Data & methods
Data sources
| Field | Greenland | Antarctica |
|---|---|---|
| Bed and surface topography, ice mask, thickness | BedMachine Greenland v6, 150 m (Morlighem et al., 2017) | BedMachine Antarctica v4, 500 m (Morlighem et al., 2020) |
| Surface ice velocity | MEaSUREs multi-year mosaic, 250 m (Joughin et al., 2018) | MEaSUREs InSAR-based velocity v2, 450 m (Rignot et al., 2011) |
| Drainage regions | IMBIE 2 (Rignot & Mouginot) | IMBIE 2 (Rignot & Mouginot) |
| Beyond the BedMachine domain | ETOPO 2022 (NOAA NCEI) and RGI 6.0 glacier outlines | — |
| Sea-ice edge | Sea Ice Index v4, median 1981–2010 (Fetterer et al., 2017) | Sea Ice Index v4, median 1981–2010 |
| Place names | GeoNames and a curated list | SCAR Composite Gazetteer of Antarctica and a curated list |
Methods
All fields are averaged onto the polar stereographic grids of the posters (EPSG:3413 at 500 m for Greenland, EPSG:3031 at 1 km for Antarctica) with GDAL. The maps combine a hillshade of the ice surface (or the bed) with surface ice velocity on a logarithmic colour scale; slow ice fades into the hillshade.
The key numbers are computed on the same grids, with cell areas corrected for the distortion of the projection. The sea-level equivalent counts the grounded ice above flotation (ice density 917 kg m⁻³, sea water 1027 kg m⁻³ for flotation, melt water 1000 kg m⁻³, ocean area 3.625 × 10⁸ km²). The regions come from the IMBIE 2 drainage basins (East and West Antarctica, the Antarctic Peninsula; for Greenland the ice sheet without the peripheral ice caps). These polygons cover the grounded ice, so ice outside them (ice shelves, islands, the ice margin) is given to the nearest region.
Place names in Greenland
The maps give the Greenlandic name of a place first, with its historical name in parentheses (e.g., “Nuuk (Godthåb)”, “Sermeq Kujalleq (Jakobshavn Isbræ)”). Since 1996, only Greenlandic names are standardised in Greenland, by the Greenland Place Name Committee at the Language Secretariat, Oqaasileriffik. Many glaciers, however, are still known by the Danish names of the colonial period and the early expeditions, which are used throughout the scientific literature. Showing both names puts the official name first, while the historical name links the map to the literature.
Most names come from GeoNames, which usually lists the Danish name first and the Greenlandic name, where known, among the alternate names. We chose the Greenlandic names by hand, since an automatic choice was not reliable: GeoNames marks few names by language, and many of its Greenlandic names are in the orthography used before 1973. A Greenlandic name was added only where GeoNames or Wikipedia gives it in the modern orthography. Where GeoNames itself lists a Greenlandic name first, it is kept as given. Features without a known Greenlandic name keep their Danish or English name. This is the case for most of northern and northeastern Greenland, where nearly all names were given by expeditions (e.g., “Petermann Gletscher”, “Zachariæ Isstrøm”). Note that “Gletscher” is the older Danish spelling of “glacier” (modern Danish “gletsjer”), not German. The open seas keep their English names, while bays along the coast take their Greenlandic names (e.g., “Qimusseriarsuaq (Melville Bay)”).
The official register of the Place Name Committee holds about 33,000 names, but it is not available for download. We will use it once it is (issue #2). The names chosen here are listed in data/labels_greenland.csv (poster labels) and data/greenlandic_names.csv (glaciers of the gazetteer) in the repository.
Paleo maps
The paleo maps show the ice sheets at the Last Glacial Maximum (20 000 years ago) from the PaleoMIST 1.0 reconstruction (Gowan et al., 2021; doi:10.1594/PANGAEA.905800). The changes since then in PaleoMIST are added to present-day topography: ETOPO 2022 (NOAA NCEI) north of 24°N, on a 5 km grid (EPSG:3413), and BedMachine Antarctica v4 on a 4 km grid (EPSG:3031).
- Bed: the present-day bed minus the relative sea-level change of PaleoMIST (Earth deformation and the lower sea level), so the bed is given relative to the sea level of the time.
- Ice surface: the present-day surface plus the change of the PaleoMIST surface (taken as sea level over the ocean), smoothed over 15 km to remove the noise of the 5 km PaleoMIST grids. Present-day ice keeps the detail of the present-day data, and ice beyond it follows the PaleoMIST surface.
- Ice: where PaleoMIST has ice at the time; its thickness is the surface minus the bed, and ice thinner than flotation floats. PaleoMIST reconstructs grounded ice only, so present-day ice shelves beyond it are left out.
The key numbers are computed as for the present-day posters. The regions of the Northern Hemisphere numbers (North America, Greenland, Iceland, Eurasia) are approximate.
The website
The site is built with Quarto and hosted on GitHub Pages. The poster gallery shows the sharing versions of the posters with links to the A0 PDFs.
The interactive maps use OpenLayers with proj4js, in the same polar stereographic projections as the posters (EPSG:3413 and EPSG:3031), so nothing is reprojected in the browser.
- Raster layers. Each map style (ice velocity in two colour maps, surface elevation, bed elevation) is rendered by the same Julia code as the posters, at the full grid resolution (500 m for Greenland, 1 km for Antarctica). The image is cut into a pyramid of 256 × 256 pixel JPEG tiles (JpegTurbo.jl), halving the resolution by 2 × 2 averaging from one zoom level to the next. OpenLayers loads them through a custom tile grid with the extent and resolutions of the poster grid.
- Vector layers. The surface contours, ice margin, grounding line and drainage divides are traced from the grids with Contour.jl, as on the posters. The sea-ice edges are reprojected and clipped with GDAL (ogr2ogr). All are stored as GeoJSON in projected coordinates.
- Names. The place names of the posters and the full gazetteers (GeoNames for Greenland, the SCAR Composite Gazetteer for Antarctica) are GeoJSON points. Names of tier 1 show at all zoom levels, tier 2 and the gazetteer as you zoom in; OpenLayers leaves out labels that would overlap. Clicking a name shows its other names, position and source.
- Search. The search box suggests all names. A name is matched on any of its names (ignoring case), and the map zooms to it. The drainage regions can be found by their label (e.g., “NW”) or, for Greenland, by their full name (“Northwest”), and the map zooms to the whole region.
The site is published as a single commit of the gh-pages branch, replaced at each update, so the tiles and PDFs do not build up a history in the repository.
Reproducing the maps
The repository contains all scripts, with the steps to download and prepare the data, plot the posters and build this site in its README.
Versions
The website shows the latest version of the maps. The posters (A0 PDFs and PNGs) of each version are archived as a GitHub release.
- v1.0 (October 2026, current): first release.