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）长期通过统计描述指标刻画海底剪切应力与沉积物活动性的区域变异特征。本项目旨在识别剪切应力的分布模式，为大陆架生境划分或人类开发利用决策提供依据。本次统计覆盖范围为沿岸至约120米水深的大陆架区域，空间分辨率约5千米。研究团队通过数值模型生成波浪与环流的时间序列，结合近底稳态流速、振荡流速数据及底床粗糙度估算值，以1小时间隔计算海底剪切应力的时间序列。随后计算中位数、95百分位数等统计指标（即本数据库附带的输出项），以此生成剪切应力区域分布模式的二维可视化图谱。此外，将剪切应力时间序列与选定点位的临界应力值进行比对——临界应力值由实测表层沉积物粒度数据计算得出，进而估算海底沉积物的活动性。