Monthly Surface Elevation Changes over the Greenland Ice Sheet from 2003 to 2020 by Merging Multi-Mission Observations

Abstract:

Satellite altimetry is a critical tool to measure surface elevation changes (SEC) over the Greenland Ice Sheet (GrIS), which is the major source of the global sea-level rise during the past decades. Producing a long-term SEC time series allows for the investigation of the time-varying GrIS evolution over various time scales. In this study, we first apply a modified repeat-track analysis to generate monthly SEC time series for laser (ICESat-1/2) and radar (CryoSat-2) altimeter missions. The individual time series obtained for the missions are then aligned by estimating the inter-mission biases (i.e., ICESat-1/CryoSat-2 and CryoSat-2/ ICESat-2). Finally, a spatiotemporal Gaussian smoothing procedure is applied to obtain the monthly multi-mission SEC estimates, which allow for the study of the spatiotemporal variabilities in the GrIS mass balance. Our results show that the largest sustained ice melting during the past two decades came from the southwest region of Greenland. Moreover, the thinning of Jakobshavn Glacier during 2009-2015 (-1.43 ± 0.03 m/yr) was two times faster than that during 2003-2009 (-0.73 ± 0.08 m/yr). However, after 2015, the thinning dramatically decelerated to -0.33 ± 0.06 m/yr, about one-fourth of the rate during the previous 6-year period. By checking the SEC time series, we find the accelerating then decelerating behaviors are common for many major outlet glaciers, including Jakobshavn, Helheim, Kangerlussuaq, Upernavik, Zachariae, and Petermann glaciers, and agree with the monthly mass changes estimated by GRACE/GRACE-FO gravity missions. Additionally, our results show paused thinning of Helheim and Upernavik glaciers since 2013 and 2017, respectively. We conclude that the monthly SEC time series by merging multi-mission data reveals significant stochastic changes that reflect complex interactions among the ice sheet, atmosphere and oceans.