Locations and grain-size analysis results of sediment samples collected in the vicinity of Buffalo Reef, Michigan, within Lake Superior during USGS Field Activity 2021-005-FA using the USGS MiniSEABOSS (CSV, GCS WGS 84)

STEP 1: COLLECT SEDIMENT SAMPLES WITH THE MINISEABOSS.
A geophysical and geological sampling survey (field activity 2021-005-FA) was conducted in Lake Superior, Michigan, in August 2021. The R/V Rafael occupied preselected target sites, and the MiniSEABOSS was deployed off the vessel's port side from a davit just aft of the cabin. The MiniSEABOSS was equipped with a modified Van Veen grab sampler, Canon PowerShot G12 digital still camera, an independent strobe, an oblique downward-looking monochrome video camera with a topside feed and a dive light to illuminate the lakebed for photograph collection. The elements of this particular MiniSEABOSS were held within a stainless-steel frame that measured ~1 x 1 meter. The frame had a stabilizer fin that oriented the system as it drifted over the lakebed. Two red lasers were set 20 centimeters apart (both as they were mounted on the MiniSEABOSS frame and as seen in photographs and video on the lake) for scale measurements. The red laser dots can usually be seen in the lakebed photos depending on the bottom type and distance to the bottom. The winch operator lowered the MiniSEABOSS until the lakebed was observed in the topside live video feed. Generally, the vessel and MiniSEABOSS drifted with wind and current for up to a few minutes to ensure a decent photo with a clear view of the lakebed was acquired. The Canon camera was triggered manually by an operator watching the video stream. The photographed area is usually 0.5 to 1.25 meters (across) from left to right. Bottom video used to guide the photo-taking and avoid obstacles was not recorded. Fourteen sites did not have any usable photographs. After photographs were taken, the winch operator lowered the Van Veen grab sampler until it rested on the bottom. When the system was raised, the Van Veen grab sampler closed and collected a sample as it was lifted off the lakebed. The sampler was recovered to the deck of the survey vessel where a photograph of the sample in the Van Veen grab was taken. Then a subsample was taken for grain-size analysis at the sediment laboratory at the USGS Woods Hole Coastal and Marine Science Center. During the survey, DGPS navigation from a Hemisphere R131 DGPS receiver was logged through a serial connection to a computer running the Global Mapper software package to visualize and record the vessel's spatial location throughout the sampling survey. The DGPS was set to receive fixes at a 1-second interval in geographic coordinates (WGS 84). Dates and times were recorded in UTC. Log files were saved for each survey in NMEA text format.

STEP 2: SUBMIT SAMPLES TO USGS SEDIMENT LAB.
Samples submitted to the sediment analysis laboratory for grain size analysis using the Horiba laser diffraction unit (LA-960) and sieving of the ≥ -2 phi fraction are assigned unique analysis identifiers (ANALYSIS_ID) and divided into batches of no more than 30 samples. Each batch is entered into a Microsoft Excel data entry spreadsheet (LD Worksheet Template_xxxx.xlsx, where xxxx is the identifier assigned to the sample submission) to record the initial and dried sample weights, as well as the sieved coarse fraction weights. Each batch is also is entered into macro-enabled Microsoft Excel data entry spreadsheets (GrainSizeWorksheet_LD1-30_xxxx(batch_yy).xlsm or GrainSizeWorksheet_LD31-600_xxxx(batch_yy).xlsm, where xxxx is the identifier assigned to the sample submission, “LD1-30” and “LD31-60” refer to the pre-labeled and weighed glass laser diffraction vials the samples will be run in, and “batch_yy” refers to the sample batch) to record the measurement data coming from the laser diffraction unit and incorporate the initial, dried, and sieved weights.
About 10-15 grams of wet sediment are placed in a pre-weighed beaker and the gross weight is recorded. The sample is wet sieved through a 4 mm (No. 5) sieve. If there is any coarse fraction remaining in the sieve, the coarse material is oven dried at 100°C in a pre-weighed beaker and weighed again when dry. This coarse fraction is dry sieved to determine the individual weights of the -2 to -5 phi fractions, and the weights are recorded in the data entry spreadsheet LD Worksheet Template_xxxx.xlsx. The fine fraction in water is collected in a pre-labeled and weighed glass laser diffraction vial. If there is any coarse fraction remaining in the sieve from wet sieving, this vial is also oven dried at 100°C and weighed when dry. If there is no coarse fraction remaining from wet sieving, the sample can proceed directly to processing for analyses by the Horiba laser diffraction unit (LA-960).
Fine fractions ready for analysis by the Horiba laser diffraction unit are rehydrated with distilled water if they’ve been dry. Fifteen (15) ml of pre-mixed 40 g/l sodium hexametaphosphate [(NaPO3)6] are added to each sample. If the height of the fluid in the laser diffraction vial is less than 5 cm, more distilled water is added to raise the level to no more than 8 cm in the vial. The samples are gently stirred, covered, and allowed to soak for at least 1 hour (for samples that were not dried) up to 24 hours (for samples that were dried). Soaked vials are placed into an ultrasonic bath and run for 10 minutes at a frequency of 37 Hz with a power level of 100. If the samples appear to be fully disaggregated, they are placed into pre-determined autosampler locations, and are run using the Horiba LA-960 for Windows software to get the fine fraction grain size distributions. The fine fraction distribution data are added to the appropriate data entry spreadsheets (GrainSizeWorksheet_LD1-30_xxxx(batch_yy).xlsm or GrainSizeWorksheet_LD31-600_xxxx(batch_yy).xlsm). The spreadsheet is used to calculate a continuous phi class distribution from the original fractions.

STEP 3: QA/QC
Continuous phi class distribution from the original fractions are transposed to the "results" tab in the macro-enabled Microsoft Excel data entry workbook (GrainSizeWorksheet_LD1-30_xxxx(batch_yy).xlsm or GrainSizeWorksheet_LD31-600_xxxx(batch_yy).xlsm, where xxxx is the identifier assigned to the sample submission, “LD1-30” and “LD31-60” refer to the pre-labeled and weighed glass laser diffraction vials the samples will be run in, and “batch_yy” refer to the sample batch). Macros in the workbook (“GS_MoM_Arithmatic,” "GS_statistics," and "sedimentname") are run to calculate grain size classification and statistical analyses and finish processing the data. Sample, navigation, and field identifiers, along with continuous phi class distribution data, grain size classification, and statistical analysis results are copied and pasted into a final Microsoft Excel spreadsheet (xxxx_GS-LD_results.xlsx, where xxxx is the batch number assigned to the sample submission). The processed data are quality control checked and assigned a quality grade based on the examination of the analytical data. Processed data are released to the submitter in xlsx and csv format and incorporated into the laboratory's database. All raw analytical data generated by the samples are archived in the sediment analysis laboratory.