Rapid response of the Greenland ice sheet to climate extremes revealed by GPS bedrock shift: the mid-August 2021 extreme melting

Abstract In mid-August 2021, an atmospheric river (AR) triggered unprecedented rainfall over Greenland, inducing widespread extreme melting across the ice sheet. Here, we use daily Global Positioning System (GPS) observations to quantify the response of the Greenland Ice Sheet to this extreme event, focusing on the Central-West/South-West (CW-SW) and South-East (SE) basins. By employing Empirical Orthogonal Function (EOF), we isolate melting signals from GPS vertical displacement. GPS shows that the AR-induced large-scale ice sheet ablation began on August 14 and lasted about one week, which is consistent with Automated Weather Station (AWS) records and satellite microwave derived ablation maps. By linking GRACE (Gravity Recovery and Climate Experiment) mass changes to GPS displacements with mass–displacement conversion factors, we quantify the impact of the extreme melting event on ice sheet mass balance. The CW-SW basin experienced more intensive ablation, with an average mass loss of 27.2 $$\pm $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>±</mml:mo> </mml:math> 6.9 Gt, compared to 15.3 $$\pm $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>±</mml:mo> </mml:math> 5.6 Gt in the SE basin. Our study demonstrates the advantages of GPS in capturing rapid changes in the ice sheet, providing critical insights into the effects of climate extremes on ice sheet dynamics. Graphical Abstract