Click on figures for larger images

Figure 21. Map showing locations of sediment samples collected in the study area during cruise 2013-005-FA on the research vessel (RV) Rafael.

Figure 22. Photograph of a boulder at station 298_33. Hydrozoans cover a boulder, and shrimp, starfish, and a crab are present.

Figure 23. Photograph from station 298_36 showing an outcrop and rip-up clasts of silty clay that make up the steep eastern wall of Deep Hole, the largest and deepest bathymetric depression within the study area.

Figure 24. Photograph of semiconsolidated clasts of glaciolacustrine sediment obtained in the grab sample at station 298_36.

Sediments

Sediment Distribution

The sea floor in the study area is mostly composed of sand with gravel and gravelly sediment on bathymetric highs (fig. 21). One station (298_33; fig. 22) in the bottom of the northern bathymetric depression is classified as gravel on the basis of photography because a sample could not be obtained. Sand waves and megaripples cover much of the southern, western, and northeastern parts of the study area; they tend to be coarser grained in the west, where the mean grain sizes are about 1 to 2 phi, than in the east, where mean grain sizes are about 3 phi. A station (298_7) on the side of an east-west channel, in moderately deep water near the eastern border, has a sea floor of silty sand. The steep eastern wall of the Deep Hole (station 298_36) is composed of layered semiconsolidated outcrops and rip-up clasts of gray and reddish brown silty clay sediments (figs. 23 and 24).

Sediment Data

The sediment grain-size dataset provided in this report contains information on the collection, description, and texture of sediments at 36 stations in the study area. The sea floor was sampled at only 25 of the stations owing to either coarse-grained sediment or a rough sea state that prevented a sample from being obtained. Stations where samples could not be obtained were visually classified on the basis of video and still photography obtained at the station. These stations have no-data values (-9999) in the textural and statistical sections of the sediment dataset. The basic structure of the dataset is a matrix where rows represent individual samples and columns (fields) contain sample- and station-specific information. This matrix consists of 42 fields that are defined in the “Data Dictionary” below.
In the Geographic Information System Data Catalog section of this report, a .zip file contains the sediment data in three formats (a shapefile, a Microsoft Excel spreadsheet, and a comma-delimited ASCII text file) along with metadata.

Data Dictionary

An integral part of any database is the dictionary that explains the structure and content. It contains a list of the fields and definitions of parameters measured. This compilation defines abbreviations and lists field names, which makes the data easier to use.

LABNO - Unique sample identifier assigned in the laboratory

STATIONID - Sample name or number assigned in the field

PROJECT - Project under which samples were taken or data were generated

CRUISEID - Name or number of cruise on which the sample was collected or station was occupied

PRINCIPAL - Name of the principal investigator

LATITUDE - Latitude in decimal degrees (north latitudes are positive values)

LONGITUDE - Longitude in decimal degrees (west longitudes are negative values)

DEPTH_M - Depth of water overlying sediment at the time of sampling, measured by a hull-mounted fathometer, corrected for draft, but not corrected for tides, in meters

T_DEPTH - Top depth of the sample below the sediment-water interface, in centimeters

B_DEPTH - Bottom depth of the sample below the sediment-water interface, in centimeters

DEVICE - Device used to collect the sample

MONTH - Number of calendar month during which the sample was collected

DAY - Calendar day on which the sample was collected

YEAR - Calendar year during which the sample was collected

WEIGHT - Dry weight of sample, in grams

ZGRAVEL - Gravel content in percentage of dry weight of the sample (particles with nominal diameters greater than 2 mm; -1 phi and larger)

ZSAND - Sand content in percentage of dry weight of the sample (particles with nominal diameters less than 2 mm but greater than or equal to 0.0625 mm; 0 through 4 phi, inclusive)

ZSILT - Silt content in percentage of dry weight of the sample (particles with nominal diameters less than 0.0625 mm but greater than or equal to 0.004 mm; 5 through 8 phi, inclusive)

ZCLAY - Clay content in percentage of dry weight of the sample (particles with nominal diameters less than 0.004 mm; 9 phi and smaller)

SEDCLASS - Sediment description based on a rigorous definition (Shepard, 1954; Schlee, 1973; Poppe and others, 2004)

For sediments with gravel equal to or greater than 10 percent:

GRAVEL – gravel equal to or greater than 50 percent

GRAVELLY SEDIMENT – gravel equal to or greater than 10 percent but less than 50 percent

For sediments with gravel less than 10 percent:

SAND – sand equal to or greater than 75 percent

SILTY SAND - sand less than 75 percent and equal to or greater than 50 percent, silt greater than clay, and clay less than 20 percent

CLAYEY SAND - sand less than 75 percent and equal to or greater than 50 percent, clay greater than silt, and silt less than 20 percent

SILT - silt equal to or greater than 75 percent

SANDY SILT – silt less than 75 percent and equal to or greater than 50 percent, sand greater than clay, and clay less than 20 percent

CLAYEY SILT - silt less than 75 percent and equal to or greater than 50 percent, clay greater than sand, and sand less than 20 percent

CLAY – clay equal to or greater than 75 percent

SANDY CLAY - clay less than 75 percent and equal to or greater than 50 percent, sand greater than silt, and silt less than 20 percent

SILTY CLAY - clay less than 75 percent and equal to or greater than 50 percent, silt greater than sand, and sand less than 20 percent

SAND SILT CLAY – all of these components greater than 20 percent

MEDIAN - Middle point in the grain-size distribution, in phi units

MEAN - Average value in the grain-size distribution, in phi units

STDDEV - Standard deviation (root mean square of the deviations) of the grain-size distribution, in phi units (that is, sorting)

SKEWNESS - Deviation from symmetrical form of the grain-size distribution

KURTOSIS - Degree of curvature near the mode of the grain-size distribution

PHI_11 - Weight percentage of the sample in the 11-phi fraction (nominal diameter of particles greater than or equal to 0.0005 mm but less than 0.001 mm); fine clay

PHI_10 - Weight percentage of the sample in the 10-phi fraction (nominal diameter of particles greater than or equal to 0.001 mm but less than 0.002 mm); medium clay

PHI_9 - Weight percentage of the sample in the 9-phi fraction (nominal diameter of particles greater than or equal to 0.002 mm but less than 0.004 mm); coarse clay

PHI_8 - Weight percentage of the sample in the 8-phi fraction (nominal diameter of particles greater than or equal to 0.004 mm but less than 0.008 mm); very fine silt

PHI_7 - Weight percentage of the sample in the 7-phi fraction (nominal diameter of particles greater than or equal to 0.008 mm but less than 0.016 mm); fine silt

PHI_6 - Weight percentage of the sample in the 6-phi fraction (nominal diameter of particles greater than or equal to 0.016 mm but less than 0.031 mm); medium silt

PHI_5 - Weight percentage of the sample in the 5-phi fraction (nominal diameter of particles greater than or equal to 0.031 mm but less than 0.0625 mm); coarse silt

PHI_4 - Weight percentage of the sample in the 4-phi fraction (nominal diameter of particles greater than or equal to 0.0625 mm but less than 0.125 mm); very fine sand

PHI_3 - Weight percentage of the sample in the 3-phi fraction (nominal diameter of particles greater than or equal to 0.125 mm but less than 0.25 mm); fine sand

PHI_2 - Weight percentage of the sample in the 2-phi fraction (nominal diameter of particles greater than or equal to 0.25 mm but less than 0.5 mm); medium sand

PHI_1 - Weight percentage of the sample in the 1-phi fraction (nominal diameter of particles greater than or equal to 0.5 mm but less than 1 mm); coarse sand

PHI_0 - Weight percentage of the sample in the 0-phi fraction (nominal diameter of particles greater than or equal to 1 mm but less than 2 mm); very coarse sand

PHIM1 - Weight percentage of the sample in the -1-phi fraction (nominal diameter of particles greater than or equal to 2 mm but less than 4 mm); very fine pebbles (granules)

PHIM2 - Weight percentage of the sample in the -2-phi fraction (nominal diameter of particles greater than or equal to 4 mm but less than 8 mm); fine pebbles

PHIM3 - Weight percentage of the sample in the -3-phi fraction (nominal diameter of particles greater than or equal to 8 mm but less than 16 mm); medium pebbles

PHIM4 - Weight percentage of the sample in the -4-phi fraction (nominal diameter of particles greater than or equal to 16 mm but less than 32 mm); coarse pebbles

PHIM5 - Weight percentage of the sample in the -5-phi fraction (nominal diameter of particles greater than or equal to 32 mm); very coarse pebbles to boulders