Depositional environments of the antarctic continental shelf: Fjord ...
dynamic areas of the Bransfield Strait. During the final stages of the research, a stratigraphic model integrating sedimentological and radiochemical data from the three Antarctic Pen insula sites will be developed. This work was supported in part by National Science Foundation grant DPP 85-12514. We would like to thank the crew of the Glacier as well as D. Brewster, R. Elliott, and B. McKee for their time and efforts during the 5-week field program.
DeMaster, D.J., T.M. Nelson, C.A. Nittrouer, and S.L. Harden. 1987. Biogenic silica and organic carbon accumulation in modern Bransfield Strait sediments. Antarctic Journal of the U.S., 22(5), 108-110. Kellogg, T.B., L.E. Ostermann, and M. Stuiver. 1979. Late Quaternary sedimentology and benthic foraminiferal paleoecology of the Ross Sea, Antarctica. Journal of Foraminiferal Research, 9, 322-335. Nelson, T.M., D.J. DeMaster, C.A. Nittrouer, and D. Kamykowski. In preparation. The preservation and accumulation of biogenic silica and organic carbon in a high latitude environment: The Bransfield
References
Stuiver, M., and T.F. Braziunas. 1985. Compilation of isotopic dates from Antarctica. Radiocarbon, 27, 117-304. Venkatesan, MI., and I.R. Kaplan. 1987. The lipid geochemistry of Antarctic marine sediments: Bransfield Strait. Marine Chemistry, 21, 347-375.
Anderson, J.B., D.J. DeMaster, and C.A. Nittrouer. 1986. Preliminary results from marine geological cruises aboard the U.S. Coast Guard icebreaker Glacier. Antarctic Journal of the U.S., 21(5) 144-148.
Depositional environments of the antarctic continental shelf: Fjord studies from the
RN Polar Duke
EUGENE W. DOMACK
Geology Department Hamilton College Clinton, New York 13323
On 22 December 1987 the RN Polar Duke left Punta Arenas, Chile, for the Antarctic Peninsula. Scientific operations included two programs and commenced on Christmas Day. Eight undergraduate students from Hamilton college, under my direction, conducted water-column and bottom sampling experiments within fjords along the western side of the Peninsula, between 62°S and 65°S latitude. A second group under the direction of John Anderson (Rice University) investigated the continental shelf between 68°W and 63°W longitude (Antarctic Journal, this issue). The fjord survey intended to test current models for glacial marine sedimentation by assessing the relative role of modern biogenic and terrigenous (meltwater-derived) sedimentation. The Peninsula region is ideally suited to this study, because mean summer temperatures (the major determinant of surface melting) range from 2°C in the north to - 2°C in the south. The field program also attempted to aquire a sedimentary record suitable for examining temporal changes in sedimentary process, in so much as they may reflect climatic variation during the Holocene. Data collected included water-column measurements, bottom sampling (table 1), and seismic profiling. Water-column data were collected using a combination conductivity, temperature, depth, and transmissometer system (CTDT, Sea Bird model SBE-19 & Sea Tech model ST010-A). Over 211 highquality casts were made with the system using both the RIV Polar Duke and its complement of small craft (zodiacs; table 2). Over 200 water samples were collected for quantitative analysis of suspended sediment and approximately 100 oxygen mea96
Strait. Limnology and Oceanography.
surements were also completed. Approximately 86 SmithMcIntyre grab samples were obtained and 28 modified piston cores were collected as part of the fjord survey (table 1). Sediment samples are available to investigators and are currated at the Antarctic Research Facility of Florida State University. Copies of the oceanographic data are available upon request. The water-column data indicate that significant amounts of suspended particulates are transported within fine-scale density layers in mid-water depth (figure, block a). Surprisingly, we observed this phenomenon within fjords which are polar to sub-polar in climatic regime (i.e., mean summer temperature of around 0°C). These layers are not interfiows, because they do not occur along mid-water pycnoclines. Rather, they may be related to differential melting along the glacial terminus or evacuation of basal melt from within sub-ice tunnels, possibly under tidal influence. Fine-scale salinity maxima (figure, block a) are associated with the features and may be related to diffusive mixing or boundary layer effects. Attenuation of such layers takes place within the innermost basins of the fjord system. Hence, ice-proximal sediments in these polar fjords contain significant fine-grained terrigenous facies. Beyond the innermost sill, biogenic (siliceous) muds dominate. This facies change is accompanied by a ubiquitous increase in organic carbon and iceberg rafted debris, away from the glacial terminus. The gradient of these facies changes within each fjord appears to reflect the regional variation in climatic regime. In addition, some piston cores from ice-proximal basins show well-defined interbedding of biogenic and terrigenous facies, with a dominance of biogenic muds observed below the uppermost few meters down to at least 10 meters. This may reflect a relatively recent increase in terrigenous input, hence melting. In sub-polar regions, such as Admiralty Bay (King George Island), meltwater processes and terrigenous sediment transport appeared in the form of conventional overflow plumes, of infrequent occurrence (figure, block b). These surface layers, of relatively low salinity, contained the highest suspended sediment concentrations observed in our study (i.e., up to 12 milligrams per liter). Overflow transport does not restrict terrigeneous components to the inner basins. Rather, terrigenous muds are found in both ice-proximal and relatively distal (outer bay) environments. Other processes such as sediment gravity flows, coastal currents (figure, block c) and ice rafting exert strong control on ANTARCTIC JOURNAL
Table 1. U.S. Antarctic Program 1988 cruise Ill, bottom sampling stations
Gravity Piston (trigger) core core
Smith McIntyre bottom grab
Station
Latitude (S)
Longitude (W)
Depth (in meters)
2 3 4 5 6
62008.245' 62009.756' 62007.238' 62006.010' 62005.350
58025.575 58°36.016 58026.269' 58023.480' 5822.250'
350 110 396 285 135
7 8 9 10 13
62005.000' 64026.507' 64021.927' 64020.974' 64045.695'
58020.700' 63020.340' 63009.804' 63007.094' 63027.979
14 15a 15b 16 17
64043.347 64043.303' 64049.523' 64051.694' 64°52.911'
63026.878 63026.824' 62039.148' 62038.224 62036.008'
280 200 433 190 227
18 19 20 21 22
64054.472 64054.394' 64053.394' 64053.548' 64°49.625'
62035.057' 62036.458' 62033.825' 62035.649' 62039.001'
310 120 410 190 440
23 24 25 26 27
64027.765' 64027.524' 64027.782' 64029.066' 65004.200'
62030.709' 62030.073' 62031.053' 62031.070' 63010.600'
140
28 29 30 31 32
65007.100' 65006.358' 65005.108' 65005.054' 65005.741
63009.900' 63010.302' 63057.043 63055.012' 63053.903'
467 620 260 300 180
33 34 35 36 37
65007.810' 65007.780 65008.570' 65008.540' 65008.134'
63059.156' 63058.760' 63057.880' 63057.170 63057.889'
358 240 278 321 240
x x x x x
38 39 40 41 42
65007.552 65013.346' 65013.615' 65013.854 65042.000
63059.067' 64004.576' 64004.342' 64005.133' 66052.000'
240 60 190 200 290
x x x x x
105 106 107 108
65026.967' 63053.730a 63054.952a 63053.237a 63053 . 041a
64006.994' 60009.756' 60008.470' 60006.660' 60007.167
270 196 155 230 230
109 110 111 112 113
63054.828a 63055.760a 63056.250a 63055.871,a 63053.080a
60004.549' 60002.066 60002.492 60004.748' 60°39.641'
260 502 125 280 470
114 115 116 117 118
63056.907a 63056.917a 63057.626a 63058.214a 63057.783a
60032.791 60030.225' 60032.725 60031.395' 60029.839
250 320 225 95 260
x
x
x
x
x x x
x
x x x x x
x
370 680 615 280 x
x x x x
x
x x x x x x x x x x
50 130 585
x x x x
x
x
x
x x
x
x
x
x x x x x
x x x x x x x x x x
a Positions do not correspond to actual location with respect to coastal features and bathymetry 1988 REVIEW
97
Table 1. U.S. Antarctic Program 1988 cruise Ill, bottom sampling stations (continued)
Station
Latitude (S)
Gravity Longitude Depth Piston (trigger) (W) (in meters) core core
119 120 121 122 123
63057.439a 63057.023!a 63056.798!a 63056.324'a 63055.767'a
60028.783!
124 125 126 127 128
63057.070'a 63058.575a 63058.812!a 64009.293' 64010.125'
60043.965' 60038.959 60034.538! 60052.066
129 130 131 132 133
64008.963' 64009.382' 64009.164' 64008.546' 64007.896'
134 135 136 137 138
60027.532' 60025.894! 60024.798' 60033.740
360 120 190 160 382
x
x
Smith McIntyre bottom grab
x x x x x
60052.192'
380 460 90 260 105
x x x x x
60050.676! 60051.245' 60053.993' 60055.778! 60057.472'
100 330 250 290 300
x x x x x
64007.436' 64006.640' 64005.739' 64009.515' 64007.996'
60059.027' 61001.707' 61004-005' 60051.730' 60056.405'
210 245 385 340 270
x x x
139 140 141 142 143
64006.167' 64008.214' 64015.403' 64017.109! 64015.903'
61001.737' 61015.866' 61008.687' 60059.379' 61004.474'
477 600 390 430 340
144 145 146 147 148
64016.995' 64017.737' 64017.593' 64017.049' 64016.595'
61001.773' 60057.780' 60056.929' 60057.959' 60°59.041'
250 300 215 215 318
149 150 151 152 153
64017.094' 64016.555' 64013.108' 64026.803' 64026.350'
60059.305' 60059.824' 61014.713' 63020.141! 63021.371!
440 440 529 315 200
154 155 156 157 158
64025.511' 64025.016' 64022.932' 64020.834' 64°35.508'
63017.961' 63016.474' 63014.444' 63005.880' 62045.607'
490 560 420 740 585
159 160 161 162 163
64037.279' 64039.421' 64049.879' 64051.718' 64052.402'
62049.054' 62055.220' 62037.992' 62033.710' 62037.282'
730 660 400 530 110
164 165 166 167 168
64052.170' 64053.847' 64053.234' 64052.015' 64058.343'
62033.387' 62036.087' 62034.491' 62033.570' 63024.442'
480 190 390 480 565
172 173 174 175 176
62008.208' 62004.558'a 62004.615'a 62004.656!a 62009.487a
58027.524' 58019.694' 58019.498' 58019.222' 58025.103'
420 60 62 60 505
x x x x
x x x x x x x x x x x x
x x x
x x x x x
x x x x x
x x x x x x x x x x
x x
x
x x x x x x x x x
a Positions do not correspond to actual location with respect to coastal features and bathymetry. 98
ANTARCTIC JOURNAL
Table 2. Antarctic Program 1988 cruise Ill, CTDT, and water sample stations.
Location
Latitude Longitude Depth Water samples Station (W) (in meters) (S) (bottom, surface)
Admiralty Bay 2 3 4 5 6 7 8 9 1 0(A-H)
62013.853' 58019.503' 620 10.778' 58022.366 62008.449' 58026.572' 62009.450' 58031.300' 62009.791' 58036.210' 62°06.953' 58027.495' 62005.861 58023.456' 62005.348' 58022.314' 62°05.200' 58°20.700' Eight casts from Zodiac'
500 460 410 125 85 383 255 135 60
DeMaster, D.J., T.M. Nelson, C.A. Nittrouer, and S.L. Harden. 1987. Biogenic silica and organic carbon accumulation in modern Bransfield Strait sediments. Antarctic Journal of the U.S., 22(5), 108-110. Kellogg, T.B., L.E. Ostermann, and M. Stuiver. 1979. Late Quaternary sedimentology and benthic foraminiferal paleoecology of the Ross Sea, Antarctica. Journal of Foraminiferal Research, 9, 322-335. Nelson, T.M., D.J. DeMaster, C.A. Nittrouer, and D. Kamykowski. In preparation. The preservation and accumulation of biogenic silica and organic carbon in a high latitude environment: The Bransfield
References
Stuiver, M., and T.F. Braziunas. 1985. Compilation of isotopic dates from Antarctica. Radiocarbon, 27, 117-304. Venkatesan, MI., and I.R. Kaplan. 1987. The lipid geochemistry of Antarctic marine sediments: Bransfield Strait. Marine Chemistry, 21, 347-375.
Anderson, J.B., D.J. DeMaster, and C.A. Nittrouer. 1986. Preliminary results from marine geological cruises aboard the U.S. Coast Guard icebreaker Glacier. Antarctic Journal of the U.S., 21(5) 144-148.
Depositional environments of the antarctic continental shelf: Fjord studies from the
RN Polar Duke
EUGENE W. DOMACK
Geology Department Hamilton College Clinton, New York 13323
On 22 December 1987 the RN Polar Duke left Punta Arenas, Chile, for the Antarctic Peninsula. Scientific operations included two programs and commenced on Christmas Day. Eight undergraduate students from Hamilton college, under my direction, conducted water-column and bottom sampling experiments within fjords along the western side of the Peninsula, between 62°S and 65°S latitude. A second group under the direction of John Anderson (Rice University) investigated the continental shelf between 68°W and 63°W longitude (Antarctic Journal, this issue). The fjord survey intended to test current models for glacial marine sedimentation by assessing the relative role of modern biogenic and terrigenous (meltwater-derived) sedimentation. The Peninsula region is ideally suited to this study, because mean summer temperatures (the major determinant of surface melting) range from 2°C in the north to - 2°C in the south. The field program also attempted to aquire a sedimentary record suitable for examining temporal changes in sedimentary process, in so much as they may reflect climatic variation during the Holocene. Data collected included water-column measurements, bottom sampling (table 1), and seismic profiling. Water-column data were collected using a combination conductivity, temperature, depth, and transmissometer system (CTDT, Sea Bird model SBE-19 & Sea Tech model ST010-A). Over 211 highquality casts were made with the system using both the RIV Polar Duke and its complement of small craft (zodiacs; table 2). Over 200 water samples were collected for quantitative analysis of suspended sediment and approximately 100 oxygen mea96
Strait. Limnology and Oceanography.
surements were also completed. Approximately 86 SmithMcIntyre grab samples were obtained and 28 modified piston cores were collected as part of the fjord survey (table 1). Sediment samples are available to investigators and are currated at the Antarctic Research Facility of Florida State University. Copies of the oceanographic data are available upon request. The water-column data indicate that significant amounts of suspended particulates are transported within fine-scale density layers in mid-water depth (figure, block a). Surprisingly, we observed this phenomenon within fjords which are polar to sub-polar in climatic regime (i.e., mean summer temperature of around 0°C). These layers are not interfiows, because they do not occur along mid-water pycnoclines. Rather, they may be related to differential melting along the glacial terminus or evacuation of basal melt from within sub-ice tunnels, possibly under tidal influence. Fine-scale salinity maxima (figure, block a) are associated with the features and may be related to diffusive mixing or boundary layer effects. Attenuation of such layers takes place within the innermost basins of the fjord system. Hence, ice-proximal sediments in these polar fjords contain significant fine-grained terrigenous facies. Beyond the innermost sill, biogenic (siliceous) muds dominate. This facies change is accompanied by a ubiquitous increase in organic carbon and iceberg rafted debris, away from the glacial terminus. The gradient of these facies changes within each fjord appears to reflect the regional variation in climatic regime. In addition, some piston cores from ice-proximal basins show well-defined interbedding of biogenic and terrigenous facies, with a dominance of biogenic muds observed below the uppermost few meters down to at least 10 meters. This may reflect a relatively recent increase in terrigenous input, hence melting. In sub-polar regions, such as Admiralty Bay (King George Island), meltwater processes and terrigenous sediment transport appeared in the form of conventional overflow plumes, of infrequent occurrence (figure, block b). These surface layers, of relatively low salinity, contained the highest suspended sediment concentrations observed in our study (i.e., up to 12 milligrams per liter). Overflow transport does not restrict terrigeneous components to the inner basins. Rather, terrigenous muds are found in both ice-proximal and relatively distal (outer bay) environments. Other processes such as sediment gravity flows, coastal currents (figure, block c) and ice rafting exert strong control on ANTARCTIC JOURNAL
Table 1. U.S. Antarctic Program 1988 cruise Ill, bottom sampling stations
Gravity Piston (trigger) core core
Smith McIntyre bottom grab
Station
Latitude (S)
Longitude (W)
Depth (in meters)
2 3 4 5 6
62008.245' 62009.756' 62007.238' 62006.010' 62005.350
58025.575 58°36.016 58026.269' 58023.480' 5822.250'
350 110 396 285 135
7 8 9 10 13
62005.000' 64026.507' 64021.927' 64020.974' 64045.695'
58020.700' 63020.340' 63009.804' 63007.094' 63027.979
14 15a 15b 16 17
64043.347 64043.303' 64049.523' 64051.694' 64°52.911'
63026.878 63026.824' 62039.148' 62038.224 62036.008'
280 200 433 190 227
18 19 20 21 22
64054.472 64054.394' 64053.394' 64053.548' 64°49.625'
62035.057' 62036.458' 62033.825' 62035.649' 62039.001'
310 120 410 190 440
23 24 25 26 27
64027.765' 64027.524' 64027.782' 64029.066' 65004.200'
62030.709' 62030.073' 62031.053' 62031.070' 63010.600'
140
28 29 30 31 32
65007.100' 65006.358' 65005.108' 65005.054' 65005.741
63009.900' 63010.302' 63057.043 63055.012' 63053.903'
467 620 260 300 180
33 34 35 36 37
65007.810' 65007.780 65008.570' 65008.540' 65008.134'
63059.156' 63058.760' 63057.880' 63057.170 63057.889'
358 240 278 321 240
x x x x x
38 39 40 41 42
65007.552 65013.346' 65013.615' 65013.854 65042.000
63059.067' 64004.576' 64004.342' 64005.133' 66052.000'
240 60 190 200 290
x x x x x
105 106 107 108
65026.967' 63053.730a 63054.952a 63053.237a 63053 . 041a
64006.994' 60009.756' 60008.470' 60006.660' 60007.167
270 196 155 230 230
109 110 111 112 113
63054.828a 63055.760a 63056.250a 63055.871,a 63053.080a
60004.549' 60002.066 60002.492 60004.748' 60°39.641'
260 502 125 280 470
114 115 116 117 118
63056.907a 63056.917a 63057.626a 63058.214a 63057.783a
60032.791 60030.225' 60032.725 60031.395' 60029.839
250 320 225 95 260
x
x
x
x
x x x
x
x x x x x
x
370 680 615 280 x
x x x x
x
x x x x x x x x x x
50 130 585
x x x x
x
x
x
x x
x
x
x
x x x x x
x x x x x x x x x x
a Positions do not correspond to actual location with respect to coastal features and bathymetry 1988 REVIEW
97
Table 1. U.S. Antarctic Program 1988 cruise Ill, bottom sampling stations (continued)
Station
Latitude (S)
Gravity Longitude Depth Piston (trigger) (W) (in meters) core core
119 120 121 122 123
63057.439a 63057.023!a 63056.798!a 63056.324'a 63055.767'a
60028.783!
124 125 126 127 128
63057.070'a 63058.575a 63058.812!a 64009.293' 64010.125'
60043.965' 60038.959 60034.538! 60052.066
129 130 131 132 133
64008.963' 64009.382' 64009.164' 64008.546' 64007.896'
134 135 136 137 138
60027.532' 60025.894! 60024.798' 60033.740
360 120 190 160 382
x
x
Smith McIntyre bottom grab
x x x x x
60052.192'
380 460 90 260 105
x x x x x
60050.676! 60051.245' 60053.993' 60055.778! 60057.472'
100 330 250 290 300
x x x x x
64007.436' 64006.640' 64005.739' 64009.515' 64007.996'
60059.027' 61001.707' 61004-005' 60051.730' 60056.405'
210 245 385 340 270
x x x
139 140 141 142 143
64006.167' 64008.214' 64015.403' 64017.109! 64015.903'
61001.737' 61015.866' 61008.687' 60059.379' 61004.474'
477 600 390 430 340
144 145 146 147 148
64016.995' 64017.737' 64017.593' 64017.049' 64016.595'
61001.773' 60057.780' 60056.929' 60057.959' 60°59.041'
250 300 215 215 318
149 150 151 152 153
64017.094' 64016.555' 64013.108' 64026.803' 64026.350'
60059.305' 60059.824' 61014.713' 63020.141! 63021.371!
440 440 529 315 200
154 155 156 157 158
64025.511' 64025.016' 64022.932' 64020.834' 64°35.508'
63017.961' 63016.474' 63014.444' 63005.880' 62045.607'
490 560 420 740 585
159 160 161 162 163
64037.279' 64039.421' 64049.879' 64051.718' 64052.402'
62049.054' 62055.220' 62037.992' 62033.710' 62037.282'
730 660 400 530 110
164 165 166 167 168
64052.170' 64053.847' 64053.234' 64052.015' 64058.343'
62033.387' 62036.087' 62034.491' 62033.570' 63024.442'
480 190 390 480 565
172 173 174 175 176
62008.208' 62004.558'a 62004.615'a 62004.656!a 62009.487a
58027.524' 58019.694' 58019.498' 58019.222' 58025.103'
420 60 62 60 505
x x x x
x x x x x x x x x x x x
x x x
x x x x x
x x x x x
x x x x x x x x x x
x x
x
x x x x x x x x x
a Positions do not correspond to actual location with respect to coastal features and bathymetry. 98
ANTARCTIC JOURNAL
Table 2. Antarctic Program 1988 cruise Ill, CTDT, and water sample stations.
Location
Latitude Longitude Depth Water samples Station (W) (in meters) (S) (bottom, surface)
Admiralty Bay 2 3 4 5 6 7 8 9 1 0(A-H)
62013.853' 58019.503' 620 10.778' 58022.366 62008.449' 58026.572' 62009.450' 58031.300' 62009.791' 58036.210' 62°06.953' 58027.495' 62005.861 58023.456' 62005.348' 58022.314' 62°05.200' 58°20.700' Eight casts from Zodiac'
500 460 410 125 85 383 255 135 60
