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Figure 3. Photograph showing the starboard-side view of the National Oceanic and Atmospheric Administration Ship Thomas Jefferson, which was used to collect bathymetric data in the study area.

Figure 4. Photograph showing the National Oceanic and Atmospheric Administration Launch 3102, one of two launches used to collect bathymetric data in the study area.

Figure 5. Photograph showing a RESON SeaBat 7125 multibeam echosounder, hull-mounted to National Oceanic and Atmospheric Administration Ship Thomas Jefferson, which was used to collect bathymetric data.

Figure 6. Photograph showing a RESON SeaBat 8125 multibeam echosounder, hull-mounted to National Oceanic and Atmospheric Administration Launch 3101, which was used to collect bathymetric data.

Figure 7. Photograph showing a RESON SeaBat 8101 multibeam echosounder, hull-mounted to National Oceanic and Atmospheric Administration Launch 3102, which was used to collect bathymetric data.

Figure 8. Photograph showing the U.S. Geological Survey research vessel Rafael, which was used to collect sediment samples and photographic data.

Figure 9. Photograph showing the small Seabed Observation and Sampling System, a modified Van Veen grab sampler equipped with still and video cameras, mounted on the aft starboard side of the research vessel Rafael.

Figure 10. Chart showing the relations among phi sizes, millimeter diameters, size classifications, and American Society for Testing and Materials and Tyler sieve sizes.

Figure 11. Sediment-classification scheme from Shepard (1954), as modified by Schlee (1973) and Poppe and others (2004).

During August and September 2008, NOAA collected multibeam-echosounder (MBES) data during survey H11995. The NOAA Ship Thomas Jefferson (fig. 3) and two of its launches, 3101 and 3102 (fig. 4) collected 63 km² of bathymetric data. On the Thomas Jefferson, a RESON 7125 MBES (fig. 5), with a frequency of 400 kilohertz (kHz), collected bathymetric data. A RESON 8125 (fig. 6; frequency of 455 kHz) and RESON 8101 (fig. 7; frequency of 240 kHz) MBES were used to collect bathymetric data onboard Launch 3101 and 3102, respectively. Sounding data are referenced to tidal datum mean lower low water level and have been corrected for tides by using gages at Newport, R.I., and Menemsha Harbor, Mass. Ship positioning was determined by differential global positioning system (DGPS) with corrections from the U.S. Coast Guard beacon at Acushnet, Mass. SEACAT conductivity-temperature-depth (CTD) profiles were used to make sound-velocity corrections. CTD casts were made once every 3 to 4 hours during MBES acquisition.

MBES data were acquired in extended Triton data format (XTF) and recorded digitally through an ISIS data acquisition system. The data were processed with CARIS Hydrographic Image Processing System (HIPS) software to incorporate sound velocity and tidal corrections and perform quality assessment. The vertical resolution of the data is approximately 0.5 percent of the water depth. The MBES data were gridded to 2-m horizontal resolution and saved as a CARIS HIPS database. A vertically exaggerated (5x), hill-shaded (illuminated from 0° north at an angle of 45°) image was created using CARIS HIPS software. More details about MBES data acquisition and processing and survey information can be found in the H11995 Descriptive Report (National Oceanic and Atmospheric Administration, 2008). Bathymetric data are not to be used for navigation.

Sediment samples and bottom photography were obtained in the study area on June 15, 2011, as part of USGS cruise 2011-006-FA onboard the research vessel (RV) Rafael (fig. 8). During this survey, 27 stations were occupied in order to take sediment samples and still and video photography using the small Seabed Observation and Sampling System (SEABOSS), a modified Van Veen grab sampler with attached cameras (fig. 9). Sediment samples were taken at 11 of the stations where the sea-floor and surface conditions permitted; the other stations were described using bottom video and still photography. The grain sizes of sediment samples were analyzed at the USGS Woods Hole Coastal and Marine Science Center Sediment Laboratory, Woods Hole, Mass. Sediment descriptions are based on Wentworth's (1922) nomenclature (fig. 10) and Shepard's (1954) size classifications (fig. 11). Grain-size analysis procedures are detailed in Poppe and others (2005). The fine fractions (diameters less than 0.0625 millimeter, mm) of samples were analyzed using a Coulter Counter and coarse fractions (diameters greater than or equal to 0.0625 mm) were analyzed using sieves. Sample weights were corrected for salt, and gravel-sized shells were excluded from the analyses, as they generally form in situ and are not considered to be representative of the sedimentary environment.

Photographic data include three to seven photographs, taken by an operator, and several minutes of video collected along the entire transect of each station while the SEABOSS drifted over the sea floor. A Minolta Dimage 7Hi digital camera took photographs from a height of about 60 centimeters (cm) above the sea floor, resulting in images with widths covering from 30 cm to 1 m of the sea floor. Low-resolution versions of the still photographs are available for viewing in the Bottom Photography section of this report. Location information and full-resolution (2560 x 1920 pixels) versions of the photographs are available in the GIS Data Catalog section.

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