Percentage of time sediment is mobile for May, 2010 - May, 2011 at select points in the Gulf of Maine south into the Middle Atlantic Bight (GMAINE_mobile_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与沉积物活动性的区域差异特征。本项目旨在识别剪切应力的分布模式，为栖息地划分或大陆架的人为利用决策提供参考依据。本次统计表征覆盖了从海岸至约120米水深范围的大陆架，空间分辨率约为0.03度（依纬度不同，对应2.5至3.75千米）。研究团队通过数值模式生成波浪与环流的时间序列，结合近底稳态流速、振荡流速输出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、95百分位数等统计量（即本数据库包含的输出项），以此构建剪切应力区域分布模式的二维可视化图谱。此外，将选取点位的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值进行比对，以估算海底沉积物的活动性。