Chemical and isotopic compositions of samples from the Haakon Mosby mud volcano and nearby

Authigenic carbonates in the caldera of an Arctic (72°N) submarine mud volcano with active methane-bearing fluid discharge are formed at the bottom surface during anaerobic microbial methane oxidation. The microbial community consists of specific methane-producing bacteria, which act as methanotrophic ones in conditions of excess methane, and sulfate reducers developing on hydrogen, which is an intermediate product of microbial CH4 oxidation. Isotopically light carbon (aver. d13C = -28.9 per mil) of CO2 produced during CH4 oxidation is the main carbonate carbon source. Heavy oxygen isotope ratio (aver. d18O = 5 per mil) in carbonates is inherited from seawater sulfate. Rapid sulfate reduction (up to 12 mg S/dm**3/day) results in total exhausting of sulfate ion in the upper sediment layer (10 cm). Because of this carbonates can only be formed in surface sediments near the water-bottom interface. Salinity as well as CO3/Ca and Mg/Ca ratios correspond to the field of non-magnesian calcium carbonate precipitation. Calcite is the dominant carbonate mineral in the methane seep caldera, where it occurs in the paragenetic association with barite. Radiocarbon age of carbonates is about 10 Ka.

自生碳酸盐岩（Authigenic carbonates）形成于北极（北纬72°）海底泥火山破火山口内，该区域存在活跃的含甲烷流体喷溢活动，其形成由厌氧微生物甲烷氧化作用驱动，发生于水-沉积物界面处。该微生物群落包含两类特异性菌群：一类是在甲烷过量条件下可充当甲烷氧化菌（methanotroph）的产甲烷菌，另一类是利用微生物甲烷氧化中间产物氢气生长的硫酸盐还原菌（sulfate reducers）。甲烷氧化过程中产生的CO₂具有轻碳同位素特征，平均δ¹³C值为-28.9‰，是碳酸盐岩碳组分的主要来源。碳酸盐岩中的重氧同位素比值平均为5‰，该信号继承自海水硫酸盐（seawater sulfate）。硫酸盐还原速率最高可达12 mg S/dm³·天，致使10 cm厚的上层沉积物内硫酸根离子被完全消耗。正因如此，碳酸盐岩仅能形成于水-沉积物界面附近的表层沉积物中。盐度以及CO₃²⁻/Ca²⁺、Mg²⁺/Ca²⁺比值均处于无镁碳酸钙（non-magnesian calcium carbonate）沉淀的形成区间内。方解石（Calcite）是该甲烷渗漏破火山口中占主导的碳酸盐矿物，与重晶石（barite）形成共生组合。该碳酸盐岩的放射性碳年龄（Radiocarbon age）约为10 ka（千年）。