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Water that sublimates from Greenland’s snow does not always escape the local surface system. A 2016 study at Summit found evidence for a process in which vapor condenses onto fog particles and settles back onto the snow. The mechanism depends on a stable, relatively isolated layer of air near the surface; the study does not establish how much water is recycled across Greenland as a whole.
How can water vapor return to the ice sheet?
Sublimation is the direct change of snow or ice into water vapor. It transfers water out of the snow, but that transfer is not necessarily a permanent loss from the nearby environment. Under some conditions, vapor can condense onto tiny fog particles. Those particles then settle under gravity and return moisture to the surface.
In the authors’ words, “The isolation of the surface also acts to recycle sublimated moisture by recondensing it onto fog particles, which returns the moisture back to the surface through gravitational settling.” (2016 study abstract)
Why does a stable layer of air matter?
The atmosphere immediately above the snow is called the boundary layer. When that layer becomes increasingly stable, mixing between the surface and air higher above can weaken. The surface is then relatively decoupled from the atmosphere above it.
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That reduced exchange limits how much moisture the surface can gain by condensation from air arriving from aloft. At the same time, the more isolated near-surface air can retain and recycle some vapor produced by sublimation: the vapor condenses onto fog particles, which settle back onto the snow. The study describes these linked effects; recycling does not mean that all sublimated moisture returns.
What did the Summit study measure?
The 2016 study, “Surface-atmosphere decoupling limits accumulation at Summit, Greenland,” used three years of stable water-vapor isotope profiles at Summit, a high-altitude site on the Greenland ice sheet. The profiles supported the authors’ interpretation of surface-atmosphere decoupling and local moisture recycling (study record; study summary).
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This evidence is specific to Summit and to the processes inferred from those isotope profiles. It does not provide a Greenland-wide recycling rate, nor does it show that recycled moisture offsets the ice sheet’s overall mass loss.
How is local recycling different from net vapor flux?
Local recycling asks whether vapor leaving the snow can return nearby. Net vapor flux asks whether, over a chosen period and measurement area, the surface gains or loses water overall. A site can experience both sublimation and deposition at different times, and a net annual figure does not by itself reveal how much locally sublimated vapor returned as fog.
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Methods also affect estimates. In a 2001 analysis using Greenland Climate Network observations, Jason E. Box and Konrad Steffen found that a bulk method assuming a saturated surface underestimated deposition compared with a two-level profile method (2001 study). The two-level method estimated annual net vapor flux as low as −87 ± 27 mm at 960 m in western Greenland, while reporting positive annual fluxes of +32 ± 9 mm at NGRIP and +6 ± 2 mm at Summit. These are estimates from that earlier flux study, not measurements of the 2016 fog-recycling mechanism.
A separate 2014 dry-snow-zone study modeled seasonal changes in vapor flux, with deposition in winter and sublimation in summer. In its modeled case, deposition mass gain was less than 2% of total accumulation (2014 study). That result describes the modeled contribution to accumulation, not the fraction of Summit’s sublimated water recovered through fog.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why does the process matter for accumulation and ice cores?
Accumulation estimates concern how much snow and other moisture are added to the ice sheet. If surface exchange includes condensation, sublimation, and local recycling, interpreting net gains and losses requires distinguishing those processes and their measurement methods.
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