Sedimentary Data Collected in April 2013 From Dauphin Island and salt marshes of coastal Alabama

DGPS Acquisition: A DGPS base station was erected at NGS PID BH1755 located at the entrance to Fort Gaines on Dauphin Island, AL, within 30 km of all but two sample sites. Two marsh sites (MD21 and MD22) were within 50 km of the base station. For the Grand Bay, AL/MS marsh site measurements the base station was erected at benchmark NGS PID DO5987 (166B) located at the boat ramp at the end of Bayou Heron Road Grand Bay, AL/MS. The DGPS receivers recorded the full-carrier-phase positioning signals (L1/L2) from satellites via the choke-ring antenna at the base locations. The DGPS instrument and Ashtech marine antenna were duplicated for the roving units at the sample sites. The base receiver and the rover receiver record their positions concurrently at 5-second (s) recording intervals throughout the survey. Occupation times at the sample sites were a minimum of 30 minutes.

GPS Post-Processing: The NAD83 (2011) published coordinates for the GPS base stations located at NGS PID BH1775 (BH17) and CORS station ALDI (ALDI) were used for post-processing all sample sites except for the Grand Bay, MS/AL sample sites, which utilized the NAD83 (2011) position reported in the OPUS solution. Refer to the horizontal and vertical positional accuracy sections of this metadata file for further details. The base station coordinates and antenna heights were entered into Waypoint Product Group’s GrafNav program (version 8.40.1408 for the vibracores and version 8.70.4517 for the marsh sample sites), and the antenna profiles selected for post processing. Final positional coordinates were exported in the processing datum of NAD83 (2011) with respect to the GEOID12A model.

Sediment cores were collected at ten salt marsh sites in coastal Alabama (5 sites on Dauphin Island, 2 sites in Grand Bay marsh, 2 sites along Fowl River, and 1 site within the Mobile-Tensaw River delta). Push cores were collected with 10.2-centimeter (cm) diameter polycarbonate barrels, driven into the sediment until refusal. Measurements were taken on the inside and outside of the barrel to determine compaction or core shortening values. Upon retrieval, the push cores were capped, labeled, and inspected for integrity. Push core recovered lengths ranged between 41 and 76 cm. Russian peat auger cores were collected at each push core site in Grand Bay, Fowl River and the Mobile-Tensaw delta. The peat auger collected sediments in 5-cm diameter, 50-cm long segments. The peat auger was driven to successive 50-cm depth increments until refusal such that a continuous sediment record was obtained. Each core segment was photographed, transferred to a PVC core sleeve, and sealed in plastic wrap. Surficial water quality properties were measured with an YSI Professional Plus multi-sensor meter at the Grand Bay, Fowl River and Mobile-Tensaw delta field sites. The uppermost 1 cm of surficial sediment was collected at each core site for microfossil analysis. At most sites, replicate surface samples, labeled as a and b subsamples, were collected following standard microfossil collection protocols. At sites FR17, GB18, and GB19, a transect of microfossil samples were collected from the edge of the tidal creek to the marsh core site, labeled as {site ID}-#S with #=1 at the marsh edge and incrementing successively up to the core site. Immediately after collection, each surficial sediment sample was stained with Rose Bengal to aid in the identification of live or recently living specimens. Cores and surface sample identifiers consist of the USGS FAN (13BIM01) and a site-specific identifier (for example, DA01). An alphabetic identifier was appended to each site identifier to signify the collection method (M for push core, R for peat auger core, and S for surface sample). Site positioning and elevations were determined using an Ashtech differential GPS receiver. Site locations, elevations, date of collection, vegetation, core lengths and compaction, and YSI measurements are reported in an Excel spreadsheet. Comma-separated values data files containing the tabular data in plain text are included in the download files. Peat auger field photographs are available in Portable Document Format (pdf) files.

Within 4 days of field collection, all cores were vertically extruded and sectioned into 1-cm intervals. The outer circumference of each interval was removed to avoid use of sediment that was in contact with the polycarbonate barrel. Each sediment interval was bagged and homogenized. The bagged intervals were stored on ice until arrival at the SPCMSC, where they were refrigerated until processing.

Vibracores were collected at 15 sites on Dauphin Island, AL. The terrestrial vibracores were obtained by using the assemblage of an 8-hp Briggs and Stratton motor attached to a Dreyer 2 1/8-in concrete vibrator head with a 28-ft flexible shaft. Bolted to the vibrator head is a galvanized steel clamp with a quick release system for connecting the clamp to 3-in/7.62-cm diameter aluminum core barrels of varying length. The aluminum barrel is vibrated into the subsurface until refusal, and then cut to discard any unused portion of the barrel. Measurements were taken on the inside and outside of the barrel to determine compaction or core shortening values. The empty void within the barrel was filled with water and an expansion plug was inserted onto the top of the barrel to ensure a solid vacuum. The full core barrel was extracted from the subsurface using a 10-ft. aluminum tripod and a 2-ton come-along winch. Once the barrel was completely removed from the subsurface, core caps were affixed to the openings on both ends of the barrel and reinforced with duct tape. The core was labeled with the USGS FAN, designated sample site identifier (for example, DA01), and top/bottom indicators. Vibracore site identifiers end with the letter V to indicate the sediment collection method. Site positioning and elevations were determined using an Ashtech differential GPS receiver. Site locations, elevations, along with recovered core lengths core compaction measurements are reported in an Excel spreadsheet. Comma-separated values data files containing the tabular data in plain text are included in the download files.

The vibracores were transported to the core-analysis laboratory at the USGS St. Petersburg Coastal and Marine Science Center where they were described, photographed, sampled, and archived. Each vibracore was cut into 1-m long sections and split lengthwise. One-half of each core was described macroscopically using standard sediment-logging methods, photographed, and sealed in plastic sleeves for archive storage. The other half was subsampled for Optically Stimulated Luminescence (OSL) age dating. OSL age dating requires that the sample investigated is primarily quartz sand and has not been exposed to light of any sort. To ensure this was the case, the cores were opened in a completely dark room, using only photographic dark room red lights. Samples of the core were also extracted in the dark and placed into film canisters to be shipped off for analysis. The samples were sent to the USGS Luminescence Dating Laboratory in Lakewood, CO. Data from the OSL analysis were not available at the time of publication; consequently, they are not included in this data report. Core logs were compiled presenting the vibracore descriptions and photographs relative to both depth below sediment surface and the orthometric height of the sample site. The core logs are available as Portable Document Format (PDF) files.

In the SPCMSC laboratory, a subsample of each 1-cm interval from 9 push cores was processed for basic sediment characteristics (dry bulk density and porosity). Core FR17M was not included in any laboratory analysis as FR26M, also from the Fowl River marsh, was of greater interest to this study. Water content, porosity and dry bulk density were determined using water mass lost during drying. For each 1-cm interval, 15–115 milliliters (mL) of each wet subsample was packed into a graduated syringe with 0.5 mL resolution. The wet sediment was then extracted into a pre-weighed aluminum tray and the weight of the wet sediment and the volume was recorded. The wet sediment and tray were placed in a drying oven for a minimum of 48 hours at 60 degrees Celsius (°C). Water content (θ) was determined as the mass of water (mass lost when dried) relative to the initial wet sediment mass. Dry bulk density was determined by ratio of dry sediment to the known volume of sediment packed into the syringe. Porosity (φ) was calculated from the equation φ = θ / [θ+(1-θ)/ρs] where ρs is grain density assumed to be 2.5 grams per cubic centimeter (g/cm^3). Salt-mass contributions were removed based on the salinity measured at the time of sample collection or estimated to be 25 if a field measurement was not recorded. Water content, porosity and dry bulk density are reported in the Excel spreadsheet. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Organic matter content was determined with a mass loss technique, referred to as loss on ignition (LOI). The dry sediment from the previous process was homogenized with a porcelain mortar and pestle. Approximately 1.5-5 grams (g) of the dry sediment was placed into a pre-weighed porcelain crucible. The mass of the dried sediment was recorded. The sample was then placed inside a laboratory muffle furnace with stabilizing temperature control. The furnace was heated to 110°C for a minimum of 6 hours to remove hygroscopic water absorbed onto the sediment particles. The furnace temperature was then lowered to 60 °C, at which point the sediments could be reweighed. The dried sediment was returned to the muffle furnace. The furnace was heated to 550 °C over 30 minutes and kept at 550 °C for 6 hours. The furnace temperature was then lowered to 60 °C and held at this temperature until the sediments could be reweighed. The latter step prevents the absorption of moisture, which can affect the measurement. The mass lost during the 6-hour baking period relative to the 110 °C-dried mass is used as a metric of organic matter content. Data are reported as a ratio of mass (g) of organic matter to mass (g) of dry sediment (post-110 °C drying). Replicate analyses of loss on ignition for a representative subset are reported for quality assurance in the Excel spreadsheet. A comma-separated values data file containing the tabular data in plain text is included in the download file.

The stained microfossil samples collected in the field were transferred to the USGS SPCMSC foraminiferal lab. To ensure accurate and thorough staining, samples were inverted daily for 2 weeks. In addition to the stained surface samples, microfossil analysis was performed on subsamples from select depth intervals from eight push cores and one peat auger core. Since the core samples were not stained with Rose Bengal, only total foraminifera counts are reported. Prior to washing, the relative volume (mL) of sediment was recorded using the volume gradation on the tube (±1 mL). For the marsh push cores, a portion (3 – 25 cm^3) of the wet material from each depth interval was placed in a graduated syringe, and the volume recorded. The samples were soaked in water with a few milliliters of 10 percent sodium hexametaphosphate solution, slowly agitated for up to 1 hour to aid disaggregation, and then washed over 63- and 850-micron (μm) stainless-steel sieves under warm water. The samples retained by the sieves (63-850 and > 850 µm size fraction) were oven-dried at ≤ 60 °C and then the 63-850 µm size fraction was dry-sieved at 125 µm. The foraminifers were picked, counted, and identified from the 125-850 µm size fraction. If more than 300 specimens were encountered in a sample, the sample was split with a micro-splitter. One split fraction from each sample was counted. If splitting was not required, the entire 125-850 µm fraction was spread across a 45-square, hole-punched tray, one or more times, for examination under a microscope. When a stained specimen, which was probably alive at collection, was encountered, it was picked up with a wet brush and dropped through a hole in the tray onto a stationary, 60-square micropaleontological slide for later sorting and identification. Both the a and b subsamples were picked, sorted, and counted individually. The unstained surface samples and core samples were also picked, counted and identified from the 125-850 µm size fraction using the same processing procedures. The foraminiferal counts are reported in Excel spreadsheets. Comma-separated values data files containing the tabular data in plain text are included in the download files.

Down-core particle size analysis was performed on each 1-cm depth interval for 5 of the push cores (DA13M, GB18M, GB19M, FR26M, and DA27M). A total of 230 samples were analyzed. Prior to particle size analysis, organic material was chemically removed for the samples using 30% hydrogen peroxide (H2O2). Wet sediment was dissolved in H2O2 overnight. The H2O2 was then evaporated by gentle heating and the sediment washed and centrifuged twice with deionized water. Grain size analyses on the sediment cores were performed using a Coulter LS 200 or LS 13 320 (https://www.beckmancoulter.com/) particle-size analyzer (PSA), which uses laser diffraction to measure the size distribution of sediments ranging in size from 0.4 microns to 2 millimeters (mm) (clay to very coarse-grained sand). To prevent shell fragments from damaging the Coulter instrument, particles greater than 1 mm in diameter were separated from all samples prior to analysis using a number 18 (1000 microns 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. Two subsamples from each depth interval were processed through the instrument a minimum of four runs each. The sediment slurry made from the digested sample and deionized water was sonicated with a wand sonicator for 1 minute before being introduced into the Coulter PSA to breakdown aggregated particles. 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). The size-classification boundaries for each bin were specified based on the ASTM E11 standard.

The raw grain size data were then run through 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. GRADISTAT also calculates the fraction of sediment from each sample by size category (for example, clay, coarse silt, fine sand). 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 (6-12 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 each core on its own tab. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Dried ground sediment from the 1-cm depth intervals of the 9 push cores were used for the detection of radionuclides by standard gamma-ray spectrometry (Cutshall and Larsen, 1986) at the USGS SPCMSC radioisotope lab. The uppermost 30 cm were analyzed from each core with selected intervals analyzed below 30 cm. A total of 397 depth intervals were analyzed for radioisotopic activities. The sediments (3-50 g) were sealed in airtight polypropylene containers. The sample weights and counting container geometries were matched to pre-determined calibration standards. The sealed samples sat for a minimum of 3 weeks to allow Ra-226 to come into secular equilibrium with its daughter isotopes Pb-214 and Bi-214. The sealed samples were then counted for 24-72 hours on a planar-style, low energy, high-purity germanium, gamma-ray spectrometer. The suite of naturally-occurring and anthropogenic radioisotopes measured along with their corresponding photopeak energies in kiloelectron volts (keV) are Pb-210 (46.5 keV), Th-234 (63.3 keV), Pb-214 (295.7 and 352.5 keV; proxies for Ra-226), Be-7 (477.6 keV), Bi-214 (609.3 keV; proxy for Ra-226), Cs-137 (661.6 keV), and K-40 (1640.8 keV). Sample count rates were corrected for detector efficiency determined with International Atomic Energy Agency RGU-1 reference material, standard photopeak intensity, and self-absorption using a U-238 sealed source (Cutshall and others, 1983). Be-7 activities are only reported for 13BIM01-DA13M. In all other cores, Be-7 was either not present in the sediment or the samples were counted after Be-7 decay to non-detectable levels. All activities were decay-corrected to the date of field collection. The radioisotopic activities reported in the Excel spreadsheet include the counting error for all samples. The critical level is reported for each core. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Dried, ground sediment from the 1-cm depth intervals of 3 push cores (DA13M, DA27M, and FR26M) were submitted for element concentration analysis to the USGS Central Mineral and Environmental Resources Science Center (CMERSC). Between 0.4936 and 1.8701 g of material was sent in 25 mL glass scintillation vials for a 42-element analysis of concentrations (Taggart, 2002). For quality assurance, thirty percent of samples from each core were submitted in replicate. At CMERSC, samples were digested using hydrochloric, nitric, perchloric, and hydrofluoric acids and then aspirated into the inductively coupled plasma-atomic emission spectrometer (ICP-AES) and inductively coupled plasma-mass spectrometer (ICP-MS). The ICP-AES was calibrated using digested rock reference materials as well as a series of multi-element solution standards. The ICP-MS was calibrated with aqueous standards. To account for internal drifts and matrix effects, internal standards were used. The elemental concentrations reported in the Excel spreadsheet include the replicate sample analyses. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Sediment samples from the 1-cm depth intervals of 3 push cores (DA13M, DA27M, and FR26M) were submitted to the University of California, Davis Stable Isotope Facility (SIF) for percent organic carbon, percent nitrogen, carbon-nitrogen ratio, δ13C, and δ15N. Dried, homogenized sediment was placed in 8 x 5 millimeter (mm) silver capsules, wet with 50 microliters (µL) of deionized water, and fumigated in a desiccator with 100 mL of concentrated hydrochloric acid for 6 hours to remove inorganic carbon (Harris and others, 2001). Samples were then dried at 60 °C overnight, and double encapsulated in tin for combustion purposes. For quality assurance, thirty percent of samples from each core were submitted in replicate. All samples were analyzed using a Costech ESC 4010 Elemental Combustion System interfaced with a Thermo Finnigan DELTAplus Advantage isotope ratio mass spectrometer. Values are relative to international standards: the VPDB (Vienna Pee Dee Belemnite) for carbon, and air for nitrogen. The standard deviation of the provided values is estimated at ±0.4 per mille. The stable isotopic ratios reported in the Excel spreadsheet include the replicate sample analyses and calibrated laboratory reference sample results. Data for the cores and the laboratory reference material are reported each on their own tab. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Added keywords section with USGS persistent identifier as theme keyword.