DOI: 10.5061/dryad.xd2547dvb
title: Impacts of bed topography resolution on sea-level rise projections from coupled subglacial hydrology and ice dynamics for Thwaites Glacier, Antarctica

description: Ice sheet models require explicit knowledge of the underlying bed.
 However, much remains unknown regarding the subglacial environment due to
 difficulties associated with measuring it. Extensive radar surveys have
 been conducted across Antarctica, but the requirement of full-coverage bed
 topography for models necessitates interpolation over gaps between
 existing observations, which often span kilometers or more. Advances in
 modeling capabilities now allow for the application of dynamic coupling
 between subglacial hydrology and ice dynamics in models of Antarctica.
 While a bed resolution of ~1 km is recommended for modeling Antarctic ice
 dynamics, it has been suggested that finer spatial resolutions are
 necessary to resolve subglacial water flow. We use a coupled model
 configuration to generate projections of glacier evolution, including the
 subglacial hydrologic system, for Thwaites Glacier, West Antarctica,
 initiated with several different bed topographies. We find that the
 specific bed topography has a first-order control on accumulated mass
 loss, but that final sea-level rise does not scale with bed resolution. We
 also find that coupling between subglacial hydrology and ice dynamics
 results in faster mass loss. Our results underscore the importance of
 continued high-resolution topography mapping and suggest that current
 projections may underestimate uncertainty linked to unresolved bed
 features.
description: This dataset includes the complete output from 9 simulations
 conducted using the Ice-sheet and Sea-level System Model (ISSM). The
 simulations explore variations in the representation of subglacial
 hydrology and bed topography resolution. Alongside the model outputs, we
 include all necessary files and code used to produce the figures presented
 in the manuscript. Code/Software
 This work was done using the Ice-sheet and Sea-level System Model
 (ISSM) and the Glacier Drainage System Model (GlaDS). GlaDS is implemented
 within ISSM, which is open access and available for download at https://issm.jpl.nasa.gov/. These scripts were run using ISSM version 4.24 and MATLAB version R2021b.
description: # Impacts of bed topography resolution on sea-level rise projections from
 coupled subglacial hydrology and ice dynamics for Thwaites Glacier,
 Antarctica Dataset DOI: [10.5061/dryad.xd2547dvb](10.5061/dryad.xd2547dvb)
 ### Description of the data and file structure The data provided here is
 organized into 2 folders and 1 .mat file: Results and Figures. The file
 TG_Initialize_Transient_500mBed_NGlaDS.mat contains the model state just
 prior to running the model relaxation for the simulation using effective
 pressure from GlaDS and the 500-meter resolution bed topography. This file
 contains all fields and initial conditions necessary to launch the
 transient simulation corresponding to this bed and effective pressure
 combination. It includes results from the inversion and thermal model
 steps, as well as all required parameter values. ### Model_Forcing:
 DATA_repo.zip #### Results This folder contains all relatent model output
 used in our analysis organized into 6 subfolders: Bed, Geometry, GL, SGH,
 VAF, and Vel. All files containing model results are named to identify the
 variable contained in the file, the bed resolution used in the model
 simulation, and the representation of subglacial hydrology (SGH) used
 where "Coupled" indicates synchronous coupling between the ice
 dynamics and subglacial hydrology modules, "NGlaDS" indicates
 effecitve pressure from steady state GlaDS, and "Nparam"
 indicates effective pressure approximated from the assumption of perfect
 connectivity to the ocean. * **Bed:** 3 files (Bed_5km.mat, Bed_100m.mat,
 and Bed_500m.mat) containing the bed topography data at the 3 spatial
 resolutions used in this work projected onto our modeling domain. All bed
 topography is reported in meters and positive values indicate a bed height
 above sea-level. * **Geometry:** 18 files containing the final model
 output, corresponding to simulation year 2300, for the base of the glacier
 (Base) and ice thickness (H) for each of the 9 model simulations. All
 geometry values are reported in meters, and negative values indicate
 meters below sea-level. * **GL:** contains two subfolders (Exp and MAT), 1
 MATLAB script (get_GL_intersections.m), 3 additional .mat files, and 1
 .exp file. The MAT folder contains the grounding line location at various
 check points throughout the simulations for each of the 9 bed/SGH
 combinations. Grounding line location is saved for the years 2015, 2050,
 2100, 2150, 2200, 2250, and 2300. This folder contains a total of 63
 files. MATLAB files describing the grounding line location are converted
 to .exp files, which are saved in the Exp folder. There are 63 .exp files
 with matching naming convention to their corresponding MATLAB files. The
 .exp files are generated using an ISSM function called isoline.m. The
 following is an example of its usage: ``` &gt;&gt; GL =
 load('GL_100mBed_Coupled_2015.mat'); &gt;&gt; Contour =
 isoline(md, GL, 'value', 0, 'output',
 'GL_100mBed_Coupled_2015.exp'); ``` The .exp files are used in
 plotting functions to generate the manuscript figures. They are also used
 by the function get_GL_intersections.m to calculate the x-y position in
 Polar Stereographic coordinates where the modeled GL intersects with a
 central flowline of Thwaites at various times during the simulation. The
 flowline coordinates are contained in the file labled Thwaites_FL_GL.exp,
 and the calculated intersections are contained in the 3 files
 GL_intersection_N_Coupled.mat, GL_intersection_N_GlaDS.mat, and
 GL_intersection_N_POC.mat. * **SGH:** 6 files containing results for the
 subglacial hydrology model output from the steady state GlaDS simulations
 for each of the 3 bed topographies used. Files labeled with h correspond
 to the thickness of the distributed sheet of subglacial water in units of
 meters. Files labeled with S correspond to the channelized discharge in
 units of cubic meters per second. * **VAF:** 18 files containing
 timeseries data of the ice volume above floatation for each of the 9 model
 simulations. VAF files contain the ice volume (cubic meters) timeseries
 and files labled with time contain the corresponding model times (years)
 of each data point. * **Vel:** 9 files containing the final velocity
 corresponding to simulation year 2300 for all three model runs. Files are
 labeled to indicate the parameter combination of its simulation, and
 velocity is reported in units of meters per year. #### Figures This folder
 contains one subfolder labeled Exp and 5 plotting scripts corresponding to
 each of the 5 figures in the main document. Plotting scripts will pull
 results from the relevant subdirectory in the Results folder, and
 supplemental data files (domain outline, Thwaites flowline, etc) from the
 Figures/Exp subfolder, and then generate and save figures shown in the
 main manuscript. There is one plotting script per paper figure, and they
 each require the parameterized model
 TG_Initialize_Transient_500mBed_NGlaDS.mat to be loaded in MATLAB on a
 computer with ISSM installed before running. The following is an example
 of their usage using MATLAB in the terminal: ``` &gt;&gt; md =
 loadmodel('TG_Initialize_Transient_500mBed_NGlaDS.mat');
 &gt;&gt; cd Figures &gt;&gt; plot_context(md); ```