DOI: 10.7280/d1x12s
title: Data from: Subglacial discharge accelerates future retreat of Denman and Scott Glaciers, East Antarctica

description: Ice shelf basal melting is the primary mechanism driving mass loss from
 the Antarctic Ice Sheet, yet it is unknown how the localized melt
 enhancement from subglacial discharge will impact future Antarctic glacial
 retreat. Here, we develop a parameterization of ice shelf basal melt that
 accounts for both ocean and subglacial discharge forcing and apply it in
 future projections of Denman and Scott Glaciers, East Antarctica, through
 2300. In forward simulations, subglacial discharge accelerates retreat of
 these systems into the deepest continental trench on Earth by 25 years.
 During this retreat, Denman Glacier alone contributes 0.33 mm/yr to global
 sea level rise, comparable to half of the contemporary sea level
 contribution of the entire Antarctic Ice Sheet. Our results stress the
 importance of resolving complex interactions between the ice, ocean, and
 subglacial environments in future Antarctic Ice Sheet
 projections.  In this data publication, we present the model
 output and results associated with the following manuscript submitted to
 Science Advances: “Subglacial discharge will accelerate retreat of Denman
 and Scott Glaciers, East Antarctica”. We include yearly ice sheet model
 output between 2017-2300 for models that do and do not resolve subgalcial
 discharge in the melt calculation. We also include the ice sheet
 model's initial state. In addition, we include all ocean forcing
 time-series (temperature and salinity for the control, low emission, and
 high emission climate forcing scenarios) and the present-day chanellized
 subglacial discharge flux field over the Denman and Scott Glacier model
 domain, which are used as input into the melt parameterization. Lastly, we
 include a MATLAB script that contains the code used for ice shelf melt
 rate computation as well as a "README" file with further
 information on all data in this publication. 
description: <strong>Ice sheet model results</strong>: Direct
 results taken from the Ice-sheet and Sea-level System Model (ISSM, Larour
 et al. 2012) with no processing applied, provided yearly as *.mat
 files. <strong>Ice sheet model initial
 state</strong>: Initial state (ice geometry, mesh information,
 inversion results, etc.) of the ice sheet model containing Denman and
 Scott Galciers with no processing applied, provided as a *.mat file. The
 contents of the *.mat file is a MATLAB variable of class
 "model", which is compatible with ISSM.
 <strong>Melt parameterization script</strong>:
 Documented MATLAB script ready to run with the provided data
 sets. <strong>Ocean temperature and salinity
 timeseries</strong>: Bottom ocean temperature
 (<sup>°</sup>C) and salinity (PSU) timeseries  (January 1st,
 2017 through December 31, 2299) extracted from an East Antarctic
 configuration of the ocean component of the MITgcm (Pelle et al., 2021).
 Temperature and salinity were averaged bi-weekly along the ice fronts of
 Denman and Scott Glaciers (see white dashed contour in figure 1a of the
 main manuscript text) along the sea floor. Data are provided as *.mat
 files. Note that the ocean model in Pelle et al. (2021) was run through
 2100. In the control and low emission scenarios, we repreat the last
 20-years of simulated ocean (2079-2099) conditions through 2300. In the
 high emission scenario, where a clear warming trend was evident in the
 ocean temperature after 2050, we extrapolate this warming trend with a
 square-root function and add this onto the retreated 2079-2099 repearted
 forcing. <strong>Channelized discharge flux
 data</strong>: Present-day output from the Glacier Drainage Systems
 (GlaDS) model in units of m<sup>3</sup>/s over grounded
 elements of the domain. Data is provided in a *.xyz file (see README.txt
 for instructions on how to load the data and interpolate onto model mesh
 using MATLAB). No processing has been applied other than subglacial flux
 values less than 0.001 m<sup>3</sup>/s have been removed from
 the dataset.
description: Ice sheet modeling results and initial states are compatible with
 the open source, NASA funded Ice-sheet and Sea-level System Model (ISSM,
 Larour et al. 2012), which is freely available for download here. In addition,
 the data files provided in the publication are available as *.mat files,
 which are compatible with MATLAB but can be accessed using most scripting
 languages.
description: # Data from: Subglacial discharge accelerates future retreat of Denman and
 Scott Glaciers, East Antarctica
 [https://doi.org/10.7280/D1X12S](https://doi.org/10.7280/D1X12S) Journal:
 Science Advances Principle Investigator: * Tyler Pelle, Scripps
 Institution of Oceanography, University of California San Diego,
 [tpelle@ucsd.edu](mailto:tpelle@ucsd.edu) Co-Authors: * Dr. Jamin
 Greenbaum, Scripps Institution of Oceanography, University of California
 San Diego, [jsgreenbaum@ucsd.edu](mailto:jsgreenbaum@ucsd.edu) * Dr.
 Christine Dow, Department of Geography and Environmental Management,
 University of Waterloo,
 [christine.dow@uwaterloo.ca](mailto:christine.dow@uwaterloo.ca) * Dr.
 Adrian Jenkins, Department of Geography and Environmental Sciences,
 Northumbria University,
 [adrian2.jenkins@northumbria.ac.uk](mailto:adrian2.jenkins@northumbria.ac.uk) * Dr. Mathieu Morlighem, Department of Earth Sciences, Dartmouth College, [Mathieu.Morlighem@dartmouth.edu](mailto:Mathieu.Morlighem@dartmouth.edu) Created on September 5, 2023 ## Description of the data and file structure ### File description: 1. runme.m - MATLAB script used to compute melt rates with and without considering subglacial discharge. 2. ice_ctrl_sd.mat – Yearly ice sheet model output from 2017-2100 for the control subglacial discharge simulation. 3. ice_ctrl_nosd.mat – Yearly ice sheet model output from 2017-2100 for the control non-subglacial discharge simulation. 4. ice_ssp126_sd.mat – Yearly ice sheet model output from 2017-2100 for the low emission (SSP1-2.6) subglacial discharge simulation. 5. ice_ssp126_nosd.mat – Yearly ice sheet model output from 2017-2100 for the low emission (SSP1-2.6) non-subglacial discharge simulation. 6. ice_ssp585_sd.mat – Yearly ice sheet model output from 2017-2100 for the high emission (SSP5-8.5) subglacial discharge simulation. 7. ice_ssp585_nosd.mat – Yearly ice sheet model output from 2017-2100 for the high emission (SSP5-8.5) non-subglacial discharge simulation. 8. T_MITgcm_ctrl.mat – Bi-weekly ocean temperature (Ta) for the control simulation from January 1, 2017 to December 31, 2299 averaged at the ice shelf terminus of Denman and Scott Glaciers, used as input into the melt parameterization. 9. S_MITgcm_ctrl.mat – Bi-weekly ocean salinity (Sa) for the control simulation from January 1, 2017 to December 31, 2299 averaged at the ice shelf terminus of Denman and Scott Glaciers, used as input into the melt parameterization. 10. T_MITgcm126.mat - Same as T_MITgcm_ctrl.mat, but for the low emission scenario. 11. S_MITgcm126.mat - Same as S_MITgcm_ctrl.mat, but for the low emission scenario. 12. T_MITgcm585.mat - Same as T_MITgcm_ctrl.mat, but for the high emission scenario. 13. S_MITgcm585.mat - Same as S_MITgcm_ctrl.mat, but for the high emission scenario. 14. discharge_den.xyz - 2017 modeled channelized subglacial discharge flux output from GlaDS, used as input into the melt parameterization. 15. DenModel.mat – Ice sheet model initial state (January 1, 2021), including all mesh information, ice sheet and ice shelf geometry, inversion fields for basal friction and ice stiffness, and initial state variables. ### File specific information: **DenModel.mat**: All data associated with the ice sheet model initial state is held in DenModel.mat, which contains a MATLAB ‘model’ object (for more information, see [https://issm.jpl.nasa.gov/documentation/modelclass/](https://issm.jpl.nasa.gov/documentation/modelclass/)). In MATLAB, the model can be loaded and displayed by running load(‘DenModel.mat’), which will load in the model variable ‘md’. Of particular interest will be the following data contained in md: md.mesh (mesh information), md.geometry (initial ice sheet geometry, ice shelf geometry, and bed topography), and md.mask (ice mask and grounded ice mask). Note that all fields are defined on the mesh nodes, and one can plot a given field in MATLAB using the ISSM tool ‘plotmodel’. Once IceSheetModel.mat is loaded, we can plot the ice shelf basal melting rate by running the following command: plotmodel(md, ’data’, md.results.TransientSolution(1).BasalforcingsFloatingiceMeltingRate). For more information on plotting, please see [https://issm.jpl.nasa.gov/documentation/plotmatlab/](https://issm.jpl.nasa.gov/documentation/plotmatlab/). **ice_*_sd.mat**: Yearly ice sheet model results between 2017–2300 for the subglacial discharge experiments, where ‘*’ is either ctrl (control), ssp126 (low emission scenario), or ssp585 (high emission scenario). These files contain a MATLAB variable that is the same as the file name, which is a model object of size 1x283 that contains the following yearly variables: * Vel (velocity norm, m/yr) * Pressure (N/A since we use a 2D ice flow model) * Thickness (ice sheet thickness, m) * Surface (ice sheet surface elevation, m) * Base (ice sheet base elevation, m) * BasalforcingsFloatingiceMeltingRate (ice shelf basal melting rate field, m/yr) * MaskOceanLevelset (ground ice mask, grounded ice if &gt; 0, grounding line position if = 0, floating ice if &lt; 0) * IceVolume (total ice volume in the model domain, t) * IceVolumeAboveFloatation (total ice volume in the model domain that is above hydrostatic equilibrium, t) * TotalFloatingBmb (Total floating basal mass balance, Gt) * melt_nodis (ice shelf basal melting rate computed when discharge is set to zero, m/yr) * zgl (grounding line height field, m) * glfw (grounding line fresh water flux field, m<sup>2</sup>/s) * chan_wid (Domain average subglacial discharge channel width, m) * maxdist (5L' length scale used in melt computation, m) * maxdis (maximum discharge at each subglacial outflow location, m<sup>2</sup>/s) **ice_*_nosd.mat:** Same file information as ice_*_sd.mat, but for the non-subglacial discharge ice sheet model simulations without the following variables: melt_nodis, zgl, glfw, chan_wid, max_dist, and max_dis. **T_MITgcm*.mat**: Bi-weekly ocean temperature extracted from an East Antarctic configuration of the MITgcm from Pelle et al. (2021), where '*' is ctrl (control), ssp126 (low emission scenario), or ssp585 (high emission scenario). Ocean temperature was averaged at the ice front of Denman and Scott Glaciers (see contour in Figure 1 in the main text) at the lowest ocean level. Ocean temperature data is in units of degrees Celsius. **S_MITgcm*.mat**: Same as above, but for salinity in units on the Practical Salinity Scale (PSU). **discharge_den.xyz:** GlaDS output present-day channelized subglacial discharge flux (m<sup>3</sup>/s). To load the data and interpolate onto the model mesh, use: ``` [x,y,dis] = xyz2grid('discharge_den.xyz'); dis_den = InterpFromGridToMesh(x(1,:)',flipud(y(:,1)),flipud(dis),md.mesh.x,md.mesh.y,0); ``` where 'InterpFromGridToMesh' is a module built into ISSM.