Microstructure of Snow and Its Link to Trace Elements and Isotopic Composition at Kohnen Station, Dronning Maud Land, Antarctica

Dorothea Elisabeth Moser,Maria Hörhold,Sepp Kipfstuhl,Johannes Freitag

doi:10.3389/feart.2020.00023

Abstract

Understanding the deposition history and signal formation in ice cores from polar ice sheets is fundamental for the interpretation of paleoclimate reconstruction based on climate proxies. Polar surface snow responds to environmental changes on a seasonal time scale by snow metamorphism, displayed in the snow microstructure and archived in the snowpack. However, the seasonality of snow metamorphism and accumulation rate is poorly constrained for low-accumulation regions, such as the East Antarctic Plateau. Here, we apply core-scale microfocus X-ray computer tomography to continuously measure snow microstructure of a 3-m deep snow core from Kohnen Station, Antarctica. We compare the derived microstructural properties to discretely measured trace components and stable water isotopes, commonly used as climate proxies. Temperature and snow height data from an automatic weather station are used for further constraints. Dating of the snow profile by combining non-sea-salt sulfate and density crusts reveals a seasonal pattern in the geometrical anisotropy. Considering seasonally varying temperature-gradient metamorphism in the surface snow and the timing of the anisotropy pattern observed in the snow profile, we propose the anisotropy to display the deposition history of the site. An annually varying fraction of deposition during summer months, ranging from no or negative deposition to large deposition events, leads to the observed microstructure and affects trace components as well as stable water isotopes.

Highlights

Ice cores from polar ice sheets serve as climate archives and deep ice cores retrieved from Antarctica reveal a wealth of information on past climatic conditions (e.g. European Project for Ice Coring in Antarctica (EPICA) Community Members, 2006; Jouzel et al, 2007; Lüthi et al, 2008; Steig et al, 2013)
Arguments are (a) the dating, where we find peak anisotropy to coincide with summer-to-fall peaks in nss-SO42− and clusters of crusts, (b) the combination of highest mean air temperatures and strong gradients favoring grain growth in summer to fall, and (c) the irregular summer deposition derived from AWS 9: We find sometimes very reduced or even negative amount of deposition, i.e. erosion
We have performed combined measurements of microstructure, trace elements, and stable water isotopes on a 3-m snow core retrieved at Kohnen Station and used meteorological data from AWS 9

Summary

Introduction

Ice cores from polar ice sheets serve as climate archives and deep ice cores retrieved from Antarctica reveal a wealth of information on past climatic conditions (e.g. EPICA Community Members, 2006; Jouzel et al, 2007; Lüthi et al, 2008; Steig et al, 2013). Snow layers deposited on the icesheet’s surface carry chemical and physical proxy information for atmospheric and environmental conditions of the time of their formation. Retrieving these climate proxies from ice cores allows to reconstruct past changes in earth’s climate history from annual to glacial-interglacial time scales Sulfate concentrations in central Antarctica vary seasonally mainly due to varying aerosol fluxes from biogenic, volcanic and sea-salt emissions Göktas et al, 2002; Iizuka et al, 2004; Kaufmann et al, 2010). Legrand, 1995; Göktas et al, 2002) The non-sea-salt fraction of sulfate is assumed to originate from marine, biogenic dimethylsulfide production (e.g. Legrand, 1995; Göktas et al, 2002)

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