Setup files for MITgcm simulations (2D) of the Sherard Osborn Fjord with varying sill depth and subglacial discharge

Jonathan Wiskandt

This repository provides files to setup the MIT General Circulation Model (MITgcm, Mid 2020 Version) and run a set of experiments.

The experiments run can be used to analyze the circulation underneath the ice tongue of Ryder Glacier in Sherard Osborn Fjord. Furthermore a set of sensitivity experiments are available to investigate the response of the system and the melt rate to changes in the fjord sea floor geometry (namely the height of a sill in front of the ice shelf) and changes in subglacial discharge volume.

The simulations are in 2D (along-fjord and vertical) and span the cavity under the ice tongue and the first sill of located in the Sherard Osborn Fjord. The geometry is highly idealized and the simulations are initiated with averaged temperature and salinity profiles taken on the Ryder 2019 expedition with the Swedish icebreaker Oden.

Citation

Jonathan Wiskandt (2024) Setup files for MITgcm simulations (2D) of the Sherard Osborn Fjord with varying sill depth and subglacial discharge. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/wiskandt-2024-sof-sill-1

References

Jakobsson, M., Mayer, L. A., Nilsson, J., Stranne, C., Calder, B., O’Regan, M., Farrell, J. W., Cronin, T. M., Brüchert, V., Chawarski, J., Eriksson, B., Fredriksson, J., Gemery, L., Glueder, A., Holmes, F. A., Jerram, K., Kirchner, N., Mix, A., Muchowski, J. Padman, J. (2020). Ryder Glacier in northwest Greenland is shielded from warm Atlantic water by a bathymetric sill. In Communications Earth & Environment (Vol. 1, Issue 1). Springer Science and Business Media LLC. https://doi.org/10.1038/s43247-020-00043-0

Wiskandt, J., Koszalka, I. M., & Nilsson, J. (2023). Basal melt rates and ocean circulation under the Ryder Glacier ice tongue and their response to climate warming: a high-resolution modelling study. In The Cryosphere (Vol. 17, Issue 7, pp. 2755–2777). Copernicus GmbH. https://doi.org/10.5194/tc-17-2755-2023

Wiskandt, J., Nilsson, J., and Koszalka, I. M. (2024). Hydraulic Control of submarine glacial melt in Greenlandic fjords. Manuscript in preparation.

Data description

This dataset contains the four directories listed below.

1. l128_code Files to compile the MITgcm simulations. Here you change parameters that have to be set before compiling.

   • SIZE.h set grid dimensions and split domain for parallelization
   • SHELFICE_OPTIONS.h set options for Shelfice Package
   • packages.conf define which packages to use
   • OBCS_OPTIONS.h set options for Open Boundary Conditions (OBCS) package
   • CPP_OPTIONS.h set options for MITgcm in general

2. l128_build Empty folder for the files for compiling the model, using the instructions from the MITgcm documentation.

3. l128_run Sub-directories containing files to run the compiled model. The name of the sub-directories is constituted of 6 parameters, e.g. 64km_ryd_1SLOPE_AW02_sill810_sgd200.

   1. 64km Model domain width
   2. ryd Fjord name Ryder
   3. 1SLOPE Single shape slope (constant angle)
   4. AW02 Atlantic water temperature of ~0.2 degree Celsius
   5. sill810 Sill height
   6. sgd200 Subglacial discharge of 200% of reference experiments basal melt

4. l128_output contains the time averaged (last 40 model days) fields. The name of the files is constituted of 9 parameters, e.g. l128_64km_ryd_1SLOPE_AW02_sill250_161_200_TimeAve.

   1. I128 name of the model build (l - large domain, 128 - 128 processes)
   2. 64km Model domain width
   3. ryd Fjord name Ryder
   4. 1SLOPE Single shape slope (constant angle)
   5. AW02 Atlantic water temperature of ~0.2 degree Celsius
   6. sill250 Sill height
   7. 161 start day of model output
   8. 200 end day of model output
   9. TimeAve Time average from start day to end day

For further instructions on how to use MITgcm please refer to its documentation.

MITgcm namelist files are written to be read by Fortran code. The input data is created using a python script named gendata.py (both data and the script can be found in the repository). The script read CTD data provided in a separate dataset: Oceanographic CTD data from the Ryder 2019 expedition

Model build instructions

Please follow the simple instructions below to build the model.

% cd l128_build
% ../tools/genmake2 -mods ../code -optfile «/PATH/TO/OPTFILE»
% make depend
% make

Please refer to the full documentation for further instructions of how to build the model

Model run instructions

Please follow the simple example below to run the model.

% cd ../l128_run/64km_ryd_1SLOPE_AW02_sill810_sgd200
% python gendata.py
% cp ../l128_build/mitgcmuv .
% ./mitgcmuv

Please refer to the full documentation for further instructions of how to build the model