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Carbonates are common paleoclimate archives in a variety of environments with land carbonates recording both temperatures and hydrological conditions. Whereas δ18O has long been used for that purpose, triple oxygen isotopes (given as 17O excess) has only recently been analyzed in CaCO 3. Carbonate 17O excess is expected to reflect the temperature, in which the carbonate formed, and the triple oxygen isotopic composition of its parent water. The reconstruction of past water 17O excess values from carbonate records requires characterization of the 17O fractionation between water and CaCO 3. Here, we use freshwater mollusk shells grown in well constrained spring environments, at a temperature range of 15–28 °C, to derive the fractionation factor 17α between CO 2 extracted from CaCO 3 and the carbonate habitat water. The spring water temperature and isotopic composition are constant year-round, avoiding uncertainty associated with seasonality. The derived 18α and 17α between CO 2 extracted from mollusk aragonite and spring water are used to calculate the fractionation slope θ (=ln17α/ln18α), resulting in 0.5231 ± 0.0003, with no discernible temperature dependence. Using this value, we evaluated the fractionation slope of the acid digestion of CaCO 3 as 0.5170 ± 0.0004. The minor difference between the fractionation slope between aragonite and parent water and the reference slope of 0.528, implies that 17O excess in carbonates is only weakly temperature dependent. On the other hand, carbonate 17O excess values directly record variability in 17O excess of the parent water, making it a useful paleo-hydrological proxy. [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]

Closed-basin lakes respond strongly to climate related changes in their water balance. Lake water isotopic composition can thus serve as a sensitive indicator of paleo-hydrological conditions. Such lakes are often highly saline, so that the effect of salinity on the isotopic composition of lake water has to be accounted for in analyzing lake water evaporation and lake sediment isotopic records. Whereas the effect of salinity on δ 18 O has been well characterized, this has not been done for the emerging proxy 17O excess [ O excess 17 = 10 6 [ ln ⁡ (10 − 3 δ 17 O + 1) − 0.528 ln ⁡ (10 − 3 δ 18 O + 1) ]. To this end, we measured for the first time δ 17 O and δ 18 O of water in NaCl, CaCl 2 , and MgCl 2 solutions of a wide range of concentrations (1 to 4 molal), using CO 2 -H 2 O isotope exchange at 25 °C. The results show that although both δ 18 O and δ 17 O are sensitive to salinity, 17O excess is independent of salinity. Therefore, when analyzing lake water composition, the effect of salinity on δ 18 O and δ 17 O has to be accounted for, whereas 17O excess remains unchanged. These findings have important implications when studying evaporation in hypersaline lakes and for reconstructions of past water balance in saline closed-basin lakes. • Water δ 18 O and δ 17 O are influenced by the presence of Ca+2 and Mg+2 but not Na+. • Water 17O excess is not influenced by salinity. • This salt effect is important in reconstructing paleo water balance in saline lakes. [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]

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]

Representations of the changing global carbon cycle under climatic and environmental perturbations require highly detailed accounting of all atmosphere and biosphere exchange. These fluxes remain unsatisfactory, as a consequence of only having data with limited spatiotemporal coverage and precision, which restrict accurate assessments. Through the nature of intimate coupling of global carbon and oxygen cycles via O2 and CO2 and their unique triple oxygen isotope compositions in the biosphere and atmosphere, greater insight is available. We report analysis of their isotopic compositions with the widest geographical and temporal coverage (123 new measurements for CO2) and constrain, on an annual basis, the global CO2 recycling time (1.5 ± 0.2 year) and gross primary productivities of terrestrial (~ 170–200 PgC/year) and oceanic (~ 90–120 PgC/year) biospheres. Observed inter-annual variations in CO2 triple oxygen isotopic compositions were observed at a magnitude close to the largest contrast set by the terrestrial and oceanic biospheres. The seasonal cycles between the east and west Pacific Ocean were found to be drastically different. This intra-annual variability implies that the entire atmospheric CO2 turnover time is not much longer than the tropospheric mixing time (less than ~ 5 months), verifying the derived recycling time. The new measurements, analyses, and incorporation of other global data sets allow development of an independent approach, providing a strong constraint to biogeochemical models. [ABSTRACT FROM AUTHOR]

Abstract: The variations of δ17O and δ18O in recent meteoric waters and in ice cores have proven to be an important tool for investigating the present and past hydrologic cycle. In order to close significant information gaps in the present distribution of δ17O and δ18O of meteoric water, we have run precise measurements, with respect to VSMOW, on samples distributed globally from low to high latitudes. Based on the new and existing data, we present the Global Meteoric Water Line (GMWL) for δ17O and δ18O as: In addition to meteoric water, we carried out the first measurements of seawater from the Pacific and Atlantic oceans with respect to VSMOW. The obtained results show that the slope of the trend line ln(δ17O+1) vs. ln(δ18O+1) of seawater samples is 0.528, the same as for meteoric water, but the regression intercept is −5 per meg. Thus, the positive intercept in the GMWL indicates an excess of 17O in meteoric waters with respect to the ocean. An excess (or depletion) of 17O in water is defined as: Most meteoric water samples have positive 17O-excess of varying magnitudes with an average of 37 per meg with respect to VSMOW. We explain how these positive values originate from evaporation of sea water into marine air, which is undersaturated in water vapor, and how subsequent increase of 17O-excess occurs when atmospheric vapor condenses to form liquid and solid precipitation. We also clarify the effect of excessive evaporation on 17O-excess. Finally, based on the new results on 17O-excess of seawater we recalculated the relationship of δ17O vs. δ18O in vapor diffusion in air as 18αdiff =1.0096. [ABSTRACT FROM AUTHOR]

Abstract: Variations in oxygen and hydrogen isotope ratios of water and ice are powerful tools in hydrology and ice core studies. These variations are controlled by both equilibrium and kinetic isotope effects during evaporation and precipitation, and for quantitative interpretation it is necessary to understand how these processes affect the isotopic composition of water and ice. Whereas the equilibrium isotope effects are reasonably well understood, there is controversy on the magnitude of the kinetic isotope effects of both oxygen and hydrogen and the ratio between them. In order to resolve this disagreement, we performed evaporation experiments into air, argon and helium over the temperature range from 10 to 70°C. From these measurements we derived the isotope effects for vapor diffusion in gas phase ( for D/H and for 18O/16O). For air, the ratio / at 20°C is 0.84, in very good agreement with (0.88), but in considerable inconsistency with (0.52). Our results support Merlivat’s conclusion that measured / ratios are significantly different than ratios calculated from simplified kinetic theory of gas diffusion. On the other hand, our experiments with helium and argon suggest that this discrepancy is not due to isotope effects of molecular collision diameters. We also found, for the first time, that the / ratio tends to increase with cooling. This new finding may have important implications to interpretations of deuterium excess (d-excess=δD−8δ18O) in ice core records, because as we show, the effect of temperature on d-excess is of similar magnitude to glacial interglacial variations in the cores. [Copyright &y& Elsevier]

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]

Abstract: Recently, a new method has been introduced for the estimation of photosynthetic oxygen production from the triple isotope composition (δ17O and δ18O) of dissolved O2 in the ocean and of air O2 in ice cores. This method is based on the deviations (17Δ) from mass dependent respiratory fractionation, the major process affecting the isotopic composition of air O2. To apply this method, the slope in the 17O/16O vs. 18O/16O relationship used for 17Δ calculation must be known with high accuracy. Using numerical simulations and closed system experiments, we show how the respiratory slope is manifested in the 17Δ of O2 in situations where respiration is the only process affecting oxygen isotopic composition (kinetic slope), and in systems in steady state between photosynthesis and respiration (steady state slope). The slopes of the fractionation line in these two cases are different, and the reasons of this phenomenon are discussed. To determine the kinetic respiratory slope for the dominant O2 consumers in aquatic systems, we have conducted new experiments using a wide range of organisms and conditions and obtained one universal value (0.5179 ± 0.0006) in ln(δ17O + 1) vs. ln(δ18O + 1) plots. It was also shown that the respiratory fractionations under light and dark are identical within experimental error. We discuss various marine situations and conclude that the kinetic slope 0.518 should be used for calculating 17Δ of dissolved O2. In contrast, a steady state fractionation slope should be used in global mass balance calculations of triple isotope ratios of O2 in air records of ice cores. [Copyright &y& Elsevier]

Presents information on a study which described an approach for estimating production of photosynthetic oxygen, based on the isotopic composition of dissolved oxygen of seawater. Plant production in the sea; Rate of marine photosynthetic production; Derivation of estimates of gross production.

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.

Discusses the development of an improved procedure of 18O/16O ratio measurements by means of oxygen conversion to carbon dioxide (CO2). Isotope fractionation effects associated with different processes; Reagents and apparatus used; Optimal temperature of conversion reaction.

Carbonate bearing materials, such as foraminifera, mollusks shells, or speleothems, have the potential to preserve geochemical and isotopic signatures reflecting the environmental conditions at the time they formed. Beyond the conventional δ18O, information from triple oxygen isotopes (reported as 17O excess , which is defined as (ln (δ17O/1000 + 1) − λ ref ln (δ18O/1000 + 1)) × 106) in these archives promises to be a valuable tool to reconstruct past hydrological processes. The goal of this study is to determine the triple oxygen isotope fractionation between CaCO 3 and H 2 O under well-constrained laboratory conditions. We performed laboratory experiments to precipitate CaCO 3 polymorphs, either calcite or aragonite, at temperatures between 10 and 35 °C. We then evaluated the effect of polymorphism, temperature, and solution concentration on the 17O excess of CO 2 extracted from these carbonates and the 17O isotopic fractionation (17α) between water and CaCO 3. The obtained values of 18α and 17α between CO 2 extracted from CaCO 3 and parent water allow us to calculate the fractionation slope θ (=ln17α/ln18α). Our observations suggest that θ is indistinguishable at temperatures of 10 and 27 °C, but is slightly lower at 35 °C. The lower value at 35 °C may be related to disequilibrium during these experiments. We found that θ is independent of polymorph and of solution concentration, indicating that 17O excess is less sensitive than δ18O to these geochemical parameters and can thus be a robust proxy for reconstructing 17O excess of parent water. • The 17O fractionation between CaCO 3 and its parent water is examined experimentally. • The triple oxygen isotope fractionation slope, (ln17α/ln18α), is similar in calcite and aragonite. • The fractionation slope is independent of temperature at 10, 27 °C but somewhat lower at 35 °C. [ABSTRACT FROM AUTHOR]

δ 18 O in speleothem carbonates is a common archive for paleoclimate on land. Recently, it has been shown that triple oxygen isotopes in CaCO 3 (given as O excess 17 = 10 6 [ ln ⁡ (10 − 3 δ 17 O + 1) − 0.528 (ln ⁡ (10 − 3 δ 18 O + 1) ]) record O excess 17 of its parent water, thus providing additional paleo-hydrology information, primarily about relative humidity. The O 17 fractionation between CaCO 3 and water has been determined in biogenic and synthetic carbonates. In speleothems, however, this fractionation is expected to be modified by kinetic isotope effects associated with CO 2 degassing from cave drip water. Here, we used Soreq Cave as a case study to examine this fractionation and the use of O excess 17 in speleothems as an archive for paleo rainfall composition. We first characterized O excess 17 in rainfall collected above the cave. The O excess 17 value in amount weighted integrated rainfall was 49 per meg, consistent with the low relative humidity at the moisture source of the Eastern Mediterranean Sea. The measured cave water was slightly lower in O excess 17 and higher in δ 18 O relative to rainfall, due to modifications of the infiltrating water by epikarst processes such as evaporation and mixing. O excess 17 in CO 2 extracted from CaCO 3 of modern speleothems was compared to that in modern cave water, to calculate the carbonate-water fractionation slope (θ = ln 17 ⁡ α / ln 18 ⁡ α). The resulting θ in Soreq Cave was 0.5230 ± 0.0002 , consistent with that observed in other carbonates, indicating the lack of significant dis-equilibrium effects in speleothems O excess 17. Hence, the common fractionation slope can be used together with a speleothem-specific α 18 to reconstruct rainfall O excess 17 from speleothem carbonates. Whereas speleothems from a variety of caves can be used through this approach to reconstruct O excess 17 in paleo rainfall, the atmospheric processes that govern rainfall O excess 17 are expected to be region-specific. O excess 17 measurements in ancient Soreq speleothems are expected to reveal potential glacial-interglacial changes in moisture source conditions as well as possible changes in epikarst processes over time. • We examine O excess 17 in Soreq Cave speleothems, cave water, and rainfall. • Rainfall O excess 17 of 49 per meg reflects the low RH over the Mediterranean. • Speleothem-water fractionation slope is similar to that in other carbonates. • Kinetic effects in stalagmite formation do not significantly affect O excess 17. • Speleothems can be used as an archive for rainfall O excess 17 and moisture sources. [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]

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]