U.S. Geological Survey calculated percentage of time sediment is mobile for May 2010 to May 2011 at select points in the South Atlantic Bight (SAB_mobile_perc, point shapefile, Geographic, WGS84)

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 5 km 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）一直通过统计描述量来刻画海底剪切应力（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，以期为栖息地划定或大陆架（continental shelf）的人类开发决策提供参考。本次统计刻画覆盖了从海岸至约120米水深范围的大陆架区域，空间分辨率约为5千米。研究团队通过数值模型（numerical models）生成海浪与环流的时间序列（time-series）数据，并利用近底输出的稳态与振荡流速数据以及底床粗糙度（bottom roughness）估算值，以1小时间隔计算海底剪切应力的时间序列。随后计算得到中位数与95百分位数（95th percentile）等统计描述量（即本数据库包含的输出结果），以此构建海底剪切应力区域分布模式的二维图景。此外，研究人员将应力时间序列与选定点位的临界应力（critical stress）值进行比对——临界应力值由观测得到的表层沉积物粒度数据（surface sediment texture data）计算得出——以此估算海底沉积物活动性。