Tidewater Glacier Frontal Ablation Calculation Tool (TG_FACT)

The processing chain will automatically calculate monthly, three-monthly or annual frontal

ablation estimates for Greenlandic tidewater glaciers.

Input data

1.     TermPicks Terminus delineations (Goliber and Black, 2021)

2.     Satellite image (for manual delineation of fjord walls).

3.     Glacier velocity (code will automatically download ITS_LIVE velocities for the period 2008-2018; ~7 GB)

4.     Two Digital Elevation Models (preferably ArcticDEM v4.1 strips and AeroDEM; (Korsgaard et al., 2016; Porter et al., 2022)

5.     Surface change rate (Khan, 2023)

6.     Bedrock Topography from BedMachine v5 (Morlighem et al., 2017, 2022)

7.     Solid Ice Discharge (Mankoff et al., 2020)

Output

The output data of the processing chain is made available in Matlab (.mat), Shapefile (.shp) and NetCDF (.nc) format within the results folder. Each file contains additional data that is necessary to calculate frontal ablation estimates as well as the associated uncertainties. The following variables are contained in all files 

• Time – Midpoint of time intervals on which output data is defined [days since 01/01/1950]
• (for Matlab and Shapefile: Date – Midpoint of time intervals on which output data is defined [yyyy-mm-dd])
• Name – Name of each glacier investigated in this study [unitless]
• Lat – Latitude (EPSG:4326) [degrees]
• Lon – Longitude (EPSG:4326) [degrees]
• PolarX – Polar Stereographic X Coordinate (EPSG:3413) [m]; not include in shapefile/geopackage as part of geometry
• PolarY – Polar Stereographic Y Coordinate (EPSG:3413) [m]; not include in shapefile/geopackage as part of geometry
• F – Three-month-average frontal ablation estimates during time intervals [Gt/d]
• F_Max_U – Maximum uncertainty over total time period [Gt/d]
• F_U – three-month-average frontal ablation uncertainty for time intervals [Gt/d]
• D – Three-month-average solid ice discharge during time intervals [Gt/d]
• D_U – Three-month-average solid ice discharge uncertainty for time interval [Gt/d]
• TMC – Terminus mass change (dM/dt) during time intervals [Gt/d]
• TMC _U – Three-month-average terminus mass change uncertainty during time intervals [Gt/d]
• L – Interpolated terminus change over time () [km]
• Delta_L_W – Delineation and fjord width uncertainty (; constant) [km]
• H – Mean ice thickness within the polygon; maximum over the observation period () [km]
• Delta H – Ice thickness uncertainty with constant ArcticDEM/AeroDEM uncertainties of 0.1 m and 6 m, respectively () [km]
• Rho – Ice density (; constant) [kg/km³]
• W – Mean fjord width () [km]
• Bedrock_U – Mean uncertainty in bedrock topography along the centerline [km]
• TI – Time interval over which data are averaged (90 days for the results presented here) [d]

The latest data product (version containing frontal ablation estimates for all 49 tidewater glaciers discussed in Fahrner et al. (in prep.) can be found at https://doi.org/10.5281/zenodo.10076252

A quick tutorial on how to run the processing chain is available in the "ReadMe" PDF. 

When using this processing chain please use the citation provided in the repository.

References

Goliber, S. & Black, T. TermPicks: A century of Greenland glacier terminus data for use in machine learning applications (Version 1). Zenodo https://zenodo.org/records/5117931 (2021)

Khan, S. A. Greenland Ice Sheet Surface Elevation Change. GEUS Dataverse, V2https://doi.org/10.22008/FK2/GQJJEA (2023)

Korsgaard, N. J., Nuth, C., Khan, S. A., Kjeldsen, K. K., Bjørk, A. A., Schomacker, A. & Kjær, K. H. Digital Elevation Model and orthophotographs of Greenland based on aerial photographs from 1978-1987 (G150 AERODEM) (NCEI Accession 0145405). NOAA National Centers for Environmental Information. https://doi.org/10.7289/v56q1v72 [10/08/2022] (2016)

Mankoff, K., Solgaard, A., Larsen, S. Greenland Ice Sheet solid ice discharge from 1986 through last month: Discharge. GEUS Dataverse, V100 https://doi.org/doi/10.22008/promice/data/ice_discharge/d/v02 (2020).

Morlighem, M., Williams, C. N., Rignot, E., An, L., Arndt, J. E., Bamber, J., Catania, G., Chauché, N., Dowdeswell, J. A., Dorschel, B. & others. BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multibeam echo sounding combined with mass conservation. Geophys Res Lett44, (2017).

                Morlighem, M., Williams, C., Rignot, E., An, L., Arndt, J. E. , Bamber, J., Catania, G. , Chauché, N., Dowdeswell, J. A. , Dorschel, B., Fenty, I., Hogan, K., Howat, I., Hubbard, A., Jakobsson, M., Jordan, T. M., Kjeldsen, K. K., Millan, R., Mayer, L., Mouginot, J., Noël, B., O’Cofaigh, C., Palmer, S. J., Rysgaard, S., Seroussi, H., Siegert, M. J., Slabon, P., Straneo, F., van den Broeke, M. R., Weinrebe, W., Wood, M. & Zinglersen, K. IceBridge BedMachine Greenland. (IDBMG4, Version 5). [surface, bed, error]. NASA National Snow and Ice Data Center Distributed Active Archive Center. Boulder, Colorado USA. https://doi.org/https://doi.org/10.5067/GMEVBWFLWA7X (2022)

Porter, C. et al. ArcticDEM – Strips, Version 4.1, Harvard Dataverse, V1, [15/10/2024], https://doi.org/10.7910/DVN/C98DVS, (2022).