Taylor Dome ice-core study
This research was supported by National Science Foundation rant DPP 89-18942. Dick Kelly drafted the figure.
References /ckert, R. P., Jr. 1990. Surficial geology and stratigraphy in Njord Valley, western Asgard Range, Antarctica: Implications for late Tertiary glacial history. Master of Science thesis, University of Maine, Orono, Maine. tenton, G. H., M. L. Prentice, D. E. Kellogg, and T. B. Kellogg. 1984. Late Tertiary history of the antarctic ice sheet: Evidence from the dry valleys. Geology, 12:263-7. all, B. L. 1992. Surficial geology and geomorphology of eastern Wright Valley, Antarctica: Implications for Plio-Pleistocene ice-sheet dynamics. Master of Science thesis, University of Maine, Orono, Maine. archant, D. R. 1990. Surficial geology and stratigraphy in Arena Valley, Quartermain Mountains, Antarctica: Implications for late Tertiary glacial history. Master of Science thesis, University of Maine, Orono, Maine. ¶archant. D. R., C. H. Denton, and D. E. Sugden. 1990. Surficial geology
Taylor Dome ice-core study P. M. GR0OTES AND E. J . SmIG Quaternary Isotope Laboratory AK-60 University of Washington
From 30 November 1991 until 22 January 1992, two field parties of four (Grootes, Steig, Merrand, and Tramoni, Quaternary Isotope Laboratory; and Waddington, Morse, Balise, and Paur, Geophysics Program, University of Washington) continued the 1990-1991 surface reconnaissance and drill site selection (Grootes et al. 1991; Waddington et al. 1991) on Taylor Dome (77*40 S 158 E) and the upper Taylor Glacier (see also Waddington and Morse). A survey of boards and stakes placed the previous year showed low, irregular accumulation across most of the area. (See figure 1 for explanation of location names.) Nine of 18 boards were still exposed at the surface, one was not found, and the remaining were covered by snow ranging from 4 to 42 centimeters. Excluding the Skelton Névé southwest of Taylor Dome proper, the average accumulation is 9.8±1.5 centimeters of snow. Accumulation over the period from January to December 1991 was about half of that estimated from the 1990-1991 snowpit studies (Grootes et al. 1991). Further observations are needed to determine whether this period is representative for accumulation in the Taylor Dome area. Observations during both field seasons of snow drifts and frequent wind-packed hard layers in pit profiles indicate that an important part of the accumulation may occur as drifts, and thus is not uniform over the area. Annual layers may be missing at some locations and the mean annual accumulation will be less
1992 REVIEW
of Sessrumir Valley, western Asgard Range, Antarctica: Implications for late Tertiary ice-sheet overriding. Antarctic Journal of the U.S., 25(5),53-55. Pi entice, M. L. 1982. Surficial geology and stratigraphy of central Wright Valley, Antarctica: Implications for Antarctic Tertiary glacial history. Master of Science thesis, University of Maine, Orono, Maine. Prentice, M. L., C. H. Denton, L. H. Burckle, and D. A. Hodell. 1987. Evidence from Wright Valley for the response of the antarctic ice sheet to climate warming. Antarctic Journal of the U.S., 22:56-58. Shackleton, N. J. and J. P. Kennett. 1975. Paleotemperature history of the Cenozoic and the initiation of antarctic glaciation: Oxygen and carbon isotope analyses in DSDP sites 277,279, and 281. Initial Reports of the Deep Sea Drilling Project, 29:743-755. Webb, P. -N., D. M. Harwood, B. C. McKelvey, J. H. Mercer, and L. D. Scott. 1984. Cenozoic marine sedimentation and ice volume variation on the east antarctic craton. Geology, 12:287-291. Webb, P. -N. and D. M. Harwood. 1991. Late Cenozoic glacial history of the Ross Embayment, Antarctica. Quaternary Science Reviews, 10:215224. Wilch, T. I. 1991. Surficial geology and geochronology of middle Taylor Valley, Antarctica: Implications for Plio-Pleistocene glacial history. Master of Science thesis, University of Maine, Orono, Maine.
than the apparent seasonal cycles of about 20 centimeters in pit profiles. The strong winds may cause erosion, as evidenced by a board at iON that had been undercut by about 5 centimeters. Sastrugi were more pronounced than the previous year, especially along the N line. Snow in pits along this line (50N, a repeat of a 1990-1991 snowpit, and 20N) showed rapid metamorphosis with coarse depth hoar near the surface as in 1990-1991. Pits were also repeated at lOS in the high snow accumulation area, and at 20C near the camp and the future drill site. Little direct snowfall was observed during either field season, yet significant drifts accumulated. This indicates that a significant fraction of accumulating snow consists of reworked snow, much of it probably transported from the interior of East Antarctica. This snow may have an isotopic composition different from that of local snow fall. To check this we sampled two snowpits, one on top of Mt. Feather, the other on Mt. Crean (figure 1). These mountains rise several hundred meters above the surrounding glaciers and Taylor Dome, and may be expected to collect predominantly local snow. Both sites however, exhibit features of strong firnification, having almost continuous depth hoar. Isotopic enrichment by mass loss must thus be considered in their interpretation. A significant change in the wind pattern from 1990-1991 was the presence of a second preferred wind direction from the southeast, from the Ross Ice Shelf, in addition to the katabatic winds from the southwest. The southeasterly winds tended to be associated with clouds at about the 2,500-meter level and higher temperatures. Two 4-inch cores, the first to 128 meters at 20C and the second to 100 meters at the entrance to Taylor Valley, were drilled by PICO. Drilling ended when the quality of the cores deteriorated significantly. Stratigraphy, density, electrical conductivity measurement (ECM), and isotope sampling of most of the 128 meter and the firn part of the 100 meter core were done in the field using a snow trench to keep the core below -15 C. Above this temperature a film of liquid water may develop on crystal surfaces and affect the
57
0
composition of trapped air (CO2) The density-depth profile indicates the firn-ice transition is at about 76 meter ( p -0.82) depth. The isotope-depth profiles of the 11 pits of 1990-1991 document important isotope differences across the Taylor Dome field area. Figure 2 shows the isotope-depth profiles of the pits along the S. C, and N line averaged per depth interval. Excluded from the average were the pits at lOS and iON, both of which are located below Taylor Dome in the Portal and the entrance to Taylor Valley respectively, because they differed significantly from the others. The three lines display a clear change in average isotope values, which get heavier from S (-42J%) through C (-41.0%) to N (-39.2%), as well as poor preservation of the seasonal signal in the two N pits. The results of two chemistry and three microparticle profiles by P. Mayewski and E. MosleyThompson indicate about nine cycles per 2 meters like the oxygen isotopes. The additional results obtained in the field this year and the laboratory results from last year support the choice of the 20C area as a prospective drill site. They also show interesting variability over the Taylor Dome area which, combined with the continuous automated weather stations results of Waddington and Morse, may lead to new insights on the air-to-firn transfer function for isotopes and other ice-core parameters of interest.
50-
-. E U
-c cl
cii
D
150 N--
200
References Grootes, P. M., E. J . Steig and C. Massey. 1991. "Taylor Ice-Dome ice" study: Reconnaissance 1990-1991. Antarctic Journal of the U.S., 26(5): 69-71. Waddington, E. D., D. Morse, M. J . Balise, and J. Firestone. 1991. Glacier geophysical studies for an ice core site at "Taylor Dome." Antarctic Journal of the U.S., 26(5):71-73.
158 00 E
•
157 00 E 77 309
I
I
1 I .
-45 -40 -35 S 18 0 (V-SM0) (%)
Figure 2. Average 8180 profiles for snowpits along N, C, and S transects (see figure 1) of the Taylor Dome.
159 E
160 00 £
161 00 £
+
162 00 E
+
±J
77 30 S
+
(y\o
ASGMRD RANGE z
•.
lbep
77 45 S
+
Ur Mt Crn
H 78 00 S
+
2550 J
II
fH/ Y^UKR%
\
L M(I / 2200
tO km
+
A
+
+
Mt Feather 2985
+
78
00 S +
Figure 1. Map of the Taylor Dome area. Snowpits were sampled at most Intersections of the survey grid, denoted by the lines marked N, C, and, S, and 10 through 80. Stars show locations of last year's camp near 40 O and this year's camp and future drill site at 20°C.
58
AN-r/acnc JouRNAL
References /ckert, R. P., Jr. 1990. Surficial geology and stratigraphy in Njord Valley, western Asgard Range, Antarctica: Implications for late Tertiary glacial history. Master of Science thesis, University of Maine, Orono, Maine. tenton, G. H., M. L. Prentice, D. E. Kellogg, and T. B. Kellogg. 1984. Late Tertiary history of the antarctic ice sheet: Evidence from the dry valleys. Geology, 12:263-7. all, B. L. 1992. Surficial geology and geomorphology of eastern Wright Valley, Antarctica: Implications for Plio-Pleistocene ice-sheet dynamics. Master of Science thesis, University of Maine, Orono, Maine. archant, D. R. 1990. Surficial geology and stratigraphy in Arena Valley, Quartermain Mountains, Antarctica: Implications for late Tertiary glacial history. Master of Science thesis, University of Maine, Orono, Maine. ¶archant. D. R., C. H. Denton, and D. E. Sugden. 1990. Surficial geology
Taylor Dome ice-core study P. M. GR0OTES AND E. J . SmIG Quaternary Isotope Laboratory AK-60 University of Washington
From 30 November 1991 until 22 January 1992, two field parties of four (Grootes, Steig, Merrand, and Tramoni, Quaternary Isotope Laboratory; and Waddington, Morse, Balise, and Paur, Geophysics Program, University of Washington) continued the 1990-1991 surface reconnaissance and drill site selection (Grootes et al. 1991; Waddington et al. 1991) on Taylor Dome (77*40 S 158 E) and the upper Taylor Glacier (see also Waddington and Morse). A survey of boards and stakes placed the previous year showed low, irregular accumulation across most of the area. (See figure 1 for explanation of location names.) Nine of 18 boards were still exposed at the surface, one was not found, and the remaining were covered by snow ranging from 4 to 42 centimeters. Excluding the Skelton Névé southwest of Taylor Dome proper, the average accumulation is 9.8±1.5 centimeters of snow. Accumulation over the period from January to December 1991 was about half of that estimated from the 1990-1991 snowpit studies (Grootes et al. 1991). Further observations are needed to determine whether this period is representative for accumulation in the Taylor Dome area. Observations during both field seasons of snow drifts and frequent wind-packed hard layers in pit profiles indicate that an important part of the accumulation may occur as drifts, and thus is not uniform over the area. Annual layers may be missing at some locations and the mean annual accumulation will be less
1992 REVIEW
of Sessrumir Valley, western Asgard Range, Antarctica: Implications for late Tertiary ice-sheet overriding. Antarctic Journal of the U.S., 25(5),53-55. Pi entice, M. L. 1982. Surficial geology and stratigraphy of central Wright Valley, Antarctica: Implications for Antarctic Tertiary glacial history. Master of Science thesis, University of Maine, Orono, Maine. Prentice, M. L., C. H. Denton, L. H. Burckle, and D. A. Hodell. 1987. Evidence from Wright Valley for the response of the antarctic ice sheet to climate warming. Antarctic Journal of the U.S., 22:56-58. Shackleton, N. J. and J. P. Kennett. 1975. Paleotemperature history of the Cenozoic and the initiation of antarctic glaciation: Oxygen and carbon isotope analyses in DSDP sites 277,279, and 281. Initial Reports of the Deep Sea Drilling Project, 29:743-755. Webb, P. -N., D. M. Harwood, B. C. McKelvey, J. H. Mercer, and L. D. Scott. 1984. Cenozoic marine sedimentation and ice volume variation on the east antarctic craton. Geology, 12:287-291. Webb, P. -N. and D. M. Harwood. 1991. Late Cenozoic glacial history of the Ross Embayment, Antarctica. Quaternary Science Reviews, 10:215224. Wilch, T. I. 1991. Surficial geology and geochronology of middle Taylor Valley, Antarctica: Implications for Plio-Pleistocene glacial history. Master of Science thesis, University of Maine, Orono, Maine.
than the apparent seasonal cycles of about 20 centimeters in pit profiles. The strong winds may cause erosion, as evidenced by a board at iON that had been undercut by about 5 centimeters. Sastrugi were more pronounced than the previous year, especially along the N line. Snow in pits along this line (50N, a repeat of a 1990-1991 snowpit, and 20N) showed rapid metamorphosis with coarse depth hoar near the surface as in 1990-1991. Pits were also repeated at lOS in the high snow accumulation area, and at 20C near the camp and the future drill site. Little direct snowfall was observed during either field season, yet significant drifts accumulated. This indicates that a significant fraction of accumulating snow consists of reworked snow, much of it probably transported from the interior of East Antarctica. This snow may have an isotopic composition different from that of local snow fall. To check this we sampled two snowpits, one on top of Mt. Feather, the other on Mt. Crean (figure 1). These mountains rise several hundred meters above the surrounding glaciers and Taylor Dome, and may be expected to collect predominantly local snow. Both sites however, exhibit features of strong firnification, having almost continuous depth hoar. Isotopic enrichment by mass loss must thus be considered in their interpretation. A significant change in the wind pattern from 1990-1991 was the presence of a second preferred wind direction from the southeast, from the Ross Ice Shelf, in addition to the katabatic winds from the southwest. The southeasterly winds tended to be associated with clouds at about the 2,500-meter level and higher temperatures. Two 4-inch cores, the first to 128 meters at 20C and the second to 100 meters at the entrance to Taylor Valley, were drilled by PICO. Drilling ended when the quality of the cores deteriorated significantly. Stratigraphy, density, electrical conductivity measurement (ECM), and isotope sampling of most of the 128 meter and the firn part of the 100 meter core were done in the field using a snow trench to keep the core below -15 C. Above this temperature a film of liquid water may develop on crystal surfaces and affect the
57
0
composition of trapped air (CO2) The density-depth profile indicates the firn-ice transition is at about 76 meter ( p -0.82) depth. The isotope-depth profiles of the 11 pits of 1990-1991 document important isotope differences across the Taylor Dome field area. Figure 2 shows the isotope-depth profiles of the pits along the S. C, and N line averaged per depth interval. Excluded from the average were the pits at lOS and iON, both of which are located below Taylor Dome in the Portal and the entrance to Taylor Valley respectively, because they differed significantly from the others. The three lines display a clear change in average isotope values, which get heavier from S (-42J%) through C (-41.0%) to N (-39.2%), as well as poor preservation of the seasonal signal in the two N pits. The results of two chemistry and three microparticle profiles by P. Mayewski and E. MosleyThompson indicate about nine cycles per 2 meters like the oxygen isotopes. The additional results obtained in the field this year and the laboratory results from last year support the choice of the 20C area as a prospective drill site. They also show interesting variability over the Taylor Dome area which, combined with the continuous automated weather stations results of Waddington and Morse, may lead to new insights on the air-to-firn transfer function for isotopes and other ice-core parameters of interest.
50-
-. E U
-c cl
cii
D
150 N--
200
References Grootes, P. M., E. J . Steig and C. Massey. 1991. "Taylor Ice-Dome ice" study: Reconnaissance 1990-1991. Antarctic Journal of the U.S., 26(5): 69-71. Waddington, E. D., D. Morse, M. J . Balise, and J. Firestone. 1991. Glacier geophysical studies for an ice core site at "Taylor Dome." Antarctic Journal of the U.S., 26(5):71-73.
158 00 E
•
157 00 E 77 309
I
I
1 I .
-45 -40 -35 S 18 0 (V-SM0) (%)
Figure 2. Average 8180 profiles for snowpits along N, C, and S transects (see figure 1) of the Taylor Dome.
159 E
160 00 £
161 00 £
+
162 00 E
+
±J
77 30 S
+
(y\o
ASGMRD RANGE z
•.
lbep
77 45 S
+
Ur Mt Crn
H 78 00 S
+
2550 J
II
fH/ Y^UKR%
\
L M(I / 2200
tO km
+
A
+
+
Mt Feather 2985
+
78
00 S +
Figure 1. Map of the Taylor Dome area. Snowpits were sampled at most Intersections of the survey grid, denoted by the lines marked N, C, and, S, and 10 through 80. Stars show locations of last year's camp near 40 O and this year's camp and future drill site at 20°C.
58
AN-r/acnc JouRNAL
