Dataset: 2018 radiocarbon

Three sediment cores were collected for analytical analyses from each site for a total of six cores. Sediments were extracted using a polycarbonate push core (7 cm ID x 50 cm L) with beveled edges pushed into the marsh surface. Cores were sectioned into 1-cm intervals on site on the day of collection and stored cold until laboratory analysis at the University of North Carolina, Chapel Hill, NC. All sediment samples were weighed damp, placed into a drying oven at 60°C for at least 48 hours for evaporation of water content and re-weighed dry. Bulk plant material, such as root mats and rhizomes, was manually removed with tweezers after the samples dried. Dried sediment samples were then homogenized using a mortar and pestle.

One 2014 pre-storm core from both sites, AR2 and AN2 (sediment collected in a previous study), and one 2018 post-storm core from Aransas, B, and two 2018 post-storm cores from Anahuac, D and E, were selected for bulk radiocarbon analyses. Samples were paired, one sample from the pre-storm core and one sample from the post-storm core, based on deposition age determined by 210Pb geochronology. Four pairs of samples were selected from each study site to be analyzed for bulk 14C age. In addition, one sediment surface sample from each site from the 2018 post-storm cores was selected for bulk 14C age analyses, for a total of 18 samples.

Aliquots of approximately 300 mg of dried and homogenized sample were placed into acid cleaned and pre-baked glass tubes with 3 mL of a 10 % hydrochloric acid solution, with the sediment slightly agitated to ensure full saturation, and left to soak overnight to thoroughly remove inorganic carbon. After sediments settled the acid was carefully removed via pipette as to not resuspend or extract fine sediments. Samples were then rinsed five times with 5 mL of Milli-Q water over the course of 48 hours, with at least 4 hours between rinses to allow sediment to settle, to raise the pH of the samples back to neutral, and then placed in a 60 °C oven until dry. About 1 mg of OC, based on % TOC results, was weighed into tin capsules, sealed, and analyzed for bulk Δ14C at the National Ocean Sciences Accelerator Mass Spectrometry facility at the Woods Hole Oceanographic Institution, Woods Hole, MA (NOSAMS).

A slow thermal ramp of 5 °C min-1 was performed on only three pairs of acid rinsed aliquots of pre- and post-storm samples and the post-storm surface sample from Aransas, for a total of seven sediment samples, in order to collect fractions of evolved CO2 as temperatures increased (i.e. fraction 1 is lower temperatures and 4 are higher). Detailed RPO experimental set-up and methods are available in Rosenheim et al. (2008) and Hemingway et al. (2017b). Detailed CO2 to graphite conversion methods are provided in Pearson et al. (1998) and Shah Walter et al. (2015). Graphite was analyzed for 14C on a Continuous Flow Accelerator Mass Spectrometer at NOSAMS. Samples were normalized to OX-I (Olsson, I.U., 1970) and radiocarbon-free acetanilide (J.T. Baker, A068-03) was used for blank correction. Standards from multiple international radiocarbon intercalibration comparisons and from International Atomic Energy Agency were used for secondary standards. δ13C was analyzed from gas samples on an Optima or Prism stable isotope mass spectrometer.

Analysis of raw RPO data, described in detail in Hemingway et al. (2017a) and Hemingway (2016), was performed using the Python® package rampedpyrox.