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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. [ABSTRACT FROM AUTHOR]

Traditionally, nuclear spin is not considered to affect biological processes. Recently, this has changed as isotopic fractionation that deviates from classical mass dependence was reported both in vitro and in vivo. In these cases, the isotopic effect correlates with the nuclear magnetic spin. Here, we show nuclear spin effects using stable oxygen isotopes (16O, 17O, and 18O) in two separate setups: an artificial dioxygen production system and biological aquaporin channels in cells. We observe that oxygen dynamics in chiral environments (in particular its transport) depend on nuclear spin, suggesting future applications for controlled isotope separation to be used, for instance, in NMR. To demonstrate the mechanism behind our findings, we formulate theoretical models based on a nuclear-spin-enhanced switch between electronic spin states. Accounting for the role of nuclear spin in biology can provide insights into the role of quantum effects in living systems and help inspire the development of future biotechnology solutions. [ABSTRACT FROM AUTHOR]

Anthropogenic‐induced variations of the Atlantic Meridional Overturning Circulation (AMOC) and the associated Deep‐Water Formation (DWF) are a major concern. Using measurements of triple oxygen isotopes in the deep North Atlantic, we present novel evidence for a dramatic decadal to centennial shift in ocean conditions at the source region of DWF. These measurements suggest a recent decrease in the percentage of photosynthetic O2 derived from the source regions of AMOC in the Nordic Seas compared to the Little Ice Age. 1‐D model simulations suggest that a reduction in photosynthetic O2 production can explain the observed decrease. Alternatively, it may indicate a substantial decrease in sea‐ice cover and thus increased air‐sea gas exchange, bringing the isotopic composition of O2 closer to equilibrium with the atmosphere. Our novel data can serve as a benchmark for climate models. Plain Language Summary: In this study, we use the isotopic signature of dissolved oxygen gas in the deep North Atlantic Ocean to demonstrate a recent dramatic change in the Nordic Seas. Water in the deep Atlantic at present was at the surface of the Nordic Seas several hundred years ago, during the Little Ice Age (LIA). The isotopic signature shows that the percentage of oxygen sourced from photosynthesis was greater during the LIA. This may indicate a greater rate of photosynthesis than at present. However, we know that when sea ice covers the ocean surface, it prevents the influx of atmospheric oxygen, while sunlight penetration through the ice keeps a high rate of photosynthesis and production of biological oxygen. Therefore, it is also possible that during the LIA, sea‐ice cover was much more extensive than today. Key Points: Oxygen isotopic evidence for a recent dramatic shift in the North Atlantic source region of deep water‐massesThe isotopic measurements suggest high extent of ice cover and/or higher primary production rates during the Little Ice AgeThese new observations can serve as a benchmark for climate models [ABSTRACT FROM AUTHOR]

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 (εorganism) 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 (εapp). 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 (εorganism = −24.5‰), the in situ εapp 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. [ABSTRACT FROM AUTHOR]

Rationale Measurements of oxygen-17 excess (17Oexcess) in carbonates have become of great importance. However, to compare results obtained by different laboratories, it is necessary to normalize them to international standards. With this purpose in mind, we measured accurate and high precision δ17O and 17Oexcess values for NBS19 and NBS18, two international standards, for which δ18O values are already widely used as the references for carbonates. Methods The measurements are based on isotopic exchange at steady state between O2 and CO2 over hot platinum sponge at 750°C. Dual-inlet isotope ratio mass spectrometry (IRMS) measurements of the δ17O and δ18O values of this O2 allow δ17O values of CO2 to be obtained with very high precision (0.01 to 0.03 ‰) and, correspondingly, accurate 17Oexcess values with a precision of 5 per meg. Results We measured, for the first time, the δ17O values and 17Oexcess of CO2 liberated from NBS19 at 25°C (39.196 ± 0.026; 20.276 ± 0.015 ‰ and −227 ± 4 per meg, respectively) and NBS18 (17.591 ± 0.041 ‰; 9.253 ± 0.018 ‰ and 3 ± 5 per meg, respectively). The values are given versus VSMOW. Conclusions Accurate values of δ17O and 17Oexcess of the international standards NBS19-CO2 and NBS18-CO2 are now available. The new values should be used for normalization of measured oxygen isotope ratios of carbonates to allow meaningful comparison of results among different laboratories. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A time series of the 17O-excess (17Δ) was measured in the Gulf of Elat (Aqaba) between May 2007 and August 2009. While 17Δ is expected to behave conservatively below the photic zone, we observed a ? increase of 20 per meg in the water residing below 300 m along a period of 3 months, which was followed by a 17Δ decrease of 60 per meg, which occurred over 7 months. The 17Δ increase and decrease indicate penetration of photosynthetic O2, followed by penetration of atmospheric O2 into the deep water. In order to test whether vertical mixing could explain the observed variations in 17Δ, we compared our results with simulated values obtained from a one dimensional hydrodynamic model, which was extended to include dissolved O2 isotopes. Our model simulations successfully reproduced the observed temperatures, salinities and dissolved O2 concentrations in the gulf. In addition, the evaporation rate estimated by the model (1.7 m x year-1) and the advective heat flux from the Red Sea (110 W x m-2 over 3 months) were in good agreement with previous studies. However, the model could not reproduce the observed variations in 17Δ in the deep water, regardless of the gross O2 production and the air-sea gas exchange rates used. This discrepancy shows that horizontal mixing processes have an important role in the interaction between deep and surface water in the gulf. We suggest that for the most part, these processes occur along the boundaries of the gulf. [ABSTRACT FROM AUTHOR]

RATIONALE Measurements of δ17O and δ18O values of tropospheric CO2 are of great importance. However, to be useful, such measurements must be an order of magnitude more precise than in current published literature. With this purpose we developed a new method for high-precision mass spectrometric measurements of 17O/16O and 18O/16O ratios in CO2, which is presented in this study. METHODS The method is based on isotopic exchange equilibration between H2O and CO2 in sealed glass ampoules followed by water fluorination to produce O2. Dual inlet isotope ratio mass spectrometric (IRMS) measurements of the δ17O and δ18O values of this O2 allow δ17O values of CO2 to be obtained with very high precision (0.01 to 0.03 ‰). This method requires about 70 µmol of CO2. RESULTS Measurements of standard CO2 gas and atmospheric CO2 yield reproducibility of 0.01 to 0.03 ‰ for both δ17O and δ18O values, and 5 per meg for 17Oexcess. Fractionation factors 17α and 18α were determined in the H2O-CO2 equilibrium at 25 °C as 1.021254 ± 0.00004 and 1.041036 ± 0.00008, respectively, and the ratio ln17α/ln18α as 0.5229 ± 0.0001. CONCLUSIONS The results demonstrate that the new method is the most accurate analytical procedure ever presented for measurements of 17Oexcess of CO2 gas. It is suitable for measurements of CO2 extracted from relatively small samples of air (~5 L), and is thus useful for monitoring the 17Oexcess of CO2 on a broad global scale. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

[i] Atmospheric O2 is almost 24%o more enriched in 18O than seawater, and this enrichment is known as the Dole effect. For a long time it has been accepted that there is no oxygen isotope fractionation in photosynthesis, and thus the Dole effect should be the result of preferential terrestrial and marine respiratory consumption of 16O over 18O, and also several permil enrichment of leaf water from which terrestrial photosynthesis produces 18O enriched O2. This concept has led to the understanding that the record of past Dole effect variations was strongly affected by changes in the ratio of photosynthetic production between land and sea. However, recent studies in our lab have led to two major new observations: (1) O2 produced by certain marine phytoplankton, representing important groups of primary producers, is significantly enriched (up to 6%o) in 18O with respect to the substrate seawater and (2) effective oxygen isotope fractionation in soil respiration is considerably smaller than the intrinsic respiratory fractionation. Here we take these two observations into account and show that the magnitudes of the terrestrial and marine components of the Dole effect are close, and both are close to the measured Dole effect. As a result, the magnitude of the global Dole effect should not be sensitive to past changes in the ratio of land-to-sea photosynthetic rates. Instead of the land-sea control, variations in low-latitude hydrology, and possibly changes of fractionations in the marine biosphere, are more important in regulating the magnitude of the Dole effect and its past variations. [ABSTRACT FROM AUTHOR]

The triple isotope composition (δ170 and δ180) of dissolved O2 in the ocean and in ice cores was recently used to assess the primary productivity over broad spatial and temporal scales. However, assessment of the productivity with the aid of this method must rely on accurate measurements of the 17O/16O versus 18O/16O relationship in each of the main oxygen-producing and -consuming reactions. Data obtained here showed that cleavage of water in photosystem II did not fractionate oxygen isotopes; the δ18O and δ17O of the O2 evolved were essentially identical to those of the substrate water. The fractionation slopes for the oxygenase reaction of Rubisco and respiration were identical (0.518 ± 0.001) and that of glycolate oxidation was 0.503 ± 0.002. There was a considerable difference in the slopes of O2 photoreduction (the Mehler reaction) in the cyanobacterium Synechocystis sp. strain PCC 6803 (0.497 ± 0.004) and that of pea (Pisum sativum) thylakoids (0.526 ± 0.001). These values provided clear and independent evidence that the mechanism of O2 photoreduction differs between higher plants and cyanobacteria. We used our method to assess the magnitude of O2 photoreduction in cyanobacterial cells maintained under conditions where photorespiration was negligible. It was found that electron flow to O2 can be as high as 40% that leaving photosystem II, whereas respiratory activity in the light is only 6%. The implications of our findings to the evaluation of specific O2-producing or -consuming reactions, in vivo, are discussed. [ABSTRACT FROM AUTHOR]

Looks at triple-isotope composition of atmospheric oxygen as a tracer of biosphere productivity. The three natural occurring isotopes of oxygen; Dependence on the isotopic composition of photosynthetically produced O2 from terrestrial and aquatic plants; Estimate of the size of the 17O/16O anomaly in tropospheric O2; Reflection of the influence of the influence of biospheric cycling and stratospheric photochemical processes; Proposal.

We have recently published a new evaluation of Earth's Dole effect, which was based, in part, on measurements of δO2/Ar, δ17O and δl8O of dissolved argon and oxygen in the ocean surface. In calculations of the oxygen isotope effect due to photosynthesis and respiration (Ɛup), gross O2 production (G) was an important factor. However, our estimates of G were based on an approximate equation, and in a recent publication it has been suggested that G obtained with this equation could be underestimated by about 33%. If true, such underestimation of G might lead to different Ɛup values. To test this possibility, we have used a new rigorous equation with relevant information on isotopic composition of photosynthetic O2 and recalculated Ɛup. Given the uncertainties, the new values do not differ from the previous ones, and therefore, the implications of the strong fractionation in the upper ocean (~25‰) to the global Dole effect remain as in our original publication. [ABSTRACT FROM AUTHOR]

By use of in situ bottle incubations, we determined three variables for the characterization of plankton community primary productivity in Lake Kinneret, Israel: (1) H218O-based primary productivity (18OP), measured by 34O2 (18O16O) evolution; (2) radiocarbon-uptake-based primary productivity (14CP); and (3) net O2 production (NOP), calculated from the rate of O2 : Ar change. Six experiments were conducted in the fall, a period that is characterized by thermocline deepening, erosion of the hypolimnion, and eventual introduction of high concentration of reduced substances into the epilimnion. An additional experiment was conducted in spring. In comparison to net O2 evolution, the tracer-based methods severely underestimated primary productivity in the fall. This is indicated by unusually high NOP: 18OP and NOP: 14CP ratios (1-2.2 and 2-4, respectively). The latter is considerably different than the typical values of aquatic environments (∼1.4). In contrast to these ratios, the 18OP: 14CP appears normal (1.6-2.9) and not significantly different from previous results in the lake. Ammonium was the major nitrogen source in the fall experiments, and there is no reason to assume that the cellular composition of phytoplankton was exceptional. It is therefore unlikely that the high NOP: 14CP ratio represents genuine ratios of oxygen and carbon metabolism. We suggest that an explanation accounting for the high values of both NOP: 18O P and NOP: 14CP can be slow diffusion of the tracers in and out of phytoplankton cells. [ABSTRACT FROM AUTHOR]