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- W4254039460 abstract "<p>Ice-core analysis shows that climatic signals carried by dissolved impurities (e.g., sulphate) in the water veins exhibit peak broadening and damping with depth into the ice. Such diffusion distorts the signals progressively, limiting the retrievability of the past climatic variations, notably their time resolution. A mechanism put forward for the diffusion invokes continuous differential grain growth in creating gradients in impurity concentration in the vein water (Barnes et al., 2003). Separately, a mechanism known as &#8220;anomalous diffusion&#8221; has been proposed (Rempel et al., 2001) where vertical temperature gradients in the ice drive the migration of chemical peaks without diffusion &#8212; this migration causes age offset between the signals and the ice. Here, we show that climatic signals diffuse because of constant dynamical evolution of the vein network in polycrystalline ice that accompanies grain-boundary migration. In this new mechanism, the stochastic motion of vein segments carrying solute leads to a net diffusive transport of impurities when there is spatial gradient in the bulk impurity concentration or porosity. By modelling this phenomenon with a statistical-mechanical formulation in three dimensions, we find that the diffusivity <em>&#954;</em> for the bulk impurity concentration is given by <em>&#954;</em> = <em>K</em>(<em>T</em>)/3c, where <em>K</em> is the temperature-dependent grain growth rate and c (&#8776; 2 to 3) is a geometry constant, and that <em>&#954;</em> is independent of the mean grain size. The description of porosity follows an advection-diffusion equation that includes the other processes of Rempel et al. (2001) and Barnes et al. (2003). Our calculations for the Greenland summit ice cores and the EPICA ice core predict diffusivities of <em>&#954;</em> &#8764; 10<sup>&#8211;8</sup> &#8211; 10<sup>&#8211;7 </sup>m<sup>2</sup> yr<sup>&#8211;1</sup>, which can explain the observed amount of peak broadening. Further including into this theory the regelative transport of the solute by water flow along the veins reveals a correction of &#8776; 10% for the signal migration speed predicted by Rempel et al. (2001). Besides contributing a new diffusion mechanism, our study highlights the importance of grain-scale recrystallisation processes for understanding bulk ice properties.</p>" @default.
- W4254039460 created "2022-05-12" @default.
- W4254039460 creator A5029342420 @default.
- W4254039460 date "2020-03-10" @default.
- W4254039460 modified "2023-09-30" @default.
- W4254039460 title "Diffusion of climatic signals in ice cores by vein migration" @default.
- W4254039460 doi "https://doi.org/10.5194/egusphere-egu2020-16739" @default.
- W4254039460 hasPublicationYear "2020" @default.
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