Median of wave-current bottom shear stress in the Middle Atlantic Bight for May, 2010 - May, 2011 (MAB_median.SHP)

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刻画海底剪切应力（bottom 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，以期为栖息地划界或大陆架（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式（numerical models）构建波浪与环流的时间序列，并利用近底的恒定流速、振荡流速输出项以及海底粗糙度（bottom roughness）估算值，以1小时间隔计算海底剪切应力时间序列。随后计算中位数、95分位数等统计量作为本数据库的输出内容，以此生成剪切应力区域分布模式的二维可视化图景。此外，本数据集还将选取点位的剪切应力时间序列与由实测表层沉积物粒度数据计算得到的临界剪切应力（critical stress）值进行对比，以估算海底沉积物活动性。