Ice Velocity Data from Ice Stream C, West Antarctica (S. Anandakrishnan)

Data Set Summary

Ice velocity data from ice stream C, including the body of the ice stream and its area of onset, are available. The investigator calculated velocities from precise ice displacement measurements made with a geodetic-quality Global Positioning System (GPS). These ice displacement measurements accompanied seismic experiments aimed at understanding controls on the flow of ice streams in west Antarctica. An understanding of ice stream flow is essential to predicting the response of the West Antarctic Ice Sheet to future climate change.

Data are available in ASCII and Excel formats via ftp.

Citing These Data:

Please cite these data as follows:

Anandakrishnan, S. 2001. Ice velocity data from ice stream C, west Antarctica. Boulder, CO: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5CZ3539.

Overview Table

Category	Description
parameter(s)	GPS ice velocity data
spatial coverage	ice stream C, west Antarctica
temporal coverage	November and December 1995; January 1996
data format	ASCII files, Excel files
file size	ASCII files are 0.2 KB and 1 KB, Excel files are 14 KB and 16 KB
procedures for obtaining data	data are available via ftp

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments:

Investigator Name and Affiliation:

Sridhar Anandakrishnan
Department of Geology
University of Alabama
Tuscaloosa, AL USA

Technical Contact:

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

Acknowledgments:

This research was supported by NSF OPP awards #9318121, Microearthquake Monitoring of Ice Stream C, West Antarctica: A Sensor for Sticky Spots, and #9222121, Collaborative Research: Seismic Traverse of the Byrd Subglacial Basin-Field Test (i.e., the "Antalith" seismic experiment).

2. Detailed Data Description:

Format:

Data are available in two ASCII files:

"CWA-GPS-velocities.txt" and "CWA-GPS-velocities.xls" contain data from near the CWA camp at the onset of ice stream C.

"ISC-GPS-velocities.txt" and "ISC-GPS-velocities.xls" contain data from along the body of ice stream C.

File Size:

ASCII files are 0.2 KB and 1 KB, and Excel files are 14 KB and 16 KB each.

Sample Data Record:

Files are structured as follows:

         "Longitude, Latitude, Velocity (vector direction in degrees ccw of east, magnitude in m/a)"

         -120.018    -82.362   189.321   18.178
         -120.075    -82.3591  189.375   16.983
         -120.131    -82.3563  188.823   16.020
         -120.188    -82.3534  188.242   15.185
         -120.301    -82.3477  187.54    13.614

Spatial Coverage:

Measurement stations were located at the onset of ice stream C (near the CWA camp) and along the body of ice stream C of the West Antarctic Ice Sheet.

Study Area Location Map:

The dark gray box on the map below outlines the approximate area of ice stream C. Crosshairs mark the location of the South Pole.

Map: Location of study site

Temporal Coverage:

Data were collected in November and December 1995 and January 1996.

Parameter or Variable:

Velocities are given as vector directions in degrees counter-clockwise (ccw) of east and magnitudes in meters per annum (m/a).

3. Data Access:

Data are available via ftp.

Related Data Collections:

4. Data Acquisition and Processing:

The investigator acquired measurements at six stations along the length of ice stream C using a dual-frequency geodetic-quality Trimble 4000 GPS receiver operating in static mode. Measurements were collected in November 1995 and 50 days later in January 1996. The receiver operated for a minimum of 24 hours, and data were processed in baseline mode to both a quasi-fixed station at Upstream C camp (actual velocity 24 m/a) and a fixed station at McMurdo. Data were also processed in Precise Point Positioning mode with precise orbits. The two methods yielded very similar results.

The investigator took measurements at the onset of ice stream C (near the CWA camp) along the Antalith seismic line at 300m intervals. These measurements (in 1995) and remeasurements (in 1996) employed a dual-frequency Trimble 4000 GPS receiver operating in Kinematic mode with a fixed base station. The maximum separation between base station and roving receiver was 9 km. The fixed base station position was calculated with a long baseline to MCM4 (McMurdo) and has low accuracy (2 m horizontal and 4 m vertical); however, the relative precision of the kinematic stations was 2 cm horizontal and 4 cm vertical. Although the absolute position of these stations is poorly resolved, their relative positions (and calculated velocities) are very precise.

5. References and Related Publications:

Anandakrishnan, S., and C. R. Bentley. 1993. Microearthquakes beneath ice streams B and C, West Antarctica: Observations and implication. Journal of Glaciology 39:455-462.

Anandakrishnan, S., and R. B. Alley. 1994. Ice stream C sticky spots detected by microearthquake monitoring. Annals of Glaciology 20:183-186.

Anandakrishnan, S., and R. B. Alley. 1997a. Stagnation of ice stream C, West Antarctica by water piracy. Geophysical Research Letters 24(3):265-268.

Anandakrishnan, S., and R. B. Alley. 1997b. Tidal forcing of basal seismicity of ice stream C, West Antarctica, observed far inland. Journal of Geophysical Research 102:15,183-15,196.

Anandakrishnan, S., D. D. Blankenship, R. B. Alley, and P. A. Stoffa. 1998. Influence of subglacial geology on the position of a West Antarctic ice stream from seismic observations. Nature 394:62-65.

Anandakrishnan, S., R. B. Alley, R. W. Jacobel, and H. Conway. 2001. The flow regime of ice stream C and hypotheses concerning its recent stagnation, in The West Antarctic Ice Sheet: Behavior and Environment, edited by R. B. Alley and R. A. Bindschadler, Antarctic Research Series, pp. 283-296, American Geophysical Union.

Service Interruption

National Snow and Ice Data Center