Glaciological measurements on the Ross Ice Shelf
ty mapping. Work completed included (1) two wide-angle profiles using the 35-megahertz radar and one with the 150megahertz radar, (2) one electrical resistivity profile, (3) 50 kilometers of radar profiling (on the surface), (4) 30 kilometers of gravity profiling, (5) 2 kilometers of seismic profiling along radar wide-angle lines, (6) two seismic short refraction profiles, including all three components of motion, (7) radar polarization experiments, (8) a seismic wideangle profile, and (9) one seismic long refraction shot recorded at 23 and 25 kilometers. In December, for reasons including absence of aircraft, bad weather, and problems with navigational systems, the airlifted survey of new sites went slowly. In early January the work was delayed further by a crew change for one Twin Otter and an extended absence of the other on an emergency mission to the Antarctic Peninsula. However, by midJanuary the survey program had taken a dramatic turn for the better. At the end of the season 80 stations had been occupied (figure), most of them with all geophysical and glaciological measurements: radar sounding of ice thickness, seismic sounding of water depth, gravity, establishment of a strain rosette, position determination by navigational satellite, and near-surface snow sampling. Only three desired sites outside of the 190-kilometer operating radius from McMurdo were not occupied. (Those three stations are in an interesting area in the north central part of the ice shelf and will be occupied, if possible, during the next field season.) Three stations were occupied for 1 or 2 days each, during which electrical resistivity measurements, gravity observations, seismic short refraction shooting, radar profiling, wide-angle reflection, and polarization studies were done. Airborne radio echo sounding was completed along 4,500 kilometers of flight lines (figure). Partly because of cloudy weather, and partly because of summer snowfall, sighting of survey sites from the air was less successful than in past seasons. However, the inertial navigation system in the Twin Otter was in good operating condition and ice thickness variations are less complicated than in the eastern portion of the shelf, so correlation problems are not anticipated. Members of the field parties were D.G. Albert, C.R. Bentley, L.L. Greischar, K.C. Jezek, J.F. Kirchner, H. Pollak, and S. Shabtaie. Extensive assistance with the work at J-9 by Heinz Kohnen is gratefully acknowledged. Work was supported on National Science Foundation grant DPP 72-05802. This is University of Wisconsin, Geophysical and Polar Research Center, Contribution 343.
References
Bentley, C.R., 1976a. High electrical resistivity deep in antarctic shelf ice of ice-stream origin (abstr.) American Geophysical Union. Transactions, 57(4): 243. Bentley, C. R. 1966. Analysis of Ross Ice Shelf geophysics. Antarctic Journal of the U. S., XI(4): 276-27 7. Bentley, C. J. W. Clough. and J.D. Robertson. 1974. Geophysical work of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS) in 1973-74. AntarcticJournal of U.S., IX(4): 157-159. Clough, J.W., andJ.D. Robertson. 1975. RISP geophysical survey. AntarcticJournalof the U.S., X(4): 153. Crary, A.P., E.S. Robertson, H.F. Bennett, and W.W. Boyd, Jr. 144
Glaciological regime of the Ross Ice Shelf.Journal of Geophysical Research, 67(7): 2791-2807. Kohnen, H., and C.R. Bentley. 1977. Ultrasonic measurements on ice cores from the RISP drill hole. Antarctic Journal of the U.S., XII(4): 148-150. Bibliography
Clough, J.W. 1977. Radio echo sounding - reflections from internal layers.Journal of Glaciology, 18(78): 3-14. Clough, J.W. 1976. Observations of the electromagnetic lateral waves by earth sounding radars. Geophysics, 41: 1126-1132. Bentley, C.R. 1976. Isostatic imbalance and the past extent of the grounded ice sheet in the Ross Ice Shelf region, Antarctica.
Geology Society of America. Abstracts with Programs, 8(6).
Glaciological measurements on the Ross Ice Shelf ROBERT H. THOMAS
and DOUGLAS R. MAcAYEAL
Institute for Quaternary Studies University of Maine at Orono Orono, Maine 04473
Strain-rate measurements on the surface of the Ross Ice Shelf were continued during the 1976-1977 austral summer. The work forms part of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGs), which involves measurement of ice thickness, depth to sea bed, snow accumulation rates, local gravity, and surface strain rates at a 50-kilometer grid network of stations on the Ross Ice Shelf. At some of the stations, ice velocities are obtained from comparison of precise position fixes, and holes are drilled for 10-meter temperatures and for oxygen-isotope analysis of surface snow samples. Surface strain rates are obtained from Kehietype strain rosettes (Zumberge et al., 1960) with 1 to 1.5 kilometer "legs." RIGGS was started in 1973-1974 when 47 strain rosettes were planted in the southeast corner of the ice shelf (Thomas and Gaylord, 1974). Most of these were located and remeasured during the 1974-1975 season, when 34 new rosettes were planted in the northeast quadrant of the ice shelf (Thomas and Eilers, 1975). Logistic problems led to the cancellation of the 1975-1976 field program, so our plans for this last season included remeasurement of already-planted rosettes and installation of approximately 100 new rosettes to complete the survey in the western half of the ice shelf. Most of this work was accomplished. The 1976-1977 field party consisted of E. Penn of the University of Nebraska at Lincoln, D. Schilling of the University of Wisconsin Center, and T. Hughes, J . Lingham and ourselves, all of the University of Maine at Orono. J. Sorenson and D. Hall of the U.S. Geological Survey operated satellite-tracking equipment to obtain precise posiANTARCTIC JOURNAL
tion fixes at most of the stations. Field work began in early November 1976 with the relocation and excavation of the Roosevelt Island camp (RI on the figure). Resurvey of a 40kilometer network of stakes near the camp was completed in time for the arrival of the British Antarctic Survey (BAs) Twin Otter that was to fly us to the grid stations. All of the stations that were planted during 1974-1975 and several from the preceding season were located and remeasured by mid-December. This work was accomplished despite con tinuous problems with the Twin Otter navigation system, and our success was primarily due to the determination and complete involvement of the pilot and engineer, G. Kershaw andJ. Nicholson. Early in December E. Penn and D. MacAyeal joined Charles Bentley's RIGGS group at C-16 camp (figure) in the southwest quadrant of the ice shelf, where they continued to establish new grid stations until early February 1977. Three geophysicists then joined the group at RI camp to begin planting new grid stations in the northwest quadrant of the ice shelf. At the end of December this entire group moved to Q-13 camp (figure). Although the BAS Twin Otter was obliged to return to the Antarctic Peninsula for part of the season 82 of the planned new grid stations were established. During the 1977-1978 field season we hope to locate these stations, remeasure the strain rosettes, and repeat the precise position fixes. Preliminary analysis of RIGGS data from the southeast corner of the ice shelf revealed an apparent thickening with time of the ice in this region (Thomas, 1976a). Currently a more complete analysis (Thomas and Bentley, 1977) confirms this trend if we assume that locally there is negligible melting or freezing beneath the ice shelf. With this assumption, average thickening rates upstream of Crary Ice Rise (figure) are calculated to be about 0.3 meters of ice per year, decreasing toward the north so that, near the Ross Ice Shelf Project drill-hole, the ice shelf is approximately in equilibrium. The RIGGS data also will be used to test a finite element computer model of the ice shelf that will examine the effects on ice-shelf dynamics of ice rises and ice streams. This research was supported by National Science Foundation grant DPP 76-23047.
References
Gaylord, D.R., andJ.D. Robertson. 1975. Sediments exposed on the surface of the Ross Ice Shelf, Antarctica. Journal of Glaciology, 14: 332-333. Thomas, RH., and D.R. Gaylord. 1974. Glaciological measurements on the Ross Ice Shelf. Antarctic Journal of the U.S., IX(4): 160-162. Thomas, R.H., and D.H. Eilers. 1975. Glaciological measurements on the Ross Ice Shelf. Antarctic Journal of the U.S., X(4): 149-150. Thomas, R.H. 1976a. Thickening of the Ross Ice Shelf and the equilibrium state of the West Antarctic ice sheet. Nature, 259: 180-183. Thomas, R.H. 1976b. The distribution of 10-meter temperatures on the Ross Ice Shelf.Journal of Glaciology, 16: 111-117. Thomas, R.H. 1976c. Ice velocities on the Ross Ice Shelf. Antarctic Journal of the U. S., XI(4): 279-281. October 1977
ROSS ISLAND
ROSS ICE S
A A A A A A A %C
A A ©
CR AR Y ICE RISE
A A A D AA A®• A A ® A A A
1'
A AA
0 100 290 1cm BASE CAMP A ROSETTE (r.m.asur.d) A ROSETTE (planted)
•
o PRECISE POSITION FIX D DRILL HOLE
The Ross Ice Shelf showing positions of RIGGS stations. Thomas, RH., and C.R. Bentley. 1977. Past decay and present growth of the West Antarctic ice sheet. Paper to be presented at the X INQUA Congress, Birmingham, England. August, 1977. Zumberge,J.H., M. Giovinetto, R. Kehle, andJ. Reid. 1960. Deformation of the Ross Ice Shelf near the Bay of Whales, Antarctica. New York, American Geographical Society. IGY Glaciological Report Series, 3.
Geochemical and isotope studies, Ross Ice Shelf Project B. STAUFFER and M. MOELL
Physics Institute University of Bern, Switzerland The scientific objective of the contribution of the University of Bern to the Ross Ice Shelf Project is to determine both the age of the ice shelf at different depths and the time elapsed since the water beneath the shelf has been in contact with the atmosphere. This aim is achieved by measuring naturally produced isotopes, mainly carbon-14, argon-39, silicon-32, and hydrogen-3, in large snow, ice, and seawater samples. On 20 October 1976, B. Stauffer, M. Moell, and W. Bernhard, all of the University of Bern, arrived at McMur145
References
Bentley, C.R., 1976a. High electrical resistivity deep in antarctic shelf ice of ice-stream origin (abstr.) American Geophysical Union. Transactions, 57(4): 243. Bentley, C. R. 1966. Analysis of Ross Ice Shelf geophysics. Antarctic Journal of the U. S., XI(4): 276-27 7. Bentley, C. J. W. Clough. and J.D. Robertson. 1974. Geophysical work of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS) in 1973-74. AntarcticJournal of U.S., IX(4): 157-159. Clough, J.W., andJ.D. Robertson. 1975. RISP geophysical survey. AntarcticJournalof the U.S., X(4): 153. Crary, A.P., E.S. Robertson, H.F. Bennett, and W.W. Boyd, Jr. 144
Glaciological regime of the Ross Ice Shelf.Journal of Geophysical Research, 67(7): 2791-2807. Kohnen, H., and C.R. Bentley. 1977. Ultrasonic measurements on ice cores from the RISP drill hole. Antarctic Journal of the U.S., XII(4): 148-150. Bibliography
Clough, J.W. 1977. Radio echo sounding - reflections from internal layers.Journal of Glaciology, 18(78): 3-14. Clough, J.W. 1976. Observations of the electromagnetic lateral waves by earth sounding radars. Geophysics, 41: 1126-1132. Bentley, C.R. 1976. Isostatic imbalance and the past extent of the grounded ice sheet in the Ross Ice Shelf region, Antarctica.
Geology Society of America. Abstracts with Programs, 8(6).
Glaciological measurements on the Ross Ice Shelf ROBERT H. THOMAS
and DOUGLAS R. MAcAYEAL
Institute for Quaternary Studies University of Maine at Orono Orono, Maine 04473
Strain-rate measurements on the surface of the Ross Ice Shelf were continued during the 1976-1977 austral summer. The work forms part of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGs), which involves measurement of ice thickness, depth to sea bed, snow accumulation rates, local gravity, and surface strain rates at a 50-kilometer grid network of stations on the Ross Ice Shelf. At some of the stations, ice velocities are obtained from comparison of precise position fixes, and holes are drilled for 10-meter temperatures and for oxygen-isotope analysis of surface snow samples. Surface strain rates are obtained from Kehietype strain rosettes (Zumberge et al., 1960) with 1 to 1.5 kilometer "legs." RIGGS was started in 1973-1974 when 47 strain rosettes were planted in the southeast corner of the ice shelf (Thomas and Gaylord, 1974). Most of these were located and remeasured during the 1974-1975 season, when 34 new rosettes were planted in the northeast quadrant of the ice shelf (Thomas and Eilers, 1975). Logistic problems led to the cancellation of the 1975-1976 field program, so our plans for this last season included remeasurement of already-planted rosettes and installation of approximately 100 new rosettes to complete the survey in the western half of the ice shelf. Most of this work was accomplished. The 1976-1977 field party consisted of E. Penn of the University of Nebraska at Lincoln, D. Schilling of the University of Wisconsin Center, and T. Hughes, J . Lingham and ourselves, all of the University of Maine at Orono. J. Sorenson and D. Hall of the U.S. Geological Survey operated satellite-tracking equipment to obtain precise posiANTARCTIC JOURNAL
tion fixes at most of the stations. Field work began in early November 1976 with the relocation and excavation of the Roosevelt Island camp (RI on the figure). Resurvey of a 40kilometer network of stakes near the camp was completed in time for the arrival of the British Antarctic Survey (BAs) Twin Otter that was to fly us to the grid stations. All of the stations that were planted during 1974-1975 and several from the preceding season were located and remeasured by mid-December. This work was accomplished despite con tinuous problems with the Twin Otter navigation system, and our success was primarily due to the determination and complete involvement of the pilot and engineer, G. Kershaw andJ. Nicholson. Early in December E. Penn and D. MacAyeal joined Charles Bentley's RIGGS group at C-16 camp (figure) in the southwest quadrant of the ice shelf, where they continued to establish new grid stations until early February 1977. Three geophysicists then joined the group at RI camp to begin planting new grid stations in the northwest quadrant of the ice shelf. At the end of December this entire group moved to Q-13 camp (figure). Although the BAS Twin Otter was obliged to return to the Antarctic Peninsula for part of the season 82 of the planned new grid stations were established. During the 1977-1978 field season we hope to locate these stations, remeasure the strain rosettes, and repeat the precise position fixes. Preliminary analysis of RIGGS data from the southeast corner of the ice shelf revealed an apparent thickening with time of the ice in this region (Thomas, 1976a). Currently a more complete analysis (Thomas and Bentley, 1977) confirms this trend if we assume that locally there is negligible melting or freezing beneath the ice shelf. With this assumption, average thickening rates upstream of Crary Ice Rise (figure) are calculated to be about 0.3 meters of ice per year, decreasing toward the north so that, near the Ross Ice Shelf Project drill-hole, the ice shelf is approximately in equilibrium. The RIGGS data also will be used to test a finite element computer model of the ice shelf that will examine the effects on ice-shelf dynamics of ice rises and ice streams. This research was supported by National Science Foundation grant DPP 76-23047.
References
Gaylord, D.R., andJ.D. Robertson. 1975. Sediments exposed on the surface of the Ross Ice Shelf, Antarctica. Journal of Glaciology, 14: 332-333. Thomas, RH., and D.R. Gaylord. 1974. Glaciological measurements on the Ross Ice Shelf. Antarctic Journal of the U.S., IX(4): 160-162. Thomas, R.H., and D.H. Eilers. 1975. Glaciological measurements on the Ross Ice Shelf. Antarctic Journal of the U.S., X(4): 149-150. Thomas, R.H. 1976a. Thickening of the Ross Ice Shelf and the equilibrium state of the West Antarctic ice sheet. Nature, 259: 180-183. Thomas, R.H. 1976b. The distribution of 10-meter temperatures on the Ross Ice Shelf.Journal of Glaciology, 16: 111-117. Thomas, R.H. 1976c. Ice velocities on the Ross Ice Shelf. Antarctic Journal of the U. S., XI(4): 279-281. October 1977
ROSS ISLAND
ROSS ICE S
A A A A A A A %C
A A ©
CR AR Y ICE RISE
A A A D AA A®• A A ® A A A
1'
A AA
0 100 290 1cm BASE CAMP A ROSETTE (r.m.asur.d) A ROSETTE (planted)
•
o PRECISE POSITION FIX D DRILL HOLE
The Ross Ice Shelf showing positions of RIGGS stations. Thomas, RH., and C.R. Bentley. 1977. Past decay and present growth of the West Antarctic ice sheet. Paper to be presented at the X INQUA Congress, Birmingham, England. August, 1977. Zumberge,J.H., M. Giovinetto, R. Kehle, andJ. Reid. 1960. Deformation of the Ross Ice Shelf near the Bay of Whales, Antarctica. New York, American Geographical Society. IGY Glaciological Report Series, 3.
Geochemical and isotope studies, Ross Ice Shelf Project B. STAUFFER and M. MOELL
Physics Institute University of Bern, Switzerland The scientific objective of the contribution of the University of Bern to the Ross Ice Shelf Project is to determine both the age of the ice shelf at different depths and the time elapsed since the water beneath the shelf has been in contact with the atmosphere. This aim is achieved by measuring naturally produced isotopes, mainly carbon-14, argon-39, silicon-32, and hydrogen-3, in large snow, ice, and seawater samples. On 20 October 1976, B. Stauffer, M. Moell, and W. Bernhard, all of the University of Bern, arrived at McMur145
