Ice sheets · Sea level
Remapping Greenland's bed doubled the count of glaciers warm water can reach
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Short answer
A new Greenland bed map raises sea-level potential to 7.42 m and finds 67 of 243 glaciers connected to ocean deeper than 200 m, roughly twice the previous count.
What happened
Morlighem and colleagues merged IceBridge radar with mass conservation where ice flows faster than 50 m/yr, plus 30 bathymetry sources including Oceans Melting Greenland multibeam surveys, mapping bed and fjords within 50 km of the coast at up to 150 m posting. Ice volume came out at 2.99±0.02×10⁶ km³ and sea-level potential at 7.42±0.05 m. The previous version's beds were often about 100 m too high, and observed retreat patterns line up with the newly resolved retrograde beds.
Why it matters
Whether warm Atlantic Water can reach a glacier front depends on fjord sill depth — a metre-scale detail that decides a glacier's sensitivity. Doubling the number of glaciers with a deep pathway changes which ones models should expect to retreat, not just how precisely they are drawn.
Evidence
- Study type
- Mass-conservation bed reconstruction combining airborne radar with 30 bathymetry sources
- Sample
- Greenland-wide product at 150 m posting; 243 marine-terminating glaciers assessed
- Journal
- Geophysical Research Letters · peer reviewed
- Replication
- Superseded earlier bed maps and became a standard boundary condition for ice-sheet models
- Limitations
- True resolution degrades to about 1 km where kriging and RTopo-2 fill gaps. Radar thickness uncertainty is roughly 50 m, and thinning since the 2003–2008 surveys is mostly not accounted for.
What this connects to
Sources
The 2 studies this explanation is built from, by the role each plays. Every source links to PaperFren’s explanation of it and to the original paper.
Supporting evidence
- Small icebergs add a lot of Greenland fjord freshwater
High-resolution UNet mapping finds far more small icebergs than Sentinel-2 thresholding, raising Sermilik meltwater estimates toward ~2000 m³ s−1.
What it does not showLimitations
Two fjords and a few summer images do not give an annual cycle. Melt rates ignore fjord stratification and deep keels. Power-law extrapolation of small-berg contribution year-round is an assumption.
PaperFren explanationStudy with cards and a quizOriginal paper (DOI)cc by
Landmark research
- Greenland’s hidden fjord floors in BedMachine v3
A 150 m Greenland bed and fjord map raises sea-level potential by 7 cm and shows 30–100% more glaciers can meet warm Atlantic Water.
What it does not showLimitations
True resolution is coarser (~1 km) where kriging/RTopo-2 fill gaps; radar thickness uncertainty is ~50 m; thinning since 2003–2008 is ignored except where it exceeds that error.
PaperFren explanationStudy with cards and a quizOriginal paper (DOI)cc by
Before
Greenland bed maps were too coarse to resolve fjord sills, so the ocean pathways controlling which glaciers meet warm Atlantic Water were largely unknown.
Now
Bed and bathymetry are resolved together, and the retreat record matches the new topography. Resolution still falls to about 1 km where gaps are interpolated, and radar thickness uncertainty is roughly 50 m.