Sediment Core Microfossil Data Collected from the Coastal Marsh of Grand Bay National Estuarine Research Reserve, Mississippi, USA

In the Grand Bay National Estuarine Research Reserve, Mississippi, two salt marsh shore-perpendicular transects, identified as sites 1 and 3, each had four cores collected at distances of 5, 15, 25, and 50 meters landward of the shoreline. Push cores were collected with 10.2-cm diameter polycarbonate barrels, driven into the sediment until refusal. Upon retrieval, similar to methods described in Osbourne and DeLaune (2013; with the exception of not adding water for extraction when not necessary due to the sediments being saturated) and calculation of compaction due to coring, the cores were visually inspected for disturbances (for example, slumping, washout, scouring, cracking, bubbling, and/or discontinuities) to ensure the core was intact and representative of the site. If the core appeared disturbed, it was discarded, and a new core was collected. Upon retrieval, the push cores were capped, labeled, and inspected for integrity. Push core recovered lengths ranged between 42 and 54 cm. The cores were transported upright, in order to avoid slumping and preserve the natural sediment orientation, to the SPCMSC laboratory for sectioning. Core identifiers consist of the USGS project ID/ alternate FAN (16CCT07) and a site-specific identifier (for example, GB301). An alphabetic identifier was appended to each site identifier to differentiate the collection method (M for marsh push core). Sediment characteristics, loss-on-ignition, and site location information for the core sites can be found in Marot and others (2019). Comma-separated values data files containing the tabular data in plain text are included in the download files.

At the USGS SPCMSC, marsh push cores were extruded vertically and sectioned into 1-cm intervals using a serrated knife, pre-measured polycarbonate ring, and extruder (in accordance with methods described in Osbourne and Delaune, 2013 and in 1-cm intervals as is standard for foraminiferal microfossil analyses; Schönfeld and others, 2012; and radiochemical analyses; Nittrouer, 1979) at the USGS SPCMSC sediment core laboratory. The outer circumference of each sample interval was removed to avoid use of sediment that was in contact with the polycarbonate barrel which could result in contamination by sediment from other depths due to movement within the barrel both during collection and extruding. Each sediment interval was bagged in a zipped baggie, homogenized, and refrigerated (Osbourne and DeLaune, 2013). Select 1-cm push core interval subsamples from seven of the 8 cores collected were processed for foraminifera microfossils. One core, GB307M, was contaminated in the laboratory and not subsampled for foraminifera. The intervals selected for microfossil analyses were based on fluctuations in downcore sediment data in an attempt to capture both “background” intervals and contrasting, potential event intervals. In some cases, there was not enough sediment available to perform grain-size and microfossil analyses on a single 1-cm interval. In these cases, the 1-cm interval above or below was selected for microfossils and for comparison with grain-size, assuming dry bulk density and LOI values of the neighboring intervals were not significantly different. Foraminifera subsamples were collected from refrigerated wet sediment for processing which occurred episodically over 20 months (November 7, 2017 through June 11, 2019). Foraminifera subsample wet volume was recorded to the nearest 1 milliliter (mL) and then washed over a 63-, 125- and 500 micrometer (µm) sieve in order to remove clay material, to separate out large organics (Schönfeld and others, 2012), and for size class comparison with other foraminiferal datasets with size ranges of 125–500 µm (Haller and others, 2018a; Haller and others, 2018b; Haller and others, 2019; Ellis and Smith, 2020; Ellis and Smith, 2021). The first twelve intervals processed were sieved over only 63 and 500 micrometer (µm) sieves (GB301M: 1-2, 7-8, 16-17, and 24-25 cm, GB302M: 0-1, 5-6, 12-13, 15-16, and 19-20 cm, and GB303M: 0-1, 2-3, and 9-10 cm) and were later reassessed by measuring and separating the 63–125 µm individuals using a slide scale for consistency and comparison with the remainder of the dataset. After sieving, the 125–500 µm size fraction (or 63–500 µm in the aforementioned 12 samples) of each sample was split into equal parts with a microsplitter and spread evenly over a gridded picking tray. Entire splits were picked until at least 200 foraminiferal specimens were acquired for the calculation of foraminiferal densities. Identifications and counts were checked by Alisha Ellis following an initial sorting and identification by Jessica Jacobs. Identifications were made with assistance from Dr. Lisa Osterman, Dr. Steve Culver, and Dr. Christian Haller, and by making comparisons with published literature (Edwards and others, 2015; Haller and others, 2019).