Laboratory Methods and Analyses

Core Processing

At the SPCMSC core-analysis laboratory, each vibracore was cut into 1-m sections and split in half lengthwise. One-half of each core was described using standard sediment-logging methods then photographed, sealed, and archived at the SPCMSC core repository. The other half was sub-sampled for grain-size analysis based on physical description. The cores were photographed using a Canon Powershot SX20 IS digital camera. In addition to whole-core photographs of each 1-m section, the cores were photographed in approximately 40-cm overlapping segments using a zoom lens from a fixed height. The images were "stitched" together using The Panorama Factory version 5.3 software, providing seamless, high-resolution, whole-core photographs. The core descriptions and photographs can be viewed or downloaded from the Data Products and Downloads page.

Organic Matter Content

The percent total organic matter (TOM) for 38 samples from 10 cores was determined using a mass loss technique known as loss-on-ignition (LOI). Samples were selected when visual characteristics indicated high organic matter content. During LOI processing, samples were combusted at high temperatures, oxidizing all organic carbon and allowing determination of mass loss by weight. Bulk wet samples were split, homogenized, placed on pre-weighed aluminum trays, and weighed. All weights were recorded with a precision of 0.01 grams (g) using an analytical balance. The wet sediment and tray were placed inside a drying oven pre-heated to 60 degrees Celsius (°C) for 48 hours. Water content was determined as the mass of water (lost when dried) relative to the initial wet sediment mass. The dried samples were homogenized using a porcelain mortar and pestle. Approximately 5 g of the ground sediment was placed in a pre-weighed porcelain crucible, weighed, and then placed inside a laboratory muffle furnace equipped with stabilizing temperature controls. 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 and the sediment was reweighed. The dried sediment was returned to the furnace and heated to 550 °C for 6 hours. The furnace temperature was cooled and held at 110 °C overnight, and then cooled to 60 °C before weighing. The mass lost during the 6-hour baking period, relative to the 110 °C dry mass, was used as a metric of organic matter content (modified from Dean, 1974).

Grain-Size Analysis

Surficial sediments previously collected from Barnegat Bay were analyzed in the sediment laboratory at the Woods Hole Coastal and Marine Science Center (WHCMSC); therefore, the inorganic sample fractions were returned to WHCMSC for textural analysis to facilitate comparisons. The LOI organic content of the 38 organic-rich samples ranged from 0.91 to 77.55 percent. Prior to grain-size analysis, these samples were chemically leeched of all organic matter to prevent organics from being counted as part of the sample and biasing the grain-size distribution. Organic matter was removed from the samples using approximately 8 milliliters (mL) of 30 percent hydrogen peroxide (H₂O₂) overnight. The H₂O₂ was then evaporated through slow heating on a hot plate, and the sediment was washed and centrifuged twice with deionized water. Due to the high organic content of some samples, excess amounts of H₂O₂ were added to induce reaction and ensure full digestion.

For the analysis of the inorganic sediment fraction, approximately 50 g of wet sample were wet-sieved through a 0.062 millimeter (mm) sieve to separate the coarse and fine fractions. For several of the organic-rich samples, less than 50 g of wet sediment remained after the organic matter was removed. In two cases, the organic content was high enough that an insufficient amount of inorganic sediment remained for textural analysis. Coarse fractions (sand and gravel) were oven-dried, weighed and dry-sieved. Fine fractions (silt and clay) were analyzed using a Multisizer 3 Coulter Counter, which uses electrical impedance to measure the size distribution of sediments ranging in size from 0.4 to 1,200 microns (μm). The combination of both techniques allows for weight percentages of grain sizes from -5 to 11 phi (ϕ) to be determined. The sediment classification and frequency percentages were calculated using GSSTAT software (Poppe and others, 2004) based on the methods of Folk (1974) and Collias and others, (1963). The grain-size data can be viewed or downloaded from the Data Products and Downloads page.