheet (WAIS), its past history and potential future behavior. This project was collaborative between this institution and the University of Washington (Charlie Raymond), and the University of Colorado, NSIDC (Ted Scambos). It included studies of satellite imagery and acquisition and analysis of field data from GPS, firn cores and snow pits, and ground-based ice-penetrating radar.
The project involved two field seasons at Siple Dome, the first in 1994-95 and the second in 1996-97. During the first season, ice-penetrating radar experiments were undertaken to study the bedrock topography and internal stratigraphy in the vicinity of the summit region to determine its suitability for deep ice coring. An 80 km long radar traverse was completed across the north flank of the dome to gather similar data. This traverse was extended across a 'scar' feature seen in satellite imagery and hypothesized to be a former shear margin from a relict ice stream. Strain grids were emplaced in the vicinity of the summit and scar regions, and shallow cores were recovered near the summit to measure snow accumulation rates.
Field work during the second field season extended the radar traverse across the south flank of Siple Dome to complete depiction of bed topography and ice internal stratigraphy. Radar studies to the south also investigated a series of former margin scars of Ice Stream C. Strain grids were resurveyed, and an additional radar traverse with higher resolution was completed across the north flank and scar.
The two field seasons yielded data sets on ice thickness and internal stratigraphy along a traverse from one margin of the dome to the other, as well as a more detailed study of the summit region. Related work done principally by our collaborators resulted in data sets of surface topography and ice velocity, including strain rates in the vicinity of the summit and north scar.
These data were processed to extract information about ice flow and history in the vicinity of the dome and near its margins. Radar profiles were analyzed to determine ice thickness and bed topography. Enhancements were made to better depict internal stratigraphy and gain information about the nature of the bed. Information from the strain grids was used together with depictions of the internal stratigraphy by our colleagues at the University of Washington to model ice flow in the vicinity of the divide and on the dome flanks. Together, these studies have been used to interpret ice dynamics and history in the vicinity of Siple Dome in an effort to better understand the evolution of the West Antarctic Ice Sheet.
Work completed at St. Olaf since our last Progress Report has involved preparing a final archival data set of Siple Dome surface and bed topography for the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado, and also for 'Project Bedmap' at the British Antarctic Survey.
Activities and findings:
Our studies of the summit region of Siple Dome have shown that the divide is located over a bedrock plateau with ice thickness of approximately 1 km. Continuous and smoothly-varying internal stratigraphy depicted by the radar shows that to first order Siple Dome has been stable for at least the last 10 KY. Subtle changes in the geometry of these layers have been used by our colleagues at the University of Washington to estimate the rate of divide migration. These site characterization studies led to the conclusion that Siple Dome was a suitable site for deep ice coring, which was subsequently undertaken.
Our radar studies of the scar on the north flank of Siple Dome showed that it is the surface expression of a dynamic boundary - the former shear margin of a now extinct ice stream we have named Siple Ice Stream. Preliminary determinations from the continuity of internal layers imaged by the radar showed this shutdown occurred within the last 1.3 KYBP. This estimated was refined by subsequent work at the University of Washington to ~500 YBP.
Radar and motion survey studies of the south flank of Siple Dome near the north margin of Ice Stream C show that the shutdown of C about 150 years ago was not a single event but a sequence involving stangation of ice and migration of the ice stream boundary. Our ground-based radar and GPS results confirm the inference from satellite imagery that a series of former shear margins exist, decreasing in age towards the ice stream center. A region of ice stream trunk, including a former margin, lies sheared and folded between the (recent) inner and (older) outer margins. Ice motion and topographic surveys give some constraint on the time of shutdown of the outer margin at approximately 450 YBP.
These findings relate to the evolution of the ice stream system which drains the West Antarctic Sheet to the Ross Embayment. Results and interpretations have been presented to the community at various conferences and in the papers described below.
Six undergraduate students have been centrally involved with this project, and several others have participated in various aspects of the data analysis. Four were supported directly with project funds, and others indirectly through the REU Site in glaciology at St. Olaf College. All have learned to work with commercial image-processing software for satellite imagery and our radar data, and some have written programs in C++ to filter, manipulate and display data. In carrying out these tasks they have gained an understanding of the basics of geophysical data processing. Two have had considerable experience with electronics hardware and software development in designing and building the radar receiver system. As a part of their training, all of them have visited our field site on South Cascade Glacier and been involved with collecting, processing and interpreting radar and GPS data.
As a part of their research experience they have been involved in the preparation of manuscripts/posters and in reviewing group papers with our collaborators. Nearly all have presented papers or posters on their own work at Pew Foundation Midwest Undergraduate Research Symposia. Two have been coauthors on papers and abstracts in the glaciological literature, and one is a coauthor on the final archival Siple Dome radar data set sent to NSIDC and Project Bedmap.
Education and Outreach:
Colloquium speaker at the Department of Geology and Atmospheric Sciences, Iowa State University, Ames, IA, October 1998.
Geology Department guest lecture Carleton College, January 1999.
Elementary school presentations (two annually), Northfield, MN.
Community presentations (Northfield Seratoma, Lions, Senior Citizens).
Consultant/Reviewer for NSF-sponsored Project Glacier, PI Stephanie Shipp, Rice University.
Jacobel, R.W., Scambos, T.A., Nereson, N.A. and Raymond, C.F., "Changes in the Margin of Ice Stream C, Antarctica", Journal of Glaciology, vol. , (), p. . Accepted
Nereson, N.A., Raymond, C.F., Waddington, E.D. and Jacobel, R.W., "Migration of the Siple Dome Ice Divide, West Antarctica", Journal of Glaciology, vol. 44(148), (1998), p. 643. Published
Gades, A.M., Raymond, C.F., Conway, H. and Jacobel, R.W., "Bed Properties of Siple Dome and Adjacent Ice streams, West Antarctica, Inferred from Radio Echo-Sounding Measurements", Journal of Glaciology, vol. , (), p. . Accepted
Jacobel, R.W., Scambos, T.A., Raymond, C.F. and Gades, A.M., "Changes in the Configuration of Ice Stream Flow From the West Antarctic Ice Sheet", Journal of Geophysical Research, vol. 101(B3), (1996), p. 5499. Published
Anandakrishnan, S., Alley, R.B., Jacobel, R.W. and Conway, H., "Ice Stream C Slowdown Is Not Stabilizing West Antarctic Ice Sheet", Antarctic Research Series, vol. , (), p. . Accepted
Nereson, N.A., Raymond, C.F., Jacobel, R.W. and Waddington, E.D., "The Accumulation Pattern Across Siple Dome, West Antarctica", Journal of Glaciology, vol. , (), p. . Accepted
Book(s) or other one-time publication(s):
http://www.stolaf.edu/other/cegsic/. This web site describes the activities of our research group and shows results of our work in Antarctica and also on South Cascade Glacier, WA.
Other specific products:
Contributions within Discipline:
The radar transmitting and recording system developed by us and our collaborators for this project defines the state of the art for low-frequency, sled-based, ice-penetrating radar.
The investigative techniques used here involving ice-penetrating radar together with information from enhanced satellite imagery and GPS motion surveys has proven to be a powerful methodology for studying paleo ice flow, and thus for determining the history of a portion of the West Antarctic Ice Sheet.
Contributions to Other Disciplines:
These studies play an important role in understanding the response of the West Antarctic Ice Sheet to climate change, both in the past and potentially in the future.
Contributions to Education and Human Resources:
The six undergraduate students listed above have been central participants in this project, five of them for two years or more. Several others have worked on various aspects of the study for a portion of a summer. In addition to the specific training reported above, these students have been a part of the scientific enterprise: developoing equipment and techniques, carrying out experiments and data analysis, reporting and presenting results. Anna Wietzel just entered a graduate program in remote sensing this fall. It is unlikely she would have discovered this interest (at this small college) without having participated in this project. The other students have gone on (or will soon) to graduate programs in the basic sciences or applied areas.
Contributions to Resources for Science and Technology:
We have shared GPS technology and expertise gained as a part of this project with colleagues in the St. Olaf Biology Department.
We have contributed radar images and expertise gained as a part of this project to Dr. Stephanie Shipp's NSF-Sponsored 'Project Glacier' - a middle school curriculum on ice and climate.
Our work with image processing has introduced students at St. Olaf to visualization software and data analysis techniques not otherwise present in the physics curriculum. It has been gratifying to see students quickly find other applications for these techniques in their studies and pass the knowledge along to classmates. Several of the physics advanced laboratory experiments have benefited from this spin-off.
Contributions Beyond Science and Engineering:
The potential contribution to eustatic sea level rise from disintegration of the West Antarctic Ice Sheet is an issue with possible policy implications which has been addressed recently by the IPCC. Our studies on the history and evolution of the West Antarctic Ice Sheet contribute to this understanding.
Categories for which nothing is reported:
Participants: Other Collaborators
Products: Book or other one-time publication
Products: Other specific product