EGU23-10179
https://doi.org/10.5194/egusphere-egu23-10179
EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Isotope diffusion in ice enhanced by vein-water flow

Felix Ng
Felix Ng
  • Department of Geography, University of Sheffield, Sheffield, United Kingdom (f.ng@sheffield.ac.uk)

Diffusive smoothing of signals on the water stable isotopes in ice sheets limits the climatic information retrievable from these ice-core proxies. Previous theories explained how, in polycrystalline ice below the firn, fast diffusion in the network of intergranular water veins short-circuits the slow diffusion in crystal grains to cause “excess diffusion”, enhancing the signal smoothing rate above that implied by self-diffusion in ice monocrystals. However, the controls of excess diffusion remain poorly understood. I show that vein-water flow amplifies excess diffusion, by altering the three-dimensional field of isotope concentrations and isotope transfer between the veins and crystals. The rate of signal smoothing depends not only on temperature, vein and grain sizes, and signal wavelength, but also on vein-water flow velocity, which can increase the rate by 1 to 2 orders of magnitude. This modulation can significantly impact signal smoothing at ice-core sites in Greenland and Antarctica, as demonstrated by simulations for the GRIP and EPICA Dome C sites, which show sensitive modulation of their diffusion-length profiles when vein-water flow velocities reach ~ 101–102 m yr–1. Thus vein-flow mediated excess diffusion may help explain the mismatch between modelled and spectrally-derived diffusion lengths in other ice cores. I also show that excess diffusion biases the spectral estimation of diffusion lengths from isotopic signals and the reconstruction of surface temperature from diffusion-length profiles. These findings caution against using the single-crystal isotopic diffusivity to represent the bulk-ice diffusivity. The need to predict excess diffusion in ice cores calls for extensive study of isotope records for its occurrence and better understanding of vein-scale hydrology in ice sheets.

How to cite: Ng, F.: Isotope diffusion in ice enhanced by vein-water flow, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10179, https://doi.org/10.5194/egusphere-egu23-10179, 2023.