The GRACE monthly solutions have been filtered and analysed for Fennoscandia, Canada and neighbouring regions. Different up-to-date GRACE gravity field solutions have been used in the investigation. To extract the GIA signal from GRACE, different filter methods have been applied and tested (Steffen et al. 2008a,b). The investigations show that the Gaussian filter and the filter of Kusche (2007) give the uplift centre at the expected location.

Figure shows secular gravity variation after Gaussian filtering with 400 km radius in Fennoscandia determined from GFZ GRACE monthly solution.

As the GIA-induced signal is still superimposed by signals from hydrology, global hydrology models have been used in the absence of comprehensive large-scale observation data of total continental water storage to reduce respectively remove the hydrological part. In Europe, besides the positive trend over Fennoscandia, two other positive gravity changes can be found in Eastern Europe (Steffen et al. 2008a,b). Obviously, these patterns are not GIA-induced and may therefore be related to hydrology. The applied global hydrology models however do not represent these features in their versions used here, indicating that they may need to be revised regarding the trend components.

Figure shows secular trends in Fennoscandia computed from GFZ GRACE monthly solution and global hydrology model WGHM (Döll et al. 2006). Units are mm/yr in columns of equivalent water thickness.

A 1D Earth model was used for comparisons with the GRACE land uplift signal for Fennoscandia and North America (Steffen et al. 2008a,b). For Fennoscandia the location of the uplift maximum and its value fit quite well. For Canada, slight differences stand out in the uplift region. The model area is smaller than observed with GRACE and the distance between the two uplift peaks decreases. Nevertheless, the maximum values are comparable.

Figure shows secular gravity variations in Fennoscandia derived from the GFZ GRACE monthly solution and geodynamical 1D modelling.

The land uplift signal as determined from GRACE was also compared to results obtained from terrestrial absolute gravity campaigns (Steffen et al. 2008c). The results provide gravity changes in Fennoscandia with a sufficient accuracy to support the GRACE data evaluation. The rebound signal is clearly visible, but still seems to be interfered with environmental mass variations. The trends of the GFZ GRACE solution and the AG measurements fit quite well for stations in mid-distance from the uplift centre. In the area of maximum uplift GRACE averages too much, while at stations near the coast the influence of the Baltic cannot be neglected.

Figure shows comparison of gravity variation in GRACE data of the GFZ and AG measurements at Kiruna, Sweden. The relative vertical position of the AG and GRACE points is arbitrary and can be adjusted up or down.