Circulation of Weddell Gyre and Antarctic Circumpolar ...
definitions of debris flow and turbulent flow (Hampton, 1972; Middleton and Hampton, 1973; Enos, 1977). It appears now that sediments such as these may indicate the existence of those transitional mechanisms of sediment mass transport for which little field evidence has been obtained. Further study to determine the hydrodynamic nature of such transitional deposits will enable a clearer application of mass movement models in both the modern and ancient environments. It is also important to learn to recognize mass flow deposits as such. Otherwise paleo-oceanographic and paleoglacial reconstructions from continental margin deposits, where the most dramatic changes have occurred, cannot be made with confidence. Financial support for this project has come from National Science Foundation grants DPP 77-26407 and DPP 79-08242 and from the American Chemical Society Petroleum Research Fund (PRF-1 1 101-AC2). We thank Susan Davis for assistance in the processing of samples and Dennis Cassidy of the Antarctic Marine Geology Research Facility (Florida State University) for his assistance.
Circulation of Weddell Gyre and Antarctic Circumpolar Current in South Atlantic A. L. GORDON Lamont-Doherty Geological Observatory of Columbia University Palisades, New York 10964
Hydrographic data from ARA Islas Orcadas cruises are being used, in conjunction with the historical data set, to study water mass spreading and mixing in the South Atlantic Ocean. Specific issues being studied include the attentuation. of the water masses of the Pacific and the
References Anderson, J . B., D. D. Kurtz, and F. M. Weaver. 1979. Sedimentation on the antarctic continental slope. In Continental Slopes, ed. 0. Pilkey and L. Doyle, pp. 627-46. SEPM special publication no. 27. Daly, R. A. 1936. Origin of sub-marine 'canyons.' American Journal of Science, 31: 401-20. Enos, P. 1977. Flow regimes in debris flow. Sedimentology. 24: 133-42. Hampton, M. A. 1972. The role of subaqueous debris flow in generating turbidity currents.Jour. Sed. Pet., 42(4): 775-93. Hughes, T. 1973. Is the West Antarctic ice sheet disintegrating? Journal & Geophysical Research, 78: 7884-7910. Kurtz, D. C., and J . B. Anderson. 1979. Recognition and sedimentologic description of recent debris flow deposits from the Ross and Weddell Seas, Antarctica. Jour. Sed. Pet, (3): 63-74. Lowe, D. R. 1976. Subaqueous liquefied and fluidized sediment flows and their deposits. Sedimentology, 23: 285-308. Middleton, G. V., and M. A. Hampton. 1973. Sediment gravity flows: Mechanics of flow and deposition in turbidites and deep water sedimentation. 5EPM. Pacific Sec. Short Course Lecture Notes, pp. 1-38.
North Atlantic in the South Atlantic, the source of Weddell Gyre deep water, and the spatial pattern and water mass alteration in the Weddell Sea. It has been found that the wind-driven Sverdrup 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] and Gordon and Martinson [in preparation]). The surface flow, relative to 1,000 db, may not reflect the largescale wind-driven flow, but rather the circulation in duced by pycnocline warping from thermohaline processes. If so, there is an important difference between the subpolar Weddell Gyre and subtropical gyres, where dynamic topography matches the baroclinic flow of the upper kilometer quite well (Stommel, Niiler, and Anati, 1978; Leetmaa and Bunker, 1978). It is known that Pacific waters enter the Atlantic 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
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Atlantic boundaries of the Scotia Sea, principally over the North Scotia Ridge in the region between Burdwood Bank and South Georgia Island. Evidence of geostrophic determination in the deep gap near longitude 48°-49°W suggests high velocities for this process. It appears that Pacific waters mix by a nearly isopycnal process with the relatively warm, saline North Atlantic deep water to the north and the relatively cold, fresher Weddell Gyre waters to the south. Fine structure and largescale 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 the Weddell Gyre, however, may exit the Scotia Sea to the east of South Georgia Island. References
Figure 2. The shallowest route from South America to the Antarctic Peninsula. Pacific Ocean water has to cross this ridge on entering the open Atlantic Ocean.
ARAIsIas Orcadas cruise 17 in northern Weddell and Scotia seas ROBERT J . OLSON Scripps Institute of Oceanography University of California, San Diego La Jolla, California 92093
PAUL DUDLEY-HART Woodward-Clyde Consultants 5120 Butler Pike Plymouth Meeting, Pennsylvania 19462
ALDO ToMo Argentine Antarctic Institute Buenos Aires, Argentina
Between 2 September and 14 October 1978, ARA Islas scientific data over 4,725 miles of track.
Orcadas collected
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. Stommel, H., P. Niiler, and D. Anati. 1978. Dynamic topography and recirculation of the North Atlantic. Journal of Marine Research, 36(3): 449-68.
The scientific program of Islas Orcadas cruise 1778, which consisted of nine projects carried out by investigators from five institutions, stressed two objectives: first, the investigation of the physical and chemical factors affecting primary productivity in the late winter and early spring in the vicinity of the ice edge, and second, the collection of krill for distribution, abundance, and biochemical studies. The majority of the track from the southern portion of the Drake Passage to the South Sandwich Islands was made through ice. Ice conditions ranged in ice coverage from two- to eight-eighths and in ice quality from pancake ice to two meters or more of rotten sea ice. The vessel could maintain a 2.5-knot average speed through a six-eighths coverage of sea ice from one to two meters in thickness. Weather was excellent during most of the cruise, although gale force headwinds slowed the ship considerably between the South Sandwich Islands and South Georgia. The nine basic sets of measurements made at a typical station were as follows: 1. An in situ fluorometer/salinity-temperature-depth (STD) cast for chlorophyll-a fluorescence and temperature/salinity profiles in the upper 300 meters, using a rosette sampler to obtain discrete water samples for comparison with the instruments (responsibility of Scripps Institution of Oceanography [SIO] team). 2. A deep STD cast in order to be able to obtain phys113
Circulation of Weddell Gyre and Antarctic Circumpolar Current in South Atlantic A. L. GORDON Lamont-Doherty Geological Observatory of Columbia University Palisades, New York 10964
Hydrographic data from ARA Islas Orcadas cruises are being used, in conjunction with the historical data set, to study water mass spreading and mixing in the South Atlantic Ocean. Specific issues being studied include the attentuation. of the water masses of the Pacific and the
References Anderson, J . B., D. D. Kurtz, and F. M. Weaver. 1979. Sedimentation on the antarctic continental slope. In Continental Slopes, ed. 0. Pilkey and L. Doyle, pp. 627-46. SEPM special publication no. 27. Daly, R. A. 1936. Origin of sub-marine 'canyons.' American Journal of Science, 31: 401-20. Enos, P. 1977. Flow regimes in debris flow. Sedimentology. 24: 133-42. Hampton, M. A. 1972. The role of subaqueous debris flow in generating turbidity currents.Jour. Sed. Pet., 42(4): 775-93. Hughes, T. 1973. Is the West Antarctic ice sheet disintegrating? Journal & Geophysical Research, 78: 7884-7910. Kurtz, D. C., and J . B. Anderson. 1979. Recognition and sedimentologic description of recent debris flow deposits from the Ross and Weddell Seas, Antarctica. Jour. Sed. Pet, (3): 63-74. Lowe, D. R. 1976. Subaqueous liquefied and fluidized sediment flows and their deposits. Sedimentology, 23: 285-308. Middleton, G. V., and M. A. Hampton. 1973. Sediment gravity flows: Mechanics of flow and deposition in turbidites and deep water sedimentation. 5EPM. Pacific Sec. Short Course Lecture Notes, pp. 1-38.
North Atlantic in the South Atlantic, the source of Weddell Gyre deep water, and the spatial pattern and water mass alteration in the Weddell Sea. It has been found that the wind-driven Sverdrup 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] and Gordon and Martinson [in preparation]). The surface flow, relative to 1,000 db, may not reflect the largescale wind-driven flow, but rather the circulation in duced by pycnocline warping from thermohaline processes. If so, there is an important difference between the subpolar Weddell Gyre and subtropical gyres, where dynamic topography matches the baroclinic flow of the upper kilometer quite well (Stommel, Niiler, and Anati, 1978; Leetmaa and Bunker, 1978). It is known that Pacific waters enter the Atlantic 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
w.ri111.1
Atlantic boundaries of the Scotia Sea, principally over the North Scotia Ridge in the region between Burdwood Bank and South Georgia Island. Evidence of geostrophic determination in the deep gap near longitude 48°-49°W suggests high velocities for this process. It appears that Pacific waters mix by a nearly isopycnal process with the relatively warm, saline North Atlantic deep water to the north and the relatively cold, fresher Weddell Gyre waters to the south. Fine structure and largescale 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 the Weddell Gyre, however, may exit the Scotia Sea to the east of South Georgia Island. References
Figure 2. The shallowest route from South America to the Antarctic Peninsula. Pacific Ocean water has to cross this ridge on entering the open Atlantic Ocean.
ARAIsIas Orcadas cruise 17 in northern Weddell and Scotia seas ROBERT J . OLSON Scripps Institute of Oceanography University of California, San Diego La Jolla, California 92093
PAUL DUDLEY-HART Woodward-Clyde Consultants 5120 Butler Pike Plymouth Meeting, Pennsylvania 19462
ALDO ToMo Argentine Antarctic Institute Buenos Aires, Argentina
Between 2 September and 14 October 1978, ARA Islas scientific data over 4,725 miles of track.
Orcadas collected
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. Stommel, H., P. Niiler, and D. Anati. 1978. Dynamic topography and recirculation of the North Atlantic. Journal of Marine Research, 36(3): 449-68.
The scientific program of Islas Orcadas cruise 1778, which consisted of nine projects carried out by investigators from five institutions, stressed two objectives: first, the investigation of the physical and chemical factors affecting primary productivity in the late winter and early spring in the vicinity of the ice edge, and second, the collection of krill for distribution, abundance, and biochemical studies. The majority of the track from the southern portion of the Drake Passage to the South Sandwich Islands was made through ice. Ice conditions ranged in ice coverage from two- to eight-eighths and in ice quality from pancake ice to two meters or more of rotten sea ice. The vessel could maintain a 2.5-knot average speed through a six-eighths coverage of sea ice from one to two meters in thickness. Weather was excellent during most of the cruise, although gale force headwinds slowed the ship considerably between the South Sandwich Islands and South Georgia. The nine basic sets of measurements made at a typical station were as follows: 1. An in situ fluorometer/salinity-temperature-depth (STD) cast for chlorophyll-a fluorescence and temperature/salinity profiles in the upper 300 meters, using a rosette sampler to obtain discrete water samples for comparison with the instruments (responsibility of Scripps Institution of Oceanography [SIO] team). 2. A deep STD cast in order to be able to obtain phys113
