Modern sediments of the Terra Nova Bay polynya, Ross ...
Lyman, J. 1956. Buffer mechanism of seawater. (Doctoral thesis, University of California at Los Angeles.) Takahashi, T., W.S. Broecker, A.E. Bainbridge, and R.F. Weiss. 1980. Carbonate chemistry of the Atlantic, Pacific and Indian Oceans: The results of the GEOSECS Expeditions, 1972 - 1978, cu-1-80. Palisades, N.Y.: La-
mont Doherty Geological Observatory. Wallace, D.W.R., and R. M. Moore. 1985. Vertical profiles of CC13F(F-11) and CC1 2F2(F-12) in the central Arctic Ocean Basin. Journal of Geophysical Research, 90, 1155 - 1166.
Modern sediments of the Terra Nova Bay polynya, Ross Sea, Antarctica
Weiss, R.F., J.L. Bullister, R.H. Gammon, and M.J. Warner. 1985. Atmospheric chlorofluoromethanes in the deep equatorial Atlantic. Nature, 314, 608 - 610. Weiss, RE, H.G. Ostlund, and H. Craig. 1979. Geochemical studies of the Weddell Sea. Deep-Sea Research, 26, 1093 - 1120. Zirino, A. 1975. Measurements of the apparent pH of seawater with a combination microelectrode. Limnology and Oceanography, 20, 654 657.
Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43210
content within the polynya. Smear-slide data indicate that sediments within the polynya contain a higher ratio of terrigenous to biogenous material than sediments from surrounding icecovered areas (figure 2). This change reflects the dilution caused by the influx of eolian material in the open-water zone, rather than a decrease in the biological productivity within the polynya. Significant eolian input has been previously identified in other regions of the Ross Sea (Barrett, Pyne, and Ward 1983), and visible quantities of dust have been observed blowing over Terra Nova Bay (Bromwich personal communication).
This study is a survey of the surface sediments of the Terra Nova Bay polynya. The survey was designed to identify sediment characteristics that reflect polynya-influenced deposition. We examined surface samples from 41 piston cores taken by the U.S. Coast Guard icebreaker Glacier during its austral summer 1979 - 1980 cruise. Analysis of the cores consisted of visual examination and description, particle-size analysis, smear-slide analysis, and X-ray diffraction studies of both the less than 63micrometer and less than 2-micrometer size fractions. The Terra Nova Bay polynya is located between 75°30' and 74°30'S and 162°30' and 164°E (figure 1). The polynya is kept icefree by two factors: the strong persistent katabatic winds that blow down the Reeves Glacier valley and the Drygaiski ice tongue, which blocks the northward flow of sea ice into Terra Nova Bay (Bromwich and Kurtz 1984). The mean surface area of the polynya is 1,000 square kilometers, with a maximum area of 5,000 square kilometers. Polynya size varies by migration of its eastern boundary; the maximum eastward extent of the poly'nya is limited by the length of the Drygalski ice tongue (Kurtz and Bromwich 1983). The bathymetry of the western Ross Sea is characterized by the combination of a series of ridges and basins oriented subparallel to the coastline and a general landward slope of much of the continental shelf. This general landward slope probably resulted from glacial action during the Wisconin glacial maximum (Anderson, Brake, and Myers 1984). The tnaximum water depth within Terra Nova Bay is over 1,100 peters and occurs near the western boundary of the polynya, in he Drygaiski Basin (Anderson and Kurtz 1980). The primary process that affects sedimentation within the erra Nova Bay polynya differently than in adjacent ice-covered reas is eolian transport of terrigenous material. The katabatic inds in this region have an average velocity of 15 meters per s cond, with much greater velocities present during storms urtz and Bromwich 1983). These velocities, combined with t e presence of exposed weathering surfaces of rocks found u wind, are sufficient to explain the high terrigenous sediment
Figure 1. Location map showing Terra Nova Bay and surrounding features (from Kurtz and Bromwich 1983). ("km" denotes "kilometer," "C" denotes "Campbell Glacier," "P" denotes "Priestley Glacier," "H" denotes "Reeves Glacier," "N" denotes "Nansen Ice Sheet," "L" denotes "Larsen Glacier," "0" denotes "David Glacier," "K" denotes "Clarke Glacier:')
P. HUGHES and
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The effects of such a process in the Terra Nova Bay area are indicated by the presence of coarse-grained sediment on offshore topographic highs. While Anderson et al. (1984) suggest that sediment gravity flows should occur in areas such as Terra Nova Bay, no sedimentary structures indicative of gravity flows were observed in any of these samples. This lack of physical structures, however, may also be due to extensive bioturbation. This project was funded by a grant from Ohio State University to Lawrence Krissek.
S INSIDE POLYNyA
/
S- SAND
* OUTSIDE POLYNYA
/ /
L-SILT
0 TRANSITIONAL
I
C-CLAY
Figure 2. Plot of sediment composition based on smear slide analysis, showing the high terrigenous content of the samples from within the polynya. The volcanic rich samples are from north of the polynya, near Mount Melbourne.
. *
0 * . *
Although direct measurements are unavailable, the combination of physical factors acting within the polynya suggests that biological productivity should be higher there than in surrounding ice-covered areas. In particular, the ice-free environment of the polynya may be the site of enhanced mixing and favorable light conditions. Biogenic sediments are common all along the western Ross Sea, however, suggesting that normal ice-covered conditions are also favorable for biogenic production (Anderson et al. 1984). The most important biogenous components in the surface sediments of the Terra Nova Bay area are diatom frustules and opaline sponge spicules. Foraminifera and mollusc shells are abundant in some nearshore areas, while radiolarians and silicoflagellates occur in lower numbers throughout the study area. Glacially transported components would be expected to be less abundant in the polynya than in the surrounding icecovered regions for two reasons: dilution by other components is increased within the polynya, and glacial input from icebergs is decreased within the polynya as the strong katabatic winds quickly push icebergs out to sea. Some glacial input is evidenced by the occurrence of isolated pebbles in otherwise muddy sediments throughout the study area. Samples taken in this study were too small to quantify pebble content and glacial influence. Other sedimentary inputs show little variation from ice-free to ice-covered regions, suggesting that they are less affected by the presence of the polynya. Mount Melbourne, an active volcano located just north of Terra Nova Bay, has contributed volcanic material to the sediments of both the polynya and the ice-covered areas to the north of the polynya. Benthic sedimentary processes should not be affected by the presence of the polynya. Anderson et al. (1984) propose that vigorous currents influence the shallow (less than 350-meter) portions of the Ross Sea by winnowing away material as coarse as medium sand.
108
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•
•
*
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Figure 3. Plot of textural data showing that the sediments of the polynya are texturally similar to the sediments in surrounding areas. Water depth and distance from shore have more effect on sediment texture than the presence of the polynya.
References
Anderson, J.B., and D.D. Kurtz. 1980. USCGC Glacier Deep Freeze 80. Antarctic Journal of the U.S., 15(5), 114 - 117. Anderson, J.B., C.F. Brake, and N.C. Myers. 1984. Sedimentation on the Ross Sea continental shelf, Antarctica. Marine Geology, 57, 295 333. Barrett, P.J., A.R. Pyne, and B. L. Ward. 1983. Modern sedimentation in McMurdo Sound, Antarctica. In R.I. Oliver, P.R. James, and J.B. Jag (Eds.), Antarctic Earth science. Cambridge: Cambridge Universit' Press. Bromwich, D. H. 1985. Personal communication. Bromwich, D.H., and D.D. Kurtz. 1984. Katabatic wind forcing of t e Terra Nova Bay polynya. Journal of Geophysical Research, 89(C3), 3561 3572. Kurtz, D.D., and D.H. Bromwich. 1983. Satellite observed behavior f the Terra Nova Bay polynya. Journal of Geophysical Research, 88(C1 ), 9717-9722.
ANTARCTIC JOURN
mont Doherty Geological Observatory. Wallace, D.W.R., and R. M. Moore. 1985. Vertical profiles of CC13F(F-11) and CC1 2F2(F-12) in the central Arctic Ocean Basin. Journal of Geophysical Research, 90, 1155 - 1166.
Modern sediments of the Terra Nova Bay polynya, Ross Sea, Antarctica
Weiss, R.F., J.L. Bullister, R.H. Gammon, and M.J. Warner. 1985. Atmospheric chlorofluoromethanes in the deep equatorial Atlantic. Nature, 314, 608 - 610. Weiss, RE, H.G. Ostlund, and H. Craig. 1979. Geochemical studies of the Weddell Sea. Deep-Sea Research, 26, 1093 - 1120. Zirino, A. 1975. Measurements of the apparent pH of seawater with a combination microelectrode. Limnology and Oceanography, 20, 654 657.
Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43210
content within the polynya. Smear-slide data indicate that sediments within the polynya contain a higher ratio of terrigenous to biogenous material than sediments from surrounding icecovered areas (figure 2). This change reflects the dilution caused by the influx of eolian material in the open-water zone, rather than a decrease in the biological productivity within the polynya. Significant eolian input has been previously identified in other regions of the Ross Sea (Barrett, Pyne, and Ward 1983), and visible quantities of dust have been observed blowing over Terra Nova Bay (Bromwich personal communication).
This study is a survey of the surface sediments of the Terra Nova Bay polynya. The survey was designed to identify sediment characteristics that reflect polynya-influenced deposition. We examined surface samples from 41 piston cores taken by the U.S. Coast Guard icebreaker Glacier during its austral summer 1979 - 1980 cruise. Analysis of the cores consisted of visual examination and description, particle-size analysis, smear-slide analysis, and X-ray diffraction studies of both the less than 63micrometer and less than 2-micrometer size fractions. The Terra Nova Bay polynya is located between 75°30' and 74°30'S and 162°30' and 164°E (figure 1). The polynya is kept icefree by two factors: the strong persistent katabatic winds that blow down the Reeves Glacier valley and the Drygaiski ice tongue, which blocks the northward flow of sea ice into Terra Nova Bay (Bromwich and Kurtz 1984). The mean surface area of the polynya is 1,000 square kilometers, with a maximum area of 5,000 square kilometers. Polynya size varies by migration of its eastern boundary; the maximum eastward extent of the poly'nya is limited by the length of the Drygalski ice tongue (Kurtz and Bromwich 1983). The bathymetry of the western Ross Sea is characterized by the combination of a series of ridges and basins oriented subparallel to the coastline and a general landward slope of much of the continental shelf. This general landward slope probably resulted from glacial action during the Wisconin glacial maximum (Anderson, Brake, and Myers 1984). The tnaximum water depth within Terra Nova Bay is over 1,100 peters and occurs near the western boundary of the polynya, in he Drygaiski Basin (Anderson and Kurtz 1980). The primary process that affects sedimentation within the erra Nova Bay polynya differently than in adjacent ice-covered reas is eolian transport of terrigenous material. The katabatic inds in this region have an average velocity of 15 meters per s cond, with much greater velocities present during storms urtz and Bromwich 1983). These velocities, combined with t e presence of exposed weathering surfaces of rocks found u wind, are sufficient to explain the high terrigenous sediment
Figure 1. Location map showing Terra Nova Bay and surrounding features (from Kurtz and Bromwich 1983). ("km" denotes "kilometer," "C" denotes "Campbell Glacier," "P" denotes "Priestley Glacier," "H" denotes "Reeves Glacier," "N" denotes "Nansen Ice Sheet," "L" denotes "Larsen Glacier," "0" denotes "David Glacier," "K" denotes "Clarke Glacier:')
P. HUGHES and
1 85 REVIEW
L.A. KRISSEK
107
v-I T- 1 B- I
The effects of such a process in the Terra Nova Bay area are indicated by the presence of coarse-grained sediment on offshore topographic highs. While Anderson et al. (1984) suggest that sediment gravity flows should occur in areas such as Terra Nova Bay, no sedimentary structures indicative of gravity flows were observed in any of these samples. This lack of physical structures, however, may also be due to extensive bioturbation. This project was funded by a grant from Ohio State University to Lawrence Krissek.
S INSIDE POLYNyA
/
S- SAND
* OUTSIDE POLYNYA
/ /
L-SILT
0 TRANSITIONAL
I
C-CLAY
Figure 2. Plot of sediment composition based on smear slide analysis, showing the high terrigenous content of the samples from within the polynya. The volcanic rich samples are from north of the polynya, near Mount Melbourne.
. *
0 * . *
Although direct measurements are unavailable, the combination of physical factors acting within the polynya suggests that biological productivity should be higher there than in surrounding ice-covered areas. In particular, the ice-free environment of the polynya may be the site of enhanced mixing and favorable light conditions. Biogenic sediments are common all along the western Ross Sea, however, suggesting that normal ice-covered conditions are also favorable for biogenic production (Anderson et al. 1984). The most important biogenous components in the surface sediments of the Terra Nova Bay area are diatom frustules and opaline sponge spicules. Foraminifera and mollusc shells are abundant in some nearshore areas, while radiolarians and silicoflagellates occur in lower numbers throughout the study area. Glacially transported components would be expected to be less abundant in the polynya than in the surrounding icecovered regions for two reasons: dilution by other components is increased within the polynya, and glacial input from icebergs is decreased within the polynya as the strong katabatic winds quickly push icebergs out to sea. Some glacial input is evidenced by the occurrence of isolated pebbles in otherwise muddy sediments throughout the study area. Samples taken in this study were too small to quantify pebble content and glacial influence. Other sedimentary inputs show little variation from ice-free to ice-covered regions, suggesting that they are less affected by the presence of the polynya. Mount Melbourne, an active volcano located just north of Terra Nova Bay, has contributed volcanic material to the sediments of both the polynya and the ice-covered areas to the north of the polynya. Benthic sedimentary processes should not be affected by the presence of the polynya. Anderson et al. (1984) propose that vigorous currents influence the shallow (less than 350-meter) portions of the Ross Sea by winnowing away material as coarse as medium sand.
108
* /• 0 *5* S/00*
* * *
•
•
*
V_
\C
Figure 3. Plot of textural data showing that the sediments of the polynya are texturally similar to the sediments in surrounding areas. Water depth and distance from shore have more effect on sediment texture than the presence of the polynya.
References
Anderson, J.B., and D.D. Kurtz. 1980. USCGC Glacier Deep Freeze 80. Antarctic Journal of the U.S., 15(5), 114 - 117. Anderson, J.B., C.F. Brake, and N.C. Myers. 1984. Sedimentation on the Ross Sea continental shelf, Antarctica. Marine Geology, 57, 295 333. Barrett, P.J., A.R. Pyne, and B. L. Ward. 1983. Modern sedimentation in McMurdo Sound, Antarctica. In R.I. Oliver, P.R. James, and J.B. Jag (Eds.), Antarctic Earth science. Cambridge: Cambridge Universit' Press. Bromwich, D. H. 1985. Personal communication. Bromwich, D.H., and D.D. Kurtz. 1984. Katabatic wind forcing of t e Terra Nova Bay polynya. Journal of Geophysical Research, 89(C3), 3561 3572. Kurtz, D.D., and D.H. Bromwich. 1983. Satellite observed behavior f the Terra Nova Bay polynya. Journal of Geophysical Research, 88(C1 ), 9717-9722.
ANTARCTIC JOURN
