Sedimentary Evolution Influencing Methane Generation in Coastal Sediments of the Northern South China Sea

Methane intermittently occurred along a 52-meter sedimentary core from the coastal sediments of the northern South China Sea, offering an opportunity to comprehend better the sedimentary factors that influence methane generation. The sediment core was categorized into seven distinct sedimentary facies (U1-U7) based on different sedimentary characteristics at varying depths and dating test results (14C dating and optically stimulated luminescence dating). Sedimentary unit U4, located at a depth of 17.03-22.04 meters below the seafloor (mbsf), was the primary layer for methane generation. This unit was found to be high in total organic carbon (TOC) and trace metals associated with methanogenesis. Analyses also showed that intense historical chemical weathering in the onshore catchment provided the key metallic elements, during the deposition of Unit 4. Therefore, biological methane generation was jointly controlled by supplies of organic carbon and trace elements from chemical weathering.
Within the file "DataTable.zip", there is an "DataTable.xlsx" file, which contains two sheets: "Sediment Geochemistry" and "water saturation". In the "Sediment Geochemistry" sheet, the carbon isotope data (δ13C) are expressed in per mille (‰) relative to the Pee Dee Belemnite (PDB) and the stable isotope ratios of hydrogen (δD) are conventionally expressed as a per mil (‰) deviation from Standard Mean Ocean Water (VSMOW). Geochemistry of gas along sedimental depth includes data of CH4 content, δ13CCH4 , and δDCH4. and δDH2O of the pore water, δ13CCO2 , δ13Ccarbonates and δ13CTOC. Moisture contents along sedimental depth were also included. Solid sediment along sedimental depth includes data of median grain size (D50, Φ), total carbon content (wt%, TC content), total organic carbon content (wt%, TOC content), total inorganic carbon content (wt%, TIC), total nitrogen content (wt%, TN), δ13C-TOC , δ13C-TIC, Al2O3 (wt%), CaO (wt%), MgO (wt%), K2O (wt%), Na2O (wt%), SiO2 (wt%), TFe2O3 (wt%), Ni (ppm), W (ppm), Mo (ppm), Co (ppm). ND means no data or uncalculated.
The “water saturation” sheet shows the variation in water saturation across different depths and its detailed calculation process. In the study area, marine mud had a natural density of 1.63, terrestrial silt had a density of 1.72, and fine sand had a density of 1.82. The relative density of particles (ρs) was determined based on empirical values (2.7 for fine-grained sediment, 2.65 for sandy sediment), while moisture content (w) was obtained through laboratory measurements.
Within the file “microbial data.zip”, the sampling depth of each microbial subsample can be found in the Data Table. The sequences have been trimmed of adapters and primers and assigned to their respective samples. Each sample has two sequence files, one forward and one reverse. Quality control is required before running DADA2.