Abstract
Excess ground ice formation and melt drive surface heave and settlement,
and are critical components of the water balance in Arctic soils.
Despite the importance of excess ice for the geomorphology, hydrology
and biogeochemistry of permafrost landscapes, we lack fine-scale
estimates of excess ice profiles. Here, we introduce a Bayesian
inversion method based on remotely sensed subsidence. It retrieves
near-surface excess ice profiles by probing the ice content at
increasing depths as the thaw front deepens over summer. Ice profiles
estimated from Sentinel-1 interferometric synthetic aperture radar
(InSAR) subsidence observations at 80 m resolution were spatially
associated with the surficial geology in two Alaskan regions. In most
geological units, the estimated profiles were ice poor in the central
and, to a lesser extent, the upper active layer. In a warm summer, units
with ice-rich permafrost had elevated inferred ice contents at the base
of the active layer and the (previous years’) upper permafrost. The
posterior uncertainty and accuracy varied with depth. In simulations,
they were best (<0.1) in the central active layer,
deteriorating (>0.2) toward the surface and permafrost. At
two sites in the Brooks Foothills, Alaska, the estimates compared
favorably to coring-derived profiles down to 35 cm, while the increase
in excess ice below the long-term active layer thickness of 40 cm was
only reproduced in a warm year. Pan-Arctic InSAR observations enable
novel observational constraints on the susceptibility of permafrost
landscapes to terrain instability and on the controls, drivers and
consequences of ground ice formation and loss.