FirnR: Simulate and analyse firn and ice cores

Overview

FirnR is an R package that provides tools for working with and simulating of polar firn and ice cores, with a focus on the isotopic composition.

Methods implemented include:

• depth-dependent modelling of firn density (Herron-Langway model);
• depth-dependent modelling of the diffusion length in firn for stable water isotopologues, both in depth and temporal units;
• working with firn/ice-core depth scales:
  • retrieving/calulating top, bottom, midpoint depths and layer thicknesses;
  • conversion between true and water-equivalent depth scales;
• estimation of firn parameter changes over depth (densification rate, depth scale compression, diffusion length);
• modelling of the smoothing effect of isotope profiles by firn diffusion;
• simulation of temporal changes of firn isotope profiles from advection, depth scale compression and diffusion;
• forward simulation of isotope profiles based on meteorological data.

Installation

FirnR can be installed directly from GitHub:

# install.packages("remotes")
remotes::install_github("EarthSystemDiagnostics/FirnR")

Package data

FirnR includes example firn density data over the first 25 m of the cores B41 and B42 (Freitag et al., 2013; Laepple et al., 2016), which were drilled in close vicinity of Kohnen Station in Dronning Maud Land, Antarctica, in the field season 2012/2013 as part of the ANT-Land-2012 campaign of the COFI project; see ?b41.b42.density.

Vignettes

To highlight certain applications of FirnR, two package vignettes are provided:

• the vignette Density and diffusion length data introduces the firn density data that is provided with FirnR (see above) and showcases how to use package functions to obtain modelled density and diffusion length data;
• the vignette Estimating and modelling temporal changes of firn properties and profiles highlights the functions which can be used to estimate temporal changes, i.e. variations with depth, of firn properties, specifically density and diffusion length, and to model how these changes affect firn proxy records such as stable isotope profiles. Application of these methods is described in detail in Münch et al. (2017).

Literature cited

Freitag, J., Kipfstuhl, S., and Laepple, T.: Core-scale radioscopic imaging: a new method reveals density-calcium link in Antarctic firn, J. Glaciol., 59, 1009–1014, https://doi.org/10.3189/2013JoG13J028, 2013

Laepple, T., Hörhold, M., Münch, T., Freitag, J., Wegner, A., and Kipfstuhl, S.: Layering of surface snow and firn at Kohnen Station, Antarctica: Noise or seasonal signal?, J. Geophys. Res. Earth Surf., 121, 1849–1860, https://doi.org/10.1002/2016JF003919, 2016

Münch, T., et al., Constraints on post-depositional isotope modifications in East Antarctic firn from analysing temporal changes of isotope profiles, The Cryosphere, 11(5), 2175-2188, https://doi.org/10.5194/tc-11-2175-2017, 2017

Author and funding information

The R code in this package has been written and implemented by Dr. Thomas Münch, with contributions by Dr. Thomas Laepple, at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), Germany. For further information, code enhancements or potential bugs, please write to <thomas.muench@awi.de>, or open an issue on the repository page.

This work was supported by Helmholtz funding through the Polar Regions and Coasts in the Changing Earth System (PACES) programme of the Alfred Wegener Institute, by the Initiative and Networking Fund of the Helmholtz Association Grant VG-NH900, by the AWI strategy fund (project "COMB-i"), and by funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 716092).