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.

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

&lt;p&gt;Post-depositional processes affect the stable water isotope signal of surface snow between precipitation events.&amp;#160;Combined vapor-snow exchange processes and isotope diffusion influence the top layer of snow as well as buried layers below.&amp;#160;This implies, that ice core isotope climate proxy records can not be interpreted as a precipitation weighted temperature signal alone.&lt;/p&gt;&lt;p&gt;Here we present to what extend surface sublimation can explain in-situ observed changes of the stable water isotope signal in the snow.&lt;br&gt;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.&lt;br&gt;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.&amp;#160;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.&lt;br&gt;This improved process understanding of the formation of the climate signal found in snow is important for merging climate modeling and ice core proxies.&amp;#160;&lt;/p&gt;

scholarly journals The role of sublimation as a driver of climate signals in the water isotope content of surface snow: Laboratory and field experimental results

2021 ◽  
Author(s):  
Abigail G. Hughes ◽  
Sonja Wahl ◽  
Tyler R. Jones ◽  
Alexandra Zuhr ◽  
Maria Hörhold ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Laboratory Experiments ◽  
Ice Core ◽  
Water Isotopes ◽  
Driving Mechanism ◽  
Climate Signal ◽  
Depositional Processes ◽  
Surface Snow ◽  
Isotope Content ◽  
Water Isotope

Abstract. Ice core water isotope records from Greenland and Antarctica are a valuable proxy for paleoclimate reconstruction, yet the processes influencing the climate signal stored in the isotopic composition of the snow are being revisited. Apart from precipitation input, post-depositional processes such as wind-driven redistribution and vapor-snow exchange processes at and below the surface are hypothesized to contribute to the isotope climate signal. Recent field studies have shown that surface snow isotopes vary between precipitation events and co-vary with vapor isotopes, which demonstrates that vapor- snow exchange is an important driving mechanism. Here we investigate how vapor-snow exchange and sublimation processes influence the isotopic composition of the snowpack. Controlled laboratory experiments under dry air flow show an increase of snow isotopic composition of up to 8 ‰ δ18O in the uppermost layer, with an attenuated signal down to 3 cm snow depth over the course of 4–6 days. This enrichment is accompanied by a decrease in the second-order parameter d-excess, indicating kinetic fractionation processes. Using a simple mass-balance and diffusion box model in conjunction with our observed laboratory vapor isotope signals, we are able to reproduce the observed changes in the snow. This confirms that sublimation alone can lead to a strong enrichment of stable water isotopes in surface snow and subsequent enrichment in the layers below. To compare laboratory experiments with realistic polar conditions, we completed four 2–3 day field experiments at the East Greenland Ice Core Project site (Northeast Greenland) in summer 2019. High-resolution temporal sampling of both natural and isolated snow was conducted under clear-sky conditions, and demonstrated that the snow isotopic composition changes on hourly timescales. A change of snow isotope content associated with sublimation is currently not implemented in isotope-enabled climate models and is not taken into account when interpreting ice core isotopic records. However, our results demonstrate that post-depositional processes such as sublimation play a role in creating the climate signal recorded in the water isotopes in surface snow. This suggests that the ice core water isotope signal may effectively integrate across multiple parameters, and the ice core climate record should be interpreted as such.

scholarly journals Local scale depositional processes of surface snow on the Greenland ice sheet

2021 ◽  
Author(s):  
Alexandra M. Zuhr ◽  
Thomas Münch ◽  
Hans Christian Steen-Larsen ◽  
Maria Hörhold ◽  
Thomas Laepple
Keyword(s):  
Spatial Scales ◽  
Ice Core ◽  
Negative Relationship ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Data Set ◽  
Climate Signal ◽  
Depositional Processes ◽  
Snow Deposition

Abstract. Ice cores from polar ice sheets and glaciers are an important climate archive. Snow layers, consecutively deposited and buried, contain climatic information of the time of their formation. However, particularly low-accumulation areas are characterised by temporally intermittent precipitation, which can be further re-distributed after initial deposition. Therefore, the local conditions of accumulation at an ice core site influence the quantity and quality of the recorded climate signal in proxy records. Local surface features at different spatial scales further affect the signal imprint. This study therefore aims to characterise the local accumulation patterns and the evolution of the snow height to describe the contribution of snow (re-)deposition to noise in climate records from ice cores. By using a photogrammetry Structure-from-Motion approach, we generated near-daily elevation models of the snow surface for a 195 m2 area in the vicinity of the deep drilling site of the East Greenland Ice Core Project in northeast Greenland. Based on the snow height information we derived snow height changes on a day-to-day basis throughout our observation period from May to August 2018. Specifically, the average snow height increased by ~11 cm. The spatial and temporal data set allowed an investigation of snow deposition versus depositional modifications. We observed irregular snow deposition, erosion, and the re-distribution of snow, which caused uneven snow accumulation patterns, a removal of more than 60 % of the deposited snow, and a negative relationship between the initial snow height and the amount of accumulated snow. Furthermore, the surface roughness decreased from 4 to 2 cm throughout the spring and summer season at our study site. Finally, our study further shows that our method has several advantages over previous approaches, making it possible to demonstrate the importance of accumulation intermittency, and the potential influences of depositional processes on proxy signals in snow and ice.

scholarly journals Local-scale deposition of surface snow on the Greenland ice sheet

2021 ◽  
Vol 15 (10) ◽  
pp. 4873-4900
Author(s):  
Alexandra M. Zuhr ◽  
Thomas Münch ◽  
Hans Christian Steen-Larsen ◽  
Maria Hörhold ◽  
Thomas Laepple
Keyword(s):  
Structure From Motion ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Data Set ◽  
Simple Method ◽  
Climate Signal ◽  
Depositional Processes ◽  
Surface Snow ◽  
Snow Deposition

Abstract. Ice cores from polar ice sheets and glaciers are an important climate archive. Snow layers, consecutively deposited and buried, contain climatic information from the time of their formation. However, particularly low-accumulation areas are characterised by temporally intermittent precipitation, which can be further redistributed after initial deposition, depending on the local surface features at different spatial scales. Therefore, the accumulation conditions at an ice core site influence the quantity and quality of the recorded climate signal in proxy records. This study aims to characterise the local accumulation patterns and the evolution of the snow height to describe the contribution of the snow (re-)deposition to the overall noise level in climate records from ice cores. To this end, we applied a structure-from-motion photogrammetry approach to generate near-daily elevation models of the surface snow for a 195 m2 area in the vicinity of the deep drilling site of the East Greenland Ice-core Project in northeast Greenland. Based on the snow height information we derive snow height changes on a day-to-day basis throughout our observation period from May to August 2018 and find an average snow height increase of ∼ 11 cm. The spatial and temporal data set also allows an investigation of snow deposition versus depositional modifications. We observe irregular snow deposition and erosion causing uneven snow accumulation patterns, a removal of more than 60 % of the deposited snow, and a negative relationship between the initial snow height and the amount of accumulated snow. Furthermore, the surface roughness decreased by approximately a factor of 2 throughout the spring and summer season at our study site. Finally, our study shows that structure from motion is a relatively simple method to demonstrate the potential influences of depositional processes on proxy signals in snow and ice.

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;

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

&lt;p&gt;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.&lt;/p&gt;&lt;div&gt;&amp;#160;&lt;/div&gt;&lt;div&gt;&amp;#160;&lt;/div&gt;

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

&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;Here we present simulated SMB components for eight ice core drilling sites on the GrIS using the regional climate model MAR (Mod&amp;#232;le Atmosph&amp;#233;rique R&amp;#233;gional). 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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;

scholarly journals Experimental observation of transient <i>δ</i><sup>18</sup>O interaction between snow and advective airflow under various temperature gradient conditions

2017 ◽  
Vol 11 (4) ◽  
pp. 1733-1743 ◽  
Author(s):  
Pirmin Philipp Ebner ◽  
Hans Christian Steen-Larsen ◽  
Barbara Stenni ◽  
Martin Schneebeli ◽  
Aldo Steinfeld
Keyword(s):  
Temperature Gradient ◽  
Isotopic Composition ◽  
Ice Cores ◽  
Transport Processes ◽  
Water Isotopes ◽  
Polar Regions ◽  
Stable Water Isotopes ◽  
Climate History ◽  
Stable Isotopes Of Water ◽  
Past Climate Variability

Abstract. Stable water isotopes (δ18O) obtained from snow and ice samples of polar regions are used to reconstruct past climate variability, but heat and mass transport processes can affect the isotopic composition. Here we present an experimental study on the effect of airflow on the snow isotopic composition through a snow pack in controlled laboratory conditions. The influence of isothermal and controlled temperature gradient conditions on the δ18O content in the snow and interstitial water vapour is elucidated. The observed disequilibrium between snow and vapour isotopes led to the exchange of isotopes between snow and vapour under non-equilibrium processes, significantly changing the δ18O content of the snow. The type of metamorphism of the snow had a significant influence on this process. These findings are pertinent to the interpretation of the records of stable isotopes of water from ice cores. These laboratory measurements suggest that a highly resolved climate history is relevant for the interpretation of the snow isotopic composition in the field.

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

&lt;p&gt;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.&lt;/p&gt;

scholarly journals Experimental observation of transient δ<sup>18</sup>O interaction between snow and advective airflow under various temperature gradient conditions

2017 ◽  
Author(s):  
Pirmin P. Ebner ◽  
Hans Christian Steen-Larsen ◽  
Barbara Stenni ◽  
Martin Schneebeli ◽  
Aldo Steinfeld
Keyword(s):  
Temperature Gradient ◽  
Isotopic Composition ◽  
Ice Cores ◽  
Transport Processes ◽  
Water Isotopes ◽  
Polar Regions ◽  
Stable Water Isotopes ◽  
Equilibrium Processes ◽  
Stable Isotopes Of Water ◽  
Past Climate Variability

Abstract. Stable water isotopes (δ18O) obtained from snow and ice samples of polar regions are used to reconstruct past climate variability, but heat and mass transport processes can affect the isotopic composition. Here we present an experimental study on the effect on the snow isotopic composition by airflow through a snow pack in controlled laboratory conditions. The influence of isothermal and controlled temperature gradient conditions on the δ18O content in the snow and interstitial water vapor is elucidated. The observed disequilibrium between snow and vapor isotopes led to exchange of isotopes between snow and vapor under non-equilibrium processes, significantly changing the δ18O content of the snow. The type of metamorphism of the snow had a significant influence on this process. These findings are pertinent to the interpretation of the records of stable isotopes of water from ice cores. These laboratory measurements suggest that a highly resolved history is relevant for the interpretation of the snow isotopic composition in the field.

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