Dataset: Carpinteria Salt Marsh Elemental and Isotope Composition Data for Sediment and Biomass

To isolate major carbon and sulfur pools, a ~1 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: methanol solution to isolate lipids and elemental S. Solvent-extracted solids were rinsed with 0.7N NaCl solution, ultra-pure water, freeze dried and then acid fumigated to remove carbonates for 12 hrs with a 6N HCl solution. A 500-mg subsample of the same microwave-extracted solid residue was then subjected to a strong acid hydrolysis (6N HCl, 60°C, 2 hrs) to extract acid-volatile sulfur (AVS, operationally defined as iron monosulfides) following Canfield et al. 1986 and Raven et al. 2019b. 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. 2019b).

Subsamples of primary producer biomass (n=9) from CSMR (Ulva spp., Juamea carnosa, and Salicornia pacifica) underwent two separate chemical extractions in order to isolate important carbon and sulfur pools for x-ray absorbance spectroscopy (XAS). Briefly, ~1 g of each rinsed and freeze-dried biomass type underwent an acid hydrolysis with 1N hydrochloric acid for 2 hours at room temperature to ensure the removal of sulfate from the biomass.

The oxidation state and bonding environment of organic sulfur (OS) in both strongly acid-hydrolyzed (post-CRS extraction, which we refer to as protokerogen) sediments and mild acid-hydrolyzed (1N acid hydrolysis discussed above) whole biomass samples were characterized using synchrotron x-ray absorption spectroscopy (XAS). Sulfur K-edge XAS spectra were obtained at the Stanford Synchrotron Radiation Lightsource (SSRL) on beam line 14–3 using a spot size of 0.5 mm2 and a Si(111) (Φ = 90) double crystal monochromator calibrated to the thiol pre-edge peak of thiosulfate at 2472.02 eV. For analysis, samples were adhered onto Saint Gobain M60 S-free polyester tape and covered with 5 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 (%) of individual sulfur species were determined in sediments and biomass samples using least squares fitting and a set of OS standards (Raven et al. 2021a). 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 slightly acid hydrolyzed biomass and strongly acidified sediment.