Sediment Grain-size Data from sediment core samples collected in March/April 2014 from Assateague Island and the mainland of Virginia and Maryland (U.S. Geological Survey Field Activity Numbers 2014-301-FA, and 2014-322-FA).

Based upon visual inspection, samples with coarse material were dried at a constant 60°C. The dried samples were weighed and then dry-sieved through a number 18 (1000 microns [?m] or 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. The two size fractions were weighed and bagged. Grain-size analyses were performed using a Coulter LS200 (https://www.beckmancoulter.com/) particle-size analyzer, which uses laser diffraction to measure the size distribution of sediments ranging in size from 0.4 ?m to 2 mm (clay to very coarse-grained sand). In order to prevent shell fragments from damaging the LS200, particles greater than 1 mm in diameter were separated from all surface sediments (S) and marsh cores samples (M) prior to analysis using a number 18 U.S. standard sieve. If there was sediment > 1 mm, the material was dried and the dry weight was recorded. After the samples were washed through the sieve with filtered city water, a few milliliters of sodium hexametaphosphate solution was added to act as a deflocculant. The sediment slurry was sonicated with a wand sonicator for 30 – 60 seconds before being introduced into the Coulter LS200 to breakdown aggregated particles. The pre-sieved <1 mm dried overwash fan (W) fraction was introduced directly into the Coulter LS200. The raw grain-size data were processed with the free software program GRADISTAT ({Blott and Pye, 2001}; http://www.kpal.co.uk/gradistat), which calculates the mean, sorting, skewness, and kurtosis of each sample geometrically in metric units and logarithmically in phi units (?) ({Krumbein, 1934}) using the Folk and Ward ({Folk 1957}) method. 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 ({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 (6 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 runs included and the standard deviation of the averaged results were summarized in a series of Excel workbooks with tabs for each core location. These metadata are not complete with out the data dictionary (Grain_Size_Data_Dictionary.pdf) also included in this archive, which applies specifically to the summary statistics spreadsheets.