The isotopic composition of dissolved O₂ (δ¹⁸O) in aquatic environments is strongly affected by the preferential uptake of the lighter isotopologue during biological consumption processes. Numerous studies have shown that during incubation experiments, the isotopic effect of microorganism respiration (ε_organism) is on the order of −20‰. However, studies of the co-variations of O₂ and δ¹⁸O in natural environments show considerably weaker in situ fractionation (ε_app). A possible explanation for this discrepancy is that a significant fraction of the O₂ consumption is diffusion-limited. Although this is a generally accepted mechanism in sediments, it cannot explain the weak fractionations observed in mid-ocean sites. Here, we analyze a time series of O₂, δ¹⁸O, and auxiliary data from the northern Gulf of Aqaba (Red Sea). Although an incubation experiment showed strong fractionation against the heavy isotopologue (ε_organism = −24.5‰), the in situ ε_app was only −14‰ in deep water isolated from the photic zone. We show that this result requires an additional O₂ consumption mechanism with weak fractionation, rather than mixing, and suggest that this mechanism is diffusion-limited respiration into aggregates of organic material. We estimate that this mechanism could be responsible for 30% of the O₂ consumption in the Gulf and suggest that it may also constitute a major O₂ consumption pathway in the world's oceans.

中文翻译：

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群落呼吸过程中溶解氧的弱同位素分馏

_{水生环境中溶解的 O 2} (δ ¹⁸ O)的同位素组成受到生物消耗过程中较轻同位素体的优先吸收的强烈影响。大量研究表明，在孵化实验过程中，微生物呼吸（ε_生物）的同位素效应在-20‰ 量级。然而，对自然环境中 O ₂和 δ ^{18 O 的协变研究表明，原位分馏 (} ε _app ) 相当弱。对这种差异的一种可能解释是，很大一部分 O ₂消费是扩散受限的。尽管这是沉积物中普遍接受的机制，但它不能解释在大洋中部观察到的弱分馏。在这里，我们分析了来自亚喀巴湾北部（红海）的 O ₂、δ ^{18 O 和辅助数据的时间序列。}尽管孵化实验显示对重同位素体（ε_生物体= -24.5‰）有很强的分馏作用，但在与透光区隔离的深水 中，原位ε _{app仅为 -14‰。}我们证明这个结果需要额外的 O ₂消耗机制具有弱分馏，而不是混合，并表明这种机制是扩散限制呼吸进入有机材料的聚集体。我们估计这种机制可能导致海湾地区 30% 的 O ₂消耗，并表明它也可能构成世界海洋中O _{2消耗的主要途径。}