(Table 1) Interstitial water δ¹³C, tritation alkalinity, and sulphate concentrations of ODP Site 131-808A@en

The d13C values of total inorganic carbon (Sum CO2 ) were measured for interstitial waters extracted from the turbidite and hemipelagic sediments of the Nankai Trough accretionary prism during ODP Leg 131. At 3.0 mbsf in the bacterial sulfate reduction zone, a significant low d13C of -29.8 per mil (PDB) was found, suggesting oxidation of upward-migrated methane from the zone below. At 6.0 mbsf, below the sulfate reduction zone, the d13C value increases abruptly to a maximum value of +12.0 per mil, reflecting an enrichment of 13C in residual Sum CO2 from the bacterial reduction of some Sum CO2 to 12C-enriched CH4. Below 80 mbsf, the 13C values decrease almost linearly with depth to ~ -20 per mil at 1000 mbsf, indicating that the fraction of Sum CO2 derived from thermal degradation of organic material increases gradually with increasing in-situ temperature.本数据集针对大洋钻探计划（Ocean Drilling Program, ODP）第131航次中，从日本南海海沟增生楔的浊积岩与半远洋沉积物中提取的孔隙水，测定了其总无机碳（Sum CO2）的碳同位素比值δ¹³C。在海底以下3.0米（meters below seafloor, mbsf）的细菌硫酸盐还原带内，测得显著偏低的δ¹³C值为-29.8千分比（佩德贝列姆尼特（Pee Dee Belemnite, PDB）标准），这表明来自下方层位向上运移的甲烷发生了氧化作用。在硫酸盐还原带下方的海底以下6.0米处，δ¹³C值骤然升高至最大值+12.0千分比，这反映出部分总二氧化碳经细菌还原为富¹²C的甲烷后，残留的总二氧化碳发生了¹³C富集。在海底以下80米以深，δ¹³C值随深度近乎线性降低，至海底以下1000米处降至约-20千分比，表明源自有机质热降解的总二氧化碳占比随原位温度升高逐渐增加。