Preprints
https://doi.org/10.5194/tc-2020-217
https://doi.org/10.5194/tc-2020-217

  07 Sep 2020

07 Sep 2020

Review status: a revised version of this preprint was accepted for the journal TC and is expected to appear here in due course.

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

Felix S. L. Ng Felix S. L. Ng
  • Department of Geography, University of Sheffield, Sheffield, UK

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.

Felix S. L. Ng

 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Felix S. L. Ng

Model code and software

Computer code and simulated data of the paper "Pervasive diffusion of climate signals recorded in ice-vein ionic impurities" Felix S. L. Ng https://doi.org/10.15131/shef.data.12735191

Video supplement

Supplement of the paper "Pervasive diffusion of climate signals recorded in ice-vein ionic impurities" Felix S. L. Ng https://doi.org/10.15131/shef.data.12739169

Felix S. L. Ng

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Short summary
Current theory predicts climate signals in the vein chemistry of ice cores to migrate, hampering their dating. I show that the Gibbs-Thomson effect, which has been overlooked, causes fast diffusion that prevents signals from surviving into deep ice. Therefore the deep climate peaks in Antarctic and Greenland ice cores must be due to impurities in the ice matrix (outside veins) and safe from migration. These findings reset our understanding of postdepositional changes of ice-core climate signals.