README documentation associated with the archived dataset: "Data archive of mid-21st century projections for the Amundsen Sea (western Antarctica)", St-Laurent, P., archived on W&M ScholarWorks. Dataset version: 2025-05-07 Person of contact: Pierre St-Laurent (ORCiD 0000-0002-1700-9509), pst-laurent@vims.edu Disciplines: Physical oceanography, Cryosphere Keywords: Antarctica, Amundsen Sea, Ice shelves, Oceanography, Cryosphere, Modeling, ROMS, Sea ice, Southern Ocean, Polynyas, Blooms, Carbon Location: 68-76S, 90-140W NOTE: This archive contains files in the NetCDF format which is an open and portable file format with all the necessary metadata (list of variables, dimensions, units of the variables...) embedded inside the NetCDF file. The user of this archive is assumed to be comfortable with this file format and should seek the relevant information inside the NetCDF files. Using the open source NetCDF operators, this metadata can be accessed by simply typing: ncdump -h name_of_netcdf_file.nc **************************************************************************************************** Abstract **************************************************************************************************** A 3-D numerical model was used for multi-decadal eddy-resolving simulations of the Amundsen Sea embayment (Antarctica). A control simulation covered the historical period 2006-2023 (~2 decades) under realistic atmospheric and oceanic conditions. Three additional simulations representing the mid-21st century were conducted based on future projections from CMIP6 models ACCESS-CM2, MPI-ESM1-2-HR, MRI-ESM2-0 (scenario SSP2-4.5). These three CMIP6 models were selected based on their realism during the historical period as well as their diversity in terms of resolution and level of warming. The four simulations provided information about the regional hydrography, oceanic circulation, sea ice cover, ice shelf basal melt rates, and biogeochemical conditions (nitrogen and iron). The four simulations were then condensed into daily climatologies in order to summarize changes in the seasonal cycle of the Amundsen embayment in response to the projected warming. The present archive includes the four daily climatologies as well as all the information required to repeat the numerical experiments (code and input files). **************************************************************************************************** Information about the code **************************************************************************************************** The tarball code_v20250507.zip contains the computer code used for the numerical simulations of the Amundsen Sea (Antarctica). It includes the following directories/files: (a) artemis_roms/ Files that are specific to the Amundsen Sea implementation of ROMS *and* to the biogeochemical module used in this study. (b) depths.m A Matlab/Octave script computing the vertical position of the model grid boxes at a given time. The file originates from the Rutgers Matlab toolbox (see myroms.org), but it includes customizations for the presence of ice shelves (their presence causes a re-definition of the vertical depths inside ROMS.) The script is fairly short and can be rewritten easily for other computer languages. (c) roms_kshedstrom_git/ Generic ROMS files. The generic ROMS code (directory roms_kshedstrom_git) originates from the Git repository of Kate Hedstrom (Univ.Alaska Fairbanks, kshedstrom@alaska.edu): https://github.com/kshedstrom/roms.git GIT Revision: kate_svn commit 0baf6674f10514306a8ab81ee42af5a9a3da87cc accessed (cloned) on 2021-06-29 ...that combines the Rutgers branch of ROMS (its version 3.9 dated Apr.6, 2020 (according to roms_kshedstrom_git/ROMS/Version)), the sea ice module of Budgell 2005, and the ice shelf module of Dinniman et al. 2011 (see full references below). The present code archive is similar in scope to that of Mack et al. 2019 (see https://github.com/mnemoniko) except that the present archive is based on a more recent version of ROMS/TOMS. Note that Kate's code includes a very large number of customizations on top of the original Rutgers code, with these customizations being activated/deactivated via C Pre-Processing (CPP) directives. The Amundsen Sea configuration (defined by the file artemis_roms/artemis.h) activates only a very small fraction of these customizations. The best way to read and understand the code in this archive is to first compile the Amundsen Sea application, and then to study the preprocessed files (that will have the extension .f90) stored inside the directory amicus_roms/Build_roms/. Since the .f90 files have underwent preprocessing, they are infinitely smaller and more legible than their .F (non-preprocessed) counterpart. The Git ROMS repository of Kate Hedstrom is no longer maintained and a few of its files were not in a fully functional state at the time when her repository was accessed. Additional modifications were therefore applied by St-Laurent in order to obtain a functional configuration that produced results consistent with an earlier version of this codebase (Dinniman's SOGLOBEC3.3). These additional modifications can be tracked with a recursive "grep" command over the alias "psl" (Pierre St-Laurent). The key changes were: (a) use a non-zero value for the minimum sea ice concentration (see parameter min_a inside amicus_roms/ice.in); (b) use a non-zero value for the minimum sea ice thickness (see parameter min_h inside amicus_roms/ice.in); (c) complete the implementation of some sea ice boundary conditions that had been partially implemented (see roms_kshedstrom_git/ROMS/SeaIce/tibc.F); (d) un-comment the calculation of the wao term (see Mellor & Kantha 1989) so that it can contribute to the thermodynamics (see roms_kshedstrom_git/ROMS/SeaIce/ice_mk.h); (e) fix a typo concerning idBvar(isTice) inside roms_kshedstrom_git/ROMS/Modules/mod_ncparam.F; (f) fix the net evaporation term in the particular case where SCORRECTION is un-defined (see roms_kshedstrom_git/ROMS/Nonlinear/set_vbc.F). The code inside this archive is targeted toward users who have at least a basic experience with the Rutgers branch of ROMS (see myroms.org, which includes extensive documentation as well as introductory test-cases). Because the present code is coupled to sea ice and to ice-shelves, it is definitely not the right way to learn how to use ROMS. Minimal instructions on how to compile the code of this archive: (a) Open artemis_roms/build_roms.bash with your favorite text editor. (b) Edit the environment variable MY_ROMS_SRC so that it points toward your local copy of the directory roms_kshedstrom_git. (c) Edit the variables USE_MPI,which_MPI,FORT to reflect your computer configuration. If necessary, edit the files Linux-gfortran.mk or Linux-ifort.mk to reflect your computer configuration. (d) ./build_roms.bash (i.e. compile the code). (e) Edit the file roms_amicus.in to update the paths to the input files and to set the parameters of your calculation. The health of the code has been verified by compiling with ROMS' USE_DEBUG mode and then running the resulting executable under the GDB debugger. The code has been successfully used with both the GNU Fortran compiler (gfortran) and the Intel Fortran compiler (ifort). The original Rutgers ROMS branch is licensed under the MIT/X license. I'm quoting below an extract from this license in order to remind the user of the key passage (the full license text is available at http://www.opensource.org/licenses/mit-license.php ): THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIMS, DAMAGES OR OTHER LIABILITIES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE If you experience issues or unexpected behavior, you can contact me at the email address above and we'll see what could be done. The message board of myroms.org (which is maintained by Rutgers) is not the best resource for new questions because Kate Hedstrom's branch is relatively old (unmaintained) and her extensive customizations represent a substantial departure from the official Rutgers code hosted at myroms.org. Nevertheless, the myroms.org message board can be helpful by searching its database for answers to past questions. **************************************************************************************************** Information about the Amundsen Sea implementation of ROMS **************************************************************************************************** The implementation is specifically focused on the *continental shelf* of the Amundsen Sea. Although the model domain includes a generous portion of the continental slope and deep sea, the realism of the model in deep areas is limited by the coarse vertical resolution of the implementation (only 20 vertical levels). This is what motivates the use of nudging (see discussion about the input files) over areas of bottom depth >3000m in order to maintain a realistic stratification there at all times. No other form of relaxation is used in the simulation (e.g. the CPP option SCORRECTION of Kate Hedstrom is set to #undef.) The coarse vertical resolution over the abyssal plain (and the poorly-resolved surface mixed layer there) also motivated a modification to the drag at the sea ice/ocean interface. Over the continental slope and abyssal plain, this drag gradually becomes a function of sea ice velocity alone (CPP option LIMIT_WATER_STRESS_IN_UNRESOLVED_SURFACE_LAYER). Over the rest of the model domain, the drag at the sea ice/ocean interface follows the usual function of sea ice velocity and surface ocean velocity. The Amundsen implementation uses the Large, McWilliams and Doney (1994, "LMD") sub-grid scale diffusivity along the vertical with the background values and limiters specified inside the file artemis_roms/roms_artemis.in. Note that vertical diffusivities for temperature and salinity are limited to a maximum of 10^(-2) m2/s (AKT_LIMIT). The third-order upstream-biased advection scheme described in Shchepetkin & McWilliams (2005) is used for horizontal advection of horizontal momentum, salinity and temperature. This advection scheme is supplemented by a very weak Laplacian diffusivity of 0.1 m2/s applied on horizontal momentum (along the topography-following surfaces, MIX_S_UV), salinity and temperature (along geopotential surfaces, MIX_GEO_TS). Parameters relative to sea ice are found inside the file artemis_roms/ice.in. The basal melt rates of ice shelves (see Dinniman et al. 2011 for a description of their computation) relies on transfer coefficients that vary in time/space according to the local friction velocity (see Schmidt et al. 2004). This approach works appropriately for Abbot, Cosgrove, Pine Island, Thwaites ice shelves and leads to basal melt rates that are consistent with remote sensing estimates. However, in the case of Dotson-Crosson and Getz ice shelves, the parameterization of Schmidt et al. leads to an overestimation of the basal melt rates relative to estimates from remote sensing. Following Nakayama et al. 2017 ( https://doi.org/10.1002/2016JC012538 ), an ad hoc adjustment is made to the transfer coefficients computed under Dotson-Crosson and Getz. Specifically, the transfer coefficients under Dotson-Crosson are scaled down to 67% of the Schmidt et al. values (CPP option REDUCE_GAMMA_TS_DOTSON_CROSSON), and for Getz to 25% of the Schmidt et al. values (CPP option REDUCE_GAMMA_TS_GETZ). The results of the simulation have been evaluated against: (a) historical sea ice concentrations from SSM/I (Comiso 2017), (b) historical hydrographic profiles from the ASPIRE (austral summer 2010/2011) and ARTEMIS (summer 2022) cruises, (c) basal melt rates estimates from remote sensing (Adusumilli et al. 2020, Rignot et al. 2013, Depoorter et al. 2013), (d) tidal harmonic constituents from the pressure gauge of the mooring described in Wahlin et al. 2019, (e) biogeochemical data from the ASPIRE cruise. Most of these comparisons appear in St-Laurent et al. 2019,2024 (and their respective Supplementary material). **************************************************************************************************** About the 4 numerical simulations included in the data archive **************************************************************************************************** The data archive covers 4 numerical simulations: (1) Control simulation of 2006-2023 (18 years in duration), (2) mid-century simulation using air+water temperatures from CMIP6 ESM "ACCESS-CM2" (18 years), (3) mid-century simulation using air+water temperatures from CMIP6 ESM "MPI-ESM1-2-HR" (18 years), (4) mid-century simulation using air+water temperatures from CMIP6 ESM "MRI-ESM2-0" (18 years). The information from the CMIP6 models corresponds to a monthly "Delta" climatology between two 30 year periods (2000-2029 and 2035-2064). The "Delta" only includes atmospheric temperature and seawater temperature (interpolated over the ROMS model grid). Simulations 2-4 were obtained by superimposing the "Delta" over the forcings (atmospheric and lateral boundary conditions) of Simulation 1, spinning-up the model over a period long enough for the warming signal to fully populate the model domain, and then running over the same 18 year period as in Simulation 1. Given the choice of the two 30 year periods (see above), simulations 2-4 can be considered as representing years 2035-2064. Specifically, simulation 1 corresponds to the set of input files: clm_amicus1076x516x20_YYYY_vxxxxxxxx.nc (lateral boundary conditions for calendar year YYYY) bry_amicus1076x516x20_ssmiYYYY_vxxxxxxxx.nc (lateral boundary conditions for calendar year YYYY) frc_amicus_era5_YYYY_swrad0.71_vxxxxxxxx.nc (atmospheric conditions for calendar year YYYY) Simulation 2 corresponds to the set of input files: clm_amicus1076x516x20_YYYY_ACCESS-CM2_vxxxxxxxx.nc (lateral) bry_amicus1076x516x20_ssmiYYYY_ACCESS-CM2_vxxxxxxxx.nc (lateral) frc_amicus_era5_YYYY_swrad0.71_ACCESS-CM2_vxxxxxxxx.nc (atmospheric) Simulation 3 corresponds to the set of input files: clm_amicus1076x516x20_YYYY_MPI-ESM1-2-HR_vxxxxxxxx.nc (lateral) bry_amicus1076x516x20_ssmiYYYY_MPI-ESM1-2-HR_vxxxxxxxx.nc (lateral) frc_amicus_era5_YYYY_swrad0.71_MPI-ESM1-2-HR_vxxxxxxxx.nc (atmospheric) Simulation 4 corresponds to the set of input files: clm_amicus1076x516x20_YYYY_MRI-ESM2-0_vxxxxxxxx.nc (lateral) bry_amicus1076x516x20_ssmiYYYY_MRI-ESM2-0_vxxxxxxxx.nc (lateral) frc_amicus_era5_YYYY_swrad0.71_MRI-ESM2-0_vxxxxxxxx.nc (atmospheric) The control simulation of 2006-2023 (as well as the three mid-century simulations) assume a time-varying "icescape" configuration: --2006-2011: Icescape configuration representative of year 2011 (Fig.2(a) of St-Laurent et al. 2024; file grd_amicus1076x516_2011_v20230201.nc); --2012-2022: Icescape configuration representative of year 2022 (Fig.2(b) of St-Laurent et al. 2024; file grd_amicus1076x516_2022_v20230220.nc); --2023: Icescape configuration representative of 2023/2024 (file grd_amicus1076x516_2024_v20241121.nc). The switch to a different icescape configuration took place on 1 January of the years listed and included a re-interpolation of the 3-D model outputs (to reflect the change in the position of the topography-following levels after the translation of the icebergs.) **************************************************************************************************** Information about the input files **************************************************************************************************** Abundant documentation is available in the metadata embedded inside the NetCDF input files; the following is only an overview. GRID FILE: grd_amicus1076x516_2011_v20230201.nc (used over period 2006-2011), grd_amicus1076x516_2022_v20230220.nc (used over period 2012-2022), grd_amicus1076x516_2024_v20241121.nc (used over period >=2023). Additional notes: Although ROMS overwrites the following parameters at runtime based on the values provided inside roms_my_app.in, the grid was designed assuming: N=20, Vtransform=1, Vstretching=1, THETA_S=2.5, THETA_B=0, TCLINE=15. Although the configuration Vtransform=Vstretching=1 is considered to be "obsolete" in non-Antarctic implementations of ROMS, the more recent Vtransform/Vstretching configurations were designed under the assumption of a quasi-horizontal free surface, which is not at all the case in presence of ice shelves. This is the rationale for favoring the traditional Vtransform=Vstretching=1 configuration. TIDAL FORCING: tides_amicus1076x516_v20211128.nc NUDGING COEFFICIENTS: nud_amicus1076x516x20_v20240918.nc For 3-D horizontal velocities, salinity, temperature, and dissolved iron at the sea floor. The "nud" file works in combination with the "clm" files. Their purpose is to complement the approach of Marchesiello et al. 2001 (which is only active at the immediate edge of the model domain) by providing additional relaxation over the off-shelf area of the domain. The nudging is inactive (i.e. zero) outside of the off-shelf area. BOUNDARY FILES: bry_amicus1076x516x20_ssmiYYYY_vxxxxxxxx.nc (conditions for calendar year YYYY) or bry_amicus1076x516x20_ssmiYYYY_ACCESS-CM2_vxxxxxxxx.nc or bry_amicus1076x516x20_ssmiYYYY_MPI-ESM1-2-HR_vxxxxxxxx.nc or bry_amicus1076x516x20_ssmiYYYY_MRI-ESM2-0_vxxxxxxxx.nc These "bry" fields are only applied at the immediate edge of the model domain, following the passive/active approach of Marchesiello et al. 2001 ( https://doi.org/10.1016/S1463-5003(00)00013-5 ). Note that the use of a monthly climatology for oceanic fields at the edges of the model domain imply that year-to-year changes in the position/characteristics of large-scale features such as the Antarctic Circumpolar Current or Ross Gyre are not represented in the present simulation. All year-to-year changes visible in the model results must be the result of the atmospheric forcing and/or from the daily sea ice concentration (from SSM/I) prescribed at the edges of the model domain (see St-Laurent et al. 2022 on this topic.) CLIMATOLOGY FILES: clm_artemis_bgc1076x516x20_YYYY_vxxxxxxxx.nc (bottom concentration of dissolved iron for year YYYY) and: clm_amicus1076x516x20_YYYY_vxxxxxxxx.nc (conditions for calendar year YYYY) or clm_amicus1076x516x20_YYYY_ACCESS-CM2_vxxxxxxxx.nc or clm_amicus1076x516x20_YYYY_MPI-ESM1-2-HR_vxxxxxxxx.nc or clm_amicus1076x516x20_YYYY_MRI-ESM2-0_vxxxxxxxx.nc ATMOSPHERIC FORCING: frc_amicus_era5_YYYY_swrad0.71_vxxxxxxxx.nc (conditions for calendar year YYYY) or frc_amicus_era5_YYYY_swrad0.71_ACCESS-CM2_vxxxxxxxx.nc or frc_amicus_era5_YYYY_swrad0.71_MPI-ESM1-2-HR_vxxxxxxxx.nc or frc_amicus_era5_YYYY_swrad0.71_MRI-ESM2-0_vxxxxxxxx.nc INITIAL CONDITIONS (1 January 2006 00:00 UTC): ini_roms20060101_control.nc or ini_roms20060101_access.nc or ini_roms20060101_mpihr.nc or ini_roms20060101_mri.nc All initial conditions were preceded by a spinp-up period and thus represent an ocean/sea ice system in equilibrium (assuming the user faithfully mimics the HPC environment that was used to produce the original simulations). **************************************************************************************************** Information about the biogeochemical module **************************************************************************************************** The biogeochemical module included with the code is thoroughly described in St-Laurent et al. 2019 (in the text but particularly in the Supplementary Information) and has been evaluated against in situ biogeochemical data in the same publication. It has been used for this study with no modification except that: (a) ice shelf basal melt no longer contributes to the supply of dissolved iron (#undef ISBM_AS_SOURCE_OF_DFE) following Steffen 2024; (b) the bottom concentration of dissolved iron prescribed in the lowest vertical level of the model (dfe_bottom(x,y)) has been updated to take advantage of new in situ data that became available after the ASPIRE cruise. The files associated with the biogeochemical module are: artemis_roms/npzd_iron.in (parameters) artemis_roms/npzd_iron.h (equations) artemis_roms/npzd_iron_var.h (...other files associated with the module...) artemis_roms/npzd_iron_def.h artemis_roms/npzd_iron_inp.h artemis_roms/npzd_iron_wrt.h artemis_roms/npzd_iron_mod.h **************************************************************************************************** About the daily climatologies included in this archive **************************************************************************************************** Each of the four ROMS simulations (control + 3 mid-century simulations, each 18 years in duration) spans 3 different "icescape" configurations (see above) in which case the vertical position of the topography-following levels of ROMS changes considerably over the years (particularly because of the migration of tabular iceberg B22). Therefore, in order to compute the multi-year climatology included in this archive, the daily 3-D outputs of ROMS had to be re-interpolated over a common (and time-invariant) set of depths (variable `zdim' inside the climatologies) and then averaged over time to produce the final daily climatologies. `zdim' has more resolution in the upper portion of the water column and its maximum depth (1600m) was selected to encompass the range of bathymetry found on the continental shelf: zdim (meters) = -2.5, -7.5, -15, -25, -35, -45, -62.5, -87.5, -112.5, -137.5, -175, -225, -275, -350, -450, -550, -650, -800, -1000, -1200, -1400, -1600 Areas off the continental shelf that are deeper than 1600m are thus not included in the 3-D daily climatologies. An exception was made for the horizontal heat flux vector (variable `horiz_heat_flux') because of its importance for ice shelf basal melt in the region. In this particular case, the flux vector was computed over the full range of depths (see Section 2.4 of St-Laurent et al. 2024) and then summed vertically (units of GW/m; e.g., Fig.4 of St-Laurent et al. 2024). Additional details about the creation of the daily climatologies: (a) As mentioned above, the 18 years long simulations span 3 different icescape configurations. Changes in the position of tabular iceberg B22 over the years leave visible artefacts in the daily climatologies, and there is no obvious way to avoid this. (b) Model variables normally positioned at the *edges* of the grid cells (e.g. currents, fluxes, stresses) were averaged at the *center* of the cells to match other fields such as water temperature. Note that there is a loss of accuracy involved in this operation. (c) Variables such as `sustr' and `svstr' are the two components of a vector (surface stress) and they were averaged over time *separately*. Given that: mean( sqrt( sustr.^2 + svstr.^2 ) ) /= sqrt( mean( sustr ).^2 + mean( svstr ).^2 ), ...the values in the daily climatologies thus *underestimate* the true magnitude of the surface stress vector on that day. As mentioned above, all the information relative to the name, dimensions, units... of a variable is embedded inside the metadata of the NetCDF files, and the user is expected to extract this information themselves. Only a very brief, general overview is provided below: control_clim_VARIABLE_vxxxxxxxx.nc (daily climatology from control simulation for variable VARIABLE) access_clim_VARIABLE_vxxxxxxxx.nc (daily climatology from simulation with warming projected by ACCESS-CM2) mpihr_clim_VARIABLE_vxxxxxxxx.nc (daily climatology from simulation with warming projected by MPI-ESM1-2-HR) mri_clim_VARIABLE_vxxxxxxxx.nc (daily climatology from simulation with warming projected by MRI-ESM2-0) Variables: sustr x-component of surface stress svstr y-component of surface stress bustr x-component of bottom stress bvstr y-component of bottom stress zeta sea surface height swrad shortwave radiation at sea surface shflux heat flux at sea surface ssflux salinity flux at sea surface aice sea ice concentration hice sea ice thickness iomflx sea ice/ocean mass flux uice x-component of sea ice velocity vice y-component of sea ice velocity salt seawater practical salinity temp seawater potential temperature NO3 nitrate concentration phytoplankton phytoplankton nitrogen concentration phytoplanktonFe phytoplankton iron concentration zooplankton zooplankton nitrogen concentration detritus small detritus nitrogen concentration iron dissolved iron concentration iron_on_small_POM small biogenic particle iron concentration iron_on_large_POM large biogenic particle iron concentration LdetritusN large detritus nitrogen concentration AKt Vertical sub-grid scale diffusivity w Vertical ocean velocity horiz_heat_flux Horizontal heat flux horiz_current Horizontal ocean velocities **************************************************************************************************** About advection schemes and negative values **************************************************************************************************** The simulations relied on ROMS' 3rd order upstream-biased advection scheme on the horizontal, and the 4th order `Akima' (harmonic averaging) advection scheme on the vertical (Shchepetkin & McWilliams 2005). These advection schemes are conservative and have little-to-no implicit ("numerical") diffusivity, but their drawback is that they are dispersive and non-monotonic. As a result of this, tracer fields that are naturally close to zero, e.g. surface nutrients during the peak bloom, may occasionally exhibit negative values. The field remains conservative and meaningful and these occasional `undershoots' should not be cause for concern---it is a well-known and well-documented behavior of non-monotonic advection schemes. (Monotonic schemes do exist and are available in ROMS, but they have their own set of drawbacks.) **************************************************************************************************** Using the model outputs: Extracting a 3-D modeled field **************************************************************************************************** To read the modeled practical salinity on the 5th day of the year, under Matlab/Octave: salt = ncread( 'control_clim_salt_v20250326.nc', 'salt', [1, 1, 1, 5], [inf, inf, inf, 1] ); (type `help ncread' to learn the syntax of command `ncread'.) ...which returns a three-dimensional array of size 1076x516x22 corresponding to axes xdim,ydim,zdim (respectively). The vertical axis is ordered from sea surface to sea floor. **************************************************************************************************** Using the model outputs: Horizontal position of the model grid boxes **************************************************************************************************** The latitude/longitude of the 1076x516 grid boxes defining the horizontal plane of the model grid are stored inside variables `longitude' and `latitude': Example in Matlab/Octave: lon = ncread( 'control_clim_aice_v20250326', 'longitude' ); lat = ncread( 'control_clim_aice_v20250326', 'latitude' ); These values are constant over time and available in any of the output files. They correspond to the *center* of the grid boxes, i.e. the so-called "rho" point in ROMS' lingo. The 1076x516 grid corresponds to a conformal, oblique stereographic projection with `proj' parameters: +proj=stere +lon_0=245.5 +lat_0=-72.2 +ellps=WGS84 ...and a uniform horizontal mesh size of 1.5km. The (x,y) position corresponding to the 1076x516 grid boxes is stored inside variables `xdim' and `ydim': xdim = ncread( 'control_clim_aice_v20250326', 'xdim' ); % Vector of 1076 values (meters). ydim = ncread( 'control_clim_aice_v20250326', 'xdim' ); % Vector of 516 values (meters). ...which are available in any of the output files. The ROMS outputs can be re-interpolated horizontally to arbitrary longitudes,latitudes by: (a) converting the arbitrary points (longitude,latitude) to (x,y) locations of the stereographic projection (using the projection information listed above and a software such as `proj'); (b) doing a bi-linear horizontal interpolation. Example in Matlab/Octave: result = interp2( xdim, ydim, roms_output, x_arbitrary, y_arbitrary ); Note that this archive includes variables that are normally not defined at the center of the grid boxes. These include sea ice velocities, horizontal ocean currents, horizontal heat flux, x/y components of the bottom/surface stress, etc. These fields were re-interpolated from the edges of the grid boxes to the center of the grid boxes for the sake of this archive. Note that ROMS uses the same variable nomenclature regardless of the map projection of the model domain. In the case of this Amundsen configuration, the variables "uice" and "vice" are *not* the zonal (west/east) and meridional (south/north) components of sea ice velocity. They are actually the components of sea ice velocity in the x,y directions of the model grid. The same is true for ocean currents, horizontal heat fluxes, etc. **************************************************************************************************** Using the model outputs: Deriving basal melt rates under ice shelves **************************************************************************************************** Basal melt under an ice shelf corresponds to a sink of oceanic heat, i.e. a negative value for the heat flux at the ice shelf/ocean interface. The interfacial heat flux is stored inside the field shflux and has units of Watts per square meter. A shflux value from under an ice shelf can be converted into a mass of ice melted using Eq.3 of Holland & Jenkins 1999: mass_ice = - shflux / 334.e3, ...where 334.e3 J/kg is the latent heat fusion and mass_ice has units of kg per second per square meter. **************************************************************************************************** Using the model outputs: Deriving the vertical position of the model grid boxes inside the climatology files **************************************************************************************************** The ROMS climatology forcing files (e.g., clm_amicus1076x516x20_2006_v20220919.nc) are defined on the native ROMS topography-following vertical levels (s_rho, with 20 vertical levels). The Matlab script `depths.m' (provided with this archive) can be used to extract the vertical position (in meters) corresponding to those 20 topography-following levels. **************************************************************************************************** Acknowledgements **************************************************************************************************** This research was supported by NASA (award 80NSSC21K0746, Antarctic sea ice, fast ice and icebergs: Modulators of ocean-ice shelf interactions (AMICUS)) and by NSF award 1941292 (NSFGEO-NERC: Collaborative Research: Accelerating Thwaites Ecosystem Impacts for the Southern Ocean (ARTEMIS)). The authors acknowledge William & Mary Research Computing (https://www.wm.edu/it/rc) for providing computational resources and/or technical support that have contributed to the results reported within this study. This work used Delta CPU at the National Center for Supercomputing Applications (NCSA) through allocation EES240130 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program, which is supported by U.S. National Science Foundation grants #2138259, #2138286, #2138307, #2137603, and #2138296. **************************************************************************************************** References **************************************************************************************************** Adusumilli, S. H.A. Fricker, B. Medley, M.R. Siegfried, 2020, Interannual variations in meltwater input to the Southern Ocean from Antarctic ice shelves, Nature Geoscience, https://doi.org/10.1038/s41561-020-0616-z Brodzik, M. J. and J. S. Stewart. 2016. Near-Real-Time SSM/I-SSMIS EASE-Grid Daily Global Ice Concentration and Snow Extent, Version 5. Boulder, Colorado USA. 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