Bunce Elizabeth T.

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Elizabeth T.

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  • Technical Report
    Abyssal sediment waves in the Amirante Passage, western Indian Ocean
    (Woods Hole Oceanographic Institution, 1977-02) Johnson, David A. ; Bunce, Elizabeth T.
    The deep western boundary current (DWBC) of the Indian Ocean flows northward along the western margin of the Mascarene Basin, and is funneled through a narrow passage (near 09°S, 52°E) prior to entering the Somali Basin to the north. Recently completed geological and geophysical operations within this passage reveal the presence of fields of well-developed abyssal sediment waves, with amplitudes of 10 to 50 meters and wavelengths of hundreds of meters to ~1 km. The two principal fields of sediment waves are confined to the flanks of the passages, and are restricted to a narrow depth interval (~3950 to 4150 meters). Individual waves appear to be elongated parallel to the passage axis and the presumed flow direction of the DWBC. The waves are relatively transparent to low-frequency echo sounding (3.5 kHz) and seismic profiling (17-70Hz), although weak internal reflectors are present within individual waves. These reflectors are conformable with the overlying sea floor, thereby suggesting neither upslope nor downslope migration of the waves. The sediment comprising the waves is a well-sorted calcareous ooze dominated by fine silt components (principally coccoliths), in marked contrast to the heterogeneous biogenic ooze on the adjacent channel floor. The lithology and local distribution pattern of the waves suggest that they are constructional bedforms associated with the flow of the DWBC, and not slump structures. A deep hydrocast at the sill of the channel indicates a near-bottom layer of Antarctic Bottom Water (Θ <0.9°C) approximately 200 meters thick, whose depth range corresponds with that of the sediment waves. Interpretations of the origin of the sediment waves in terms of the local flow regime will require (1) a more precise description of the physiography and structure of individual sediment waves; and (2) closely-spaced measurements of the nearbottom velocity structure of the DWBC within regions of the passage where sediment waves are apparently forming.
  • Technical Report
    Assessment of seabed seismic systems
    (Woods Hole Oceanographic Institution, 1980-04) Bunce, Elizabeth T.
    This project was initiated to accomplish the necessary research and documentation of existing seismic techniques and systems for the study of sediments and sedimentary structures in the oceans. In this respect , it is an 'inventory' of methods and techniques for looking at small-scale features or changes in structures lying from 10 to 1000 m beneath the sea floor. It attempts to assess the vertical and lateral resolution capabilities of existing and technically feasible seismic systems. Some of the questions posed are: how closely can we determine vertical variation such as sediment layer thickness and vertical variation with depth; also lateral coherence or its disruption by such agents as facies changes, thinning or thickening, slumping, faulting; the nature of the basement structure, its areal coherence, velocity structure and associated anomalies?
  • Technical Report
    Identification of generic study areas for the disposal of low level radioactive waste : western North Atlantic Ocean
    (Woods Hole Oceanographic Institution, 1979-07) Hollister, Charles D. ; Bunce, Elizabeth T. ; Chandler, Richard S.
    There is a growing need to effectively dispose of the low level radioactive waste presently accumulating in the United States. It may be decided to "dump" radioactive contamination products onto the deep sea floor (within 200 miles of the U.S.) in accordance with present IAEA guidelines (see Appendix A) for ocean dumping of low level waste; in the event of such a decision suitable areas must be identified and carefully studied to determine the subsequent influence of the waste on the environment. Using the site suitability criteria mentioned above we have identified two areas of possible use for low level waste disposal, one north of Puerto Rico and one east of Cape Hatteras, as deserving further study. The following report describes the relevant physical and geological characteristics of these two areas that may be important in considering a dumping operation. We have also made some recommendations for confirmatory research. The Hatteras Abyssal Plain, lying close to the 200 mile limit, appears to be a viable region for the focus of future research efforts.