Doomed descent? How fast sulphate signals diffuse in the EPICA Dome C ice column

作者：Felix Ng, Rachael H. Rhodes, T. J. Fudge, Eric Wolff · 年份：2025 · DOI：10.5194/egusphere-2025-1566 · 被引用次数：1 · 研究领域：Astrophysics and Cosmic Phenomena、Gamma-ray bursts and supernovae、Neutrino Physics Research

Abstract. The loss of climate information due to smoothing of ionic impurity signals in ice provides a strong motivation for understanding their diffusion rates at ice-core sites. By analysing sulphate signals in the EPICA Dome C (EDC) core, recent studies estimated the vertical profile of effective diffusivity Deff at that site. However, Deff crudely approximates the local diffusivity D in the ice, it being a nonuniform-weighted average of D over large intervals. We formulate the mathematical inversion for retrieving the D profile from observed signals, which reconciles the findings of the earlier studies as well as elucidating the averaging approximation. Inversion for EDC sulphate reveals a rapid decrease in D through the firn layer – from ≈ 10–6 m2 yr–1 at the surface to ≈ 1.7 × 10–8 m2 yr–1 at the firn-ice transition (≈ 100 m depth, ≈ 2.5 ka), followed by a gradual decline to ≈ 10–10 m2 yr–1 through 100–2700 m (2.5–390 ka). This profile enables new interpretation of sulphate transport in the EDC column. We propose vapour diffusion of H2SO4 through interconnecting air pores as the cause of the high firn diffusivity. By evaluating the mechanisms controlling D below the firn (diffusion through ice crystals, liquid veins and grain boundaries and diffusion arising from interfacial motion), we infer a dominant partitioning of signals immediately below the firn to a connected vein system, and progressive smoothing of vein signals by Gibbs–Thomson diffusion down to ≈ 2000 m dept...