Taylor lceDome* study: Reconnaissance 1990-1991
Wade, EA., C.A. Cathey, and J.B. Oldham. 1977c. Reconnaissance geologic map of the Alexandra Mountains quadrangle, Marie Byrd Land, Antarctica, 1:250,000. (U.S. Antarctic Research Program Map, A-8.) Reston, Virginia: U.S. Geological Survey. Wade, EA., C.A. Cathey, and J.B. Oldham. 1978. Reconnaissance geologic map of the Gutenko Nunataks quadrangle, Marie Byrd Land, Antarctica, 1:250,000. (U.S. Antarctic Research Program Map, A-li.) Reston, Virginia: U.S. Geological Survey. Wade, EA., and D.R. Couch. 1982. The Swanson Formation, Ford Ranges, Marie Byrd Land, Evidence for and against a direct relation-
"Taylor lceDome* study: Reconnaissance 1990-1991 P.M. GROOTES, E.J. STEIG, and C. MASSEY Quaternary Isotope Laboratory, AK-60 University of Washington Seattle, Washington 98195
"Taylor Dome" is a small ice dome (center above 2,450 meters at about 77°40'S 158°00'E) separated from a ridge of the main east antarctic ice sheet by a saddle at least 100 meters lower (Drewry 1980). Flowline reconstruction by Drewry (1982) shows this dome as a local center of outflow supplying ice to the glaciers entering the McMurdo Dry Valleys of southern Victoria Land from the west. Climatic changes have been recorded both in the ice accumulating on "Taylor Dome" and in the glacial geology in the McMurdo Dry Valleys. An ice core retrieved from "Taylor Dome" thus offers the opportunity to compare the ice-core record of past climatic and environmental changes from an area of simple ice flow with the directly related geological record of past glaciations in the adjacent McMurdo Dry Valleys (e.g., Denton et al. 1989; Stuiver et al. 1981). From 29 November 1990 to 28 January 1991, two field parties of three members each (Grootes, Steig, and Massey of the Quaternary Isotope Laboratory and Balise, Morse, and Firestone of the Geophysics Program of the University of Washington) carried out a joint reconnaissance of "Taylor Dome" in preparation for the selection of an ice-core drill site (see also Waddington et al., Antarctic Journal, this issue). The goals of the Quaternary Isotope Laboratory party were to select a site (that is, to identify the area where the accumulating snow best preserves an environmental record) and to determine transfer functions (that is, to determine the relationship between the properties of the accumulating snow and environmental conditions). • Site selection. Two qualities classify a preserved environmental record in the ice as suitable for study. First, the record must represent an accumulation sufficiently sizeable and uni-
*Taylor Ice-Dome," also referred to as "Taylor Dome," is not listed in the Gazeteer of the Antarctic as an official name, but it is a distinct geographic feature.
1991 REVIEW
ship with the Robertson Bay Group, northern Victoria Land. In C. Craddock (Ed.), Antarctic geoscience. Madison, Wisconsin: University of Wisconsin Press. Wade, EA., and T.R. Wilbanks. 1972. Geology of Marie Byrd and Ellsworth Lands. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Weaver, S.D., J.D. Bradshaw, and C.J. Adams. 1991. Granitoids of the Ford Ranges, Marie Byrd Land, Antarctica. In M.R.A. Thomson, J.A. Crame, and J.W. Thomson (Eds.), Geological evolution of Antarctica. Cambridge, England: Cambridge University Press.
form that no years are missing in the record. Second, the record must have a stratigraphy that is preserved through the firnification process. To determine the suitability for icecore studies of different areas of "Taylor Dome," we dug 11 snow-pits across an 80 x 20-kilometer grid (figure 1). Ten pits to about 2 meters were sampled in detail (1-centimeter intervals) for istopic oxygen-18. Stratigraphy, temperature as a function of depth, and hardness of the snow were recorded in each pit. Microparticle samples were taken in two of the pits, and chemistry samples and snow density were taken in one. Detailed stratigraphy, isotope, chemistry, and microparticle samples as well as measurements of temperature, density, and hardness of the snow were obtained on a 4.5meter pit near camp. Using a Polar Ice Coring Office handauger system, two cores were drilled to about 11 meters to measure for microparticles and methanesulfonic acid and one core was drilled to about 19 meters to measure for isotopes near this pit. Most pits show a predominantly horizontal layering with occasional hard, wind-packed layers representing buried sastrugi (figure 2). A pattern of multiple thin layers and crusts separated by thicker, more uniform snow layers probably marks the seasonal pattern and suggests an annual accumulation of about 10-centimeter water equivalent. The area to the northeast of the crest of the dome, downwind for the predominant (katabatic) winds, shows more and larger sastrugi at the surface and in the pit profiles. Because sastrugi deposit locally over a short period and may consist largely of reworked snow, this area is less suitable for an ice-core study. Because our goal is to connect the "Taylor Dome" ice-core record to the glacial geology of the McMurdo Dry Valleys, the southwestern flank of the dome, which drains via The Portal into the Skelton Glacier, is likewise less suitable for a deep-drill site. Near the Lashly Mountains, "Taylor Dome" ends abruptly with a distinct step in ice elevation. The crest area between 20C and 30C (figure 1), away from this step has been chosen as the most suitable drill area. A drill site will be selected during the coming year based on detailed radar studies of the bedrock topography. • Transfer functions. Pale oenvironmental studies using ice cores aim to reconstruct the past (local) atmospheric conditions from the information contained in the ice. It is, thus, essential to make detailed weather observations (Waddington et al., Antarctic Journal, this volume) and to measure atmospheric water vapor, frost/rime, and falling snow to determine the relationships between those conditions and deposited snow. An array of mylar-covered boards placed in the snow, level with the snow surface, near bamboo poles marked with 69
/ " 80 ®1570O.E 7°30'S
1 60°00E
:--------
IS 44 0/
'Ybl
78°00S +
\LASHLY't'
+ THE PORTAL
Figure 1. Map of "Taylor Dome" and its location relative to the Ross Ice Shelf and Ross Island (inset). The 1990-1991 bamboo-stake grid ) is oriented southeast to northwest along the axis of "Taylor Dome" as indicated by the regional surface contours (from Drewry (1982) within grid from 1990-1991 survey, c.f. Waddington et al, Antarctic Journal, this issue). Snow pits localities are shown as: C properties studied isotopes, temperature, stratigraphy, hardness, and diatoms; 0 same plus microparticles; same plus microparticles, chemistry, and snow density. Accumulation boards are indicated by V. N, C, S are the grid lines "north," "center," and "south," respectively, and 10 through 80 indicate distance of gridline from the zero gridpoint on bedrock at the Lashly Mountains.
0
a depth scale (figure 1) will provide readings of the accumulation over the 1991 austral winter across the dome. Pit studies repeated over the coming field seasons will provide information on the changes in the snow during firnification. We sampled fresh snowfall, frost, and rime on a nylon screen over a plastic tray placed 1.5 meter above the snow. Snow was also collected in a mylar covered basket at the top of a mast, 9.2 meters above the snow. Even with strong winds, little or no reworked snow is expected to get into the basket. This set-up will allow us to compare the isotopic signal of new snowfall with that of reworked drifting snow. Atmospheric water vapor was sampled daily from 24 December 1990 to 12 January 1991 by pumping air through a trap cooled below -80 °C. The isotopic composition of the water vapor will be compared with that of the snow and frost/rime samples and with weather conditions. A similar set of samples collected at the Greenland Ice Sheet Project 2 camp at the summit of the Greenland ice sheet during the summers of 1989 and 1990 showed an excellent correlation between the isotopic composition of atmospheric water vapor and that of snow, frost, and rime. Large, rapid variations in isotopic composition during the summer appear to correlate with changes in atmospheric pressure and indicate the effect of air-mass history. 70
We thank VXE-6 and Antarctic Support Associates for the excellent support. John Simonson of Antarctic Support Associates contributed to the Geophysical Program survey work 1730 December 1990. This research was supported by National Science Foundation grant DPP 89-15924.
References Denton, G.H., J.G. Bockheim, 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. 1980. Pleistocene bimodal response of Antarctic ice. Nature (London), 287, 214-216. 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. Stuiver, M., G.H. Denton, T.J. Hughes, and J.L. Fastook. 1981. History of the marine ice sheet in West Antarctica during the last glaciation: A working hypothesis. In G.H. Denton and T.J. Hughes (Eds.), The last great ice sheets. New York: Wiley-Interscience. Waddington, E.D., D. Morse, M.J. Balise, and I.E Firestone. 1991. Glacier geophysical studies for an ice core site at "Taylor Dome," Antarctic Journal of the U.S., 26(5).
ANTARCTIC JOURNAL
50 N
0.00
los -
30 C
S M/S
M/S M
M/S
M-MIS M 'j -a
E I I-
w
M S-M/S
L-L.2
0.50
100LijJ±r4
1L
M/H 150
MH
iii7RW
-
S4M si
.T
M/H M/H
L
- - 000 050- 1.00 w
hard layer low density layer jmultiple density / hardness contrasts bonded grain crust - - density I hardness contrast
M/H M/H
M -
M/S M/S_
(m)
LEGEND
M MH
_-
- - -iTHTE - - - - - - - M/H ^
0.00
0.00
0.50
H
•ITT::1:TT
0.50
(m)
1.00
1.00
(m)
Figure 2. Snowpit stratigraphy at gridpoints 50N, 30C, and lOS (figure 1) across "McMurdo Dome." Pit lOS, located south of the dome in the Portal, shows horizontal layering of fine grained firn with an increase in density continuous with depth. At the 30C locality layering is mostly horizontal while the profile shows considerable fine structure in density contrasts, grain size, and bonded grain crusts. Occasional hard layers, representing buried sastrugi, break the horizontal layering, but these account for less than 20 percent of the profile. At 50N the fir, except for a windpacked hard layer at the surface, is coarse grained and shows no fine structure comparable to that at 30C. Hard layers (buried sastrugi) make up more than 40 percent of the profile, reflecting the rough local surface. The 50N profile is an extreme case of the snow stratigraphy in the north grid area, and indicates that this area is less suitable for a deep core site. H, M, 5, and VS indicate hard, medium, soft, and very soft firn layers, respectively. A hardness gradient within a layer is indicated by a vertical arrow.
Glacier geophysical studies for an ice core site at "Taylor Dome* E.D. WADDINGTON, D. MORSE, M.J. BALISE, and J. FIRESTONE Geophysics Program AK-50 University of Washington Seattle, Washington 98195
Based on an airborne radio-echo-sounding survey at 10-15kilometer line spacing, Drewry (1982) identified a distinct topographic dome centered at 77°40'S 15°00'E, above and west of *"Taylor Dome" is not listed in the Gazetteer of the Antarctic as anofficial name, but it is a distinct geographic feature. 1991 REVIEW
the McMurdo Dry Valleys, McMurdo Sound area (figure 1). "Taylor Dome" is a promising target for an ice-core paleoclimate study (Grootes, Steig, and Massey, Antarctic Journal, this issue) because the record will be relatively simple to interpret if all the ice originated locally. Such an ice core, taken to bedrock at 600-1,000 meters depth, could provide a climate record for the McMurdo Dry Valleys area over the past 20,000 years or more. Our goals over the next 3 years are the following: • to characterize the surface and bed topography and the ice flow regime, • to select a drill site, and • to analyze the ice-flow and temperature data through models to provide a time scale for the core, a paleotemperature and paleoprecipitation record for the area, and ice flow-related corrections and interpretations for time series in the ice core. Three programs in 1990-1991 contributed to site characterization. • Early in the field season, we installed an automatic weather station (star in figure 1) to monitor air and snow tempera71
"Taylor lceDome* study: Reconnaissance 1990-1991 P.M. GROOTES, E.J. STEIG, and C. MASSEY Quaternary Isotope Laboratory, AK-60 University of Washington Seattle, Washington 98195
"Taylor Dome" is a small ice dome (center above 2,450 meters at about 77°40'S 158°00'E) separated from a ridge of the main east antarctic ice sheet by a saddle at least 100 meters lower (Drewry 1980). Flowline reconstruction by Drewry (1982) shows this dome as a local center of outflow supplying ice to the glaciers entering the McMurdo Dry Valleys of southern Victoria Land from the west. Climatic changes have been recorded both in the ice accumulating on "Taylor Dome" and in the glacial geology in the McMurdo Dry Valleys. An ice core retrieved from "Taylor Dome" thus offers the opportunity to compare the ice-core record of past climatic and environmental changes from an area of simple ice flow with the directly related geological record of past glaciations in the adjacent McMurdo Dry Valleys (e.g., Denton et al. 1989; Stuiver et al. 1981). From 29 November 1990 to 28 January 1991, two field parties of three members each (Grootes, Steig, and Massey of the Quaternary Isotope Laboratory and Balise, Morse, and Firestone of the Geophysics Program of the University of Washington) carried out a joint reconnaissance of "Taylor Dome" in preparation for the selection of an ice-core drill site (see also Waddington et al., Antarctic Journal, this issue). The goals of the Quaternary Isotope Laboratory party were to select a site (that is, to identify the area where the accumulating snow best preserves an environmental record) and to determine transfer functions (that is, to determine the relationship between the properties of the accumulating snow and environmental conditions). • Site selection. Two qualities classify a preserved environmental record in the ice as suitable for study. First, the record must represent an accumulation sufficiently sizeable and uni-
*Taylor Ice-Dome," also referred to as "Taylor Dome," is not listed in the Gazeteer of the Antarctic as an official name, but it is a distinct geographic feature.
1991 REVIEW
ship with the Robertson Bay Group, northern Victoria Land. In C. Craddock (Ed.), Antarctic geoscience. Madison, Wisconsin: University of Wisconsin Press. Wade, EA., and T.R. Wilbanks. 1972. Geology of Marie Byrd and Ellsworth Lands. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Weaver, S.D., J.D. Bradshaw, and C.J. Adams. 1991. Granitoids of the Ford Ranges, Marie Byrd Land, Antarctica. In M.R.A. Thomson, J.A. Crame, and J.W. Thomson (Eds.), Geological evolution of Antarctica. Cambridge, England: Cambridge University Press.
form that no years are missing in the record. Second, the record must have a stratigraphy that is preserved through the firnification process. To determine the suitability for icecore studies of different areas of "Taylor Dome," we dug 11 snow-pits across an 80 x 20-kilometer grid (figure 1). Ten pits to about 2 meters were sampled in detail (1-centimeter intervals) for istopic oxygen-18. Stratigraphy, temperature as a function of depth, and hardness of the snow were recorded in each pit. Microparticle samples were taken in two of the pits, and chemistry samples and snow density were taken in one. Detailed stratigraphy, isotope, chemistry, and microparticle samples as well as measurements of temperature, density, and hardness of the snow were obtained on a 4.5meter pit near camp. Using a Polar Ice Coring Office handauger system, two cores were drilled to about 11 meters to measure for microparticles and methanesulfonic acid and one core was drilled to about 19 meters to measure for isotopes near this pit. Most pits show a predominantly horizontal layering with occasional hard, wind-packed layers representing buried sastrugi (figure 2). A pattern of multiple thin layers and crusts separated by thicker, more uniform snow layers probably marks the seasonal pattern and suggests an annual accumulation of about 10-centimeter water equivalent. The area to the northeast of the crest of the dome, downwind for the predominant (katabatic) winds, shows more and larger sastrugi at the surface and in the pit profiles. Because sastrugi deposit locally over a short period and may consist largely of reworked snow, this area is less suitable for an ice-core study. Because our goal is to connect the "Taylor Dome" ice-core record to the glacial geology of the McMurdo Dry Valleys, the southwestern flank of the dome, which drains via The Portal into the Skelton Glacier, is likewise less suitable for a deep-drill site. Near the Lashly Mountains, "Taylor Dome" ends abruptly with a distinct step in ice elevation. The crest area between 20C and 30C (figure 1), away from this step has been chosen as the most suitable drill area. A drill site will be selected during the coming year based on detailed radar studies of the bedrock topography. • Transfer functions. Pale oenvironmental studies using ice cores aim to reconstruct the past (local) atmospheric conditions from the information contained in the ice. It is, thus, essential to make detailed weather observations (Waddington et al., Antarctic Journal, this volume) and to measure atmospheric water vapor, frost/rime, and falling snow to determine the relationships between those conditions and deposited snow. An array of mylar-covered boards placed in the snow, level with the snow surface, near bamboo poles marked with 69
/ " 80 ®1570O.E 7°30'S
1 60°00E
:--------
IS 44 0/
'Ybl
78°00S +
\LASHLY't'
+ THE PORTAL
Figure 1. Map of "Taylor Dome" and its location relative to the Ross Ice Shelf and Ross Island (inset). The 1990-1991 bamboo-stake grid ) is oriented southeast to northwest along the axis of "Taylor Dome" as indicated by the regional surface contours (from Drewry (1982) within grid from 1990-1991 survey, c.f. Waddington et al, Antarctic Journal, this issue). Snow pits localities are shown as: C properties studied isotopes, temperature, stratigraphy, hardness, and diatoms; 0 same plus microparticles; same plus microparticles, chemistry, and snow density. Accumulation boards are indicated by V. N, C, S are the grid lines "north," "center," and "south," respectively, and 10 through 80 indicate distance of gridline from the zero gridpoint on bedrock at the Lashly Mountains.
0
a depth scale (figure 1) will provide readings of the accumulation over the 1991 austral winter across the dome. Pit studies repeated over the coming field seasons will provide information on the changes in the snow during firnification. We sampled fresh snowfall, frost, and rime on a nylon screen over a plastic tray placed 1.5 meter above the snow. Snow was also collected in a mylar covered basket at the top of a mast, 9.2 meters above the snow. Even with strong winds, little or no reworked snow is expected to get into the basket. This set-up will allow us to compare the isotopic signal of new snowfall with that of reworked drifting snow. Atmospheric water vapor was sampled daily from 24 December 1990 to 12 January 1991 by pumping air through a trap cooled below -80 °C. The isotopic composition of the water vapor will be compared with that of the snow and frost/rime samples and with weather conditions. A similar set of samples collected at the Greenland Ice Sheet Project 2 camp at the summit of the Greenland ice sheet during the summers of 1989 and 1990 showed an excellent correlation between the isotopic composition of atmospheric water vapor and that of snow, frost, and rime. Large, rapid variations in isotopic composition during the summer appear to correlate with changes in atmospheric pressure and indicate the effect of air-mass history. 70
We thank VXE-6 and Antarctic Support Associates for the excellent support. John Simonson of Antarctic Support Associates contributed to the Geophysical Program survey work 1730 December 1990. This research was supported by National Science Foundation grant DPP 89-15924.
References Denton, G.H., J.G. Bockheim, 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. 1980. Pleistocene bimodal response of Antarctic ice. Nature (London), 287, 214-216. 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. Stuiver, M., G.H. Denton, T.J. Hughes, and J.L. Fastook. 1981. History of the marine ice sheet in West Antarctica during the last glaciation: A working hypothesis. In G.H. Denton and T.J. Hughes (Eds.), The last great ice sheets. New York: Wiley-Interscience. Waddington, E.D., D. Morse, M.J. Balise, and I.E Firestone. 1991. Glacier geophysical studies for an ice core site at "Taylor Dome," Antarctic Journal of the U.S., 26(5).
ANTARCTIC JOURNAL
50 N
0.00
los -
30 C
S M/S
M/S M
M/S
M-MIS M 'j -a
E I I-
w
M S-M/S
L-L.2
0.50
100LijJ±r4
1L
M/H 150
MH
iii7RW
-
S4M si
.T
M/H M/H
L
- - 000 050- 1.00 w
hard layer low density layer jmultiple density / hardness contrasts bonded grain crust - - density I hardness contrast
M/H M/H
M -
M/S M/S_
(m)
LEGEND
M MH
_-
- - -iTHTE - - - - - - - M/H ^
0.00
0.00
0.50
H
•ITT::1:TT
0.50
(m)
1.00
1.00
(m)
Figure 2. Snowpit stratigraphy at gridpoints 50N, 30C, and lOS (figure 1) across "McMurdo Dome." Pit lOS, located south of the dome in the Portal, shows horizontal layering of fine grained firn with an increase in density continuous with depth. At the 30C locality layering is mostly horizontal while the profile shows considerable fine structure in density contrasts, grain size, and bonded grain crusts. Occasional hard layers, representing buried sastrugi, break the horizontal layering, but these account for less than 20 percent of the profile. At 50N the fir, except for a windpacked hard layer at the surface, is coarse grained and shows no fine structure comparable to that at 30C. Hard layers (buried sastrugi) make up more than 40 percent of the profile, reflecting the rough local surface. The 50N profile is an extreme case of the snow stratigraphy in the north grid area, and indicates that this area is less suitable for a deep core site. H, M, 5, and VS indicate hard, medium, soft, and very soft firn layers, respectively. A hardness gradient within a layer is indicated by a vertical arrow.
Glacier geophysical studies for an ice core site at "Taylor Dome* E.D. WADDINGTON, D. MORSE, M.J. BALISE, and J. FIRESTONE Geophysics Program AK-50 University of Washington Seattle, Washington 98195
Based on an airborne radio-echo-sounding survey at 10-15kilometer line spacing, Drewry (1982) identified a distinct topographic dome centered at 77°40'S 15°00'E, above and west of *"Taylor Dome" is not listed in the Gazetteer of the Antarctic as anofficial name, but it is a distinct geographic feature. 1991 REVIEW
the McMurdo Dry Valleys, McMurdo Sound area (figure 1). "Taylor Dome" is a promising target for an ice-core paleoclimate study (Grootes, Steig, and Massey, Antarctic Journal, this issue) because the record will be relatively simple to interpret if all the ice originated locally. Such an ice core, taken to bedrock at 600-1,000 meters depth, could provide a climate record for the McMurdo Dry Valleys area over the past 20,000 years or more. Our goals over the next 3 years are the following: • to characterize the surface and bed topography and the ice flow regime, • to select a drill site, and • to analyze the ice-flow and temperature data through models to provide a time scale for the core, a paleotemperature and paleoprecipitation record for the area, and ice flow-related corrections and interpretations for time series in the ice core. Three programs in 1990-1991 contributed to site characterization. • Early in the field season, we installed an automatic weather station (star in figure 1) to monitor air and snow tempera71
