Water Isotopic Signature of Surface Snow Metamorphism in Antarctica

Mathieu Casado,Frederic Prié,Giuliano Dreossi,Barbara Stenni,Ghislain Picard,Laurent Arnaud,Amaelle Landais

doi:10.1029/2021gl093382

Abstract

AbstractWater isotope ratios of ice cores are a key source of information on past temperatures. Through fractionation within the hydrological cycle, temperature is imprinted in the water isotopic composition of snowfalls. However, this signal of climatic interest is modified after deposition when snow remains at the surface exposed to the atmosphere. Comparing time series of surface snow isotopic composition at Dome C with satellite observations of surface snow metamorphism, we found that long summer periods without precipitation favor surface snow metamorphism altering the surface snow isotopic composition. Using excess parameters (combining D,17O, and18O fractions) allow the identification of this alteration caused by sublimation and condensation of surface hoar. The combined measurement of all three isotopic compositions could help identifying ice core sections influenced by snow metamorphism in sites with very low snow accumulation.

Highlights

In low accumulation regions of Antarctica, precipitation is so sparse that the processes occurring after snowfall, such as surface metamorphism (Picard et al, 2012), sublimation and solid condensation (Genthon et al, 2017), as well as the redistribution of snow by wind (Groot Zwaaftink et al, 2013; Picard et al, 2019), play a prominent role in how snow accumulates to build the snowpack
Comparing time series of surface snow isotopic composition at Dome C with satellite observations of surface snow metamorphism, we found that long summer periods without precipitation favor surface snow metamorphism altering the surface snow isotopic composition
We explore the link between the surface snow isotopic composition and grain size, the latter being a measure for the degree of exposure to metamorphic processes at the surface (Ebner et al, 2017): During metamorphism, sublimation and re-condensation on slightly colder grains lead to a coarsening of the snow grains

Summary

Introduction

In low accumulation regions of Antarctica, precipitation is so sparse that the processes occurring after snowfall (post-deposition), such as surface metamorphism (Picard et al, 2012), sublimation and solid condensation (Genthon et al, 2017), as well as the redistribution of snow by wind (Groot Zwaaftink et al, 2013; Picard et al, 2019), play a prominent role in how snow accumulates to build the snowpack. Snow grain size, which controls the albedo (Grenfell et al, 1994; Wiscombe & Warren, 1980), is the result of the competition between precipitation which brings small size grains on the surface and metamorphism which coarsens existing grains (Picard et al, 2012) These post-deposition processes influence the snow isotopic composition (δ18O or δD for the first order) that are traditionally interpreted as proxies of past temperatures in ice cores.

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Discussion

Conclusion