(Table S1) Stable carbon isotope composition of dissolved inorganic carbon and Ion activity product of dolomite of IODP Exp 323 sites@en

We studied microbially mediated diagenetic processes driven by carbon mineralization in subseafloor sediment of the northeastern Bering Sea Slope to a depth of 745 meters below seafloor (mbsf). Sites U1343, U1344 and U1345 were drilled during Integrated Ocean Drilling Program (IODP) Expedition 323 at water depths of 1008 to 3172 m. They are situated in the high productivity “Green Belt” region, with organic carbon burial rates typical of the high-productivity upwelling domains on western continental margins. The three sites show strong geochemical similarities. The downward sequence of microbially mediated processes in the sediment encompasses (1) organoclastic sulfate reduction, (2) anaerobic oxidation of methane (AOM) coupled to sulfate reduction, and (3) methanogenesis. The sediment contains two distinct zones of diagenetic carbonate formation, located at the sulfate–methane transition zone (SMTZ) and between 300 and 400 mbsf. The SMTZ at the three sites is located between 6 and 9 mbsf. The upward methane fluxes into the SMTZ are similar to fluxes in SMTZs underlying high-productivity surface waters off Chile and Namibia. Our Bering Sea results show that intense organic carbon mineralization drives high ammonium and dissolved inorganic carbon (DIC) production rates (> 4.2 mmol/m**3/y1) in the uppermost 10 mbsf and strongly imprints on the stable carbon isotope composition of DIC, driving it to a minimum value of -27 per mil (VPDB) at the SMTZ. Pore-water calcium and magnesium profiles demonstrate formation of diagenetic Mg-rich calcite in the SMTZ. Below the SMTZ, methanogenesis results in 13C-enrichment of pore-water DIC, with a maximum value of +11.9 per mil. The imprint of methanogenesis on the DIC carbon isotope composition is evident down to a depth of 150 mbsf. Below this depth, slow or absent microbially mediated carbon mineralization leaves DIC isotope composition unaffected. Ongoing carbonate formation between 300 and 400 mbsf strongly influences pore-water DIC and magnesium concentration profiles. The linked succession of organic carbon mineralization and carbonate dissolution and precipitation patterns that we observe in the Bering Sea Slope sediment may be representative of passive continental margin settings in high-productivity areas of the world's ocean.我们针对白令海斜坡东北部海底以下745米（meters below seafloor，以下简称mbsf）范围内的沉积物，开展了由碳矿化作用驱动的微生物介导成岩过程研究。 综合大洋钻探计划（Integrated Ocean Drilling Program, IODP）第323航次在水深1008至3172米的区域钻取了U1343、U1344和U1345三个站位，这些站位地处高生产力“绿带”区域，其有机碳埋藏速率符合西大陆边缘高生产力上升流区的典型特征。 三个站位的地球化学特征具有高度相似性。沉积物中微生物介导的碳转化过程自上而下依次为：（1）有机碎屑硫酸盐还原作用，（2）耦合硫酸盐还原的甲烷厌氧氧化（anaerobic oxidation of methane, AOM），（3）产甲烷作用。沉积物中存在两个截然不同的成岩碳酸盐形成带，分别位于硫酸盐-甲烷转换带（sulfate–methane transition zone, SMTZ）以及300至400 mbsf范围内。三个站位的SMTZ均分布于6至9 mbsf处。 向上输入至SMTZ的甲烷通量，与智利和纳米比亚近海高生产力表层水之下的SMTZ通量水平相当。本次白令海的研究结果显示，强烈的有机碳矿化作用在最上部10 mbsf的沉积物中造就了极高的铵态氮与溶解无机碳（dissolved inorganic carbon, DIC）生成速率（>4.2 mmol/m³·a⁻¹），并显著改变了DIC的稳定碳同位素组成：在SMTZ处，其δ¹³C值最低可达-27‰（VPDB）。孔隙水钙、镁离子剖面数据证实，SMTZ处形成了成岩富镁方解石。在SMTZ之下，产甲烷作用导致孔隙水DIC的碳同位素发生¹³C富集，最高值可达+11.9‰。产甲烷作用对DIC碳同位素组成的影响可延伸至150 mbsf的深度。在此深度之下，微生物介导的碳矿化作用趋于缓慢或停滞，未对DIC同位素组成产生显著影响。 300至400 mbsf范围内持续进行的碳酸盐形成作用，对孔隙水DIC与镁离子浓度剖面产生了强烈调控作用。我们在白令海斜坡沉积物中观测到的有机碳矿化与碳酸盐溶解-沉淀模式的耦合序列，可能代表了全球海洋高生产力区域内被动大陆边缘环境的典型特征。