Geodetic measurements reveal similarities between post-Last Glacial Maximum and present-day mass loss from the Greenland ice sheet

Abstract

Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year.

Keywords: GPS; Greenland Ice Sheet; Last Glacial Maximum; Sea level rise; climate change; glacial isostatic adjustment.

Fig. 1. Location map.

Locations of the GNET GPS stations (red dots) and RSL observations (green dots). Black curves denote the major drainage basins numbered from 1 to 7; drainage 3 is separated into subbasins 3A and 3B (inset), the latter representing the near field of the KUAQ glacier. The yellow curve shows a reconstruction of the Iceland hot spot track (57, 58). Bathymetry is shown over the ocean and surface elevation over the land/ice (25).

Fig. 2. Uplift at KULU.

(A) Daily GPS values of the vertical solutions at KULU, southeast Greenland. (B) Monthly mean values of the vertical solutions at KULU. The associated uncertainties are shown as vertical lines. The red curve denotes the estimated elastic vertical displacement based on load changes inferred from radar/laser altimetry observations. (C) Monthly mean values of vertical solutions after removing the annual, semiannual, and elastic vertical displacement, which represents the ongoing GIA vertical displacement from ice load changes following the LGM. Green line, ICE-5G GIA trend; blue, Green1 GIA trend; light blue, GPS inferred GIA trend; purple, HUY3 GIA trend; red, observed.

Fig. 3. Glacial isostatic adjustment.

(A) Inferred GIA vertical displacement rates at GNET sites. Gray curves denote major drainage basins, and the numbers represent SLE estimates of each basin. (B) GIA vertical displacement rates from new model entitled “GNET-GIA.” (C) Uncertainties of GIA vertical displacement rates.

Fig. 4. GIA rates in basin 3B.

Spatial pattern of GIA-induced uplift by the retreat of the KUAQ glaciers in the past century for different LT and AV; best fit to the measured GIA uplift is achieved for LT = 40 km and AV = 1 × 10¹⁹ Pa·s. The UMV and LMV are constant with 5 × 10²⁰ and 2 × 10²² Pa·s, respectively (VM-GPS).