Abstract:
The use of a boundary-layer parameterization of buttressing and ice flux across grounding lines in a
two-dimensional ice-sheet model is improved by allowing general orientations of the grounding line.
This and another modification to the model's grounding-line parameterization are assessed in three
settings: rectangular fjord-like domains (MISMIP+ and MISMIP3d), and 10 future simulations of
West Antarctic ice retreat under RCP8.5-based climates. The new modifications are found to have
significant effects on the fjord-like results, which are now within the envelopes of other models
in the MISMIP+ and MISMIP3d intercomparisons. In contrast, the modifications have little effect on
West Antarctic retreat, presumably because dynamics in the wider major Antarctic basins are
adequately represented by the model's previous simpler one-dimensional formulation. As future
grounding lines retreat across very deep bedrock topography in the West Antarctic simulations,
buttressing is weak and 15 deviatoric stress measures exceed the ice yield stress, implying that
structural failure at these grounding lines would occur. We suggest that these grounding-line
quantities should be examined in similar projections by other ice models, to better assess the
potential for future structural failure.
Purpose:
Throughout, files fort.92_*.nc are Netcdf-format files with 2-D maps of selected variables at regular time intervals through a run. The main variables are: alatd, alond latitudes and longitudes at grid centers. h ice thickness. hs surface elevation (ice, land, or ocean). hb bedrock elevation. utop, vtop surface ice velocities (in x,y directions of the polar stereographic grid). maskwater 0 if grounded ice or land, 1 if floating ice or/ocean. alatd, alond grid cell-center latitude, longitude, for the polar stereographic grid. time = years BP (negative) or AP (positive). fort.22 are tabular ascii files with time series of overall quantities (column 1 = time, column 16 = total ice volume, last column = equivalent sea level change allowing for ice over flotation). fort.885 are tabular ascii files with time series of center-line x-axis locations of the grounding line in idealized-fjord experiments (column 1 = time, column 2 = x-axis position). The files and directories in the archive are: README_PD2020.txt ----------------- This file RunMISMIP+ (subdirectory) ------------------------- Contains subdirectories with files fort.92.nc and fort.22, for idealized fjord-like MISMIP+ experiments: Run_<ctl,1ra,1rr,2ra,2rr>_<1,2>_<v1,v2,v3> where ctl = control, 1ra to 2rr = MISMIP+ label as in Cornford et al., The Cryo. Disc., 2020. 1 or 2 = model resolution (1 km or 2 km). v1, v2, v3 = model version with various improvements, described in PD2020. RunWAIS (subdirectory) ---------------------- Contains subdirectories with files fort.92.nc, fort.22 and fort.885 for idealized fjord-like MISMIP+ experiments: Run_<ctl,fua,fub>_<v1,v2,v3> where ctl = control, fua = RCP8.5-like future climate, no hydrofracturing or cliff failure. fub = RCP8.5-like future climate, with hydrofracturing and cliff failure. v1, v2, v3 = model version as described in PD2020. Code_031420 ----------- Fortran code source (*.F) and include (*.h) files for the ice-sheet model and version number used in the paper: PSUICE3D v2. These files are also in tar file allcode.sheetshelf_031420.tar. Make ---- make files to compile and link the model. They can use either gfortran or Intel Fortran (ifort) compilers. For the West Antarctic cases to compile and run, edits for pathnames on different machines are needed in the make files and comicepath.h, and additional Antarctic observational dataset and boundary-driving files are needed as inputs. make_eg_for_mismip+ typical MISMIP+ experiment (idealized channel) make_eg_for_wais typical West Antarctic simulation Netcdf_gfortran --------------- Netcdf library files (libnetcdf.a and netcdf.inc) used in compiling and linking, with gfortran selected in the make file. Netcdf_ifort ------------ Netcdf library files (libnetcdf.a and netcdf.inc) used in compiling and linking, with ifort selected in the make file.
Supplemental_Information:
Pollard, D., and R.M. DeConto. 2020. Improvements in one-dimensional
grounding-line parameterizations in an ice-sheet model with lateral
variations. Geosci. Model Dev. Disc, in review,
https://doi.org/10.5194/gmd-2020-131.
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