Lyman, J. 1956. Buffer mechanism of seawater. (Doctoral thesis, Univer- Weiss, R.F., J.L. Bullister, R.H. Gammon, and M.J. Warner. 1985. At- sity of California at Los Angeles.) mospheric chlorofluoromethanes in the deep equatorial Atlantic. Takahashi, T., W.S. Broecker, A.E. Bainbridge, and R.F. Weiss. 1980. Nature, 314, 608 - 610. Carbonate chemistry of the Atlantic, Pacific and Indian Oceans: The results of Weiss, RE, H.G. Ostlund, and H. Craig. 1979. Geochemical studies of the GEOSECS Expeditions, 1972 - 1978, cu-1-80. Palisades, N.Y.: La- the . Deep-Sea Research, 26, 1093 - 1120. mont Doherty Geological Observatory. Zirino, A. 1975. Measurements of the apparent pH of seawater with a Wallace, D.W.R., and R. M. Moore. 1985. Vertical profiles of CC13F(F-11) combination microelectrode. Limnology and Oceanography, 20, 654 - and CC1 2F2(F-12) in the central Arctic Ocean Basin. Journal of 657. Geophysical Research, 90, 1155 - 1166.

content within the polynya. Smear-slide data indicate that sedi- Modern sediments of the ments within the polynya contain a higher ratio of terrigenous Bay polynya, , to biogenous material than sediments from surrounding ice- covered areas (figure 2). This change reflects the dilution caused by the influx of eolian material in the open-water zone, rather P. HUGHES and L.A. KRISSEK than a decrease in the biological productivity within the poly- nya. Significant eolian input has been previously identified in Department of Geology and Mineralogy other regions of the Ross Sea (Barrett, Pyne, and Ward 1983), Ohio State University and visible quantities of dust have been observed blowing over Columbus, Ohio 43210 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 sedi- ment 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 63- micrometer and less than 2-micrometer size fractions. The Terra Nova Bay polynya is located between 75°30 and 74°30S and 162°30 and 164°E (figure 1). The polynya is kept ice- free 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 (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 Wiscon- in 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 Figure 1. Location map showing Terra Nova Bay and surrounding inds in this region have an average velocity of 15 meters per features (from Kurtz and Bromwich 1983). ("km" denotes "kilo- s cond, with much greater velocities present during storms meter," "C" denotes "Campbell Glacier," "P" denotes "Priestley urtz and Bromwich 1983). These velocities, combined with Glacier," "H" denotes "Reeves Glacier," "N" denotes "Nansen Ice t e presence of exposed weathering surfaces of rocks found Sheet," "L" denotes "Larsen Glacier," "0" denotes "David Glacier," u wind, are sufficient to explain the high terrigenous sediment "K" denotes "Clarke Glacier:)

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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 off- v-I shore topographic highs. While Anderson et al. (1984) suggest that sediment gravity flows should occur in areas such as Terra T- 1 Nova Bay, no sedimentary structures indicative of gravity flows B- I 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 Univer- sity to Lawrence Krissek.

/ S INSIDE POLYNyA S- SAND / OUTSIDE POLYNYA / L-SILT I 0 TRANSITIONAL

C-CLAY

Figure 2. Plot of sediment composition based on smear slide analy- sis, showing the high terrigenous content of the samples from within the polynya. The volcanic rich samples are from north of the . 0 polynya, near . .

Although direct measurements are unavailable, the combina- / • 0 tion of physical factors acting within the polynya suggests that • biological productivity should be higher there than in sur- 5 rounding ice-covered areas. In particular, the ice-free environ- S/00

ment of the polynya may be the site of enhanced mixing and • V_ \C favorable light conditions. Biogenic sediments are common all along the western Ross Sea, however, suggesting that normal Figure 3. Plot of textural data showing that the sediments of the ice-covered conditions are also favorable for biogenic produc- polynya are texturally similar to the sediments in surrounding areas. tion (Anderson et al. 1984). The most important biogenous Water depth and distance from shore have more effect on sediment components in the surface sediments of the Terra Nova Bay area texture than the presence of the polynya. 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 ice- covered regions for two reasons: dilution by other components References 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 evi- Anderson, J.B., and D.D. Kurtz. 1980. USCGC Glacier Deep Freeze 80. denced by the occurrence of isolated pebbles in otherwise mud- Antarctic Journal of the U.S., 15(5), 114 - 117. dy sediments throughout the study area. Samples taken in this Anderson, J.B., C.F. Brake, and N.C. Myers. 1984. Sedimentation on study were too small to quantify pebble content and glacial the Ross Sea continental shelf, Antarctica. Marine Geology, 57, 295 - influence. 333. Other sedimentary inputs show little variation from ice-free Barrett, P.J., A.R. Pyne, and B. L. Ward. 1983. Modern sedimentation in to ice-covered regions, suggesting that they are less affected by McMurdo Sound, Antarctica. In R.I. Oliver, P.R. James, and J.B. Jag the presence of the polynya. Mount Melbourne, an active vol- (Eds.), Antarctic Earth science. Cambridge: Cambridge Universit cano located just north of Terra Nova Bay, has contributed Press. volcanic material to the sediments of both the polynya and the Bromwich, D. H. 1985. Personal communication. ice-covered areas to the north of the polynya. Benthic sedimen- 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 - tary processes should not be affected by the presence of the 3572. polynya. Anderson et al. (1984) propose that vigorous currents Kurtz, D.D., and D.H. Bromwich. 1983. Satellite observed behavior f influence the shallow (less than 350-meter) portions of the Ross the Terra Nova Bay polynya. Journal of Geophysical Research, 88(C1 ), Sea by winnowing away material as coarse as medium sand. 9717-9722.

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