Johnson David A.

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Johnson
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David A.
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  • Technical Report
    Descriptions of WHOI sediment cores
    (Woods Hole Oceanographic Institution, 1975-05) Johnson, David A. ; Driscoll, A. H.
    This report presents visual core descriptions and smear slide analyses for all cores in the Woods Hole Oceanographic Institution geological samples collection which were obtained prior to November 1973. Approximately 1000 coring stations from the Atlantic, Indian and Pacific oceans and adjacent seas are represented. Charts of ships' track and computer listings of all cores are also included.
  • 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
    Initial cruise report : Chain 115, leg 6
    (Woods Hole Oceanographic Institution, 1974-06) Johnson, David A.
    Leg 6 of CHAIN Cruise 115 began in Rio de Janeiro on 22 April 1974, and terminated in Recife on 18 May 1974. A multi-disciplinary scientific program was carried out within the Vema Channel and on the northern flanks of the Rio Grande Rise (see Figure 1). Personnel and scientific programs representing several institutions (W.H.O.I., Scripps, Lamont-Doherty) were included in the project; Brazilian observers representing PETROBRAS and the National Research Council also participated in the program.
  • Technical Report
    Descriptions of WHOI sediment cores : volume 5
    (Woods Hole Oceanographic Institution, 1977-04) Johnson, David A. ; Driscoll, A. H.
    This report supplements Volumes 1-4 of the core descriptions published previously in this sequence (Johnson and Driscoll, 1975). It contains visual descriptions and smear slide analyses for all cores received in the geological samples collection of the Woods Hole Oceanographic Institution between November, 1973 and November, 1976. Approximately 368 sample localities from the North Atlantic, Mediterranean, and South Atlantic are represented. Charts of ships' tracks and updated computer listings of all cores in the W.H.O.I. collection are also included.