This biogeochemical, molecular genetic and lipid biomarker study of sediments ( approximately 4 m cores) from the Skagerrak (Denmark) investigated methane cycling in a sediment with a clear sulfate-methane-transition zone (SMTZ) and where CH(4) supply was by diffusion, rather than by advection, as in more commonly studied seep sites. Sulfate reduction removed sulfate by 0.7 m and CH(4) accumulated below. (14)C-radiotracer measurements demonstrated active H(2)/CO(2) and acetate methanogenesis and anaerobic oxidation of CH(4) (AOM). Maximum AOM rates occurred near the SMTZ ( approximately 3 nmol cm(-3) day(-1) at 0.75 m) but also continued deeper, overall, at much lower rates. Maximum rates of H(2)/CO(2) and acetate methanogenesis occurred below the SMTZ but H(2)/CO(2) methanogenesis rates were x 10 those of acetate methanogenesis, and this was consistent with initial values of (13)C-depleted CH(4) (delta(13)C c.-80 per thousand). Areal AOM and methanogenic rates were similar ( approximately 1.7 mmol m(-2) day(-1)), hence, CH(4) flux is finely balanced. A 16S rRNA gene library from 1.39 m combined with methanogen (T-RFLP), bacterial (16S rRNA DGGE) and lipid biomarker depth profiles showed the presence of populations similar to some seep sites: ANME-2a (dominant), ANME-3, Methanomicrobiales, Methanosaeta Archaea, with abundance changes with depth corresponding to changes in activities and sulfate-reducing bacteria (SRB). Below the SMTZ to approximately 1.7 m CH(4) became progressively more (13)C depleted (delta(13)C -82 per thousand) indicating a zone of CH(4) recycling which was consistent with the presence of (13)C-depleted archaeol (delta(13)C -55 per thousand). Pore water acetate concentrations decreased in this zone (to approximately 5 microM), suggesting that H(2), not acetate, was an important CH(4) cycling intermediate. The potential biomarkers for AOM-associated SRB, non-isoprenoidal ether lipids, increased below the SMTZ but this distribution reflected 16S rRNA gene sequences for JS1 and OP8 bacteria rather than those of SRB. At this site peak rates of methane production and consumption are spatially separated and seem to be conducted by different archaeal groups. Also AOM is predominantly coupled to sulfate reduction, unlike recent reports from some seep and gassy sediment sites.

译文

这项对来自Skagerrak (丹麦) 的沉积物 (约4 m核心) 的生物地球化学,分子遗传和脂质生物标志物研究了具有透明硫酸盐-甲烷过渡区 (SMTZ) 的沉积物中的甲烷循环,其中CH(4) 的供应是通过扩散而不是平流,就像在更常见的研究渗漏位点一样。硫酸盐还原去除硫酸盐由下面累积的0.7 m和CH(4)。(14)C-放射性示踪剂测量显示了活性H(2)/CO(2) 和乙酸甲烷生成以及CH(4) (AOM) 的厌氧氧化。最大AOM速率发生在SMTZ附近 (在0.75 m处约3 nmol cm(-3) 天 (-1)),但总体上仍以更低的速率持续更深。H(2)/CO(2) 和乙酸甲烷生成的最大速率发生在SMTZ以下,但H(2)/CO(2) 甲烷生成的速率为x 10乙酸甲烷生成的速率,这与 (13)C耗尽的CH(4) (δ (13)C c.-80每千) 的初始值一致。面积AOM和产甲烷速率相似 (约1.7 mmol m(-2) 天 (-1)),因此,CH(4) 通量是精细平衡的。1.39 m的16S rRNA基因库与产甲烷菌 (t-rflp),细菌 (16S rRNA DGGE) 和脂质生物标志物深度图谱相结合,表明存在与某些seep位点相似的种群: ANME-2a (显性),ANME-3,甲烷菌,甲烷菌,随着深度的变化,相应于活性和硫酸盐还原细菌 (SRB) 的变化。低于SMTZ至约1.7 m CH(4) 逐渐变得更 (13)C耗尽 (δ (13)C -82每千),表明CH(4) 再循环区域与 (13)C耗尽古细菌 (δ (13)C -55 ‰)。该区域的孔隙水乙酸盐浓度降低 (约为5微米),表明H(2) 而不是乙酸盐是重要的CH(4) 循环中间体。与AOM相关的SRB (非异戊二烯醚脂质) 的潜在生物标志物在SMTZ以下增加,但这种分布反映了JS1和OP8细菌的16S rRNA基因序列,而不是SRB。在这个地点,甲烷生产和消耗的峰值速率在空间上是分开的,似乎是由不同的古细菌群体进行的。与最近一些渗漏和瓦斯沉积物站点的报道不同,AOM主要与硫酸盐的减少有关。

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