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Circulation of Weddell Gyre and Antarctic Circumpolar Current In definitions of debris flow and turbulent flow (Hampton, References 1972; Middleton and Hampton, 1973; Enos, 1977). It appears now that sediments such as these may in- Anderson, J . B., D. D. Kurtz, and F. M. Weaver. 1979. Sedi- dicate the existence of those transitional mechanisms of mentation on the antarctic continental slope. In Continental sediment mass transport for which little field evidence Slopes, ed. 0. Pilkey and L. Doyle, pp. 627-46. SEPM special has been obtained. Further study to determine the hy- publication no. 27. drodynamic nature of such transitional deposits will en- Daly, R. A. 1936. Origin of sub-marine canyons. American able a clearer application of mass movement models in Journal of Science, 31: 401-20. both the modern and ancient environments. It is also Enos, P. 1977. Flow regimes in debris flow. Sedimentology. 24: important to learn to recognize mass flow deposits as 133-42. Hampton, M. A. 1972. The role of subaqueous debris flow in such. Otherwise paleo-oceanographic and paleoglacial generating turbidity currents.Jour. Sed. Pet., 42(4): 775-93. reconstructions from continental margin deposits, where Hughes, T. 1973. Is the West Antarctic ice sheet disintegrating? the most dramatic changes have occurred, cannot be Journal & Geophysical Research, 78: 7884-7910. made with confidence. Kurtz, D. C., and J . B. Anderson. 1979. Recognition and se- Financial support for this project has come from Na- dimentologic description of recent debris flow deposits from tional Science Foundation grants DPP 77-26407 and DPP the Ross and Weddell Seas, Antarctica. Jour. Sed. Pet, (3): 79-08242 and from the American Chemical Society Pe- 63-74. troleum Research Fund (PRF-1 1 101-AC2). We thank Su- Lowe, D. R. 1976. Subaqueous liquefied and fluidized sediment san Davis for assistance in the processing of samples and flows and their deposits. Sedimentology, 23: 285-308. Middleton, G. V., and M. A. Hampton. 1973. Sediment gravity Dennis Cassidy of the Antarctic Marine Geology Re- flows: Mechanics of flow and deposition in turbidites and search Facility (Florida State University) for his assis- deep water sedimentation. 5EPM. Pacific Sec. Short Course tance. Lecture Notes, pp. 1-38. Circulation of Weddell Gyre and North Atlantic in the South Atlantic, the source of Wed- dell Gyre deep water, and the spatial pattern and water Antarctic Circumpolar Current in mass alteration in the Weddell Sea. It has been found that the wind-driven Sverdrup South Atlantic transport in the Weddell Gyre region is quite different from the baroclinic flow of the upper kilometers (figure 1, derived from Gordon, Molinelli, and Baker [1978] A. L. GORDON and Gordon and Martinson [in preparation]). The sur- face flow, relative to 1,000 db, may not reflect the large- Lamont-Doherty Geological Observatory of Columbia University scale wind-driven flow, but rather the circulation in- Palisades, New York 10964 duced by pycnocline warping from thermohaline pro- cesses. If so, there is an important difference between the subpolar Weddell Gyre and subtropical gyres, where Hydrographic data from ARA Islas Orcadas cruises are dynamic topography matches the baroclinic flow of the being used, in conjunction with the historical data set, upper kilometer quite well (Stommel, Niiler, and Anati, to study water mass spreading and mixing in the South 1978; Leetmaa and Bunker, 1978). Atlantic Ocean. Specific issues being studied include the It is known that Pacific waters enter the Atlantic attentuation. of the water masses of the Pacific and the Ocean by passing over the ridge system forming the Figure 1. Streamlines of Sverdrup transport in Weddell Gyre (from Gordon and Martinson, 1979). Streamlines are given in 106 cubic meters per second. Light dashed line = 0-1,000 db dynamic topography; heavy dashed line = 1,000-2,500 db dynamic topography (from Gordon, Molinelli and Baker, 1978); shaded area = site of the 1976 Weddell poiynya. 112 Atlantic boundaries of the Scotia Sea, principally over the North Scotia Ridge in the region between Burdwood Bank and South Georgia Island. Evidence of geos- trophic determination in the deep gap near longitude 48°-49°W suggests high velocities for this process. It ap- pears that Pacific waters mix by a nearly isopycnal pro- cess with the relatively warm, saline North Atlantic deep water to the north and the relatively cold, fresher Wed- dell Gyre waters to the south. Fine structure and large- scale gradients indicate that the mixing is quite vigorous at most levels, although waters of Pacific origin clearly dominate some levels of the water column and survive to enter the Weddell Gyre. The main Pacific input into w.ri111.1 the Weddell Gyre, however, may exit the Scotia Sea to the east of South Georgia Island. References Gordon, A. L., E. Molinelli, and T. Baker. 1978. Large-scale relative dynamic topography of the Southern Ocean.Journal of Geophysical Research, 83(C6): 3023-32. Gordon, A. L., and D. Martinson. In preparation. Sverdrup transport of the Weddell Gyre. Leetmaa, A., and A. F. Bunker. 1978. Updated charts of the mean annual wind stress, convergences in the Ekman layers, and Sverdrup transports in the North Atlantic. Journal of Marine Research, 36(2): 311-22. Figure 2. The shallowest route from South America to the Stommel, H., P. Niiler, and D. Anati. 1978. Dynamic topog- Antarctic Peninsula. Pacific Ocean water has to cross this raphy and recirculation of the North Atlantic. Journal of ridge on entering the open Atlantic Ocean. Marine Research, 36(3): 449-68. The scientific program of Islas Orcadas cruise 1778, ARAIsIas Orcadas cruise 17 in which consisted of nine projects carried out by investi- northern Weddell and Scotia seas gators from five institutions, stressed two objectives: first, the investigation of the physical and chemical fac- tors affecting primary productivity in the late winter and early spring in the vicinity of the ice edge, and second, ROBERT J . OLSON the collection of krill for distribution, abundance, and biochemical studies. Scripps Institute of Oceanography The majority of the track from the southern portion University of California, San Diego of the Drake Passage to the South Sandwich Islands was La Jolla, California 92093 made through ice. Ice conditions ranged in ice coverage from two- to eight-eighths and in ice quality from pan- cake ice to two meters or more of rotten sea ice. The PAUL DUDLEY-HART vessel could maintain a 2.5-knot average speed through a six-eighths coverage of sea ice from one to two meters Woodward-Clyde Consultants in thickness. Weather was excellent during most of the 5120 Butler Pike cruise, although gale force headwinds slowed the ship Plymouth Meeting, Pennsylvania 19462 considerably between the South Sandwich Islands and South Georgia. The nine basic sets of measurements made at a typical ALDO ToMo station were as follows: 1. An in situ fluorometer/salinity-temperature-depth Argentine Antarctic Institute (STD) cast for chlorophyll-a fluorescence and tempera- Buenos Aires, Argentina ture/salinity profiles in the upper 300 meters, using a rosette sampler to obtain discrete water samples for comparison with the instruments (responsibility of Between 2 September and 14 October 1978, ARA Islas Scripps Institution of Oceanography [SIO] team). Orcadas collected scientific data over 4,725 miles of track. 2. A deep STD cast in order to be able to obtain phys- 113.
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