Grain-size analysis of sediment samples collected in the nearshore zone offshore of Marconi Beach, Wellfleet, MA, December 9, 2024

Collected 3 sediment grab samples from the R/V Tioga using a Shipek surficial grab sampler offshore of Marconi Beach, Wellfleet, MA. Samples were placed into plastic bags and put into a cooler. Samples were then transferred to cold storage until processing.

Samples submitted to the Sediment 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_RB06.xlsx, where RB06 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 (RB06_GrainSizeWorksheet_LD1-30.xlsm or RB06_GrainSizeWorksheet_LD31-60.xlsm, where RB06 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) to record the measurement data coming from the laser diffraction unit and incorporate the initial, dried, and sieved weights.
About 5-10 grams of wet sediment or 3-5 grams of dry 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_RB06.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 (RB06_GrainSizeWorksheet_LD1-30 or RB06_GrainSizeWorksheet_LD31-60.xlsm). The spreadsheet is used to calculate a continuous phi class distribution from the original fractions. Data from this submission were processed using version 2.3 of the data entry spreadsheet.

Continuous phi class distribution from the original fractions are transposed to the "results" tab in the macro-enabled Microsoft Excel data entry workbook (RB06_GrainSizeWorksheet_LD1-30.xlsm or RB06_GrainSizeWorksheet_LD31-60.xlsm, where RB06 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). Macros in the workbook (“GS_MoM_Arithmetic_1”, “GS_MoM_Arithmetic_2”, "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 (RB06_GS-LD_results.xlsx, where RB06 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 and incorporated into the laboratory's database. All raw analytical data generated by the samples are archived in the Sediment Laboratory.

The results from the Microsoft Excel spreadsheet were imported into MATLAB R2024B where the column headings were given unique names, and the significant figures were adjusted appropriately. The final data were then exported to a CSV file. A second CSV file was made to create a shapefile where negative phi values appearing in the field names were replaced with an 'M' for minus, since the shapefile cannot accommodate negative values in the field names (e.g. PHI_-1 is written as PHI_M1). This CSV file was imported into ArcGIS Pro 3.1.0 and a shapefile (.shp) and associated files were saved.

Added the cross-reference of a related data release that serves the time-series oceanographic data. (20260112)