scholarly journals Continuous measurements of isotopic composition of water vapour on the East Antarctic Plateau

2016 ◽  
Author(s):  
Mathieu Casado ◽  
Amaelle Landais ◽  
Valérie Masson-Delmotte ◽  
Christophe Genthon ◽  
Erik Kerstel ◽  
...  
Keyword(s):  
Infrared Spectroscopy ◽  
Surface Water ◽  
Isotopic Composition ◽  
Water Vapour ◽  
Isotopic Fractionation ◽  
Ice Cores ◽  
Strong Impact ◽  
Diurnal Cycles ◽  
Surface Snow ◽  
Dry Conditions

Abstract. Water stable isotopes in central Antarctic ice cores are critical to quantify past temperature changes. Accurate temperature reconstructions require to understand the processes controlling surface snow isotopic composition. Isotopic fractionation processes occurring in the atmosphere and controlling snowfall isotopic composition are well understood theoretically and implemented in atmospheric models. However, post-deposition processes are poorly documented and understood. To quantitatively interpret the isotopic composition of water archived in ice cores, it is thus essential to study the continuum between surface water vapour, precipitation, surface snow and buried snow. Here, we target the isotopic composition of surface snow, precipitation and water vapour at Concordia Station, where the oldest EPICA Dome C ice cores have been retrieved. While snowfall and surface snow sampling is routinely performed, accurate measurements of surface water vapour are challenging in such cold and dry conditions. New developments in infrared spectroscopy enable now the measurement of isotopic composition in water vapour traces. Two infrared spectrometers have been deployed at Concordia, allowing continuous, in situ measurements for one month in December–January 2014–2015. Comparison of the results from infrared spectroscopy with laboratory measurements of discrete samples trapped using cryogenic sampling validates the relevance of the method to measure isotopic composition in dry conditions. We observe very large diurnal cycles in isotopic composition well correlated with temperature diurnal cycles. Identification of different behaviours of isotopic composition in the water vapour associated with turbulent or stratified regime indicates a strong impact of meteorological processes in local vapour/snow interaction. Even if the vapour isotopic composition seems to be, at least part of the time, at equilibrium with the local snow, the slope of δD against δ18O prevents us from identifying a unique origin leading to this isotopic composition.

scholarly journals Continuous measurements of isotopic composition of water vapour on the East Antarctic Plateau

2016 ◽  
Vol 16 (13) ◽  
pp. 8521-8538 ◽  
Author(s):  
Mathieu Casado ◽  
Amaelle Landais ◽  
Valérie Masson-Delmotte ◽  
Christophe Genthon ◽  
Erik Kerstel ◽  
...  
Keyword(s):  
Infrared Spectroscopy ◽  
Surface Water ◽  
Isotopic Composition ◽  
Water Vapour ◽  
Isotopic Fractionation ◽  
Ice Cores ◽  
Strong Impact ◽  
Diurnal Cycles ◽  
Surface Snow ◽  
Dry Conditions

Abstract. Water stable isotopes in central Antarctic ice cores are critical to quantify past temperature changes. Accurate temperature reconstructions require one to understand the processes controlling surface snow isotopic composition. Isotopic fractionation processes occurring in the atmosphere and controlling snowfall isotopic composition are well understood theoretically and implemented in atmospheric models. However, post-deposition processes are poorly documented and understood. To quantitatively interpret the isotopic composition of water archived in ice cores, it is thus essential to study the continuum between surface water vapour, precipitation, surface snow and buried snow. Here, we target the isotopic composition of water vapour at Concordia Station, where the oldest EPICA Dome C ice cores have been retrieved. While snowfall and surface snow sampling is routinely performed, accurate measurements of surface water vapour are challenging in such cold and dry conditions. New developments in infrared spectroscopy enable now the measurement of isotopic composition in water vapour traces. Two infrared spectrometers have been deployed at Concordia, allowing continuous, in situ measurements for 1 month in December 2014–January 2015. Comparison of the results from infrared spectroscopy with laboratory measurements of discrete samples trapped using cryogenic sampling validates the relevance of the method to measure isotopic composition in dry conditions. We observe very large diurnal cycles in isotopic composition well correlated with temperature diurnal cycles. Identification of different behaviours of isotopic composition in the water vapour associated with turbulent or stratified regime indicates a strong impact of meteorological processes in local vapour/snow interaction. Even if the vapour isotopic composition seems to be, at least part of the time, at equilibrium with the local snow, the slope of δD against δ18O prevents us from identifying a unique origin leading to this isotopic composition.

Spatial variability of surface snow isotopic composition on the East Antarctic Plateau and implications for climate reconstructions

2020 ◽  
Author(s):  
Maria Hörhold ◽  
Alexander Weinhart ◽  
Sepp Kipfstuhl ◽  
Johannes Freitag ◽  
Georgia Micha ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Ice Core ◽  
Empirical Relationship ◽  
Ice Cores ◽  
Stable Water Isotopes ◽  
Antarctic Plateau ◽  
Mean Temperature ◽  
Spatial Coverage ◽  
Surface Snow ◽  
Relationship Of

<p>The reconstruction of past temperatures based on ice core records relies on the quantitative but empirical relationship of stable water isotopes and annual mean temperature. However, its relation varies through space and time. On the East Antarctic Plateau, temperature reconstructions from ice cores are poorly constrained or even fail on decadal and smaller time scales. The observed discrepancy between annual mean temperature and isotopic composition partly relies on surface processes altering the signal after deposition but also, to a great deal, on spatially coherent processes prior to or during deposition. However, spatial coverage over larger areas on the East Antarctic Plateau is challenging. We here present in-situ measurements of the isotopic composition of surface snow with unprecedented statistical quality and coverage. 1m surface snow profiles were collected during an overland traverse between Kohnen station and Plateau Station, covering a 1200km long transect. We explore regional differences of the temperature-isotope relationship and discuss possible mechanisms affecting the isotopic composition in areas with accumulation rates lower than 60mmWEa^-1.</p>

scholarly journals Archival processes of the water stable isotope signal in East Antarctic ice cores

2017 ◽  
Author(s):  
Mathieu Casado ◽  
Amaelle Landais ◽  
Ghislain Picard ◽  
Thomas Münch ◽  
Thomas Laepple ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Climate Models ◽  
Ice Core ◽  
Ice Cores ◽  
Climatic Conditions ◽  
Antarctic Plateau ◽  
Surface Snow ◽  
Rayleigh Distillation ◽  
The Difference ◽  
Ice Core Records

Abstract. The oldest ice core records are obtained from the East Antarctic plateau. Water isotopes records are key to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all the processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in Rayleigh distillation and isotope enabled climate models. However, a quantitative understanding of processes potentially altering the snow isotopic composition after the deposition is still missing. In low accumulation sites, such as those found in Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretation of isotopic composition. Here, we combine observations of isotopic composition in the vapour, the precipitation, the surface snow and the buried snow from Dome C, a deep ice core site on the East Antarctic Plateau. At the seasonal scale, we suggest a significant impact of metamorphism on surface snow isotopic signal compared to the initial precipitation signal. Particularly, in summer, exchanges of water molecules between vapour and snow are driven by the sublimation/condensation cycles at the diurnal scale. Using highly resolved isotopic composition profiles from pits in five Antarctic sites, we identify common patterns, despite different accumulation rates, which cannot be attributed to the seasonal variability of precipitation. Altogether, the difference in the signals observed in the precipitation, surface snow and buried snow isotopic composition constitute evidences of post-deposition processes affecting ice core records in low accumulation areas.

scholarly journals Isotopic exchange on the diurnal scale between near-surface snow and lower atmospheric water vapor at Kohnen station, East Antarctica

2016 ◽  
Vol 10 (4) ◽  
pp. 1647-1663 ◽  
Author(s):  
François Ritter ◽  
Hans Christian Steen-Larsen ◽  
Martin Werner ◽  
Valérie Masson-Delmotte ◽  
Anais Orsi ◽  
...  
Keyword(s):  
Water Vapor ◽  
Isotopic Composition ◽  
East Antarctica ◽  
Atmospheric Water Vapor ◽  
Box Model ◽  
Snow Surface ◽  
Atmospheric Water ◽  
Near Surface ◽  
Diurnal Cycles ◽  
Surface Snow

Abstract. Quantifying the magnitude of post-depositional processes affecting the isotopic composition of surface snow is essential for a more accurate interpretation of ice core data. To achieve this, high temporal resolution measurements of both lower atmospheric water vapor and surface snow isotopic composition are required. This study presents continuous measurements of water vapor isotopes performed in East Antarctica (Kohnen station) from December 2013 to January 2014 using a laser spectrometer. Observations have been compared with the outputs of two atmospheric general circulation models (AGCMs) equipped with water vapor isotopes: ECHAM5-wiso and LMDZ5Aiso. During our monitoring period, the signals in the 2 m air temperature T, humidity mixing ratio q and both water vapor isotopes δD and δ18O are dominated by the presence of diurnal cycles. Both AGCMs simulate similar diurnal cycles with a mean amplitude 30 to 70 % lower than observed, possibly due to an incorrect simulation of the surface energy balance and the boundary layer dynamics. In parallel, snow surface samples were collected each hour over 35 h, with a sampling depth of 2–5 mm. A diurnal cycle in the isotopic composition of the snow surface is observed in phase with the water vapor, reaching a peak-to-peak amplitude of 3 ‰ for δD over 24 h (compared to 36 ‰ for δD in the water vapor). A simple box model treated as a closed system has been developed to study the exchange of water molecules between an air and a snow reservoir. In the vapor, the box model simulations show too much isotopic depletion compared to the observations. Mixing with other sources (advection, free troposphere) has to be included in order to fit the observations. At the snow surface, the simulated isotopic values are close to the observations with a snow reservoir of  ∼ 5 mm depth (range of the snow sample depth). Our analysis suggests that fractionation occurs during sublimation and that vapor–snow exchanges can no longer be considered insignificant for the isotopic composition of near-surface snow in polar regions.

scholarly journals Exploring the role of snow metamorphism on the isotopic composition of the surface snow at EastGRIP

2021 ◽  
Author(s):  
Romilly Harris Stuart ◽  
Anne-Katrine Faber ◽  
Sonja Wahl ◽  
Maria Hörhold ◽  
Sepp Kipfstuhl ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Pore Space ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Water Isotopes ◽  
Climate Signal ◽  
Depositional Processes ◽  
Decay Model ◽  
Surface Snow ◽  
Snow Metamorphism

Abstract. Stable water isotopes from polar ice cores are invaluable high-resolution climate proxy records. Recent studies have aimed to improve knowledge of how the climate signal is stored in the water isotope record by addressing the influence of post-depositional processes on the surface snow isotopic composition. In this study, the relationship between changes in surface snow microstructure after precipitation/deposition events and water isotopes is explored using measurements of snow specific surface area (SSA). Continuous daily SSA measurements from the East Greenland Ice Core Project site (EastGRIP) situated in the accumulation zone of the Greenland Ice Sheet during the summer seasons of 2017, 2018 and 2019 are used to develop an empirical decay model to describe events of rapid decrease in SSA, driven predominantly by vapour diffusion in the pore space and atmospheric vapour exchange. The SSA decay model is described by the exponential equation SSA(t) = (SSA0 −26.8) e−0.54t + 26.8. The model performance is optimal for daily mean values of surface temperature in the range 0 °C to −25 °C and wind speed < 6 m s−1. The findings from the SSA analysis are used to explore the influence of surface snow metamorphism on altering the isotopic composition of surface snow. It is found that rapid SSA decay events correspond to decreases in d-excess over a 2-day period in 72 % of the samples. Detailed studies using Empirical Orthogonal Function (EOF) analysis revealed a coherence between the dominant mode of variance of SSA and d-excess during periods of low spatial variability of surface snow over the sampling transect, suggesting that processes driving change in SSA also influence d-excess. Our findings highlight the need for future studies to decouple the processes driving surface snow metamorphism in order to quantify the fractionation effect of individual processes on the snow isotopic composition.

scholarly journals Acquisition of isotopic composition for surface snow in East Antarctica and the links to climatic parameters

2015 ◽  
Vol 9 (6) ◽  
pp. 6275-6313 ◽  
Author(s):  
A. Touzeau ◽  
A. Landais ◽  
B. Stenni ◽  
R. Uemura ◽  
K. Fukui ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Ice Cores ◽  
Order Parameters ◽  
Second Order ◽  
East Antarctica ◽  
Distillation Process ◽  
Past Climate ◽  
Climatic Signal ◽  
Surface Snow ◽  
The Relationship

Abstract. The isotopic composition of oxygen and hydrogen in ice cores are invaluable tools for the reconstruction of past climate variations. Used alone, they give insights into the variations of the local temperature, whereas taken together they can provide information on the climatic conditions at the point of origin of the moisture. However, recent analyses of snow from shallow pits indicate that the climatic signal can become erased in very low accumulation regions, due to local processes of snow reworking. The signal to noise ratio decreases and the climatic signal can then only be retrieved using stacks of several snow pits. Obviously, the signal is not completely lost at this stage, otherwise it would be impossible to extract valuable climate information from ice cores as has been done, for instance, for the last glaciation. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. First, we look at the relationship between isotopes and temperature from a geographical point of view, using results from three traverses across Antarctica, to see how the relationship is built up through the distillation process. We also take advantage of these measures to see how second order parameters (d-excess and 17O-excess) are related to δ18O and how they are controlled. d-excess increases in the interior of the continent (i.e. when δ18O decreases), due to the distillation process, whereas 17O-excess decreases in remote areas, due to kinetic fractionation at low temperature. In both cases, these changes are associated with the loss of original information regarding the source. Then, we look at the same relationships in precipitation samples collected over one year at Dome C and Vostok, as well as in surface snow at Dome C. We note that the slope of the δ18O / T relationship decreases in these samples compared to those from the traverses, and thus advocate caution when using spatial slopes for past climate reconstruction. The second-order parameters behave in the same way in the precipitation as in the surface snow from traverses, indicating that similar processes are active. Finally we check if the same relationships between δ18O and second-order parameters are also found in the snow from four snow pits. While the d-excess remains opposed to δ18O in most snow pits, the 17O-excess is no longer positively correlated to δ18O and even shows anti-correlation to δ18O at Vostok. This may be due to a stratospheric influence at this site and/or to post-deposition processes.

scholarly journals Archival processes of the water stable isotope signal in East Antarctic ice cores

2018 ◽  
Vol 12 (5) ◽  
pp. 1745-1766 ◽  
Author(s):  
Mathieu Casado ◽  
Amaelle Landais ◽  
Ghislain Picard ◽  
Thomas Münch ◽  
Thomas Laepple ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Climate Models ◽  
Ice Core ◽  
Ice Cores ◽  
Climatic Conditions ◽  
Antarctic Plateau ◽  
Surface Snow ◽  
Rayleigh Distillation ◽  
Deposition Processes ◽  
Ice Core Records

Abstract. The oldest ice core records are obtained from the East Antarctic Plateau. Water isotopes are key proxies to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in trajectory-based Rayleigh distillation and isotope-enabled climate models. However, a quantitative understanding of processes potentially altering snow isotopic composition after deposition is still missing. In low-accumulation sites, such as those found in East Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretability of an ice core's isotopic composition. By combining observations of isotopic composition in vapour, precipitation, surface snow and buried snow from Dome C, a deep ice core site on the East Antarctic Plateau, we found indications of a seasonal impact of metamorphism on the surface snow isotopic signal when compared to the initial precipitation. Particularly in summer, exchanges of water molecules between vapour and snow are driven by the diurnal sublimation–condensation cycles. Overall, we observe in between precipitation events modification of the surface snow isotopic composition. Using high-resolution water isotopic composition profiles from snow pits at five Antarctic sites with different accumulation rates, we identified common patterns which cannot be attributed to the seasonal variability of precipitation. These differences in the precipitation, surface snow and buried snow isotopic composition provide evidence of post-deposition processes affecting ice core records in low-accumulation areas.

Using triple water isotopes signatures of surface snow to gauge metamorphism in Antarctica

2020 ◽  
Author(s):  
Mathieu Casado ◽  
Amaelle Landais ◽  
Ghislain Picard ◽  
Laurent Arnaud ◽  
Giuliano Dreossi ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Ice Core ◽  
Chemical Properties ◽  
Ice Cores ◽  
Blowing Snow ◽  
Climate Reconstructions ◽  
Climatic Signal ◽  
Surface Snow ◽  
Snow Metamorphism ◽  
Deposition Processes

&lt;p&gt;Water isotopic composition is a key proxy for past climate reconstructions using deep ice cores from Antarctica. As precipitation forms, the local temperature is imprinted in the snowfalls &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O. However, this climatic signal can be erased after snow deposition when snow is exposed to the atmosphere for a long time in regions with extremely low accumulation. Understanding this effect is crucial for the interpretation of ice core records from the extremely dry East Antarctic Plateau, where post-deposition processes such as blowing snow or metamorphism affect the physical and chemical properties of snow during the long periods of snow exposure to the atmosphere. Despite the importance of these processes for the reliable reconstruction of temperature from water isotopic composition in ice cores, the tools required to quantify their impacts are still missing. Here, we present a first year-long comparison between (a) time series of surface snow isotopic composition including d-excess and &lt;sup&gt;17&lt;/sup&gt;O-excess at Dome C and (b) satellite observations providing information on snow grain size, a marker of surface metamorphism. Long summer periods without precipitation tend to produce a surface snow metamorphism signature erasing the climatic signal in the surface snow &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O. Using a simple model, we demonstrate that d-excess and &lt;sup&gt;17&lt;/sup&gt;O-excess allow the identification of the latent fluxes induced by metamorphism, and their impact on surface snow isotopic composition. In turn, their measurements can help improve climate reconstructions based on &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O records ice by removing the influence of snow metamorphism.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document