Secular gravity variation at Svalbard (Norway) from ground observations and GRACE satellite data

Abstract

S U M M A R YThe Svalbard archipelago, Norway, is affected by both the present-day ice melting (PDIM) and Glacial Isostatic Adjustment (GIA) subsequent to the Last Pleistocene deglaciation. The induced deformation of the Earth is observed by using different techniques. At the Geodetic Observatory in Ny-Ålesund, precise positioning measurements have been collected since 1991, a superconducting gravimeter (SG) has been installed in 1999, and six campaigns of absolute gravity (AG) measurements were performed between 1998 and 2007. Moreover, the Gravity Recovery and Climate Experiment (GRACE) satellite mission provides the time variation of the Earth gravity field since 2002. The goal of this paper is to estimate the present rate of ice melting by combining geodetic observations of the gravity variation and uplift rate with geophysical modelling of both the GIA and Earth's response to the PDIM. We estimate the secular gravity variation by superimposing the SG series with the six AG measurements. We collect published estimates of the vertical velocity based on GPS and VLBI data. We analyse the GRACE solutions provided by three groups (CSR, GFZ, GRGS). The crux of the problem lies in the separation of the contributions from the GIA and PDIM to the Earth's deformation. To account for the GIA, we compute the response of viscoelastic Earth models having different radial structures of mantle viscosity to the deglaciation histories included in the models ICE-3G or ICE-5G. To account for the effect of PDIM, we compute the deformation of an elastic Earth model for six models of ice-melting extension and rates. Errors in the gravity variation and vertical velocity are estimated by taking into account the measurement uncertainties and the variability of the GRACE solutions and GIA and PDIM models. The ground observations agree with models that involve a current ice loss of 25 km 3 water equivalent yr −1 over Svalbard, whereas the space observations give a value in the interval [5, 18] km 3 water equivalent yr −1 . A better modelling of the PDIM, which would include the precise topography of the glaciers and altitude-dependency of ice melting, is necessary to decrease the discrepancy between the two estimates.

The recognition of transient compressional fault slow−slip along the northern shore of Hornsund Fjord, Sw Spitsbergen, Svalbard

“…formed contemporaneously (Lindner et al 1991). The geodetic observatory at Ny−Ålesund has been recording GPS measurements since 1991 while a supercon− ducting gravimeter to monitor the effect of present−day ice melting and glacial iso− static adjustment was installed in 1999 (Mémin et al 2011). The results have shown that the mean isostatic uplift rate is around 8.5 mm/year while the rate of uplift from 2003 to 2006 was two and a half times greater than it had been during the preceding period (11.2 mm/year against 4.8 mm/year) see Kierulf et al (2009), Omang andKierulf (2011).…”

Current Ice Loss in Small Glacier Systems of the Arctic Islands (Iceland, Svalbard, and the Russian High Arctic) from Satellite Gravimetry

“…Past GRACE studies in this region suggested the rate as 8.8 ± 3 Gt yr -1 (Wouters et al 2008), 9.1 ± 1.1 Gt yr -1 (Mémin et al 2011), and 3 ± 2 Gt yr -1 (Jacob et al 2012). The latest estimate by Jacob et al (2012) is considerably smaller than the two earlier estimates.…”

“…The latest estimate by Jacob et al (2012) is considerably smaller than the two earlier estimates. This difference would reflect the inclusion of the GRACE data after 2009, i.e., Jacob et al (2012) included the data up to 2010.12 while Wouters et al (2008) and Mémin et al (2011) used those up to 2008.01 and 2009.01, respectively. As described before, Svalbard shows significant mass increase around the 2009/2010 winter.…”

Glacial Isostatic Adjustment modelling: historical perspectives, recent advances, and future directions

“…Peltier, 2004;Steffen et al, 2009;Mazzotti et al, 2011;Memin et al, 2011;Sato et al, 2012), while the relationship between surface gravity change and uplift rates can be employed to constrain GIA in regions where ice history and Earth structure are poorly known (e.g. Wahr 425 et al, 1995;Purcell et al, 2011;van Dam et al, 2017 …”