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.
Highlights
The traditional interpretation of stable water isotopes in ice cores is based on the linear relationship between local temperature 20 and first order parameters δ18O and δD of surface snow on ice sheets (Dansgaard, 1964)
295 In this study, we present an empirical specific surface area (SSA) decay model for surface snow of polar ice sheets based on continuous daily SSA measurements
This study addresses the rapid SSA decay driven by surface snow metamorphism
Summary
The traditional interpretation of stable water isotopes in ice cores is based on the linear relationship between local temperature 20 and first order parameters δ18O and δD of surface snow on ice sheets (Dansgaard, 1964). Many factors must be accounted for when reconstructing temperature in ice cores, including precipitation intermittency (Casado et al, 2020; Laepple et al, 2018), past variations in ice-sheet elevation (Vinther et al, 2009), sea ice extent (Faber 25 et al, 2017; Sime et al, 2013), and firn diffusion (Johnsen et al, 2000; Landais et al, 2006; Holme et al, 2018). Recent studies have documented isotopic composition change during precipitation-free periods (Steen-Larsen et al, 2014; Ritter et al, 2016; Casado et al, 2018; Hughes et al, 2021), linked to synoptic variations in atmospheric water vapour composition and subsequent snow-vapour exchange (Steen-Larsen et al, 2014). Current research aims to quantify the influence of postdepositional processes on isotopic change of the surface snow (Steen-Larsen et al, 2014; Ritter et al, 2016; Madsen et al, 30 2019; Wahl et al, 2021)
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