Dataset: Speciation of sulfur in sediment, dissolved organic matter, and biogenic material determined by x-ray absorbance spectroscopy of samples collected at two mangrove locations in June 2022 through February 2024

Sediment cores, biomass, and dissolved organic matter were collected from two mangrove locations in Rookery Bay National Estuarine Research Reserve (Florida, USA) and Little Ambergris Caye (Turks and Caicos) during the time period of June 2022 through February 2024. Sediment cores were extruded in the field and kept at -20 degrees Celsius (°C) until analysis could be carried out back in the lab at UC Santa Barbara along with biogenic material. Dissolved organic matter was kept refrigerated in SPE cartridges until eluted back in the lab at UC Santa Barbara.

To isolate major carbon and sulfur pools, a ~1 gram (g) aliquot of the freeze-dried sample from each sediment interval was subjected to two sequential microwave extractions (MARS-6, CEM, 70°C for 15 minutes) using a 9:1 dichloromethane. Solvent-extracted solids were rinsed with 0.7N NaCl solution, ultra-pure water, freeze dried, and then acid fumigated to remove carbonates for 12 hours with a 6N HCl solution. A 500-milligram (mg) subsample of the same microwave-extracted solid residue was then subjected to a strong acid hydrolysis (6N HCl, 60°C, 2 hours) to extract acid-volatile sulfur (AVS, operationally defined as iron monosulfides) following Canfield et al. 1986 and Raven et al. 2019. The remaining solid residue underwent a chromium (II) chloride extraction at 60°C for 2 hours to isolate chromium reducible sulfur (CRS, operationally defined as pyrite) following Canfield et al. 1986. The leftover solid residue following the CRS extraction contains highly hydrolysis-resistant OM that we refer to as protokerogen (Burdige 2007; Raven et al. 2019). Biogenic material went under the same set of extractions while the dissolved organic matter was eluted with methanol and dried down in a fume hood (Phillips et al. 2022).

The oxidation state and bonding environment of organic sulfur in the post-CRS extraction, post-CRS extraction biogenic material, and dissolved organic matter were characterized using x-ray absorption spectroscopy (XAS). Spectra were obtained on Stanford Synchrotron Radiation Lightsource (SSRL) on beam line 14–3 using a spot size of 0.5 square millimeters (mm2) and a Si(111) (Φ = 90) double crystal monochromator calibrated to the thiol pre-edge peak of thiosulfate at 2472.02 electron volts (eV). Samples were adhered onto Saint Gobain M60 S-free polyester tape and covered with 5-micrometer (µm) SPEX 3520 polypropylene XRF film. Spectra were averaged and normalized in the SIXPACK (Webb 2005) software package using a K-edge E0 of 2473 and pre-edge and post-edge linear normalization ranges of -20 to -7 and 35 to 70 eV, respectively. The relative abundance (percent (%)) of individual sulfur species were determined in sediments and biomass samples using least squares fitting and a set of OS standards (Raven et al. 2021). The relative abundances of different sulfur species were then used to determine the percentage of reduced (disulfide, monosulfide, aromatic) and oxidized (sulfoxide, sulfone/sulfonate, sulfate ester) sulfur in samples.