The degradation of organic matter in the anoxic seabed proceeds through a complex microbial network in which the terminal steps are dominated by oxidation with sulfate or conversion into methane and CO₂. The controls on pathway and rate of the degradation process in different geochemical zones remain elusive. Radiotracer techniques were used to perform measurements of sulfate reduction, methanogenesis, and acetate oxidation with unprecedented sensitivity throughout Holocene sediment columns from the Baltic Sea. We found that degradation rates transition continuously from the sulfate to the methane zone, thereby demonstrating that terminal steps do not exert feedback control on upstream hydrolytic and fermentative processes, as previously suspected. Acetate was a key intermediate for carbon mineralization in both zones. However, acetate was not directly converted into methane. Instead, an additional subterminal step converted acetate to CO₂ and reducing equivalents, such as H₂, which then fed autotrophic reduction of CO₂ to methane.

中文翻译：

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海底厌氧有机碳降解速率和途径的控制

缺氧海床中有机物的降解通过复杂的微生物网络进行，其中最终步骤以硫酸盐氧化或转化为甲烷和 CO _2为主. 对不同地球化学区降解过程的路径和速率的控制仍然难以捉摸。放射性示踪剂技术被用于在波罗的海全新世沉积物柱中以前所未有的灵敏度测量硫酸盐还原、甲烷生成和醋酸盐氧化。我们发现降解速率从硫酸盐区连续过渡到甲烷区，从而证明终端步骤不会对上游水解和发酵过程施加反馈控制，正如之前所怀疑的那样。醋酸盐是这两个区域碳矿化的关键中间体。然而，乙酸盐没有直接转化为甲烷。相反，一个额外的亚末端步骤将乙酸盐转化为 CO ₂和还原当量，例如 H _{2，然后将CO 2}自养还原为甲烷。