Dataset: Biogeochemical data on cryptic methane cycling in hypersaline sediments of the Carpinteria Salt Marsh Reserve, California

Sediments were collected from the hypersaline pool within the Carpinteria Salt Marsh Reserve using large (20 cm i.d.) and small (2.6 cm i.d.) pushcores. Porewater was separated from sediment by centrifugation (4300 x g for 20 mins) and subsampled for further analysis described below.

Porewater sulfate and chloride concentrations were determined by ion chromatography (Metrohm 761). Porewater salinity was calculated from porewater chloride concentrations, using Knudson’s equation (Knudsen, 1901). Porewater sulfide and iron (II) concentrations were determined spectrophotometrically (Shimadzu UV-Spectrophotometer UV-1800) according to Cline, (1969) and Grasshoff et al., (1999) respectively. Porewater methane concentrations were determined by gas chromatography (Shimadzu GC-2014). Sediment porosity was determined by drying sediments at 75°C for five days and calculated using the difference between wet and dry weights, divided by the volume of sediment.

Sulfate reduction rates were determined by injecting carrier-free 35S-Sulfate into intact whole round cores according to Jørgensen (1978); and incubated for 1 day. Sediment samples were then analyzed according to the cold-chromium distillation (Kallmeyer et al., 2004).

AOM rates were determined by injecting 14C-Methane dissolved in anoxic Milliq into intact whole round cores similar to sulfate reduction rate determinations; and incubated for 1 day. Sediment samples were then analyzed according to Treude et al. (2005) and Joye et al. (2004).