scholarly journals <sup>2</sup>H and <sup>18</sup>O depletion of water close to organic surfaces

2016 ◽  
Vol 13 (10) ◽  
pp. 3175-3186 ◽  
Author(s):  
Guo Chen ◽  
Karl Auerswald ◽  
Hans Schnyder
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Filter Paper ◽  
Surface Effect ◽  
Isotope Composition ◽  
Isotopic Fractionation ◽  
Adsorbed Water ◽  
Organic Soil ◽  
Surface Areas ◽  
Isotope Composition Of Water

Abstract. Hydrophilic surfaces influence the structure of water close to them and may thus affect the isotope composition of water. Such an effect should be relevant and detectable for materials with large surface areas and low water contents. The relationship between the volumetric solid : water ratio and the isotopic fractionation between adsorbed water and unconfined water was investigated for the materials silage, hay, organic soil (litter), filter paper, cotton, casein and flour. Each of these materials was equilibrated via the gas phase with unconfined water of known isotopic composition to quantify the isotopic difference between adsorbed water and unconfined water. Across all materials, isotopic fractionation was significant (p<0.05) and negative (on average −0.91 ± 0.22 ‰ for 18∕16O and −20.6 ± 2.4 ‰ for 2∕1H at an average solid : water ratio of 0.9). The observed isotopic fractionation was not caused by solutes, volatiles or old water because the fractionation did not disappear for washed or oven-dried silage, the isotopic fractionation was also found in filter paper and cotton, and the fractionation was independent of the isotopic composition of the unconfined water. Isotopic fractionation became linearly more negative with increasing volumetric solid : water ratio and even exceeded −4 ‰ for 18∕16O and −44 ‰ for 2∕1H. This fractionation behaviour could be modelled by assuming two water layers: a thin layer that is in direct contact and influenced by the surface of the solid and a second layer of varying thickness depending on the total moisture content that is in equilibrium with the surrounding vapour. When we applied the model to soil water under grassland, the soil water extracted from 7 and 20 cm depth was significantly closer to local meteoric water than without correction for the surface effect. This study has major implications for the interpretation of the isotopic composition of water extracted from organic matter, especially when the volumetric solid : water ratio is larger than 0.5 or for processes occurring at the solid–water interface.

scholarly journals Isotopic offset between unconfined water and water adsorbed to organic matter in equilibrium

2016 ◽  
Author(s):  
Guo Chen ◽  
Karl Auerswald ◽  
Hans Schnyder
Keyword(s):  
Organic Matter ◽  
Isotopic Composition ◽  
Soil Water ◽  
Filter Paper ◽  
Surface Effect ◽  
Isotope Composition ◽  
Adsorbed Water ◽  
Organic Soil ◽  
Surface Areas ◽  
Isotope Composition Of Water

Abstract. Hydrophilic surfaces influence the structure of water close to them and may thus affect the isotope composition of water. Such an effect should be relevant and detectable for materials with large surface areas and low water contents. The relationship between the volumetric solid:water ratio and the enrichment of heavy isotopes in adsorbed water compared with unconfined water was investigated for the materials silage, hay, organic soil (litter), filter paper, cotton, casein and flour. Each of these materials was equilibrated via the gas phase with unconfined water of known isotopic composition to quantify the isotopic difference between adsorbed water and unconfined water. Across all materials, enrichment of the adsorbed water was significant and negative (on average −0.91 ‰ for 18O and −20.6 ‰ for 2H at an average solid:water ratio of 0.9). The observed enrichment was not caused by solutes, volatiles or old water because the enrichment did not disappear for washed or oven dried silage, the enrichment was also found in filter paper and cotton, and the enrichment was independent of the isotopic composition of the unconfined water. Enrichment became linearly more negative with increasing volumetric solid:water ratio and even exceeded −4 ‰ for 18O and −44 ‰ for 2H. This enrichment behavior could be modeled by assuming two water layers: a thin layer that is in direct contact and influenced by the surface of the solid and a second layer of varying thickness depending on the total moisture content that is in equilibrium with the surrounding vapor. When we applied the model to soil water under grassland, the soil water extracted from 7 cm and 20 cm depth was significantly closer to local meteoric water than without correction for the surface effect. This study has major implications for the interpretation of the isotopic composition of water extracted from organic matter, especially when the volumetric solid:water ratio is larger than 0.5 or for processes occurring at the solid-water interface.

Stable carbon isotope analysis of faecal and blood samples of sheep in relation to the diet

2003 ◽  
Vol 2003 ◽  
pp. 159-159
Author(s):  
A. Balcaen ◽  
E. Claeys ◽  
V. Fievez ◽  
P. Boeckx ◽  
O. van Cleemput ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Carbon Isotope ◽  
Carbon Fixation ◽  
Isotope Composition ◽  
Stable Carbon Isotope ◽  
Isotope Analysis ◽  
Calvin Cycle ◽  
Isotopic Fractionation ◽  
Woody Species ◽  
Stable Carbon

Stable isotopes have been extraordinarily helpful in understanding animal migration, diet, food webs and nutrient flow (Hilderbrand et al., 1996), based on the property that C3 and C4 plants possess distinctly different 13C/12C ratios (δ13C value) due to isotopic fractionation during photosynthetic carbon fixation (Smith & Epstein, 1971). Most woody species and temperate graminoids assimilate carbon via the Calvin cycle (C3), which discriminates stronger against the heavier isotope (13C) than Hatch-Slack (C4) species (tropical and subtropical graminoids and some shrubs). C3 and C4 plant species have mean δ13C values of -27 ‰ and -13 ‰ respectively (O’Leary, 1981). DeNiro & Epstein (1978) were one of the first to show that the isotopic composition of the whole animal body is similar to that of its diet. Other authors have also found relationships between the isotopic composition of animal tissues and the diet (González-Martin et al., 1999; Jones et al., 1979). The aim of this study was to investigate stable carbon isotope composition in sheep fed diets consisting of either C3 or C3+C4 plants.

scholarly journals Combination of soil water extraction methods quantifies isotopic mixing of waters held at separate tensions in soil

2020 ◽  
Author(s):  
William H. Bowers ◽  
Jason J. Mercer ◽  
Mark S. Pleasants ◽  
David G. Williams
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Isotope Exchange ◽  
Sandy Loam ◽  
Isotope Composition ◽  
Chemical Properties ◽  
Mixing Model ◽  
Time Dependent ◽  
High Tension ◽  
Isotopic Mixing

Abstract. Measurements of the isotopic composition of water recovered from soil at different tensions provide a powerful means to identify potential plant water sources and quantify heterogeneity in residence time and connectivity among soil water regions. Yet incomplete understanding of mechanisms affecting isotopic composition of different soil water pools and the interactions between antecedent and new event water hinders interpretation of the isotope composition of extracted soil and plant waters. Here we present an approach for quantifying the time-dependent isotopic mixing of water held at separate tensions in soil. We wetted oven-dried, homogenized sandy loam soil first with isotopically “light” water (𝛿2H = −130 ‰; 𝛿18O = −17.6 ‰) using a sufficient volume to fill only the smallest soil pores, and then with “heavy” water (𝛿2H = −44 ‰; 𝛿18O = −7.8 ‰) to fully saturate the remaining soil regions. Soil water effluents were then sequentially extracted at three tensions (low centrifugation = 0.016 MPa; medium centrifugation = 1.14 MPa; and high cryogenic vacuum distillation at an estimated tension greater than 100 MPa) starting after variable equilibration periods of 0 h, 8 h, 1 d, 3 d and 7 d. We assessed differences in the isotopic composition of extracted effluents over the 7 d equilibration period with a MANOVA and a mixing model describing the time-dependent effects of isotope self-diffusion and exchange. The saturated moisture conditions used in our experiment likely facilitated rapid isotope exchange and equilibration among different pools. Despite this, the isotope composition of waters extracted at medium compared to high tension remained significantly different (MANOVA) for up to 1 day, and that for waters extracted at low compared to high tension remained significantly different for greater than 3 days after soil wetting. Equilibration (assuming no fractionation) predicted from the time-dependent mixing model for water held at high tension occurred after approximately 4.33 days. Our approach will be useful for assessing how soil texture and other physical and chemical properties influence isotope exchange and mixing times for studies aiming to properly characterize and interpret the isotopic composition of extracted soil and plant waters, especially under variably unsaturated conditions.

Stable isotope composition of walleye: 15N accumulation with age and area-specific differences in δ13C

2001 ◽  
Vol 58 (6) ◽  
pp. 1253-1260 ◽  
Author(s):  
Nathanael C Overman ◽  
Donna L Parrish
Keyword(s):  
Stable Isotope ◽  
Isotopic Composition ◽  
Carbon Isotope ◽  
Trophic Position ◽  
Isotope Composition ◽  
Isotope Analysis ◽  
Isotopic Fractionation ◽  
Stomach Content Analysis ◽  
Metabolic Effects ◽  
N Accumulation

Stable nitrogen and carbon isotope ratios were measured for walleye (Stizostedion vitreum) collected across Lake Champlain, Vermont, to determine relationships between isotopic composition and diet, location of capture, length, weight, and age. Variation in δ13C values reflected area-specific differences in isotopic composition of organisms collected across the lake. A critical assumption in the application of isotope techniques is that a predictable relationship exists between the diet and isotopic composition of an organism. Our results indicate that isotopic fractionation factors may not be independent of age as has largely been assumed. By combining stable nitrogen and carbon isotope analysis with conventional stomach content analysis, we documented significant age effects in the δ15N composition of adult walleye that were not attributable to observed changes in diet. Age accounted for 81% of the variation in δ15N values of walleye (ages 2–27, N = 65, δ15N range = 15.3–19.2‰), providing evidence supporting 15N accumulation over the life span of walleye. Therefore, the risk of making faulty inferences of trophic position and food web interactions based on δ15N values may be increased when age is unknown. Our results indicate that metabolic effects associated with age require greater consideration in applications of stable isotope analysis.

scholarly journals A combination of soil water extraction methods quantifies the isotopic mixing of waters held at separate tensions in soil

2020 ◽  
Vol 24 (8) ◽  
pp. 4045-4060 ◽  
Author(s):  
William H. Bowers ◽  
Jason J. Mercer ◽  
Mark S. Pleasants ◽  
David G. Williams
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Sandy Loam ◽  
Isotope Composition ◽  
Chemical Properties ◽  
Extraction Methods ◽  
Time Dependent ◽  
High Tension ◽  
Release Curve ◽  
Isotopic Mixing

Abstract. Measurements of the isotopic composition of separate and potentially interacting pools of soil water provide a powerful means to precisely resolve plant water sources and quantify water residence time and connectivity among soil water regions during recharge events. Here we present an approach for quantifying the time-dependent isotopic mixing of water recovered at separate suction pressures or tensions in soil over an entire moisture release curve. We wetted oven-dried, homogenized sandy loam soil first with isotopically “light” water (δ2H =-130 ‰; δ18O =-17.6 ‰) to represent antecedent moisture held at high matric tension. We then brought the soil to near saturation with “heavy” water (δ2H =-44 ‰; δ18O =-7.8 ‰) that represented new input water. Soil water samples were subsequently sequentially extracted at three tensions (“low-tension” centrifugation ≈0.016 MPa; “mid-tension” centrifugation ≈1.14 MPa; and “high-tension” cryogenic vacuum distillation at an estimated tension greater than 100 MPa) after variable equilibration periods of 0 h, 8 h, 1 d, 3 d, and 7 d. We assessed the differences in the isotopic composition of extracted water over the 7 d equilibration period with a MANOVA and a model quantifying the time-dependent isotopic mixing of water towards equilibrium via self-diffusion. The simplified and homogenous soil structure and nearly saturated moisture conditions used in our experiment likely facilitated rapid isotope mixing and equilibration among antecedent and new input water. Despite this, the isotope composition of waters extracted at mid compared with high tension remained significantly different for up to 1 d, and waters extracted at low compared with high tension remained significantly different for longer than 3 d. Complete mixing (assuming no fractionation) for the pool of water extracted at high tension occurred after approximately 4.33 d. Our combination approach involving the extraction of water over different domains of the moisture release curve will be useful for assessing how soil texture and other physical and chemical properties influence isotope exchange and mixing times for studies aiming to properly characterize and interpret the isotopic composition of extracted soil and plant waters, especially under variably unsaturated conditions.

scholarly journals Evidence for distinct isotopic composition of sap and tissue water in tree stems: consequences for plant water source identification

2020 ◽  
Author(s):  
Adrià Barbeta ◽  
Régis Burlett ◽  
Paula Martín-Gómez ◽  
Bastien Fréjaville ◽  
Nicolas Devert ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Water Cycle ◽  
Isotopic Fractionation ◽  
Water Source ◽  
Source Water ◽  
Plant Water ◽  
Stem Water ◽  
Micrometer Scale ◽  
Water Isotope

AbstractFor decades, theory has upheld that plants do not fractionate water isotopes as they move across the soil-root interface or along plant stems. This theory is now being challenged by several recent studies reporting that the water held in woody stems has an isotopic composition that cannot be attributed to any potential water source. Isotopic offsets between stem and source water still need to be explained, as they prevent identifying unambiguously tree water’s origin from water isotope measurements. Here we show that isotopic offsets between stem and source water can be explained by micrometer-scale water isotope heterogeneity within woody stems and soil micropores. Using a novel technique to extract sap water in xylem conduits separately from the water held in other xylem tissues, we show that these non-conductive xylem tissues are more depleted in deuterium than sap water. We also report that, in cut stems and well-watered potted plants, the isotopic composition of sap water reflects well that of irrigation water, demonstrating that no isotopic fractionation occurs during root water uptake or the sap water extraction process. Previous studies showed that isotopic heterogeneity also exists in soils at the pore scale where water adsorbed onto soil particles is more depleted than capillary/mobile soil water. Data collected at a beech (Fagus sylvatica) forest indicate that sap water matches best the capillary/mobile soil water from deep soil horizons, indicating that micrometer-scale water isotope heterogeneity in soils and stems must be accounted for to unambiguously identify where trees obtain their water within catchments.Significance StatementForests are prime regulators of the water cycle over land. They return, via transpiration, a large fraction of precipitation back to the atmosphere, influence surface runoff, groundwater recharge or stream flow, and enhance the recycling of atmospheric moisture inland from the ocean. The isotopic composition of water in woody stems can provide unique information on the role forests play in the water cycle only if it can be unambiguously related to the isotopic composition of source water. Here, we report a previously overlooked isotopic fractionation of stem water whereby non-conductive tissues are more depleted in deuterium than sap water, and propose a new technique to extract sap water separately from bulk stem water to unambiguously identify plant water sources.

scholarly journals Stratospheric carbon isotope fractionation and tropospheric histories of CFC-11, CFC-12 and CFC-113 isotopologues

2020 ◽  
Author(s):  
Max Thomas ◽  
Johannes C. Laube ◽  
Jan Kaiser ◽  
Samuel Allin ◽  
Patricia Martinerie ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Carbon Isotope ◽  
Ozone Depletion ◽  
Isotope Composition ◽  
Stratospheric Ozone ◽  
Isotopic Fractionation ◽  
Base Case ◽  
Model Base ◽  
The Difference ◽  
First Time

Abstract. We present novel measurements of the carbon isotope composition of CFC-11 (CCl3F), CFC-12 (CCl2F2), and CFC-113 (CF2ClCFCl2), three atmospheric trace gases that are important for both stratospheric ozone depletion and global warming. These measurements were carried out on air samples collected in the stratosphere – the main sink region for these gases – and on air extracted from deep polar firn snow. We quantify, for the first time, the apparent isotopic fractionation, εapp(13C), for these gases as they are destroyed in the high- and mid-latitude stratosphere: εapp(CFC-12, high-lat) = (−20.2 ± 4.4) ‰ and εapp(CFC-113, high-lat) = (−9.4 ± 4.4) ‰, εapp(CFC-12, mid-lat) = (−30.3 ± 10.7) ‰, and εapp(CFC-113, mid-lat) = (−34.4 ± 9.8) ‰. Our CFC-11 measurements were not sufficient to calculate εapp(CFC-11) so we instead used previously reported photolytic fractionation for CFC-11 and CFC-12 to scale our εapp(CFC-12), resulting in εapp(CFC-11, high-lat) = (−7.8 ± 1.7) ‰ and εapp(CFC-11, mid-lat) = (−11.7 ± 4.2) ‰. Measurements of firn air were used to construct histories of the tropospheric isotopic composition, δT(13C), for CFC-11 (1950s to 2009), CFC-12 (1950s to 2009), and CFC-113 (1970s to 2009) – with δT(13C) increasing for each gas. We used εapp(high-lat), which were derived from more data, and a constant isotopic composition of emissions, δE(13C), to model δT(13C, CFC-11), δT(13C, CFC-12), and δT(13C, CFC-113). For CFC-11 and CFC-12, modelled δT(13C) was consistent with measured δT(13C) for the entire period covered by the measurements, suggesting no dramatic change in δE(13C, CFC-11) or δE(13C, CFC-12) has occurred since the 1950s. For CFC-113, our modelled δT(13C, CFC-113) did not agree with our measurements earlier than 1980. While this discrepancy may be indicative of a change in δE(13C, CFC-113), it is premature to assign one. Our modelling predicts increasing δT(13C, CFC-11), δT(13C, CFC-12), and δT(13C, CFC-113) into the future. We investigated the effect of recently reported new CFC-11 emissions on background δT(13C, CFC-11) by fixing model emissions after 2012, and comparing δT(13C, CFC-11) in this scenario to the model base case. The difference in δT(13C, CFC-11) between these scenarios was 1.4 ‰ in 2050. This difference is smaller than our model uncertainty envelope and would therefore require improved modelling and measurement precision, as well as better quantified isotopic source compositions, to detect.

Development of cryogenic extraction system for δ18O and δ2H measurement of water in soils and plants.

2021 ◽  
Author(s):  
Nunzio Romano ◽  
Carolina Allocca ◽  
Luisa Stellato ◽  
Fabio Marzaioli ◽  
Paolo Nasta
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Isotope Composition ◽  
Isotopic Ratio ◽  
Plant Root ◽  
Root Water Uptake ◽  
Vacuum System ◽  
Operational Parameters ◽  
Vacuum Equipment ◽  
Preliminary Results

&lt;p&gt;The stable isotope composition of water (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H) represents a useful tool to distinguish among different water pools along the soil-plant-atmosphere continuum. Using &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O as tracers helps gain a better understanding of plant root water uptake and dominant ecohydrological processes. To determine which pools of water are used for plant physiologic functions and returned to the atmosphere by transpiration, a common approach is to analyze the isotopic composition of water in both soil and plant. Cryogenic water extraction (CWE; Orlowski et al., 2016) is the most widely used laboratory-based technique to extract water from soil samples for isotopic analysis. However, recent studies have shown that the extraction conditions (time, temperature, and vacuum) and soil physical and chemical properties may affect the extracted soil-water isotope composition even significantly.&lt;/p&gt;&lt;p&gt;We have developed an efficient and cost-effective cryogenic vacuum equipment to extract water from soil or vegetation and this presentation aims at discussing some preliminary results. The equipment has been specifically designed to meet the following requirements: i) enable to quantify the accuracy of a CWE continuous flow extraction line, and ii) identify a specific extraction standard protocol for soil and vegetation samples. Two experiments have been carried out to evaluate the isotope fractionation induced by the system and how different operational parameters (i.e. times and temperature of extraction) can affect the results. Firstly, a known water isotopic ratio was processed by the vacuum system to determine the measurement accuracy and reproducibility by comparing pre- and post-processed water isotopic signatures. The likely causes of observed biases induced by sample processing are assessed and a relevant correction procedure is suggested. Subsequently, measurements were carried out on replicated samples taken from two differently-textured soils that, after being dried, were saturated in the laboratory up to different water content values with water of known isotopic composition. Also, plant samples were collected from plants grown in a greenhouse and irrigated with water of known isotopic composition.&lt;/p&gt;&lt;p&gt;Water from all samples was extracted by our CWE system and then analyzed using an isotope ratio mass spectrometer in Gas Bench mode for analyses and in temperature conversion elemental analysis (TC/EA) mode for. Preliminary results have quantified the isotope fractions on average of -1.6 &amp;#8240; for &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and 14.2 &amp;#8240; for &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H. Normalization of stable isotopes from unknown samples according to observed fractionation has enabled the observed bias to become virtually zero, leading to a replicate reproducibility of &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H for soil water of 0.6 &amp;#8240; and 3 &amp;#8240;, respectively. The analyses carried out up to now did not find statistical evidence that the soil types and soil-water contents may affect the extraction method and the accuracy of our protocol.&lt;/p&gt;

A simple glasshouse experiment to test the isotopic fractionation in olive trees

2021 ◽  
Author(s):  
Anam Amin ◽  
Giulia Zuecco ◽  
Chiara Marchina ◽  
Michael Engel ◽  
Daniele Penna ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Isotopic Composition ◽  
Soil Water ◽  
Water Uptake ◽  
Vacuum Distillation ◽  
Isotopic Fractionation ◽  
Plant Water ◽  
Cryogenic Vacuum ◽  
Olive Trees ◽  
Uptake And Transport

&lt;p&gt;Plant transpiration is a main component of the global water cycle and plays a key role in regulating ecohydrological process. Stable isotopes of oxygen and hydrogen are often used for the identification and quantification of plant water sources in ecohydrology. However, the isotopic tracing technique assumes that the isotopic signal in the water taken up by the plants remains unaltered during uptake at the soil-roots interface and transport to the distal twigs, i.e., isotopic fractionation does not occur during the water uptake and along the transport pathway. Nevertheless, recent studies showed that isotopic fractionation can occur under different environmental conditions. In this study, we performed a simple experiment with two olive (&lt;em&gt;Olea europaea&lt;/em&gt;) trees utilizing labelled water to test isotopic fractionation of plant water during uptake and transport within the plants under controlled conditions. In addition, we performed the cryogenic vacuum distillation in two different laboratories to examine any possible effects of the extraction system on the isotopic composition of plant water extracts.&lt;/p&gt;&lt;p&gt;We set up the olive trees in pots inside a glasshouse and measured sap flow rates with Granier thermal dissipation probe, and shallow soil moisture by using a portable soil moisture probe. Air temperature, global solar radiation, and relative humidity were measured by a weather station installed inside the glasshouse nearby the olive trees. We irrigated the two plants with water of known isotopic composition and sampled the twigs, wood cores, roots, and soils at different depths (0-5, 5-15, and 15-25 cm). We extracted plant and soil waters by means of cryogenic vacuum distillation performed in two different laboratories.&lt;/p&gt;&lt;p&gt;Our results showed that the plant water samples reflected the isotopic signature of labelled water and mobile soil water, suggesting no isotopic fractionation during water transport. No significant differences were detected for twigs and wood cores extracted from distinct sections of the tree. However, only significant differences were obtained between plant tissue water (twigs, cores) and cryogenically-extracted deep soil water (i.e., &gt;15 cm depths). Furthermore, we found no significant effects of the two cryogenic extraction systems on the isotopic composition of water extracts. Our results indicate that isotopic fractionation might not occur during root water uptake and transport processes in olive trees, at least under the specified experimental conditions, validating the conventional isotope-tracing approach. Further work both in the field and under controlled conditions, and on different plant species, is needed to check for this consistency, as well as testing other plant water extraction methods.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Keywords: olive tree; stable isotope analysis; plant water; cryogenic vacuum distillation; fractionation; labelled water.&lt;/p&gt;

scholarly journals Atmospheric Effects on the Isotopic Composition of Ozone

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1673
Author(s):  
Mao-Chang Liang ◽  
Yi-Chun Chen ◽  
Yi-Qin Gao ◽  
Xi Zhang ◽  
Yuk L. Yung
Keyword(s):  
Isotopic Composition ◽  
Isotope Composition ◽  
Laboratory Data ◽  
Isotopic Fractionation ◽  
Isotopic Signature ◽  
Atmospheric Effects ◽  
Ozone Sensitivity ◽  
Sensitivity Studies ◽  
Oxygen Isotopic ◽  
The Difference

The delta values of the isotope composition of atmospheric ozone is ~100‰ (referenced to atmospheric O2). Previous photochemical models, which considered the isotope fractionation processes from both formation and photolysis of ozone, predicted δ49O3 and δ50O3 values, in δ49O3 versus δ50O3 space, that are >10‰ larger than the measurements. We propose that the difference between the model and observations could be explained either by the temperature variation, Chappuis band photolysis, or a combination of the two and examine them. The isotopic fractionation associated with ozone formation increases with temperature. Our model shows that a hypothetical reduction of ~20 K in the nominal temperature profile could reproduce the observations. However, this hypothesis is not consistent with temperatures obtained by in situ measurements and NCEP Reanalysis. Photolysis of O3 in the Chappuis band causes O3 to be isotopically depleted, which is supported by laboratory measurements for 18O18O18O but not by recent new laboratory data made at several wavelengths for 49O3 and 50O3. Cloud reflection can significantly enhance the photolysis rate and affect the spectral distribution of photons, which could influence the isotopic composition of ozone. Sensitivity studies that modify the isotopic composition of ozone by the above two mechanisms are presented. We conclude isotopic fractionation occurring in photolysis in the Chappuis band remains the most plausible solution to the model-observation discrepancy. Implications of our results for using the oxygen isotopic signature for constraining atmospheric chemical processes related to ozone, such as CO2, nitrate, and the hydroxyl radical, are discussed.

Sign in / Sign up

Export Citation Format

Share Document