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In-situ geophysical measurements in marine sediments: Applications in seafloor acoustics and paleoceanography.

机译：海洋沉积物中的原位地球物理测量：在海底声学和古海洋学中的应用。

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摘要

Acoustic in-situ sound speeds and attenuation were measured on the Eel River shelf, CA, with the Acoustic Lance between 5 and 15 kHz to 2.0 meters below seafloor (mbsf). A comparison with laboratory ultrasonic geoacoustic data obtained at 400 kHz on cored sediments showed faster in-situ and ultrasonic sound speeds in coarse-grained deposits in water depths to 60 m than in fine-grained deposits below that contour line. Ultrasonic attenuation was often greater than in-situ values and remained almost constant below 0.4 mbsf in these heterogeneous deposits. In-situ attenuation decreased with depth. These observations partly agree with results from other field studies, and with theoretical models that incorporate intergranular friction and dispersion from viscosity as main controls on acoustic wave propagation in marine sediments. Deviations among in-situ and laboratory acoustic data from the Eel Margin with theoretical studies were linked to scattering effects. Acoustic Lance was also deployed in homogeneous, fine-grained sediments on the inner shelf of SE Korea, where free gas was identified in late-September, but not in mid-September 1999. Free gas was evidenced by an abrupt decrease of in-situ sound speed and by characteristic changes in acoustic waveforms. These results suggest the presence of a gassy sediment layer as shallow as 2 mbsf along the 70 m bathymetry line, and was attributed to a variable abundance of free gas on short-term and/or small-regional scales on the SE Korea shelf.; Bulk density variations in marine sediments obtained along the Walvis Ridge/Basin, SW Africa, at Ocean Drilling Program (ODP) Sites 1081 to 1084 were spectral-analyzed to compute high-resolution sedimentation rates (SRs) in both the time- and age domains by correctly identifying Milankovitch cycles (MCs). SRs for the ODP sites yielded age-depth models that often correlate positively with biostratigraphic data and with organic mass accumulation rates (MAR Corg), a proxy for productivity, and negatively with Sea Surface Temperatures (SSTs), a proxy for wind strength. These results suggest that strong amplitudes of all main MCs existed for periods of high SRs and high MAR Corg and low SSTs, indicating a positive link between wind stress, upwelling vigor, productivity and insolation patterns in this area.
机译：在加利福尼亚州的鳗鱼河架子上测量了声学原位声速和衰减，声学长枪在海底（mbsf）下方5至15 kHz至2.0米之间。与在400 kHz处获得的带芯沉积物的实验室超声地声数据的比较表明，水深达60 m的粗粒沉积物的原位和超声速度要比轮廓线以下的细粒沉积物快。在这些异质沉积物中，超声波衰减通常大于原位值，并且几乎保持恒定，低于0.4 mbsf。原位衰减随深度而减小。这些观察结果与其他野外研究的结果部分相符，并​​且与理论模型相吻合，该理论模型将晶间摩擦和来自粘度的色散作为海洋沉积物中声波传播的主要控制因素。根据理论研究，Eel Margin的现场和实验室声学数据之间的偏差与散射效应有关。声学长枪也部署在韩国东南部内陆的均匀，细粒沉积物中，在那里，在9月下旬而非1999年9月中旬发现了游离气。原位突然减少证明了游离气。声速和声波形的特征变化。这些结果表明，沿70 m的测深线存在浅至2 mbsf的气态沉积物层，这归因于SE Korea陆架上短期和/或小区域尺度上的游离气体数量不等。在海洋钻探计划（ODP）站点1081至1084沿非洲西南部的沃尔维斯山脊/盆地获得的海洋沉积物中的体积密度变化进行了频谱分析，以计算时域和年龄域中的高分辨率沉积率（SR）通过正确识别米兰科维奇周期（MC）。 ODP站点的SR生成了年龄深度模型，该模型通常与生物地层数据和有机物质累积速率（MAR Corg）（生产力的代表）正相关，而与海面温度（SSTs）（作为风强度的代表）负相关。这些结果表明，在高SR，高MAR Corg和低SST期间，所有主要MC都存在强振幅，表明该地区的风应力，上升气势，生产力和日射模式之间存在正向联系。

著录项

  • 作者

    Gorgas, Thomas Joerg.;

  • 作者单位

    University of Hawaii.;

  • 授予单位 University of Hawaii.;
  • 学科 Geology.; Geophysics.
  • 学位 Ph.D.
  • 年度 2001
  • 页码 165 p.
  • 总页数 165
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地质学;地球物理学;
  • 关键词

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