scholarly journals Photolytic control of the nitrate stable isotope signal in snow and atmosphere of East Antarctica and implications for reactive nitrogen cycling

2009 ◽  
Vol 9 (3) ◽  
pp. 12559-12596 ◽  
Author(s):  
M. M. Frey ◽  
J. Savarino ◽  
S. Morin ◽  
J. Erbland ◽  
J. M. F. Martins
Keyword(s):  
Isotopic Exchange ◽  
Isotopic Fractionation ◽  
Ice Cores ◽  
Skin Layer ◽  
Reactive Nitrogen ◽  
Lab Experiments ◽  
15N Enrichment ◽  
Oxygen Stable Isotopes ◽  
Significant Enrichment ◽  
Isotopic Signal

Abstract. The nitrogen (δ15N) and triple oxygen (δ17/18O) isotopic composition of nitrate (NO3−) was measured year-round in the atmosphere and snow pits at Dome C (DC, 75.1° S, 123.3° E), and in surface snow on a transect between DC and the coast. Snow pit profiles of δ15N (δ18O) in NO3− show significant enrichment (depletion) of >200 (<40) ‰ compared to the isotopic signal in atmospheric NO3−, whereas post-depositional fractionation in Δ17O(NO3−) is small, allowing reconstruction of past shifts in tropospheric oxidation pathways from ice cores. Assuming a Rayleigh-type process we find in the DC04 (DC07) pit fractionation factors ε of −50±10 (−71±12) ‰, 6±3 (9±2) ‰ and 1±0.2 (2±0.6) ‰, for δ15N, δ18O and Δ17O, respectively. A photolysis model reproduces ε for δ15N within the range of uncertainty at DC and for lab experiments reported by Blunier et al. (2005), suggesting that the current literature value for photolytic isotopic fractionation in snow is significantly underestimated. Depletion of oxygen stable isotopes is attributed to photolysis followed by isotopic exchange with water and hydroxyl radicals. Conversely, 15N enrichment of the NO3− fraction in the snow implies 15N depletion of emissions. Indeed, δ15N in atmospheric NO3− shows a strong decrease from background levels (4.4±6.8‰) to −35.1‰ in spring followed by recovery during summer, consistent with significant snow pack emissions of reactive nitrogen. Field and lab evidence therefore suggest that photolysis dominates fractionation and associated NO3− loss from snow in the low-accumulation regions of the East Antarctic Ice Sheet (EAIS). The Δ17O signature confirms previous coastal measurements that the peak of atmospheric NO3− in spring is of stratospheric origin. After sunrise photolysis drives then redistribution of NO3− from the snowpack photic zone to the atmosphere and a snow surface skin layer, thereby concentrating NO3− at the surface. Little NO3− is exported off the EAIS plateau, still snow emissions from as far as 600 km inland can contribute to the coastal NO3− budget.

scholarly journals Photolysis imprint in the nitrate stable isotope signal in snow and atmosphere of East Antarctica and implications for reactive nitrogen cycling

2009 ◽  
Vol 9 (22) ◽  
pp. 8681-8696 ◽  
Author(s):  
M. M. Frey ◽  
J. Savarino ◽  
S. Morin ◽  
J. Erbland ◽  
J. M. F. Martins
Keyword(s):  
Ice Cores ◽  
High Sensitivity ◽  
Field Measurements ◽  
Skin Layer ◽  
Reactive Nitrogen ◽  
The Earth ◽  
15N Enrichment ◽  
Oxygen Stable Isotopes ◽  
Uv Lamp ◽  
Isotopic Signal

Abstract. The nitrogen (δ15N) and triple oxygen (δ17O and δ18O) isotopic composition of nitrate (NO3−) was measured year-round in the atmosphere and snow pits at Dome C, Antarctica (DC, 75.1° S, 123.3° E), and in surface snow on a transect between DC and the coast. Comparison to the isotopic signal in atmospheric NO3− shows that snow NO3− is significantly enriched in δ15N by >200‰ and depleted in δ18O by <40‰. Post-depositional fractionation in Δ17O(NO3−) is small, potentially allowing reconstruction of past shifts in tropospheric oxidation pathways from ice cores. Assuming a Rayleigh-type process we find fractionation constants ε of −60±15‰, 8±2‰ and 1±1‰, for δ15N, δ18O and Δ17O, respectively. A photolysis model yields an upper limit for the photolytic fractionation constant 15ε of δ15N, consistent with lab and field measurements, and demonstrates a high sensitivity of 15ε to the incident actinic flux spectrum. The photolytic 15ε is process-specific and therefore applies to any snow covered location. Previously published 15ε values are not representative for conditions at the Earth surface, but apply only to the UV lamp used in the reported experiment (Blunier et al., 2005; Jacobi et al., 2006). Depletion of oxygen stable isotopes is attributed to photolysis followed by isotopic exchange with water and hydroxyl radicals. Conversely, 15N enrichment of the NO3− fraction in the snow implies 15N depletion of emissions. Indeed, δ15N in atmospheric NO3− shows a strong decrease from background levels (4±7‰) to −35‰ in spring followed by recovery during summer, consistent with significant snowpack emissions of reactive nitrogen. Field and lab evidence therefore suggest that photolysis is an important process driving fractionation and associated NO3− loss from snow. The Δ17O signature confirms previous coastal measurements that the peak of atmospheric NO3− in spring is of stratospheric origin. After sunrise photolysis drives then redistribution of NO3− from the snowpack photic zone to the atmosphere and a snow surface skin layer, thereby concentrating NO3− at the surface. Little NO3− appears to be exported off the EAIS plateau, still snow emissions from as far as 600 km inland can contribute to the coastal NO3− budget.

scholarly journals O Registro de Isótopos Estáveis de Hidrogênio em Testemunhos de Gelo da Ilha Rei George, Antártica

2000 ◽  
Vol 27 (2) ◽  
pp. 87
Author(s):  
FRANCISCO ADOLFO FERRON ◽  
JEFFERSON CARDIA SIMÕES
Keyword(s):  
Isotopic Exchange ◽  
Isotopic Fractionation ◽  
Ice Cores ◽  
Isotopic Ratios ◽  
King George Island ◽  
The West ◽  
Water Percolation ◽  
Stable Isotopic ◽  
Ice Field ◽  
The Antarctic

The hydrogen stable isotopic record in four ice cores drilled on King George Island ice field (to the west of the Antarctic Peninsula) are examined. Isotopic composition variations are strongly homogenized, exceptly in the few upper meters of cores drilled above 650-m of elevation. Intensive melting followed by water percolation throughout the snow and firn pack lead to isotopic exchange and consequently strong homogenization. A stratigraphic profile showing several ice layers and a water table detected in the glacier strengthen this hypothesis. Isotopic ratios decrease with elevation, reflecting the strong melting and isotopic fractionation in lower areas.

scholarly journals Quantifying the nitrogen isotope effects during photochemical equilibrium between NO and NO<sub>2</sub>: implications for <i>δ</i><sup>15</sup>N in tropospheric reactive nitrogen

2020 ◽  
Vol 20 (16) ◽  
pp. 9805-9819 ◽  
Author(s):  
Jianghanyang Li ◽  
Xuan Zhang ◽  
John Orlando ◽  
Geoffrey Tyndall ◽  
Greg Michalski
Keyword(s):  
Atmospheric Chemistry ◽  
Isotopic Exchange ◽  
Isotope Effects ◽  
Isotopic Fractionation ◽  
Field Measurements ◽  
Nitrogen Isotope ◽  
Dominant Factor ◽  
Reactive Nitrogen ◽  
Fractionation Factor ◽  
The Impact

Abstract. Nitrogen isotope fractionations between nitrogen oxides (NO and NO2) play a significant role in determining the nitrogen isotopic compositions (δ15N) of atmospheric reactive nitrogen. Both the equilibrium isotopic exchange between NO and NO2 molecules and the isotope effects occurring during the NOx photochemical cycle are important, but both are not well constrained. The nighttime and daytime isotopic fractionations between NO and NO2 in an atmospheric simulation chamber at atmospherically relevant NOx levels were measured. Then, the impact of NOx level and NO2 photolysis rate on the combined isotopic fractionation (equilibrium isotopic exchange and photochemical cycle) between NO and NO2 was calculated. It was found that the isotope effects occurring during the NOx photochemical cycle can be described using a single fractionation factor, designated the Leighton cycle isotope effect (LCIE). The results showed that at room temperature, the fractionation factor of nitrogen isotopic exchange is 1.0289±0.0019, and the fractionation factor of LCIE (when O3 solely controls the oxidation from NO to NO2) is 0.990±0.005. The measured LCIE factor showed good agreement with previous field measurements, suggesting that it could be applied in an ambient environment, although future work is needed to assess the isotopic fractionation factors of NO+RO2/HO2→NO2. The results were used to model the NO–NO2 isotopic fractionations under several NOx conditions. The model suggested that isotopic exchange was the dominant factor when NOx>20 nmol mol−1, while LCIE was more important at low NOx concentrations (<1 nmol mol−1) and high rates of NO2 photolysis. These findings provided a useful tool to quantify the isotopic fractionations between tropospheric NO and NO2, which can be applied in future field observations and atmospheric chemistry models.

scholarly journals Air–snow transfer of nitrate on the East Antarctic Plateau – Part 2: An isotopic model for the interpretation of deep ice-core records

2015 ◽  
Vol 15 (20) ◽  
pp. 12079-12113 ◽  
Author(s):  
J. Erbland ◽  
J. Savarino ◽  
S. Morin ◽  
J. L. France ◽  
M. M. Frey ◽  
...  
Keyword(s):  
Mass Fraction ◽  
Ice Core ◽  
Ice Cores ◽  
Reactive Nitrogen ◽  
Antarctic Plateau ◽  
Surface Snow ◽  
Rate Building ◽  
The Antarctic ◽  
The Impact ◽  
Ice Core Records

Abstract. Unraveling the modern budget of reactive nitrogen on the Antarctic Plateau is critical for the interpretation of ice-core records of nitrate. This requires accounting for nitrate recycling processes occurring in near-surface snow and the overlying atmospheric boundary layer. Not only concentration measurements but also isotopic ratios of nitrogen and oxygen in nitrate provide constraints on the processes at play. However, due to the large number of intertwined chemical and physical phenomena involved, numerical modeling is required to test hypotheses in a quantitative manner. Here we introduce the model TRANSITS (TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow), a novel conceptual, multi-layer and one-dimensional model representing the impact of processes operating on nitrate at the air–snow interface on the East Antarctic Plateau, in terms of concentrations (mass fraction) and nitrogen (δ15N) and oxygen isotopic composition (17O excess, Δ17O) in nitrate. At the air–snow interface at Dome C (DC; 75° 06' S, 123° 19' E), the model reproduces well the values of δ15N in atmospheric and surface snow (skin layer) nitrate as well as in the δ15N profile in DC snow, including the observed extraordinary high positive values (around +300 ‰) below 2 cm. The model also captures the observed variability in nitrate mass fraction in the snow. While oxygen data are qualitatively reproduced at the air–snow interface at DC and in East Antarctica, the simulated Δ17O values underestimate the observed Δ17O values by several per mill. This is explained by the simplifications made in the description of the atmospheric cycling and oxidation of NO2 as well as by our lack of understanding of the NOx chemistry at Dome C. The model reproduces well the sensitivity of δ15N, Δ17O and the apparent fractionation constants (15&amp;varepsilon;app, 17Eapp) to the snow accumulation rate. Building on this development, we propose a framework for the interpretation of nitrate records measured from ice cores. Measurement of nitrate mass fractions and δ15N in the nitrate archived in an ice core may be used to derive information about past variations in the total ozone column and/or the primary inputs of nitrate above Antarctica as well as in nitrate trapping efficiency (defined as the ratio between the archived nitrate flux and the primary nitrate input flux). The Δ17O of nitrate could then be corrected from the impact of cage recombination effects associated with the photolysis of nitrate in snow. Past changes in the relative contributions of the Δ17O in the primary inputs of nitrate and the Δ17O in the locally cycled NO2 and that inherited from the additional O atom in the oxidation of NO2 could then be determined. Therefore, information about the past variations in the local and long-range processes operating on reactive nitrogen species could be obtained from ice cores collected in low-accumulation regions such as the Antarctic Plateau.

scholarly journals Determination of respiration and photosynthesis fractionation coefficients for atmospheric dioxygen inferred from a vegetation-soil-atmosphere analog of the terrestrial biosphere in closed chambers

2021 ◽  
Author(s):  
Clémence Paul ◽  
Clément Piel ◽  
Joana Sauze ◽  
Nicolas Pasquier ◽  
Frédéric Prié ◽  
...  
Keyword(s):  
Festuca Arundinacea ◽  
Dark Respiration ◽  
Relative Concentration ◽  
Ice Core ◽  
Isotopic Fractionation ◽  
Ice Cores ◽  
Terrestrial Biosphere ◽  
Soil Atmosphere ◽  
Photosynthetic Fractionation ◽  
Closed Chambers

Abstract. The isotopic composition of dioxygen in the atmosphere is a global tracer which depends on the biosphere flux of dioxygen toward and from the atmosphere (photosynthesis and respiration) as well as exchanges with the stratosphere. When measured in fossil air trapped in ice cores, the relative concentration of 16O, 17O and 18O of O2 can be used for several applications such as ice core dating and past global productivity reconstruction. However, there are still uncertainties about the accuracy of these tracers as they depend on the integrated isotopic fractionation of different biological processes of dioxygen production and uptake, for which we currently have very few independent estimates. Here we determined the respiration and photosynthesis fractionation coefficients for atmospheric dioxygen from experiments carried out in a replicated vegetation-soil-atmosphere analog of the terrestrial biosphere in closed chambers with growing Festuca arundinacea. The values for 18O discrimination during soil respiration and dark respiration in leave are equal to −12.3 ± 1.7 ‰ and −19.1 ± 2.4 ‰, respectively. We also found a value for terrestrial photosynthetic fractionation equal to +3.7 ± 1.3 ‰. This last estimate suggests that the contribution of terrestrial productivity in the Dole effect may have been underestimated in previous studies.

scholarly journals New insights into the ~74 ka Toba eruption from sulfur isotopes of polar ice cores

2021 ◽  
Author(s):  
Laura Crick ◽  
Andrea Burke ◽  
William Hutchison ◽  
Stephen Sparks ◽  
Sue Mahony ◽  
...  
Keyword(s):  
Inductively Coupled Plasma ◽  
Sulfur Isotopes ◽  
Ice Core ◽  
Isotopic Fractionation ◽  
Ice Cores ◽  
Photochemical Reactions ◽  
Quaternary Period ◽  
Inductively Coupled ◽  
Precise Timing ◽  
Volcanic Events

&lt;p&gt;The ~74ka Toba eruption in Indonesia was one of the largest volcanic events of the Quaternary and loaded an estimated 100 million tonnes of H&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt; into the atmosphere. Understanding the precise timing of this colossal eruption is vital to unravelling the climatic and environmental impacts of the largest volcanic events on Earth. Sulfur aerosols injected into the stratosphere following large volcanic events scatter incoming radiation and lead to global cooling, and in the case of Toba it has been suggested that it led to cooling of 1 &amp;#8211; 5&amp;#176;C and extinctions of some local hominin populations. One of the most enigmatic features of the Toba eruption is that the S peak has yet to be identified in the ice core records, although numerous candidate sulfate peaks have been identified in both Arctic and Antarctic ice cores. To address this, we analysed the sulfur isotope fingerprint (&amp;#948;&lt;sup&gt;34&lt;/sup&gt;S and &amp;#916;&lt;sup&gt;33&lt;/sup&gt;S) of 11 Toba candidates from two Antarctic ice cores by multi-collector inductively coupled plasma mass spectrometry. This approach allows us to evaluate injection altitudes and to distinguish large tropical eruptions from proximal eruptions because stratospheric sulfur aerosols undergo UV photochemical reactions that impart a sulfur mass-independent isotopic fractionation (S-MIF). In contrast, tropospheric sulfur aerosols do not exhibit S-MIF because they are shielded from the relevant UV radiation by the ozone layer.&lt;/p&gt;&lt;p&gt;We identify three stratospheric, tropical eruption candidates with two recording the largest &amp;#916;&lt;sup&gt;33&lt;/sup&gt;S signals measured to date in the ice core archives. The largest of these &amp;#916;&lt;sup&gt;33&lt;/sup&gt;S signals is &gt;2 &amp;#8240; more negative than previous measurements of the 1257 Samalas eruption (the largest eruption of the last 2000 years), despite having a similar integrated sulfate flux for this event to the ice core. These three candidates are within uncertainly of the Ar&lt;sup&gt;40&lt;/sup&gt;/Ar&lt;sup&gt;39 &lt;/sup&gt;age estimates for the Toba eruption and when considered with other paleoclimate proxies place the event during the transition into Greenland Stadial 20. &amp;#160;Finally, we further analyse the relationship between the Toba eruption candidates and these proxies to determine the precise timing and potential climatic impacts of one of the largest eruptions of the Quaternary period.&lt;/p&gt;

scholarly journals An introduction to stable water isotopes in climate models: benefits of forward proxy modelling for paleoclimatology

2010 ◽  
Vol 6 (1) ◽  
pp. 115-129 ◽  
Author(s):  
C. Sturm ◽  
Q. Zhang ◽  
D. Noone
Keyword(s):  
Atmospheric Circulation ◽  
Climate Models ◽  
Regional Climate ◽  
Isotopic Fractionation ◽  
Water Isotopes ◽  
Mean Annual Temperature ◽  
Stable Water Isotopes ◽  
Wide Range ◽  
Precipitation Seasonality ◽  
Isotopic Signal

Abstract. Stable water isotopes have been measured in a wide range of climate archives, with the purpose of reconstructing regional climate variations. Yet the common assumption that the isotopic signal is a direct indicator of temperature proves to be misleading under certain circumstances, since its relationship with temperature also depends on e.g. atmospheric circulation and precipitation seasonality. Here we introduce the principles, benefits and caveats of using climate models with embedded water isotopes as a support for the interpretation of isotopic climate archives. A short overview of the limitations of empirical calibrations of isotopic proxy records is presented. In some cases, the underlying hypotheses are not fulfilled and the calibration contradicts the physical interpretation of isotopic fractionation. The simulation of climate and its associated isotopic signal, despite difficulties related to downscaling and intrinsic atmospheric variability, can provide a "transfer function" between the isotopic signal and the considered climate variable. The relationship between modelled temperature and isotopic signal is analysed under present-day, pre-industrial and mid-Holocene conditions. The linear regression relationship is statistically more significant for precipitation-weighted annual temperature than mean annual temperature, yet the regression slope varies greatly between the time-slice experiments. Temperature reconstructions that do not account for the slope variations will in this case underestimate the low-frequency variability and overestimate high-frequency variability from the isotopic proxy record. The spatial variability of the simulated δ18O-temperature slope further indicates that the isotopic signal is primarily controlled by synoptic atmospheric circulation rather than local temperature.

scholarly journals Surface-atmosphere decoupling limits accumulation at Summit, Greenland

2016 ◽  
Vol 2 (4) ◽  
pp. e1501704 ◽  
Author(s):  
Max Berkelhammer ◽  
David C. Noone ◽  
Hans Christian Steen-Larsen ◽  
Adriana Bailey ◽  
Christopher J. Cox ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Moisture Flux ◽  
Blowing Snow ◽  
Direct Observations ◽  
Surface Condensation ◽  
Significant Area ◽  
Isotopic Signal

Despite rapid melting in the coastal regions of the Greenland Ice Sheet, a significant area (~40%) of the ice sheet rarely experiences surface melting. In these regions, the controls on annual accumulation are poorly constrained owing to surface conditions (for example, surface clouds, blowing snow, and surface inversions), which render moisture flux estimates from myriad approaches (that is, eddy covariance, remote sensing, and direct observations) highly uncertain. Accumulation is partially determined by the temperature dependence of saturation vapor pressure, which influences the maximum humidity of air parcels reaching the ice sheet interior. However, independent proxies for surface temperature and accumulation from ice cores show that the response of accumulation to temperature is variable and not generally consistent with a purely thermodynamic control. Using three years of stable water vapor isotope profiles from a high altitude site on the Greenland Ice Sheet, we show that as the boundary layer becomes increasingly stable, a decoupling between the ice sheet and atmosphere occurs. The limited interaction between the ice sheet surface and free tropospheric air reduces the capacity for surface condensation to achieve the rate set by the humidity of the air parcels reaching interior Greenland. The isolation of the surface also acts to recycle sublimated moisture by recondensing it onto fog particles, which returns the moisture back to the surface through gravitational settling. The observations highlight a unique mechanism by which ice sheet mass is conserved, which has implications for understanding both past and future changes in accumulation rate and the isotopic signal in ice cores from Greenland.

Stable-isotope pattern predicted in surge-type glaciers

1988 ◽  
Vol 25 (5) ◽  
pp. 657-668 ◽  
Author(s):  
E. D. Waddington ◽  
G. K. C. Clarke
Keyword(s):  
Stable Isotope ◽  
Background Noise ◽  
Ice Cores ◽  
Stable Isotope Ratio ◽  
Yukon Territory ◽  
Ice Streams ◽  
Ice Flow ◽  
Order Of Magnitude ◽  
Longitudinal Sampling ◽  
Isotopic Signal

The distribution pattern of stable-isotope ratio δ18O in cold glaciers, ice streams, and ice sheets has the potential to reveal past changes in flow rate, for example those associated with surges. In this study, we use a time-dependent numerical model of ice flow to establish that each surge creates a stratigraphic horizon across which δ18O is discontinuous. Two plausible relations between glacier geometry and δ18O in snowfall allow us to bracket the expected magnitude of this isotopic signal. These stratigraphic markers could be located by δ18O analysis of a longitudinal series of ice cores or by detailed longitudinal sampling of exposed ice.Calculations for a model with characteristics resembling those of Steele Glacier, Yukon Territory, showed that at most three stratigraphic markers could be detected at any one time. The discontinuities in δ18O were as large as 0.8‰. This is an order of magnitude larger than mass spectrometer precision but comparable to observed background noise at Steele Glacier.

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