Glacier geophysical studies for an ice-core site at Taylor Dome: Year two
Glacier geophysical studies for an ice-core site at Taylor Dome: Year two D.L. MORSE AND E.D. WADDINGTON Geophysics Program, AK-50 University of Washington Seattle, Washington 98195
Taylor Dome is an ice dome first identified by Drewry (1982, 1983) from an aerial survey of the polar plateau region west of the dry valleys. Its dimensions are approximately 100 kilometers by 50 kilometers with a peak elevation near 2450 meters. Its crest is approximately 100 meters above a saddle connecting it with the East Antarctic Plateau. During the 1990-1991 field season, we began a program (Waddington et al. 1991) to study the ice dynamics at this site in support of an ice-core paleoclimate project (Grootes et al. 1991). A motivation for the paleoclimate study on Taylor Dome is the opportunity to compare the ice core results with the geologic record obtained in the Taylor Glacier terminus region by other researchers (e.g., Denton et al. 1989; Stuiver et al. 1978). Our main objectives are to provide the depth-age relationship for the ice core, and to predict the Taylor Glacier terminus response to climate forcing. Our initial goal is to find a drill site in a simple ice-flow regime where climatic indicators are well preserved. During the first season we installed a 20-by-80-kilometer network of survey poles on the dome with which to immediately measure topography and, after a few years of displacement,
• 157 00 E 77 30
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surface velocities and strain rates. From our initial observations, we chose a region within our network that would most likely contain the planned ice core. In this 10-kilometer square region we installed a more closely spaced array of poles for more detailed topographic and velocity measurements. We also used radio-echo sounding to survey the bottom topography. Installation of an automatic weather station (AWS), and a satellite positioning survey to measure absolute locations within the strain network, completed our first season's effort. A more detailed description of this work can be found in Waddington et al. 1991. During the 1991-1992 field season, we expanded the scope of the regional survey. Figure 1 shows the strain net after the second year. We extended the surface strain survey in three ways: we increased the survey node density in the region of the planned ice core, extended the network across the entrance of Taylor Glacier, and placed three transects across the glacier. Reduction and analysis of survey and radar data allowed us to further constrain the future coring site. In this 5-by-1-kilometer region we increased the survey-pole density to one every 1.25 kilometers (note the high-pole-density region near the center of the network in figure 1). We also collected radar sounding profiles at 1.25-kilometer line spacing. Figure 2 shows surface and bedrock topography in this region derived from these surveys. Toward our goal of characterizing the entire Taylor drainage system, we extended our survey network to bedrock across the entrance of Taylor Valley (see figure 1). This arm encompasses the site of a 100-meter firn core drilled this season. In addition, three cross-glacier profiles were installed further down-glacier. The lower two of these profiles (G and F) were originally surveyed by Robinson (1984) to measure ice flux. Weather observations will be used to relate ice-core properties to the conditions of the modern depositional environment of
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Figure 1. Topographic view of Taylor Dome and Taylor Glacier in relation to nearby geographic features. Elevations are in meters. Survey poles are Indicated by points. The closely spaced array of poles near the center of the network surrounds the expected location of the main core. The site marked with the circle (In the cluster of poles above the entrance to Taylor Glacier) Indicates the location of the 100-meter ice core drilled this season. Stars show the locations of the two weather stations. The westernmost AWS was installed during the first season. Also shown are the three Taylor Glacier transect lines: F, G, and H.
1992 REVIEW
59
-7
-. Figure 2. Orthographic view of surface and bed topography in the region of the main ice core. The surface contour Interval is 5 meters. The short vertical lines on the surface indicate positions of survey poles. The bottom topography is vertically exaggerated by a factor of five. in this view, the surface map is displaced upward to avoid overlap with the bottom topography; the zero on the vertical axis indicates the true surface position relative to the bottom. Taylor Dome. A summary of 1991 weather data collected with the first AWS (see figure 1) is shown in figure 3. This season we installed a second AWS near the site of the anticipated main ice core. The new unit is near the crest of the dome, 20 kilometers closer to the Transantarctic Mountains. By comparing their results, we will examine small-scale spatial climate variability. In late January 1992, a regional airborne radio-echo survey was performed by researchers from the University of Texas with the TUD (Technical University of Denmark) radar aboard a Twin Otter aircraft. They flew a 55-kilometer square grid, with 5kilometer line spacing centered over the dome. These profiles will provide the regional surface and bedrock topography needed to model the accumulation basin of Taylor Glacier. This is an ongoing project. Next season we plan to: Increase the survey node density around the selected core site, continue the radio-echo bedrock survey, repeat the satellite survey on the first year to look for two-year displacements, resurvey much of the network installed in the first season to measure two-year strains, and install an AWS at the upper Taylor Glacier core site. Mike Balise and Jason Paur assisted with the field work. We would like to acknowledge the assistance of the many Antarctic Support Associates, National Science Foundation, and U.S. Navy
60
support personnel at McMurdo Station, without whom our field work would be impossible. This work is supported by National Science Foundation grant DPP 89-15924. References Denton, C. H., J . G. Brockheim, S. C. Wilson, and M. Stuiver. 1989. Late Wisconsin and early Holocene glacial history, Inner Ross Embayment, Antarctica. Quaternary Research. 31:151-182. Drewry, D. J. 1982. Ice flow, bedrock, and geothermal studies from radioecho sounding inland of McMurdo Sound, Antarctica. In C. Craddock (Ed.), Antarctic Geoscience. Madison: University of Wisconsin Press, 977-983. Drewry, D. J. (Ed.) 1983. Antarctica: Glaciological and geophysical folio, Cambridge, U.K.: Scott Polar Research Institute. Grootes, P.M., E. J. Steig, and C. Massey. 1991. "Taylor Ice-Dome" study: Reconnaissance 1990-1991. Antarctic Journal of the U.S., 26(5):69-71. Robinson, P. H. 1984. Ice dynamics and thermal regime of Taylor Glacier, south Victoria Land, Antarctica. Journal of Glaciology, 30(105):153-160. Stuiver, M., G. H. Denton, and D. E. Kellogg. 1978. Glacial geologic studies in the McMurdo Sound region. Antarctic Journal of the U.S., 13:44-45. Waddington, E. D., D. L. Morse, M. J . Balise, and J . F. Firestone. 1991. Glacier geophysical studies for an ice core site at "Taylor Dome." Antarctic Journal of the U.S., 26(5):71-73.
ANTARCTIC JOURNAL
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day of year Figure 3. Summary of selected 1991 weather data from the first AWS. The top scatter plot shows wind speed (meters per second) as distance from plot center. The lower panels show air temperature (degrees C) and pressure (millibars), visible Isolation (Watts per square meter), and wind speed (the gap from day 212 to 310 is due to instrument failure).. 1992 REvIEw
61
Taylor Dome is an ice dome first identified by Drewry (1982, 1983) from an aerial survey of the polar plateau region west of the dry valleys. Its dimensions are approximately 100 kilometers by 50 kilometers with a peak elevation near 2450 meters. Its crest is approximately 100 meters above a saddle connecting it with the East Antarctic Plateau. During the 1990-1991 field season, we began a program (Waddington et al. 1991) to study the ice dynamics at this site in support of an ice-core paleoclimate project (Grootes et al. 1991). A motivation for the paleoclimate study on Taylor Dome is the opportunity to compare the ice core results with the geologic record obtained in the Taylor Glacier terminus region by other researchers (e.g., Denton et al. 1989; Stuiver et al. 1978). Our main objectives are to provide the depth-age relationship for the ice core, and to predict the Taylor Glacier terminus response to climate forcing. Our initial goal is to find a drill site in a simple ice-flow regime where climatic indicators are well preserved. During the first season we installed a 20-by-80-kilometer network of survey poles on the dome with which to immediately measure topography and, after a few years of displacement,
• 157 00 E 77 30
( /15
surface velocities and strain rates. From our initial observations, we chose a region within our network that would most likely contain the planned ice core. In this 10-kilometer square region we installed a more closely spaced array of poles for more detailed topographic and velocity measurements. We also used radio-echo sounding to survey the bottom topography. Installation of an automatic weather station (AWS), and a satellite positioning survey to measure absolute locations within the strain network, completed our first season's effort. A more detailed description of this work can be found in Waddington et al. 1991. During the 1991-1992 field season, we expanded the scope of the regional survey. Figure 1 shows the strain net after the second year. We extended the surface strain survey in three ways: we increased the survey node density in the region of the planned ice core, extended the network across the entrance of Taylor Glacier, and placed three transects across the glacier. Reduction and analysis of survey and radar data allowed us to further constrain the future coring site. In this 5-by-1-kilometer region we increased the survey-pole density to one every 1.25 kilometers (note the high-pole-density region near the center of the network in figure 1). We also collected radar sounding profiles at 1.25-kilometer line spacing. Figure 2 shows surface and bedrock topography in this region derived from these surveys. Toward our goal of characterizing the entire Taylor drainage system, we extended our survey network to bedrock across the entrance of Taylor Valley (see figure 1). This arm encompasses the site of a 100-meter firn core drilled this season. In addition, three cross-glacier profiles were installed further down-glacier. The lower two of these profiles (G and F) were originally surveyed by Robinson (1984) to measure ice flux. Weather observations will be used to relate ice-core properties to the conditions of the modern depositional environment of
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ASGMRD RANGE IN
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Figure 1. Topographic view of Taylor Dome and Taylor Glacier in relation to nearby geographic features. Elevations are in meters. Survey poles are Indicated by points. The closely spaced array of poles near the center of the network surrounds the expected location of the main core. The site marked with the circle (In the cluster of poles above the entrance to Taylor Glacier) Indicates the location of the 100-meter ice core drilled this season. Stars show the locations of the two weather stations. The westernmost AWS was installed during the first season. Also shown are the three Taylor Glacier transect lines: F, G, and H.
1992 REVIEW
59
-7
-. Figure 2. Orthographic view of surface and bed topography in the region of the main ice core. The surface contour Interval is 5 meters. The short vertical lines on the surface indicate positions of survey poles. The bottom topography is vertically exaggerated by a factor of five. in this view, the surface map is displaced upward to avoid overlap with the bottom topography; the zero on the vertical axis indicates the true surface position relative to the bottom. Taylor Dome. A summary of 1991 weather data collected with the first AWS (see figure 1) is shown in figure 3. This season we installed a second AWS near the site of the anticipated main ice core. The new unit is near the crest of the dome, 20 kilometers closer to the Transantarctic Mountains. By comparing their results, we will examine small-scale spatial climate variability. In late January 1992, a regional airborne radio-echo survey was performed by researchers from the University of Texas with the TUD (Technical University of Denmark) radar aboard a Twin Otter aircraft. They flew a 55-kilometer square grid, with 5kilometer line spacing centered over the dome. These profiles will provide the regional surface and bedrock topography needed to model the accumulation basin of Taylor Glacier. This is an ongoing project. Next season we plan to: Increase the survey node density around the selected core site, continue the radio-echo bedrock survey, repeat the satellite survey on the first year to look for two-year displacements, resurvey much of the network installed in the first season to measure two-year strains, and install an AWS at the upper Taylor Glacier core site. Mike Balise and Jason Paur assisted with the field work. We would like to acknowledge the assistance of the many Antarctic Support Associates, National Science Foundation, and U.S. Navy
60
support personnel at McMurdo Station, without whom our field work would be impossible. This work is supported by National Science Foundation grant DPP 89-15924. References Denton, C. H., J . G. Brockheim, S. C. Wilson, and M. Stuiver. 1989. Late Wisconsin and early Holocene glacial history, Inner Ross Embayment, Antarctica. Quaternary Research. 31:151-182. Drewry, D. J. 1982. Ice flow, bedrock, and geothermal studies from radioecho sounding inland of McMurdo Sound, Antarctica. In C. Craddock (Ed.), Antarctic Geoscience. Madison: University of Wisconsin Press, 977-983. Drewry, D. J. (Ed.) 1983. Antarctica: Glaciological and geophysical folio, Cambridge, U.K.: Scott Polar Research Institute. Grootes, P.M., E. J. Steig, and C. Massey. 1991. "Taylor Ice-Dome" study: Reconnaissance 1990-1991. Antarctic Journal of the U.S., 26(5):69-71. Robinson, P. H. 1984. Ice dynamics and thermal regime of Taylor Glacier, south Victoria Land, Antarctica. Journal of Glaciology, 30(105):153-160. Stuiver, M., G. H. Denton, and D. E. Kellogg. 1978. Glacial geologic studies in the McMurdo Sound region. Antarctic Journal of the U.S., 13:44-45. Waddington, E. D., D. L. Morse, M. J . Balise, and J . F. Firestone. 1991. Glacier geophysical studies for an ice core site at "Taylor Dome." Antarctic Journal of the U.S., 26(5):71-73.
ANTARCTIC JOURNAL
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day of year Figure 3. Summary of selected 1991 weather data from the first AWS. The top scatter plot shows wind speed (meters per second) as distance from plot center. The lower panels show air temperature (degrees C) and pressure (millibars), visible Isolation (Watts per square meter), and wind speed (the gap from day 212 to 310 is due to instrument failure).. 1992 REvIEw
61
