In ocean waters, anaerobic microbial respiration should be confined to the anoxic waters found in coastal regions and tropical oxygen minimum zones, where it is energetically favourable. However, recent molecular and geochemical evidence has pointed to a much broader distribution of denitrifying and sulfate-reducing microbes. Anaerobic metabolisms are thought to thrive in microenvironments that develop inside sinking organic aggregates, but the global distribution and geochemical significance of these microenvironments is poorly understood. Here, we develop a new size-resolved particle model to predict anaerobic respiration from aggregate properties and seawater chemistry. Constrained by observations of the size spectrum of sinking particles, the model predicts that denitrification and sulfate reduction can be sustained throughout vast, hypoxic expanses of the ocean, and could explain the trace metal enrichment observed in particles due to sulfide precipitation. Globally, the expansion of the anaerobic niche due to particle microenvironments doubles the rate of water column denitrification compared with estimates based on anoxic zones alone, and changes the sensitivity of the marine nitrogen cycle to deoxygenation in a warming climate.

在海水中，应将厌氧微生物呼吸作用限制在沿海地区和热带最低需氧量区域中的缺氧水域，这些区域应在有利的条件下进行。但是，最近的分子和地球化学证据表明反硝化微生物和硫酸盐还原微生物的分布范围更广。人们认为，厌氧代谢在沉没的有机团聚体内部形成的微环境中蓬勃发展，但是人们对这些微环境的全球分布和地球化学意义知之甚少。在这里，我们开发了一个新的尺寸解析粒子模型，可以根据聚集体性质和海水化学性质预测厌氧呼吸。该模型受下沉颗粒尺寸谱的观察所约束，该模型预测，反硝化作用和硫酸盐还原作用可在整个大范围，海洋中的低氧区域，可以解释由于硫化物沉淀而在颗粒中观察到的痕量金属富集。在全球范围内，由于颗粒微环境导致的厌氧生态位的扩展与仅基于缺氧区域的估计相比，使水柱反硝化的速度增加了一倍，并且改变了海洋氮循环对变暖气候的敏感性。