Pervasive diffusion of climate signals recorded in ice-vein ionic impurities

Abstract

Abstract. A theory of vein impurity transport conceived two decades ago predicts that signals in the bulk concentration of soluble ions in ice migrate under a temperature gradient. If valid, it would mean that some palaeoclimatic signals deep in ice cores (signals from vein impurities as opposed to matrix/grain-boundary impurities) suffer displacements that upset their dating and alignment with other proxies. We revisit the vein physical interactions to show that a strong diffusion prevents such signals from surviving into deep ice. It arises because the Gibbs–Thomson effect, which the original theory had neglected, perturbs the impurity concentration of the vein water wherever the bulk impurity concentration carries a signal. Thus no distinct vein signals will reach a depth where their displacement matters; accordingly, the palaeoclimatic concern posed by the original theory no longer stands. Simulations with signal peaks introduced in shallow ice at the GRIP and EPICA Dome C ice-core sites confirm that rapid damping and broadening eradicates their form by two-thirds way down the ice column; artificially reducing the solute diffusivity in water (to mimic partially-connected veins) by 103 times or more is necessary for signals to penetrate into the lowest several hundred metres with minimal loss of amplitude. The deep solute peaks observed in ice cores can only be explained by widespread vein disconnection or a dominance of matrix/grain-boundary impurities at depth (including their recent transfer to veins); in either case, the deep peaks would not have displaced far. Decomposing the vein and matrix impurity contributions will aid robust reconstruction from ion records.

Geochemical Characterization of Insoluble Particle Clusters in Ice Cores Using Two‐Dimensional Impurity Imaging

“…As ice grains grow in size, especially in deep ice, they can either displace impurities which are subsequently preferentially located at the grain boundaries, or experience drag by inclusions of insoluble impurities (Stoll, Eichler, Hörhold, Shigeyama, & Weikusat, 2021 and references within). On the one hand, especially soluble species are affected by the diffusion along the network of ice veins, which can cause possible post‐depositional alteration of ice core paleoclimate records (Ng, 2021; Rempel et al., 2001). On the other hand, post‐depositional change has also been documented for insoluble impurities related to dust deposition.…”

Biolocomotion and premelting in ice

“…The latter represents the active fluctuations of the system, such as those originating in particular processes described in [60][61][62][63]. Nutrient sources, such as dissolved silica, oxygen, nitrogen and methane, play a vital role in the life of ice-bound micro-organisms, such as algae and bacteria [64][65][66][67][68][69][70]. Here we assume that Dch > Da , consistent with [71][72][73][74], and Dch > D(z).…”

Effective diffusivity of sulfuric acid in Antarctic ice cores

“…The modeling of diffusion of sulfate (e.g. Rempel et al, 2001;2002;B03;Ng et al, 2021) has focused on sulfate in a vein network. However, the location of sulfate is not well established and will affect the ability for sulfate to diffuse.…”

“…Addressing the diffusion of sulphate in veins, Rempel et al (2001) showed that impurity fluctuations may retain their amplitude but migrate towards warmer temperatures and away from the ice the impurity was deposited with; however, Ng (2021) showed that including the Gibbs-Thompson effect due to the grain curvature may cause these peaks to diffuse rapidly and therefore not retain their amplitude nor migrate. The sulfate and electrical conductivity measurements (ECM) of Antarctic ice cores also show reduced amplitude (Barnes et al, 2003, hereafter B03;Fujita et al, 2015;Fudge et al, 2016) in older ice.…”