ICESHEET 1.0
This is software to create perfectly plastic ice sheets. I used this to create reconstructions of the Laurentide Ice Sheet (see The NAICE model below). There is a paper on this in Geoscience Model Development. I have included a sample problem with the Greenland Ice Sheet with the scripts that should make it pretty easy to run the program. I usually modify these scripts to suit the problem I am working on. They require Generic Mapping Tools and NETCDF Tools. In particular, ICESHEET requires GMT formatted binary files as input for the basal shear stress and basal topography. Note if you downloaded the version of this file from the GMD website, I forgot to include the shapefiles needed to create the shear stress files, so download it again below. Instructions to run this can be found here.
I’ve created a Github repository for ICESHEET. All new modifications can be found there.
The NAICE model
This is a model of the North American ice sheet model covering the last glacial cycle. It was constructed using a simple plastic ice sheet assumption. The model was adjusted to fit GIA constraints as closely as possible. Due to the enormous size of the ice complex, I focused on the western half of the Laurentide ice sheet, basically everything east of the Cordillera, and west of a line running from Hudson Bay through to Minnesota (capturing the James and Des Moines lobes). The model resolution is 0.25 degrees latitude by 0.5 degrees longitude. The Earth model parameters used to construct the model and determine paleotopography are as follows:
Lithosphere: 120 km
Upper Mantle (< 670 km depth): 4×1020 Pa s
Lower Mantle (> 670 km depth): 1022 Pa s
Ice thickness values are relative to modern day (i.e. you have to add any ice volume in the ice caps in Arctic Canada and glaciers in the Cordillera to get the true ice thickness).
Please cite this paper if you use this model:
- Gowan, E.J., Tregoning, P., Purcell, A., Montillet, J.-P., and McClusky, S., 2016. A model of the western Laurentide Ice Sheet, using observations of glacial isostatic adjustment. Quaternary Science Reviews, 139, 1-16, doi:10.1016/j.quascirev.2016.03.003
Note that the paleotopography does not include Greenland, which was part of the ANU ice sheet model.
NetCDF files of thickness and paleotopography
Postscript plots of thickness and paleotopography
Manipulating NAICE
If you want to calculate the NAICE reconstructions from scratch, or maybe create your own reconstructions, I have created a bundle that will allow you to do this. Included are the GIA deformation files, since the sea level calculator I used (calsea) is not open source, so I cannot distribute it. An option might be SELEN, by Spada et al. The drawback of this software versus calsea is that it doesn’t take into account changing shorelines, so in places like around Hudson Bay (where the shoreline has changed substantially over the past 8000 years), it will not give the correct response. If you want to run this, I suggest reading the readme file, which gives the instructions that should allow you to run this. I’ve included some pre-compiled binaries of the programs needed (such as ICESHEET), which was done using ifort, which is a lot faster than gfortran.
Downlaod the NAICE_setup
If you have questions, email me at evangowan@gmail.com
Raised Beaches 