Concentrations of dissolved anions in porewater and gaseous alkanes in sediments retrieved from the Guaymas Basin hydrothermal sediments in 2018

The Guaymas Basin hydrothermal vents in the Gulf of California (Mexico) were visited with the research vessel RV Atlantis in November to December 2018 (mission AT 42-05). Due to its proximity to land, this area is covered with thick organic-rich sediments. In the subsurface heated fluids enrich in hydrocarbons gases, leading to complex biogeochemical reactions in surface sediments (Teske et al., 2016; doi:10.3389/fmicb.2016.00075). We used the submarine ALVIN to collect sediments with push cores at sites covered with different mat types and surrounding areas. Aim of this effort was to describe the biogeochemistry and the fluxes of dissolved species in these sediments. We collected porewater from these push cores using Rhizon technology (Seeberg-Elverfeldt et al., 2005; doi:10.4319/lom.2005.3.361). Porewater sampling was performed in anoxic tents to preserve oxygen-sensitive dissolved metal species. Samples were preserved according to established protocols. In the home laboratory we measured concentrations of dissolved inorganic carbon, chloride, sulfate, sulfide, dissolved inorganic carbon, nitrate, nitrite, ammonium, phosphate and silicate and concentrations of dissolved iron using two approaches and manganese were assessed. Sediment cores is the direct vicinity of these cores were taken as replicates for the measurement of dissolved gases. Cores were sectioned and 2 ml sediments were sampled into glass-vials filled with 5 ml sodium hydroxide solutions and were sealed gas-tight. Concentrations of the hydrocarbon gases methane, ethane, propane, i-butane and butane were measured using gas chromatography coupled to flame ionization detection.