Rapid Earth uplift in southeast Greenland driven by recent ice melt above low-viscosity upper mantle

Along the periphery of the Greenland ice sheet, Global Navigation Satellite System (GNSS) stations observe uplift of a few mm/yr, reflecting Earth’s response to past and contemporary changes in Greenland’s ice mass. On the coast of southeast Greenland, near the Kangerlussuaq glacier, GNSS stations show abnormally rapid ground uplift, faster than 10 mm/yr. Current earth deformation models, which employ a layered Earth structure, cannot explain such rapid uplift. Here we develop 3D regional models of uplift in response to deglaciation occurring over timescales corresponding to the last glacial cycle (past 1000s of years), the last millennium (past 100s of years), and recent rapid deglaciation (past 10s of years). These 3D models incorporate a track of low-viscosity upper mantle and thin lithosphere, consistent with the passage of Greenland over the Iceland plume during the past ~50 Myr. We find that the fastest ground uplift occurs where rapid deglaciation occurs above the low-viscosity plume track of the Iceland plume. This uplift reflects viscous deformation of the upper mantle, and is much larger than the (instantaneous) elastic deformation that also results from this deglaciation. Above the low-viscosity plume track, the uplift contribution is greatest for the most recent deglaciation (past decades), followed by the contribution from deglaciation during the last millennium. The combination of these viscous contributions can explain uplift observations of more than 10 mm/yr near the rapidly deglaciating Kangerlussuaq glacier, which lies above the Iceland plume track, and slower uplift in the surrounding areas. Rapid uplift observed to the south of the Kangerlussuaq glacier can be explained if the low-viscosity plume track extends farther southward beneath the Helheim glacier, which is also rapidly deglaciating. Such rapid viscous uplift from recent and local ice melt is not usually considered in glacial isostatic adjustment (GIA) models, but likely happened in the past in response to previous deglaciation. It will also become increasingly important in the future as deglaciation accelerates.