Station and data summary for data collected on Stellwagen Bank on U.S. Geological Survey field activity 2017-009-FA, aboard the R/V Auk, Jan. 30, 2017

Sediment sampling methods:

As a part of the process of mapping the sea floor, the USGS developed the SEABed Observation and Sampling System (SEABOSS) to collect samples and video and photographic images of the seabed to aid in the interpretation of seabed sonar imagery. A modified Van Veen sediment grab sampler is mounted in the center of the SEABOSS frame, which ensures the sampler is properly oriented on the seabed when a sample is collected. Before deployment, the sampler bucket’s 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 sediment sample, the SEABOSS frame was lowered gently onto the seabed, reducing tension on the cable, which caused the two locking catches to be automatically released by gravity. As the cable was retrieved, the grab sampler’s arms were pulled upward, closing the bucket around the sediment, and the SEABOSS was lifted off the seabed.

The SEABOSS was retrieved and set upon a wooden platform that kept the sampler bucket and camera systems above the deck. The sampler’s arms were held in the upright position manually or by tension on the cable, the two doors on the upper side of the bucket were opened, and the sediment was removed. For this project, the upper 2 cm of sediment, representing the surface of the seabed, were removed with a rectangular shovel 2-cm deep and stored in a plastic bag for grain-size analysis. The remaining sediment was dumped into a tray on the deck below the sampler and discarded, after which the sampler was washed in preparation for sampling at the next site. Further information on the SEABOSS can be found in Valentine and others (2000).

Grain-size analyses of the sediment samples were performed at the USGS Woods Hole Coastal and Marine Science Center in Woods Hole, Massachusetts, by using a standard suite of analytical methods (Poppe and others, 2014). This laboratory has been in operation since 1963 and has analyzed many thousands of sediment samples collected by the USGS in New England.

Video methods and data availability

Seabed video images were collected using two battery-operated, high-definition (1920 x 1080 pixels) GoPro digital video cameras mounted on the USGS SEABed Observation and Sampling System (SEABOSS). The SEABOSS system also had a Seaviewer, high-definition (1920 x 720 pixels), digital camera attached to it with a live feed to the surface. It was mounted a little higher on the frame and was used to observe obstacles, like gill nets and lobster gear, in order to avoid entanglement. In case of camera failure, the additional cameras provided backup video. As the SEABOSS drifted over the seabed, the cameras imaged the seabed at a rate of 60 frames per second from an altitude of ~1 meter. Lighting was provided by two, battery-operated Keldan LED video lights. Each light provided a light flux of up to 9000 lumens at a correlated color temperature of 5000 kelvins. Two parallel red lasers mounted 20 centimeters apart provided a scale in the video images.

Video imagery includes the launch and recovery of the SEABOSS, transit through the water column, and the drift over the seabed. The duration of individual video files ranges from 6 to 12 minutes. Video files range in size from 1.4 to 2.7 gigabytes. These video files are not part of this data release.

The position (lat/lon) and time of the start of the video drift was recorded (from the navigation receiver) by hand in the log book at the time of the deployment of the SEABOSS, when it reached the seabed, when a grab sample was attempted, and when it left the seabed. Latitude and longitude positions recorded by hand in the log book were later adjusted by reference to the data recorded in the GPS navigation file. Video was recorded during the descent through the water column (1-2 minutes), during the drift over the seabed, and during the ascent to the surface. The position (lat/lon) of the end of the video drift was recorded at the beginning of the ascent through the water column.

Photos:

No still photos of the seabed were acquired during this field activity. Video frame grabs were recorded to show typical images of the seabed. These images are available from the Larger Work citation.

The station position (lat/lon) represents the location of the sediment sample (if collected), which usually occurred at the end of the video drift. If a sediment sample was not collected, the station position represents the end of the video drift.

Water depth was determined using a Simrad ES60, 120 kHz, single beam echosounder using a 120-25 transducer, which detects the seabed to a depth of 800 m. Depth values (from the echo sounder monitor) and position (lat/lon) values (from the navigation receiver) were recorded in a log book at the time of deployment of the Seaboss. Depth values were rounded to the nearest meter to account for ship motion.

This information was entered into an Excel (2016) spreadsheet, with a column for each piece of information as described in the entity and attribute section of the metadata. The first row is an explanation header, the second row contains descriptive column headers, and the third row contains brief column headers that are compatible with importing the data into a GIS.

The spreadsheet was opened in Excel (2016). The first row (the explanation header) and the second row (descriptive column headers) were deleted and the third row (brief column headers that are compatible with importing the data into a GIS) was retained. Then the spreadsheet was exported as an MS-DOS CSV.

Using ArcGIS 10.3.1, the CSV file was converted to a shapefile within ArcMap using File - Add Data - Add XY data. The CSV file was selected, with the x-coordinate set to STA_LON and the y-coordinate set to STA_LAT. The coordinate system of the input coordinates was set to the geographic coordinate system GCS_WGS_1984. Once the event theme was added to ArcMap, the data were then converted to a shapefile by right-clicking on the event theme - Data - Export Data. All of the features were exported using the layer's source data for the coordinate system. The output shapefile was set to 2017-009-FA_station_data_summary.shp.

Added keywords section with USGS persistent identifier as theme keyword.