The 95th percentile of bottom shear stress for the Gulf of Maine south into the Middle Atlantic Bight, May 2010 to May 2011 (GMAINE_95th_perc.shp, Geographic, WGS 84)

The U.S. Geological Survey has been characterizing the regional variation in shear stress on the sea floor and sediment mobility through statistical descriptors. The purpose of this project is to identify patterns in stress in order to inform habitat delineation or decisions for anthropogenic use of the continental shelf. The statistical characterization spans the continental shelf from the coast to approximately 120 m water depth, at approximately 0.03 degree (2.5-3.75 km, depending on latitude) resolution. Time-series of wave and circulation are created using numerical models, and near-bottom output of steady and oscillatory velocities and an estimate of bottom roughness are used to calculate a time-series of bottom shear stress at 1-hour intervals. Statistical descriptions such as the median and 95th percentile, which are the output included with this database, are then calculated to create a two-dimensional picture of the regional patterns in shear stress. In addition, time-series of stress are compared to critical stress values at select points calculated from observed surface sediment texture data to determine estimates of sea floor mobility.美国地质调查局（U.S. Geological Survey）长期通过统计描述量表征海底剪切应力（shear stress）与沉积物活动性（sediment mobility）的区域差异。本项目旨在识别剪切应力的分布模式，为大陆架的栖息地划定或人类活动开发决策提供科学参考。该统计表征覆盖了从海岸至约120米水深的大陆架区域，空间分辨率约为0.03度（依纬度不同，对应实地距离约2.5-3.75公里）。研究团队利用数值模式构建波浪与环流时间序列，通过定常与振荡流速的近底输出结果以及底床粗糙度（bottom roughness）估算值，以1小时间隔计算底剪切应力（bottom shear stress）的时间序列。随后计算中位数、95分位数这类统计描述量（即本数据库收录的输出结果），从而生成剪切应力区域分布模式的二维可视化图景。此外，研究团队将剪切应力时间序列与通过观测表层沉积物质地数据计算得到的选定点位临界应力值进行对比，以估算海底沉积物活动性。