A site at the gas hydrate stability limit was investigated offshore northwestern Svalbard to study methane transport in sediment. The site was characterized by chemosynthetic communities (sulfur bacteria mats, tubeworms) and gas venting. Sediments were sampled with in situ porewater collectors and by gravity coring followed by analyses of porewater constituents, sediment and carbonate geochemistry, and microbial activity, taxonomy, and lipid biomarkers. Sulfide and alkalinity concentrations showed concentration maxima in near‐surface sediments at the bacterial mat and deeper maxima at the gas vent site. Sediments at the periphery of the chemosynthetic field were characterized by two sulfate‐methane transition zones (SMTZs) at ~204 and 45 cm depth, where activity maxima of microbial anaerobic oxidation of methane (AOM) with sulfate were found. Amplicon sequencing and lipid biomarker indicate that AOM at the SMTZs was mediated by ANME‐1 archaea. A 1D numerical transport reaction model suggests that the deeper SMTZ‐1 formed on centennial scale by vertical advection of methane, while the shallower SMTZ‐2 could only be reproduced by nonvertical methane injections starting on decadal scale. Model results were supported by age distribution of authigenic carbonates, showing youngest carbonates within SMTZ‐2. We propose that nonvertical methane injection was induced by increasing blockage of vertical transport or formation of sediment fractures. Our study further suggests that the methanotrophic response to the nonvertical methane injection was commensurate with new methane supply. This finding provides new information about for the response time and efficiency of the benthic methane filter in environments with fluctuating methane transport.

中文翻译：

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斯瓦尔巴德群岛西北部近海沉积物中非垂直甲烷运移的生物地球化学后果。

在西北斯瓦尔巴特群岛近海调查了天然气水合物稳定极限的一个站点，以研究甲烷在沉积物中的传输。该地点的特点是化学合成群落（硫细菌垫，结核虫）和排气。使用原位孔隙水收集器并通过重力取芯对沉积物进行采样，然后分析孔隙水成分，沉积物和碳酸盐地球化学以及微生物活性，分类学和脂质生物标志物。硫化物和碱度浓度在细菌垫处的近地表沉积物中显示出最大浓度，而在排气口处显示出更深的浓度。化学合成场外围的沉积物的特征是在约204和45 cm深度处有两个硫酸盐甲烷转换区（SMTZ），在其中发现了微生物对硫酸盐的微生物厌氧氧化（AOM）的最大活性。扩增子测序和脂质生物标记表明SMTZ处的AOM由ANME-1古细菌介导。一维数值传输反应模型表明，较深的SMTZ-1由甲烷的垂直对流以百年尺度形成，而较浅的SMTZ-2只能通过以十年尺度开始的非垂直甲烷注入来复制。模型结果得到自生碳酸盐的年龄分布的支持，显示出SMTZ-2中最年轻的碳酸盐。我们建议通过增加垂直输送的阻塞或沉积物裂缝的形成来诱导非垂直甲烷注入。我们的研究进一步表明，对非垂直甲烷注入的甲烷营养响应与新的甲烷供应相当。