准确评估冷泉区甲烷通量是认识其环境效应的前提。相对于现今海底甲烷冒泡区，以溶解为主的甲烷渗漏区分布更广。溶解甲烷渗漏沉积物孔隙水中硫酸根由甲烷厌氧氧化（AOM）和有机质氧化（OSR）所消耗。通过孔隙水地球化学结合数值模拟研究能够确定现今海底溶解甲烷渗漏环境中AOM和OSR消耗硫酸根的比例和甲烷通量。然而，对地质历史时期溶解甲烷渗漏环境中硫酸根的消耗途径及对应的甲烷通量的确定还缺乏有效的手段。近期发现孔隙水硫酸根硫、氧同位素及其比值可用于限定硫酸根的消耗途径，为研究溶解甲烷渗漏环境甲烷通量提供了新的契机。本申请项目拟通过南海北部东沙、神狐和琼东南海域冷泉区柱状沉积物孔隙水硫酸根硫、氧同位素及其他孔隙水参数特征，确定甲烷通量与硫酸根硫、氧同位素比值之间的关系，建立识别地质历史时期溶解甲烷渗漏的指标，为理解地质历史时期中富甲烷环境的碳、硫循环提供重要线索。

Accurate assessment of methane fluxes in continental margin sediments is critical for understanding the environmental effects of cold seeps. Among seeps, methane transport within the pore space of marine sediments via diffusion is more common than as methane bubbles. The porewater sulfate consumption in methane diffusion environments is depended on anaerobic oxidation of methane (AOM) and organoclastic sulfate reduction (OSR). The relative proportions of sulfate consumed by AOM and OSR, and methane fluxes at modern seeps can be determined by porewater geochemical parameters and numerical simulation. However, an effective method is lacking to constrain sulfate reduction pathways and corresponding methane fluxes in methane diffusion environments in the geological history. Recent studies showed that sulfate reduction pathways (AOM and OSR) can be identified by sulfur and oxygen isotope values and their ratios of porewater sulfate, providing a unique opportunity to constrain methane fluxes in methane diffusion environments at ancient seeps. The present project is designed to measure sulfur and oxygen isotopes of sulfate and other geochemical parameters in pore waters at cold seeps from Dongsha, Shenhu, and Qiongdongnan area of the South China Sea. The aim of the project is to determine the link of methane fluxes and sulfate sulfur/oxygen isotope ratios, and to establish a proxy for identification of diffusion methane seeps in the geological records, which provide important clues for the understanding of the carbon and sulfur cycling in methane-rich environment in the geological history.