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

Alexandra M Zuhr,Hans Christian Steen-Larsen,Thomas Laepple,Thomas Münch,Maria Hörhold

doi:10.5194/tc-15-4873-2021

Abstract

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.

Highlights

Ice cores from polar ice sheets and glaciers are one of the most important climate archives
We evaluated our digital elevation model (DEM) by analysing the trueness of our DEM-derived snow height estimates compared to reference heights, i.e. manually measured snow heights
The DEM-derived net accumulation corresponds only to ∼ 35 % of the total amount of temporarily deposited snow, while the ERA5 snowfall is only ∼ 24 %. Even though this could suggest that the ERA5 data might be biased towards drier conditions, we assume that both differences between the DEM-derived net accumulation and all positive contributions as well as between the DEM-derived estimate and the ERA5 snowfall are caused by substantial contributions of snowdrift and redistribution, which emphasise their influence on the final snow accumulation during the observation period

Summary

Introduction

Ice cores from polar ice sheets and glaciers are one of the most important climate archives. The accuracy and interpretability of reconstructed parameters depend on the understanding of the initial signal formation and the processes that potentially thereafter change the original signal imprinted in the deposited precipitation. Amongst these are local processes such as snow–air exchange processes; alteration of the isotopic composition (i.e. δ18O or δD) by diffusion, sublimation, vapour deposition, or metamorphism (Steen-Larsen et al, 2014; Dadic et al, 2015; Ritter et al.); depositional losses of chemical compounds (Weller et al, 2004), local-to-regional processes such as the spatial variability in snowfall and wind-driven redeposition leading with the local topography to stratigraphic. Zuhr et al.: Local-scale deposition of surface snow on the Greenland ice sheet noise (Fisher et al, 1985; Münch et al, 2016); and largerscale processes such as precipitation intermittency (Persson et al, 2011)

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Conclusion