U.S. Geological Survey Data Series 469
Seabed Photographs, Sediment Texture Analyses, and Sun-illuminated Sea Floor Topography in the Stellwagen Bank National Marine Sanctuary Region off Boston, Massachusetts
|
|
Sediment Collection and Processing MethodsSEABed Observation and Imaging System (SEABOSS) – As a part of the process of mapping the sea floor, the U.S. Geological Survey developed a sediment sampling system to aid in the interpretation of seabed sonar imagery. The modified Van Veen sediment grab sampler is mounted in the center of the SEABOSS frame. Before deployment, the grab's buckets (jaws) are opened by collapsing the extended arms to a near-horizontal position and locking them in place with two catches. The sampler operates passively to sample the seabed; it is not spring loaded. To collect a sample, the SEABOSS is lowered gently to the seabed, and the time is recorded for navigation purposes. When the cable is slack, the two locking catches automatically release by gravity. As the cable is retrieved, the grab sampler's arms are pulled upward, closing the bucket around the sediment, and the SEABOSS is lifted off the seabed. Weight can be added to the SEABOSS frame to make it harder to lift off the seabed; as a result the grab buckets close more tightly around the sediment. The SEABOSS is retrieved and set upon a wooden platform that keeps the sampler buckets and camera systems above the deck. The sampler's arms are held in the upright position manually or by tension on the cable, the doors on the upper sides of the buckets are opened, and the sediment is retrieved. For this project, the upper 2 cm of sediment, representing the surface of the seabed, was removed with a rectangular shovel 2 cm deep and stored in a plastic bag for analysis. The remaining sediment was dumped into a tray on the deck below the sampler, and the sampler was washed in preparation for sampling at the next site. For further information on the SEABOSS see http://woodshole.er.usgs.gov/operations/sfmapping/seaboss.htm https://pubs.usgs.gov/fs/fs142-00/fs142-00.pdf Sediment Analysis MethodsAnalytical procedure – Grain sizes of the sediment samples were analyzed at the USGS Woods Hole Coastal and Marine Science Center in Woods Hole, MA, by using a standard suite of analytical methods https://pubs.usgs.gov/of/2005/1001/. This laboratory has been in operation since 1963 and has analyzed most of the sediment samples collected by the USGS in the New England region https://pubs.usgs.gov/ds/2005/118/. Spreadsheet for sediment grain-size analyses – Sediment-sample data, including analytical results, are available in Excel spreadsheet format for download. An ESRI shapefile of all sediment-sample analyses with FGDC-compliant metadata is also available for download from the Data Catalog page. Explanation of Sediment Spreadsheet Columns
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
