Grain-Size and Site Data From Sediment Samples Collected at Seven Mile Island, New Jersey and Rockaway Peninsula, New York, Between May 2021 and June 2021

Surface sediment grabs were collected by USGS scientists from the Research Vessel (R/V) Sallenger off the coast of Seven Mile Island, NJ and Rockaway Peninsula, NY. The marine sediment grabs were collected in May 2021 and June 2021 during the same time interval as the multibeam bathymetric surveys. A Petite Ponar grab sampler was used to sample sediment from a previously undisturbed layer of sediment atop the seafloor to ensure all grain sizes were sampled. The only onshore sample collected was on Rockaway Beach from an exposed alluvium section from the undercut boardwalk (sample identifier RKWY70). The surficial layer was scraped away before RKWY70 was sampled by hand. Samples were brought back to the SPCMSC Sediment Laboratory for analysis.

Particle-size analysis was performed on all the sediment grabs collected from the Rockaway Peninsula, NY and Seven Mile Island, NY study sites. Grain-size analyses on the samples were performed using a Coulter LS13 320 (https://www.beckmancoulter.com/) particle-size analyzer (PSA), that uses laser diffraction to measure the size distribution of sediments from 0.4 microns to 2 millimeters (mm), encompassing clay to very coarse-grained sand. To prevent large shell fragments from damaging the instrument, particles greater than 1 mm in diameter were separated from all samples prior to analysis using a number 18 (1 mm) U.S. standard sieve, which meets the American Society for Testing and Materials (ASTM) E11 standard specifications for determining particle size using woven-wire test sieves. For any dry sediments, the material removed by sieving at 1 mm is recorded and reported as a percent of the total bulk dry weight with the final processed grain-size data. Two subsamples from each sample were processed through the instrument a minimum of four runs each. Once introduced into the Coulter PSA, the sediment in the sample well was sonicated with a sonicator wand for 30 seconds to separate any aggregates before starting the first run for both subsamples. The Coulter PSA measures the particle-size distribution of each sample by passing sediment suspended in solution between two narrow panes of glass in front of a laser. Light is scattered by the particles into characteristic refraction patterns measured by an array of photodetectors as intensity per unit area and recorded as relative volume for 92 size-related channels (bins).

All raw grain-size data was run through the free software GRADISTAT version 8, (Blott and Pye, 2001; kpal.co.uk/gradistat), which calculates the mean, sorting, skewness and kurtosis of each sample geometrically, in metric units and logarithmically in phi units (Φ) (Krumbein, 1934) using the Folk and Ward (1957) scale. The compilation of the raw Coulter output files for all grain-size samples as they appear imported into GRADISTAT, before any statistics have been computed, is included in this data release for advanced users. GRADISTAT also calculates the fraction of sediment from each sample by size category (for example, clay, coarse silt, fine sand) based on a modified Wentworth (1922) size scale. A macro function in Microsoft Excel, developed by the USGS SPCMSC, was applied to the data to calculate average and standard deviation for each sample set (8 runs per sample), and highlight runs that varied from the set average by more than ±1.5 standard deviations. Excessive deviations from the mean are likely the result of equipment error or extraneous organic material in the sample and are not considered representative of the sample. The highlighted runs were removed from the results and the sample average was recalculated using the remaining runs. The averaged results for all samples, including the number of averaged runs and the standard deviation of the averaged results, were summarized in an Excel workbook with samples from each FAN on its own tab. A comma-separated values (CSV) data file containing the tabular data in plain text is included in the download file.

The summary statistics files were appended with sample location attributes (latitude, longitude, and location description). These sample locations and selected grain-size metrics were imported into Esri ArcMap version 10.6 to create shapefiles (.shp). The conversion tool within ArcToolBox was used to convert the shapefiles into Keyhole Markup Language Zipped (.kmz) files.