The isotopic ratio 18O/16O of dissolved O2 in aquatic systems is affected by the preferential biological uptake of 16O (ε). Studies over the past six decades reveal that during incubation experiments, the isotopic effect of microorganism respiration (εorganism) varies in the range of −18‰ to −22‰. In contrast, natural variations in the deep‐ocean O2 concentration and δ18O levels show a considerably weaker effect (~ −10‰). The differences between these observations have been explained to result from either O2 uptake by sediments or organic particles that, due to diffusion‐limited respiration, are expected to weakly fractionate oxygen isotopes, by mixing processes or by weak fractionation at low temperatures. To gain better insight, we studied oxygen demand and δ18O in the deep, cold hypolimnion of Lake Stechlin between 2018 and 2021 as well as in various laboratory incubations. Our incubation results demonstrate an εorganism of about −24‰. Simple model calculations demonstrate a sediment O2 demand isotope effect (εSOD) of about −8.4‰, and a variated water‐column O2 demand isotope effect (εWOD) which is lower than εorganism, ranging from −13.9‰ in 2019 to −23‰ in 2021. Accompanying experiments indicate that the lower magnitude of εWOD may be related to respiration at organic particles lending to a weaker fractionation effect. Thus, variations in εWOD may reflect a changing partitioning of hypolimnion oxygen uptake between suspended particles and their containing microorganisms. Based on own incubation experiments with Daphnia carcasses, we discuss how possible changes of particle rigidity might influence εWOD.

中文翻译：

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深湖中氧气消耗的同位素效应可作为了解微生物、颗粒和沉积物之间氧气需求分配的手段

同位素比18奥/16溶解 O 的 O2水生系统中的生物优先吸收16欧（ε）。过去六十年的研究表明，在孵化实验中，微生物呼吸的同位素效应（ε生物）的变化范围为-18‰至-22‰。相比之下，深海 O 的自然变化2浓度和δ18O 水平的影响相当弱（~−10‰）。这些观察结果之间的差异已被解释为由 O2沉积物或有机颗粒的吸收，由于扩散限制呼吸作用，预计会通过混合过程或低温下的弱分馏来弱分馏氧同位素。为了获得更好的见解，我们研究了需氧量和 δ182018 年至 2021 年间，O 存在于 Stechlin 湖深处寒冷的地下层以及各种实验室孵化器中。我们的孵化结果表明ε生物约-24‰。简单的模型计算表明沉积物 O2需求同位素效应（ε草皮）约为-8.4‰，以及变化的水柱O2需求同位素效应（ε沃德) 低于ε生物，范围从2019年的-13.9‰到2021年的-23‰。伴随的实验表明，较低的幅度ε沃德可能与有机颗粒的呼吸作用有关，导致分馏效应较弱。因此，变化ε沃德可能反映了悬浮颗粒及其所含微生物之间低浓度氧吸收分配的变化。根据自己的孵化实验水蚤屠体，我们讨论颗粒刚性的可能变化如何影响ε沃德。