A Snapshot on the Buildup of the Stable Water Isotopic Signal in the Upper Snowpack at EastGRIP on the Greenland Ice Sheet

Abstract

The stable water isotopic composition in firn and ice cores provides valuable information on past climatic conditions. Because of uneven accumulation and post‐depositional modifications on local spatial scales up to hundreds of meters, time series derived from adjacent cores differ significantly and do not directly reflect the temporal evolution of the precipitated snow isotopic signal. Hence, a characterization of how the isotopic profile in the snow develops is needed to reliably interpret the isotopic variability in firn and ice cores. By combining digital elevation models of the snow surface and repeated high‐resolution snow sampling for stable water isotope measurements of a transect at the East Greenland Ice‐core Project campsite on the Greenland Ice Sheet, we are able to visualize the buildup and post‐depositional changes of the upper snowpack across one summer season. To this end, 30 cm deep snow profiles were sampled on six dates at 20 adjacent locations along a 40 m transect. Near‐daily photogrammetry provided snow height information for the same transect. Our data shows that erosion and redeposition of the original snowfall lead to a complex stratification in the δ18O signature. Post‐depositional processes through vapor‐snow exchange affect the near surface snow with d‐excess showing a decrease in surface and near‐surface layers. Our data suggests that the interplay of stratigraphic noise, accumulation intermittency, and local post‐depositional processes form the proxy signal in the upper snowpack.

Post-depositional modication on seasonal and 1 interannual timescales resets the deuterium excess 2 signals in summer snow layers in Greenland

“…stratigraphic noise, e.g. Steensen, 1985;Münch et al, 2017;Zuhr et al, 2021Zuhr et al, , 2023. The surface snow and near-surface vapor water isotopes co-vary on an hourly-to-daily basis during summer in Northern Greenland (Steen-Larsen et al, 2014;Hughes et al, 2021;Wahl et al, 2021Wahl et al, , 2022.…”

“…The top 1-m of snow has a nearly constant density prole of approximately 337 kg/m 3 , presumably constant because of the persistently high winds at EastGRIP (Schaller et al, 2016;Nakazawa et al, 2021;Komuro et al, 2021). The snow surface is spatially heterogeneous in height, with surface features smoothing slightly throughout the summer seasons (Zuhr et al, 2021(Zuhr et al, , 2023.…”

“…Proles taken along one track and adjacent in time are then considered to represent the same snow. These proles are still susceptible to stratigraphic noise documented by Zuhr et al (2023). A single prole was taken by gently pushing a 10-cm diameter carbon ber tube (i.e.…”

“…At EastGRIP, the uneven surface and concomitant heterogeneous distribution of precipitation results in spatially heterogeneous isotopic concentrations of snow (Zuhr et al, 2023). A perfectly horizontal average of δ 18 O in snow then represents a mixture of events across time (Münch et al, 2017).…”

“…A perfectly horizontal average of δ 18 O in snow then represents a mixture of events across time (Münch et al, 2017). Zuhr et al (2023) estimates that the 2σ spread around mean δ 18 O values as a function of depth is 2.9 o /oo due to the impact of this stratigraphic noise. For this study, tracking chronological layers is critical so that wind-driven spatial heterogeneity in δ 18 O is separated from other processes at work in the near-surface snow.…”