Elevation change of the Greenland Ice Sheet due to surface mass balance and firn processes, 1960–2014

摘要

Observed changes in the surface elevation of the Greenland Ice Sheet arecaused by ice dynamics, basal elevation change, basal melt, surface massbalance (SMB) variability, and by compaction of the overlying firn. Thelast two contributions are quantified here using a firn model that includescompaction, meltwater percolation, and refreezing. The model is forced withsurface mass fluxes and temperature from a regional climate model for theperiod 1960–2014. The model results agree with observations of surfacedensity, density profiles from 62 firn cores, and altimetric observationsfrom regions where ice-dynamical surface height changes are likely small. Inareas with strong surface melt, the firn model overestimates density. We findthat the firn layer in the high interior is generally thickening slowly(1–5 cm yr?1). In the percolation and ablation areas, firn and SMBprocesses account for a surface elevation lowering of up to20–50 cm yr?1. Most of this firn-induced marginal thinning is causedby an increase in melt since the mid-1990s and partly compensated by anincrease in the accumulation of fresh snow around most of the ice sheet. Thetotal firn and ice volume change between 1980 and 2014 is estimated at?3295 ± 1030 km3 due to firn and SMB changes, corresponding toan ice-sheet average thinning of 1.96 ± 0.61 m. Most of this volumedecrease occurred after 1995. The computed changes in surface elevation canbe used to partition altimetrically observed volume change into surface massbalance and ice-dynamically related mass changes.