scholarly journals What controls the isotopic composition of Greenland surface snow?

2014 ◽  
Vol 10 (1) ◽  
pp. 377-392 ◽  
Author(s):  
H. C. Steen-Larsen ◽  
V. Masson-Delmotte ◽  
M. Hirabayashi ◽  
R. Winkler ◽  
K. Satow ◽  
...  
Keyword(s):  
Water Vapor ◽  
Isotopic Composition ◽  
Air Temperature ◽  
Ice Core ◽  
Snow Surface ◽  
Atmospheric Models ◽  
Near Surface ◽  
Core Data ◽  
Surface Snow ◽  
Precipitation Events

Abstract. Water stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically enabled atmospheric models. However, post-depositional processes linked with snow metamorphism remain poorly documented. For this purpose, monitoring of the isotopic composition (δ18O, δD) of near-surface water vapor, precipitation and samples of the top (0.5 cm) snow surface has been conducted during two summers (2011–2012) at NEEM, NW Greenland. The samples also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between near-surface vapor δ18O and air temperature (0.85 ± 0.11‰ °C−1 (R = 0.76) for 2012). The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess) is strongly anti-correlated with δ18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1–5-day periods between precipitation events, our data demonstrate parallel changes of δ18O and d-excess in surface snow and near-surface vapor. The changes in δ18O of the vapor are similar or larger than those of the snow δ18O. It is estimated using the CROCUS snow model that 6 to 20% of the surface snow mass is exchanged with the atmosphere. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or deposition. Comparisons with atmospheric models show that day-to-day variations in near-surface vapor isotopic composition are driven by synoptic variations and changes in air mass trajectories and distillation histories. We suggest that, in between precipitation events, changes in the surface snow isotopic composition are driven by these changes in near-surface vapor isotopic composition. This is consistent with an estimated 60% mass turnover of surface snow per day driven by snow recrystallization processes under NEEM summer surface snow temperature gradients. Our findings have implications for ice core data interpretation and model–data comparisons, and call for further process studies.

scholarly journals What controls the isotopic composition of Greenland surface snow?

2013 ◽  
Vol 9 (5) ◽  
pp. 6035-6076 ◽  
Author(s):  
H. C. Steen-Larsen ◽  
V. Masson-Delmotte ◽  
M. Hirabayashi ◽  
R. Winkler ◽  
K. Satow ◽  
...  
Keyword(s):  
Water Vapor ◽  
Isotopic Composition ◽  
Air Temperature ◽  
Ice Core ◽  
Data Interpretation ◽  
Snow Surface ◽  
Atmospheric Models ◽  
Core Data ◽  
Surface Snow ◽  
Precipitation Events

Abstract. Water stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically-enabled atmospheric models. However, post-deposition processes linked with snow metamorphism remain poorly documented. For this purpose, a monitoring of the isotopic composition (δ18O, δD) of surface water vapor, precipitation and samples of top (0.5 cm) snow surface has been conducted during two summers (2011–2012) at NEEM, NW Greenland. The measurements also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between surface vapor δ18O and air temperature (0.85 ± 0.11 ‰ °C−1 (R = 0.76) for 2012). The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess) is strongly anti-correlated with δ18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1–5 days periods between precipitation events, our data demonstrate parallel changes of δ18O and d-excess in surface snow and surface vapor. The changes in δ18O of the vapor are similar or larger than those of the snow δ18O. It is estimated that 6 to 20% of the surface snow mass is exchanged with the atmosphere using the CROCUS snow model. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or condensation. Comparisons with atmospheric models show that day-to-day variations in surface vapor isotopic composition are driven by synoptic weather and changes in air mass trajectories and distillation histories. We suggest that, in-between precipitation events, changes in the surface snow isotopic composition are driven by these changes in surface vapor isotopic composition. This is consistent with an estimated 60% mass turnover of surface snow per day driven by snow recrystallization processes under NEEM summer surface snow temperature gradients. Our findings have implications for ice core data interpretation and model-data comparisons, and call for further process studies.

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

2016 ◽  
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 ◽  
Depth Range ◽  
Snow Surface ◽  
Atmospheric Water ◽  
Near Surface ◽  
Depositional Processes ◽  
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 the first continuous measurements of water vapor isotopes performed in East Antarctica (Kohnen station) from December 2013 to January 2014 using a laser spectrometer. During our monitoring period, the synoptic variability of the water vapor isotopic composition is found to be low compared to the diurnal cycle and we therefore concentrate our study on interaction between the isotopic composition of the vapor and the snow surface on a diurnal timescale. The peak-to-peak amplitude of the snow surface isotopic composition over 24 h reaches 3 ‰ for δD, in phase with the diurnal variations of δD in surface vapor, which itself has an amplitude of 36 ‰. 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 simulations show too much isotopic depletion compared to the observations. Mixing with other sources (wind 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 vapor-snow exchanges can no longer be considered insignificant for the isotopic composition of near surface snow in central Antarctica.

Quantifying the role of post-depositional processes on the isotopic composition of surface snow – new findings from the SNOWISO project

2020 ◽  
Author(s):  
Hans Christian Steen-Larsen ◽  
Maria Hörhold ◽  
Sonja Wahl ◽  
Abigail Hughes ◽  
Anne-Katrine Faber ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Time Scales ◽  
Ice Core ◽  
Atmospheric Temperature ◽  
Snow Surface ◽  
Climate Signal ◽  
Depositional Processes ◽  
Surface Snow ◽  
Temperature And Humidity

<p>The goal of the SNOWISO project is to quantify the role of the post-depositional processes, which are influencing the isotopic composition of the surface snow and hence the ice core water isotope climate signal. Here we are reporting on findings from field campaigns carried out at EastGRIP over the four summers 2016-2019. We have collected a suite of observations containing the isotopic composition of the surface snow and the snowpack, together with direct observations of atmospheric water vapor isotopes and fluxes between the snow surface and the atmosphere. To support the analysis of the isotopic data we also collected meteorological observations comprising of atmospheric temperature and humidity gradients alongside with sub-surface and snow surface temperature along with atmospheric temperature and humidity gradients. With this dataset we are able to document significant changes in the snow isotopic composition, which are driven by post-depositional processes. The changes in the snow surface isotopic composition is observed to occur on time scales ranging from diurnal to several days. The changes in the snow surface isotopic composition is observed to occur on time scales ranging from diurnal to several days. We can show that the changes in the snow surface is consistent with the flux of the isotopologues between the snow surface and the atmosphere. This gives us confidence that we will be able to develop parameterizations of post-depositional effects, and model their influence on the ice core isotopic climate signal.</p><div> </div><div> </div>

scholarly journals Numerical simulation of extreme snow melt observed at the SIGMA-A site, northwest Greenland, during summer 2012

2015 ◽  
Vol 9 (1) ◽  
pp. 495-539
Author(s):  
M. Niwano ◽  
T. Aoki ◽  
S. Matoba ◽  
S. Yamaguchi ◽  
T. Tanikawa ◽  
...  
Keyword(s):  
Heat Flux ◽  
Grain Size ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
In Situ Measurements ◽  
The Arctic ◽  
Snow Surface ◽  
Near Surface ◽  
Surface Snow

Abstract. The surface energy balance (SEB) from 30 June to 14 July 2012 at site SIGMA (Snow Impurity and Glacial Microbe effects on abrupt warming in the Arctic)-A, (78°03' N, 67°38' W; 1490 m a.s.l.) on the northwest Greenland Ice Sheet (GrIS) was investigated by using in situ atmospheric and snow measurements, as well as numerical modeling with a one-dimensional, multi-layered, physical snowpack model called SMAP (Snow Metamorphism and Albedo Process). At SIGMA-A, remarkable near-surface snowmelt and continuous heavy rainfall (accumulated precipitation between 10 and 14 July was estimated to be 100 mm) were observed after 10 July 2012. Application of the SMAP model to the GrIS snowpack was evaluated based on the snow temperature profile, snow surface temperature, surface snow grain size, and shortwave albedo, all of which the model simulated reasonably well. However, comparison of the SMAP-calculated surface snow grain size with in situ measurements during the period when surface hoar with small grain size was observed on-site revealed that it was necessary to input air temperature, relative humidity, and wind speed data from two heights to simulate the latent heat flux into the snow surface and subsequent surface hoar formation. The calculated latent heat flux was always directed away from the surface if data from only one height were input to the SMAP model, even if the value for roughness length of momentum was perturbed between the possible maximum and minimum values in numerical sensitivity tests. This result highlights the need to use two-level atmospheric profiles to obtain realistic latent heat flux. Using such profiles, we calculated the SEB at SIGMA-A from 30 June to 14 July 2012. Radiation-related fluxes were obtained from in situ measurements, whereas other fluxes were calculated with the SMAP model. By examining the components of the SEB, we determined that low-level clouds accompanied by a significant temperature increase played an important role in the melt event observed at SIGMA-A. These conditions induced a remarkable surface heating via cloud radiative forcing in the polar region.

scholarly journals The influence of the forest on night-time snow surface temperature

2001 ◽  
Vol 32 ◽  
pp. 217-222 ◽  
Author(s):  
Peter Höller
Keyword(s):  
Surface Temperature ◽  
Open Field ◽  
Air Temperature ◽  
Forest Canopy ◽  
Small Range ◽  
Snow Surface ◽  
Net Radiation ◽  
Night Time ◽  
Near Surface ◽  
Snow Surface Temperature

AbstractSnow surface temperature (Ts) plays an important role in the formation of surface hoar or near-surface faceted crystals The goal of this study was to obtain detailed information on Ts in different forest stands nelr the timberline. The investigations were conducted during clear nights and showed that the snow surface temperature is influenced very strongly by the forest canopy. While the air temperature was very similar on the different experimental sites, Ts was higher in the forest than in the open field; on the south-facing slope the difference between the forest and the open field was 3–4.5°C, and on the north-facing slope approximately 3–7°C. Taking into account that εair is 0.7 and εtree is 0.94, the incoming radiation (I ↓) for the different experimental sites was calculated by the equation of Brunt (the canopy density was estimated using photographs taken with an 8 mm fish-eye). To calculate Ts, air temperature and averaged values of the net radiation (because the net radiation (I) has only a small range of variation during clear nights) were used. The results show that the calculated values were higher than the measured values (by approximately 2°C). However, a better correlation was found by using lower values of the emissivity (εair0.67 and εtree0.91).

The Effect of Surface Sublimation on the Snow Isotope Signal

2021 ◽  
Author(s):  
Sonja Wahl ◽  
Alexandra Zuhr ◽  
Maria Hörhold ◽  
Anne-Katrine Faber ◽  
Hans Christian Steen-Larsen
Keyword(s):  
Isotopic Composition ◽  
Climate Modeling ◽  
Ice Core ◽  
Greenland Ice Sheet ◽  
Layer By Layer ◽  
Climate Signal ◽  
North East ◽  
Depositional Processes ◽  
Surface Snow ◽  
Water Isotope

<p>Post-depositional processes affect the stable water isotope signal of surface snow between precipitation events. Combined vapor-snow exchange processes and isotope diffusion influence the top layer of snow as well as buried layers below. This implies, that ice core isotope climate proxy records can not be interpreted as a precipitation weighted temperature signal alone.</p><p>Here we present to what extend surface sublimation can explain in-situ observed changes of the stable water isotope signal in the snow.<br>We use direct observations of the isotopic composition of the sublimation flux together with surface snow samples taken in the North-East of the Greenland Ice Sheet accumulation zone throughout the summer months of 2019 to demonstrate sublimation impacts.<br>We show that, contrary to the understanding of effectless layer-by-layer removal of snow, sublimation involves fractionation and therefore influences the isotopic composition of the snow. Complementary measurements of humidity as well as isotope fluxes constrain the local vapor snow exchange and allow for the quantification of post-depositional influences while the snow is exposed to the atmosphere.<br>This improved process understanding of the formation of the climate signal found in snow is important for merging climate modeling and ice core proxies. </p>

The Role of Sublimation on the Surface Mass Balance of the Interior Greenland Ice Sheet

2021 ◽  
Author(s):  
Laura Dietrich ◽  
Hans Christian Steen-Larsen ◽  
Cécile Agosta ◽  
Xavier Fettweis ◽  
Anne-Katrine Faber ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Roughness Length ◽  
Ice Core ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Climate Signal ◽  
Surface Mass ◽  
Surface Roughness Length ◽  
Surface Snow ◽  
Precipitation Events

<p>Precipitation along with sublimation and deposition are the main contributors to the surface mass balance (SMB) in the accumulation area of the Greenland Ice Sheet (GrIS). However, precipitation events are rare and intermittent. In between precipitation events the surface snow continuously undergoes sublimation and deposition. Recent studies imply that these surface exchange processes influence the isotopic composition of the surface snow which is later archived as a climate record in ice cores. In order to understand the possible implications on the recorded climate signal, sublimation needs to be quantified on a local scale.</p><p>Here we present simulated SMB components for eight ice core drilling sites on the GrIS using the regional climate model MAR (Modèle Atmosphérique Régional). We validated MAR against in-situ flux observations at the East Greenland Ice Core Project site and found a high sensitivity of sublimation to the downward long wave flux and to the parameterization of the surface roughness length. We propose a surface roughness length optimized for the interior of the GrIS which is supported by our observations.</p><p>Our results show that in the GrIS accumulation area the mass turnover via sublimation and deposition can reach the same order of magnitude as precipitation. This highlights the importance of a better understanding of how the climate signal is imprinted in the surface snow isotopic composition.</p>

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.

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